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Internet Engineering Task Force                                   PIM WG
INTERNET-DRAFT                                          Bill Fenner/AT&T
draft-ietf-pim-sm-v2-new-12.txt                         Mark Handley/UCL
                                                   Hugh Holbrook/Arastra
Obsoletes (if approved): RFC2362                   Isidor Kouvelas/Cisco
                                                           20 March 2006
                                                 Expires: September 2006


         Protocol Independent Multicast - Sparse Mode (PIM-SM):
                    Protocol Specification (Revised)


Status of this Document

By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware have
been or will be disclosed, and any of which he or she becomes aware will
be disclosed, in accordance with Section 6 of BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task
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This document is a product of the IETF PIM WG.  Comments should be
addressed to the authors, or the mailing list at pim@ietf.org.






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                                Abstract


     This document specifies Protocol Independent Multicast -
     Sparse Mode (PIM-SM).  PIM-SM is a multicast routing protocol
     that can use the underlying unicast routing information base
     or a separate multicast-capable routing information base.  It
     builds unidirectional shared trees rooted at a Rendezvous
     Point (RP) per group, and optionally creates shortest-path
     trees per source.

     This document obsoletes RFC 2362, an Experimental version of
     PIM-SM.






































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                           Table of Contents


     1. Introduction. . . . . . . . . . . . . . . . . . . . . .   6
     2. Terminology . . . . . . . . . . . . . . . . . . . . . .   6
      2.1. Definitions. . . . . . . . . . . . . . . . . . . . .   6
      2.2. Pseudocode Notation. . . . . . . . . . . . . . . . .   7
     3. PIM-SM Protocol Overview. . . . . . . . . . . . . . . .   8
     4. Protocol Specification. . . . . . . . . . . . . . . . .  13
      4.1. PIM Protocol State . . . . . . . . . . . . . . . . .  14
       4.1.1. General Purpose State . . . . . . . . . . . . . .  15
       4.1.2. (*,*,RP) State. . . . . . . . . . . . . . . . . .  15
       4.1.3. (*,G) State . . . . . . . . . . . . . . . . . . .  16
       4.1.4. (S,G) State . . . . . . . . . . . . . . . . . . .  18
       4.1.5. (S,G,rpt) State . . . . . . . . . . . . . . . . .  20
       4.1.6. State Summarization Macros. . . . . . . . . . . .  21
      4.2. Data Packet Forwarding Rules . . . . . . . . . . . .  26
       4.2.1. Last-hop Switchover to the SPT. . . . . . . . . .  28
       4.2.2. Setting and Clearing the (S,G) SPTbit . . . . . .  29
      4.3. Designated Routers (DR) and Hello Messages . . . . .  30
       4.3.1. Sending Hello Messages. . . . . . . . . . . . . .  30
       4.3.2. DR Election . . . . . . . . . . . . . . . . . . .  32
       4.3.3. Reducing Prune Propagation Delay on LANs. . . . .  34
       4.3.4. Maintaining Secondary Address Lists . . . . . . .  37
      4.4. PIM Register Messages. . . . . . . . . . . . . . . .  38
       4.4.1. Sending Register Messages from the DR . . . . . .  38
       4.4.2. Receiving Register Messages at the RP . . . . . .  42
      4.5. PIM Join/Prune Messages. . . . . . . . . . . . . . .  44
       4.5.1. Receiving (*,*,RP) Join/Prune Messages. . . . . .  45
       4.5.2. Receiving (*,G) Join/Prune Messages . . . . . . .  49
       4.5.3. Receiving (S,G) Join/Prune Messages . . . . . . .  52
       4.5.4. Receiving (S,G,rpt) Join/Prune Messages . . . . .  55
       4.5.5. Sending (*,*,RP) Join/Prune Messages. . . . . . .  61
       4.5.6. Sending (*,G) Join/Prune Messages . . . . . . . .  65
       4.5.7. Sending (S,G) Join/Prune Messages . . . . . . . .  70
       4.5.8. (S,G,rpt) Periodic Messages . . . . . . . . . . .  75
       4.5.9. State Machine for (S,G,rpt) Triggered
              Messages. . . . . . . . . . . . . . . . . . . . .  76
       4.5.10. Background: (*,*,RP) and (S,G,rpt)
               Interaction. . . . . . . . . . . . . . . . . . .  80
      4.6. PIM Assert Messages. . . . . . . . . . . . . . . . .  82
       4.6.1. (S,G) Assert Message State Machine. . . . . . . .  82
       4.6.2. (*,G) Assert Message State Machine. . . . . . . .  90
       4.6.3. Assert Metrics. . . . . . . . . . . . . . . . . .  97
       4.6.4. AssertCancel Messages . . . . . . . . . . . . . .  98
       4.6.5. Assert State Macros . . . . . . . . . . . . . . .  99
      4.7. PIM Bootstrap and RP Discovery . . . . . . . . . . . 102
       4.7.1. Group-to-RP Mapping . . . . . . . . . . . . . . . 103



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       4.7.2. Hash Function . . . . . . . . . . . . . . . . . . 104
      4.8. Source-Specific Multicast. . . . . . . . . . . . . . 105
       4.8.1. Protocol Modifications for SSM destination
              addresses . . . . . . . . . . . . . . . . . . . . 105
       4.8.2. PIM-SSM-only Routers. . . . . . . . . . . . . . . 106
      4.9. PIM Packet Formats . . . . . . . . . . . . . . . . . 107
       4.9.1. Encoded Source and Group Address Formats. . . . . 109
       4.9.2. Hello Message Format. . . . . . . . . . . . . . . 112
       4.9.3. Register Message Format . . . . . . . . . . . . . 115
       4.9.4. Register-Stop Message Format. . . . . . . . . . . 117
       4.9.5. Join/Prune Message Format . . . . . . . . . . . . 118
        4.9.5.1. Group Set Source List Rules. . . . . . . . . . 121
        4.9.5.2. Group Set Fragmentation. . . . . . . . . . . . 125
       4.9.6. Assert Message Format . . . . . . . . . . . . . . 125
      4.10. PIM Timers. . . . . . . . . . . . . . . . . . . . . 127
      4.11. Timer Values. . . . . . . . . . . . . . . . . . . . 128
     5. IANA Considerations . . . . . . . . . . . . . . . . . . 134
      5.1. PIM Address Family . . . . . . . . . . . . . . . . . 134
      5.2. PIM Hello Options. . . . . . . . . . . . . . . . . . 135
     6. Security Considerations . . . . . . . . . . . . . . . . 135
      6.1. Attacks based on forged messages . . . . . . . . . . 135
       6.1.1. Forged link-local messages. . . . . . . . . . . . 135
       6.1.2. Forged unicast messages . . . . . . . . . . . . . 136
      6.2. Non-cryptographic Authentication Mechanisms. . . . . 136
      6.3. Authentication using IPsec . . . . . . . . . . . . . 137
       6.3.1. Protecting link-local multicast messages. . . . . 137
       6.3.2. Protecting unicast messages . . . . . . . . . . . 138
        6.3.2.1. Register messages. . . . . . . . . . . . . . . 138
        6.3.2.2. Register-Stop messages . . . . . . . . . . . . 138
      6.4. Denial of Service Attacks. . . . . . . . . . . . . . 139
     7. Authors' Addresses. . . . . . . . . . . . . . . . . . . 139
     8. Acknowledgments . . . . . . . . . . . . . . . . . . . . 140
     9. Normative References. . . . . . . . . . . . . . . . . . 140
     10. Informative References . . . . . . . . . . . . . . . . 141
     11. Appendix A: PIM Multicast Border Router
         Behavior . . . . . . . . . . . . . . . . . . . . . . . 142
      11.1. Sources External to the PIM-SM Domain . . . . . . . 142
      11.2. Sources Internal to the PIM-SM Domain . . . . . . . 143
     12. Index. . . . . . . . . . . . . . . . . . . . . . . . . 145
     13. Full Copyright Statement . . . . . . . . . . . . . . . 148











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                            List of Figures


     Figure 1. Per-(S,G) register state machine at a DR . . . .  38
     Figure 2. Downstream per-interface (*,*,RP) state
               machine. . . . . . . . . . . . . . . . . . . . .  46
     Figure 3. Downstream per-interface (*,G) state
               machine. . . . . . . . . . . . . . . . . . . . .  49
     Figure 4. Downstream per-interface (S,G) state
               machine. . . . . . . . . . . . . . . . . . . . .  53
     Figure 5. Downstream per-interface (S,G,rpt) state
               machine. . . . . . . . . . . . . . . . . . . . .  56
     Figure 6. Upstream (*,*,RP) state machine. . . . . . . . .  61
     Figure 7. Upstream (*,G) state machine . . . . . . . . . .  66
     Figure 8. Upstream (S,G) state machine . . . . . . . . . .  71
     Figure 9. Upstream (S,G,rpt) state machine for
               triggered messages . . . . . . . . . . . . . . .  76
     Figure 10. Per-interface (S,G) Assert State
                machine . . . . . . . . . . . . . . . . . . . .  83
     Figure 11. Per-interface (*,G) Assert State
                machine . . . . . . . . . . . . . . . . . . . .  91






























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1.  Introduction

This document specifies a protocol for efficiently routing multicast
groups that may span wide-area (and inter-domain) internets.  This
protocol is called Protocol Independent Multicast - Sparse Mode (PIM-SM)
because, although it may use the underlying unicast routing to provide
reverse-path information for multicast tree building, it is not
dependent on any particular unicast routing protocol.

PIM-SM version 2 was originally specified in RFC 2117, and revised in
RFC 2362, both Experimental RFCs.  This document is intended to obsolete
RFC 2362, to correct a number of deficiencies that have been identified
with the way PIM-SM was previously specified, and to bring PIM-SM onto
the IETF Standards Track.  As far as possible, this document specifies
the same protocol as RFC 2362, and only diverges from the behavior
intended by RFC 2362 when the previously specified behavior was clearly
incorrect.  Routers implemented according to the specification in this
document will be able to successfully interoperate with routers
implemented according to RFC 2362.

2.  Terminology

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant PIM-SM implementations.

2.1.  Definitions

The following terms have special significance for PIM-SM:

Rendezvous Point (RP):
      An RP is a router that has been configured to be used as the root
      of the non-source-specific distribution tree for a multicast
      group.  Join messages from receivers for a group are sent towards
      the RP, and data from senders is sent to the RP so that receivers
      can discover who the senders are, and start to receive traffic
      destined for the group.

Designated Router (DR):
      A shared-media LAN like Ethernet may have multiple PIM-SM routers
      connected to it. A single one of these routers, the DR, will act
      on behalf of directly connected hosts with respect to the PIM-SM
      protocol.  A single DR is elected per interface (LAN or otherwise)
      using a simple election process.

MRIB  Multicast Routing Information Base.  This is the multicast
      topology table, which is typically derived from the unicast



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      routing table, or routing protocols such as MBGP that carry
      multicast-specific topology information.  In PIM-SM, the MRIB is
      used to decide where to send Join/Prune messages.  A secondary
      function of the MRIB is to provide routing metrics for destination
      addresses; these metrics are used when sending and processing
      Assert messages.

RPF Neighbor
      RPF stands for "Reverse Path Forwarding".  The RPF Neighbor of a
      router with respect to an address is the neighbor that the MRIB
      indicates should be used to forward packets to that address.  In
      the case of a PIM-SM multicast group, the RPF neighbor is the
      router that a Join message for that group would be directed to, in
      the absence of modifying Assert state.

TIB   Tree Information Base.  This is the collection of state at a PIM
      router that has been created by receiving PIM Join/Prune messages,
      PIM Assert messages, and IGMP or MLD information from local hosts.
      It essentially stores the state of all multicast distribution
      trees at that router.

MFIB  Multicast Forwarding Information Base.  The TIB holds all the
      state that is necessary to forward multicast packets at a router.
      However, although this specification defines forwarding in terms
      of the TIB, to actually forward packets using the TIB is very
      inefficient.  Instead a real router implementation will normally
      build an efficient MFIB from the TIB state to perform forwarding.
      How this is done is implementation-specific, and is not discussed
      in this document.

Upstream
      Towards the root of the tree.  The root of tree may either be the
      source or the RP depending on the context.

Downstream
      Away from the root of the tree.

GenID Generation Identifier, used to detect reboots.

PMBR  PIM Multicast Border Router, joining a PIM domain with another
      multicast domain.

2.2.  Pseudocode Notation

We use set notation in several places in this specification.

A (+) B
    is the union of two sets A and B.



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A (-) B
    is the elements of set A that are not in set B.

NULL
    is the empty set or list.

In addition, we use C-like syntax:

=   denotes assignment of a variable.

==  denotes a comparison for equality.

!=  denotes a comparison for inequality.

Braces { and } are used for grouping.


3.  PIM-SM Protocol Overview

This section provides an overview of PIM-SM behavior.  It is intended as
an introduction to how PIM-SM works, and is NOT definitive.  For the
definitive specification, see Section 4.

PIM relies on an underlying topology-gathering protocol to populate a
routing table with routes.  This routing table is called the MRIB or
Multicast Routing Information Base.  The routes in this table may be
taken directly from the unicast routing table, or it may be different
and provided by a separate routing protocol such as MBGP [10].
Regardless of how it is created, the primary role of the MRIB in the PIM
protocol is to provide the next hop router along a multicast-capable
path to each destination subnet.  The MRIB is used to determine the next
hop neighbor to which any PIM Join/Prune message is sent.  Data flows
along the reverse path of the Join messages.  Thus, in contrast to the
unicast RIB which specifies the next hop that a data packet would take
to get to some subnet, the MRIB gives reverse-path information, and
indicates the path that a multicast data packet would take from its
origin subnet to the router that has the MRIB.

Like all multicast routing protocols that implement the service model
from RFC 1112 [3], PIM-SM must be able to route data packets from
sources to receivers without either the sources or receivers knowing a-
priori of the existence of the others.  This is essentially done in
three phases, although as senders and receivers may come and go at any
time, all three phases may occur simultaneously.







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Phase One: RP Tree

In phase one, a multicast receiver expresses its interest in receiving
traffic destined for a multicast group.  Typically it does this using
IGMP [2] or MLD [4], but other mechanisms might also serve this purpose.
One of the receiver's local routers is elected as the Designated Router
(DR) for that subnet.  On receiving the receiver's expression of
interest, the DR then sends a PIM Join message towards the RP for that
multicast group.  This Join message is known as a (*,G) Join because it
joins group G for all sources to that group.  The (*,G) Join travels
hop-by-hop towards the RP for the group, and in each router it passes
through, multicast tree state for group G is instantiated.  Eventually
the (*,G) Join either reaches the RP, or reaches a router that already
has (*,G) Join state for that group.  When many receivers join the
group, their Join messages converge on the RP, and form a distribution
tree for group G that is rooted at the RP.  This is known as the RP Tree
(RPT), and is also known as the shared tree because it is shared by all
sources sending to that group.  Join messages are resent periodically so
long as the receiver remains in the group.  When all receivers on a
leaf-network leave the group, the DR will send a PIM (*,G) Prune message
towards the RP for that multicast group. However if the Prune message is
not sent for any reason, the state will eventually time out.

A multicast data sender just starts sending data destined for a
multicast group.  The sender's local router (DR) takes those data
packets, unicast-encapsulates them, and sends them directly to the RP.
The RP receives these encapsulated data packets, decapsulates them, and
forwards them onto the shared tree.  The packets then follow the (*,G)
multicast tree state in the routers on the RP Tree, being replicated
wherever the RP Tree branches, and eventually reaching all the receivers
for that multicast group.  The process of encapsulating data packets to
the RP is called registering, and the encapsulation packets are known as
PIM Register packets.

At the end of phase one, multicast traffic is flowing encapsulated to
the RP, and then natively over the RP tree to the multicast receivers.


Phase Two: Register-Stop

Register-encapsulation of data packets is inefficient for two reasons:

o Encapsulation and decapsulation may be relatively expensive operations
  for a router to perform, depending on whether or not the router has
  appropriate hardware for these tasks.

o Traveling all the way to the RP, and then back down the shared tree
  may entail the packets traveling a relatively long distance to reach



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  receivers that are close to the sender.  For some applications, this
  increased latency or bandwidth consumption is undesirable.

Although Register-encapsulation may continue indefinitely, for these
reasons, the RP will normally choose to switch to native forwarding.  To
do this, when the RP receives a register-encapsulated data packet from
source S on group G, it will normally initiate an (S,G) source-specific
Join towards S.  This Join message travels hop-by-hop towards S,
instantiating (S,G) multicast tree state in the routers along the path.
(S,G) multicast tree state is used only to forward packets for group G
if those packets come from source S.  Eventually the Join message
reaches S's subnet or a router that already has (S,G) multicast tree
state, and then packets from S start to flow following the (S,G) tree
state towards the RP.  These data packets may also reach routers with
(*,G) state along the path towards the RP - if so, they can short-cut
onto the RP tree at this point.

While the RP is in the process of joining the source-specific tree for
S, the data packets will continue being encapsulated to the RP.  When
packets from S also start to arrive natively at the the RP, the RP will
be receiving two copies of each of these packets.  At this point, the RP
starts to discard the encapsulated copy of these packets, and it sends a
Register-Stop message back to S's DR to prevent the DR unnecessarily
encapsulating the packets.

At the end of phase 2, traffic will be flowing natively from S along a
source-specific tree to the RP, and from there along the shared tree to
the receivers.  Where the two trees intersect, traffic may transfer from
the source-specific tree to the RP tree, and so avoid taking a long
detour via the RP.

It should be noted that a sender may start sending before or after a
receiver joins the group, and thus phase two may happen before the
shared tree to the receiver is built.


Phase 3: Shortest-Path Tree

Although having the RP join back towards the source removes the
encapsulation overhead, it does not completely optimize the forwarding
paths.  For many receivers the route via the RP may involve a
significant detour when compared with the shortest path from the source
to the receiver.

To obtain lower latencies or more efficient bandwidth utilization, a
router on the receiver's LAN, typically the DR, may optionally initiate
a transfer from the shared tree to a source-specific shortest-path tree
(SPT).  To do this, it issues an (S,G) Join towards S. This instantiates



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state in the routers along the path to S.  Eventually this join either
reaches S's subnet, or reaches a router that already has (S,G) state.
When this happens, data packets from S start to flow following the (S,G)
state until they reach the receiver.

At this point the receiver (or a router upstream of the receiver) will
be receiving two copies of the data - one from the SPT and one from the
RPT.  When the first traffic starts to arrive from the SPT, the DR or
upstream router starts to drop the packets for G from S that arrive via
the RP tree.  In addition, it sends an (S,G) Prune message towards the
RP.  This is known as an (S,G,rpt) Prune.  The Prune message travels
hop-by-hop, instantiating state along the path towards the RP indicating
that traffic from S for G should NOT be forwarded in this direction.
The prune is propagated until it reaches the RP or a router that still
needs the traffic from S for other receivers.

By now, the receiver will be receiving traffic from S along the
shortest-path tree between the receiver and S.  In addition, the RP is
receiving the traffic from S, but this traffic is no longer reaching the
receiver along the RP tree.  As far as the receiver is concerned, this
is the final distribution tree.


Source-specific Joins

IGMPv3 permits a receiver to join a group and specify that it only wants
to receive traffic for a group if that traffic comes from a particular
source.  If a receiver does this, and no other receiver on the LAN
requires all the traffic for the group, then the DR may omit performing
a (*,G) join to set up the shared tree, and instead issue a source-
specific (S,G) join only.

The range of multicast addresses from 232.0.0.0 to 232.255.255.255 is
currently set aside for source-specific multicast in IPv4.  For groups
in this range, receivers should only issue source-specific IGMPv3 joins.
If a PIM router receives a non-source-specific join for a group in this
range, it should ignore it, as described in Section 4.8.

Source-specific Prunes

IGMPv3 also permits a receiver to join a group and specify that it only
wants to receive traffic for a group if that traffic does not come from
a specific source or sources.  In this case, the DR will perform a (*,G)
join as normal, but may combine this with an (S,G,rpt) prune for each of
the sources the receiver does not wish to receive.






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Multi-access Transit LANs

The overview so far has concerned itself with point-to-point transit
links.  However, using multi-access LANs such as Ethernet for transit is
not uncommon.  This can cause complications for three reasons:

o Two or more routers on the LAN may issue (*,G) Joins to different
  upstream routers on the LAN because they have inconsistent MRIB
  entries regarding how to reach the RP.  Both paths on the RP tree will
  be set up, causing two copies of all the shared tree traffic to appear
  on the LAN.

o Two or more routers on the LAN may issue (S,G) Joins to different
  upstream routers on the LAN because they have inconsistent MRIB
  entries regarding how to reach source S.  Both paths on the source-
  specific tree will be set up, causing two copies of all the traffic
  from S to appear on the LAN.

o A router on the LAN may issue a (*,G) Join to one upstream router on
  the LAN, and another router on the LAN may issue an (S,G) Join to a
  different upstream router on the same LAN.  Traffic from S may reach
  the LAN over both the RPT and the SPT.  If the receiver behind the
  downstream (*,G) router doesn't issue an (S,G,rpt) prune, then this
  condition would persist.

All of these problems are caused by there being more than one upstream
router with join state for the group or source-group pair.  PIM does not
prevent such duplicate joins from occurring - instead when duplicate
data packets appear on the LAN from different routers, these routers
notice this, and then elect a single forwarder.  This election is
performed using PIM Assert messages, which resolve the problem in favor
of the upstream router which has (S,G) state, or if neither or both
router has (S,G) state, then in favor of the router with the best metric
to the RP for RP trees, or the best metric to the source to source-
specific trees.

These Assert messages are also received by the downstream routers on the
LAN, and these cause subsequent Join messages to be sent to the upstream
router that won the Assert.

RP Discovery

PIM-SM routers need to know the address of the RP for each group for
which they have (*,G) state.  This address is obtained either
automatically (e.g., embedded-RP), through a bootstrap mechanism or
through static configuration.





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One dynamic way to do this is to use the Bootstrap Router (BSR)
mechanism [11]. One router in each PIM domain is elected the Bootstrap
Router through a simple election process.  All the routers in the domain
that are configured to be candidates to be RPs periodically unicast
their candidacy to the BSR.  From the candidates, the BSR picks an RP-
set, and periodically announces this set in a Bootstrap message.
Bootstrap messages are flooded hop-by-hop throughout the domain until
all routers in the domain know the RP-Set.

To map a group to an RP, a router hashes the group address into the RP-
set using an order-preserving hash function (one that minimizes changes
if the RP-Set changes).  The resulting RP is the one that it uses as the
RP for that group.

4.  Protocol Specification

The specification of PIM-SM is broken into several parts:

o Section 4.1 details the protocol state stored.

o Section 4.2 specifies the data packet forwarding rules.

o Section 4.3. specifies Designated Router (DR) election and the rules
  for sending and processing Hello messages.

o Section 4.4 specifies the PIM Register generation and processing
  rules.

o Section 4.5 specifies the PIM Join/Prune generation and processing
  rules.

o Section 4.6 specifies the PIM Assert generation and processing rules.

o Section 4.7 specifies the RP discovery mechanisms.

o The subset of PIM required to support Source-Specific Multicast, PIM-
  SSM, is described in Section 4.8.

o PIM packet formats are specified in Section 4.9.

o A summary of PIM-SM timers and their default values is given in
  Section 4.10.

o Appendix A in Section 11 specifies the PIM Multicast Border Router
  behavior.






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4.1.  PIM Protocol State

This section specifies all the protocol state that a PIM implementation
should maintain in order to function correctly.  We term this state the
Tree Information Base or TIB, as it holds the state of all the multicast
distribution trees at this router.  In this specification we define PIM
mechanisms in terms of the TIB.  However, only a very simple
implementation would actually implement packet forwarding operations in
terms of this state.  Most implementations will use this state to build
a multicast forwarding table, which would then be updated when the
relevant state in the TIB changes.

Although we specify precisely the state to be kept, this does not mean
that an implementation of PIM-SM needs to hold the state in this form.
This is actually an abstract state definition, which is needed in order
to specify the router's behavior.  A PIM-SM implementation is free to
hold whatever internal state it requires, and will still be conformant
with this specification so long as it results in the same externally
visible protocol behavior as an abstract router that holds the following
state.

We divide TIB state into four sections:

(*,*,RP) state
     State that maintains per-RP trees, for all groups served by a given
     RP.

(*,G) state
     State that maintains the RP tree for G.

(S,G) state
     State that maintains a source-specific tree for source S and group
     G.

(S,G,rpt) state
     State that maintains source-specific information about source S on
     the RP tree for G.  For example, if a source is being received on
     the source-specific tree, it will normally have been pruned off the
     RP tree.  This prune state is (S,G,rpt) state.

The state that should be kept is described below.  Of course,
implementations will only maintain state when it is relevant to
forwarding operations - for example, the "NoInfo" state might be assumed
from the lack of other state information, rather than being held
explicitly.






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4.1.1.  General Purpose State

A router holds the following non-group-specific state:

     For each interface:

          o Effective Override Interval

          o Effective Propagation Delay

          o Suppression state: One of {"Enable", "Disable"}

          Neighbor State:

            For each neighbor:

                 o Information from neighbor's Hello

                 o Neighbor's GenID.

                 o Neighbor Liveness Timer (NLT)

          Designated Router (DR) State:

            o Designated Router's IP Address

            o DR's DR Priority

The Effective Override Interval, the Effective Propagation Delay and the
Interface suppression state are described in Section 4.3.3. Designated
Router state is described in Section 4.3.

4.1.2.  (*,*,RP) State

For every RP a router keeps the following state:

     (*,*,RP) state:
          For each interface:

               PIM (*,*,RP) Join/Prune State:

                    o State: One of {"NoInfo" (NI), "Join" (J), "Prune-
                      Pending" (PP)}

                    o Prune-Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)




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          Not interface specific:

               Upstream (*,*,RP) Join/Prune State:

                    o State: One of {"NotJoined(*,*,RP)",
                      "Joined(*,*,RP)"}

               o Upstream Join/Prune Timer (JT)

               o Last RPF Neighbor towards RP that was used

PIM (*,*,RP) Join/Prune state is the result of receiving PIM (*,*,RP)
Join/Prune messages on this interface, and is specified in Section
4.5.1.

The upstream (*,*,RP) Join/Prune State reflects the state of the
upstream (*,*,RP) state machine described in Section 4.5.5.

The upstream (*,*,RP) Join/Prune Timer is used to send out periodic
Join(*,*,RP) messages, and to override Prune(*,*,RP) messages from peers
on an upstream LAN interface.

The last RPF neighbor towards the RP is stored because if the MRIB
changes then the RPF neighbor towards the RP may change.  If it does so,
then we need to trigger a new Join(*,*,RP) to the new upstream neighbor
and a Prune(*,*,RP) to the old upstream neighbor.  Similarly, if a
router detects through a changed GenID in a Hello message that the
upstream neighbor towards the RP has rebooted, then it should re-
instantiate state by sending a Join(*,*,RP).  These mechanisms are
specified in Section 4.5.5.

4.1.3.  (*,G) State

For every group G a router keeps the following state:

     (*,G) state:
          For each interface:

               Local Membership:
                    State: One of {"NoInfo", "Include"}

               PIM (*,G) Join/Prune State:

                    o State: One of {"NoInfo" (NI), "Join" (J), "Prune-
                      Pending" (PP)}

                    o Prune-Pending Timer (PPT)




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                    o Join/Prune Expiry Timer (ET)

               (*,G) Assert Winner State

                    o State: One of {"NoInfo" (NI), "I lost Assert" (L),
                      "I won Assert" (W)}

                    o Assert Timer (AT)

                    o Assert winner's IP Address (AssertWinner)

                    o Assert winner's Assert Metric (AssertWinnerMetric)

          Not interface specific:

               Upstream (*,G) Join/Prune State:

                    o State: One of {"NotJoined(*,G)", "Joined(*,G)"}

               o Upstream Join/Prune Timer (JT)

               o Last RP Used

               o Last RPF Neighbor towards RP that was used

Local membership is the result of the local membership mechanism (such
as IGMP or MLD) running on that interface.  It need not be kept if this
router is not the DR on that interface unless this router won a (*,G)
assert on this interface for this group, although implementations may
optionally keep this state in case they become the DR or assert winner.
We recommend storing this information if possible, as it reduces latency
converging to stable operating conditions after a failure causing a
change of DR.  This information is used by the pim_include(*,G) macro
described in Section 4.1.6.

PIM (*,G) Join/Prune state is the result of receiving PIM (*,G)
Join/Prune messages on this interface, and is specified in Section
4.5.2. The state is used by the macros that calculate the outgoing
interface list in Section 4.1.6, and in the JoinDesired(*,G) macro
(defined in Section 4.5.6) that is used in deciding whether a Join(*,G)
should be sent upstream.

(*,G) Assert Winner state is the result of sending or receiving (*,G)
Assert messages on this interface.  It is specified in Section 4.6.2.

The upstream (*,G) Join/Prune State reflects the state of the upstream
(*,G) state machine described in Section 4.5.6.




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The upstream (*,G) Join/Prune Timer is used to send out periodic
Join(*,G) messages, and to override Prune(*,G) messages from peers on an
upstream LAN interface.

The last RP used must be stored because if the RP-Set changes (Section
4.7) then state must be torn down and rebuilt for groups whose RP
changes.

The last RPF neighbor towards the RP is stored because if the MRIB
changes then the RPF neighbor towards the RP may change.  If it does so,
then we need to trigger a new Join(*,G) to the new upstream neighbor and
a Prune(*,G) to the old upstream neighbor.  Similarly, if a router
detects through a changed GenID in a Hello message that the upstream
neighbor towards the RP has rebooted, then it should re-instantiate
state by sending a Join(*,G).  These mechanisms are specified in Section
4.5.6.

4.1.4.  (S,G) State

For every source/group pair (S,G) a router keeps the following state:

     (S,G) state:

          For each interface:

               Local Membership:
                    State: One of {"NoInfo", "Include"}

               PIM (S,G) Join/Prune State:

                    o State: One of {"NoInfo" (NI), "Join" (J), "Prune-
                      Pending" (PP)}

                    o Prune-Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

               (S,G) Assert Winner State

                    o State: One of {"NoInfo" (NI), "I lost Assert" (L),
                      "I won Assert" (W)}

                    o Assert Timer (AT)

                    o Assert winner's IP Address (AssertWinner)

                    o Assert winner's Assert Metric (AssertWinnerMetric)




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          Not interface specific:

               Upstream (S,G) Join/Prune State:

                    o State: One of {"NotJoined(S,G)", "Joined(S,G)"}

               o Upstream (S,G) Join/Prune Timer (JT)

               o Last RPF Neighbor towards S that was used

               o SPTbit (indicates (S,G) state is active)

               o (S,G) Keepalive Timer (KAT)


               Additional (S,G) state at the DR:

                    o Register state: One of {"Join" (J), "Prune" (P),
                      "Join-Pending" (JP), "NoInfo" (NI)}

                    o Register-Stop timer

               Additional (S,G) state at the RP:

                    o PMBR: the first PMBR to send a Register for this
                      source with the Border bit set.

Local membership is the result of the local source-specific membership
mechanism (such as IGMP version 3) running on that interface and
specifying that this particular source should be included.  As stored
here, this state is the resulting state after any IGMPv3 inconsistencies
have been resolved.  It need not be kept if this router is not the DR on
that interface unless this router won a (S,G) assert on this interface
for this group.  However, we recommend storing this information if
possible, as it reduces latency converging to stable operating
conditions after a failure causing a change of DR.  This information is
used by the pim_include(S,G) macro described in Section 4.1.6.

PIM (S,G) Join/Prune state is the result of receiving PIM (S,G)
Join/Prune messages on this interface, and is specified in Section
4.5.2. The state is used by the macros that calculate the outgoing
interface list in Section 4.1.6, and in the JoinDesired(S,G) macro
(defined in Section 4.5.7) that is used in deciding whether a Join(S,G)
should be sent upstream.

(S,G) Assert Winner state is the result of sending or receiving (S,G)
Assert messages on this interface.  It is specified in Section 4.6.1.




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The upstream (S,G) Join/Prune State reflects the state of the upstream
(S,G) state machine described in Section 4.5.7.

The upstream (S,G) Join/Prune Timer is used to send out periodic
Join(S,G) messages, and to override Prune(S,G) messages from peers on an
upstream LAN interface.

The last RPF neighbor towards S is stored because if the MRIB changes
then the RPF neighbor towards S may change.  If it does so, then we need
to trigger a new Join(S,G) to the new upstream neighbor and a Prune(S,G)
to the old upstream neighbor.  Similarly, if the router detects through
a changed GenID in a Hello message that the upstream neighbor towards S
has rebooted, then it should re-instantiate state by sending a
Join(S,G).  These mechanisms are specified in Section 4.5.7.

The SPTbit is used to indicate whether forwarding is taking place on the
(S,G) Shortest Path Tree (SPT) or on the (*,G) tree.  A router can have
(S,G) state and still be forwarding on (*,G) state during the interval
when the source-specific tree is being constructed.  When SPTbit is
FALSE, only (*,G) forwarding state is used to forward packets from S to
G.  When SPTbit is TRUE, both (*,G) and (S,G) forwarding state are used.

The (S,G) Keepalive Timer is updated by data being forwarded using this
(S,G) forwarding state.  It is used to keep (S,G) state alive in the
absence of explicit (S,G) Joins.  Amongst other things, this is
necessary for the so-called "turnaround rules" - when the RP uses (S,G)
joins to stop encapsulation, and then (S,G) prunes to prevent traffic
from unnecessarily reaching the RP.

On a DR, the (S,G) Register State is used to keep track of whether to
encapsulate data to the RP on the Register Tunnel; the (S,G) Register-
Stop timer tracks how long before encapsulation begins again for a given
(S,G).

On an RP, the PMBR value must be cleared when the Keepalive Timer
expires.

4.1.5.  (S,G,rpt) State

For every source/group pair (S,G) for which a router also has (*,G)
state, it also keeps the following state:

     (S,G,rpt) state:

          For each interface:

               Local Membership:
                    State: One of {"NoInfo", "Exclude"}



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               PIM (S,G,rpt) Join/Prune State:

                    o State: One of {"NoInfo", "Pruned", "Prune-
                      Pending"}

                    o Prune-Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

          Not interface specific:

               Upstream (S,G,rpt) Join/Prune State:

                    o State: One of {"RPTNotJoined(G)",
                      "NotPruned(S,G,rpt)", "Pruned(S,G,rpt)"}

                    o Override Timer (OT)

Local membership is the result of the local source-specific membership
mechanism (such as IGMPv3) running on that interface and specifying that
although there is (*,G) Include state, this particular source should be
excluded.  As stored here, this state is the resulting state after any
IGMPv3 inconsistencies between LAN members have been resolved.  It need
not be kept if this router is not the DR on that interface unless this
router won a (*,G) assert on this interface for this group.  However, we
recommend storing this information if possible, as it reduces latency
converging to stable operating conditions after a failure causing a
change of DR.  This information is used by the pim_exclude(S,G) macro
described in Section 4.1.6.

PIM (S,G,rpt) Join/Prune state is the result of receiving PIM (S,G,rpt)
Join/Prune messages on this interface, and is specified in Section
4.5.4. The state is used by the macros that calculate the outgoing
interface list in Section 4.1.6, and in the rules for adding
Prune(S,G,rpt) messages to Join(*,G) messages specified in Section
4.5.8.

The upstream (S,G,rpt) Join/Prune state is used along with the Override
Timer to send the correct override messages in response to Join/Prune
messages sent by upstream peers on a LAN.  This state and behavior are
specified in Section 4.5.9.

4.1.6.  State Summarization Macros

Using this state, we define the following "macro" definitions which we
will use in the descriptions of the state machines and pseudocode in the
following sections.




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The most important macros are those that define the outgoing interface
list (or "olist") for the relevant state.  An olist can be "immediate"
if it is built directly from the state of the relevant type.  For
example, the immediate_olist(S,G) is the olist that would be built if
the router only had (S,G) state and no (*,G) or (S,G,rpt) state.  In
contrast, the "inherited" olist inherits state from other types.  For
example, the inherited_olist(S,G) is the olist that is relevant for
forwarding a packet from S to G using both source-specific and group-
specific state.

There is no immediate_olist(S,G,rpt) as (S,G,rpt) state is negative
state - it removes interfaces in the (*,G) olist from the olist that is
actually used to forward traffic.  The inherited_olist(S,G,rpt) is
therefore the olist that would be used for a packet from S to G
forwarding on the RP tree.  It is a strict subset of
(immediate_olist(*,*,RP) (+) immediate_olist(*,G)).

Generally speaking, the inherited olists are used for forwarding, and
the immediate_olists are used to make decisions about state maintenance.

immediate_olist(*,*,RP) =
    joins(*,*,RP)

immediate_olist(*,G) =
    joins(*,G) (+) pim_include(*,G) (-) lost_assert(*,G)

immediate_olist(S,G) =
    joins(S,G) (+) pim_include(S,G) (-) lost_assert(S,G)

inherited_olist(S,G,rpt) =
        ( joins(*,*,RP(G)) (+) joins(*,G) (-) prunes(S,G,rpt) )
    (+) ( pim_include(*,G) (-) pim_exclude(S,G))
    (-) ( lost_assert(*,G) (+) lost_assert(S,G,rpt) )

inherited_olist(S,G) =
    inherited_olist(S,G,rpt) (+)
    joins(S,G) (+) pim_include(S,G) (-) lost_assert(S,G)

The macros pim_include(*,G) and pim_include(S,G) indicate the interfaces
to which traffic might be forwarded because of hosts that are local
members on that interface.  Note that normally only the DR cares about
local membership, but when an assert happens, the assert winner takes
over responsibility for forwarding traffic to local members that have
requested traffic on a group or source/group pair.

 pim_include(*,G) =
   { all interfaces I such that:
     ( ( I_am_DR( I ) AND lost_assert(*,G,I) == FALSE )



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       OR AssertWinner(*,G,I) == me )
     AND  local_receiver_include(*,G,I) }

pim_include(S,G) =
    { all interfaces I such that:
      ( (I_am_DR( I ) AND lost_assert(S,G,I) == FALSE )
        OR AssertWinner(S,G,I) == me )
       AND  local_receiver_include(S,G,I) }

pim_exclude(S,G) =
    { all interfaces I such that:
      ( (I_am_DR( I ) AND lost_assert(*,G,I) == FALSE )
        OR AssertWinner(*,G,I) == me )

       AND  local_receiver_exclude(S,G,I) }

The clause "local_receiver_include(S,G,I)" is true if the IGMP/MLD
module or other local membership mechanism has determined that local
members on interface I desire to receive traffic sent specifically by S
to G.  "local_receiver_include(*,G,I)" is true if the IGMP/MLD module or
other local membership mechanism has determined that local members on
interface I desire to receive all traffic sent to G (possibly excluding
traffic from a specific set of sources).  "local_receiver_exclude(S,G,I)
is true if "local_receiver_include(*,G,I)" is true but none of the local
members desire to receive traffic from S.

The set "joins(*,*,RP)" is the set of all interfaces on which the router
has received (*,*,RP) Joins:

joins(*,*,RP) =
    { all interfaces I such that
      DownstreamJPState(*,*,RP,I) is either Join or
          Prune-Pending }

DownstreamJPState(*,*,RP,I) is the state of the finite state machine in
Section 4.5.1.

The set "joins(*,G)" is the set of all interfaces on which the router
has received (*,G) Joins:

joins(*,G) =
    { all interfaces I such that
      DownstreamJPState(*,G,I) is either Join or Prune-Pending }

DownstreamJPState(*,G,I) is the state of the finite state machine in
Section 4.5.2.





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The set "joins(S,G)" is the set of all interfaces on which the router
has received (S,G) Joins:

joins(S,G) =
    { all interfaces I such that
      DownstreamJPState(S,G,I) is either Join or Prune-Pending }

DownstreamJPState(S,G,I) is the state of the finite state machine in
Section 4.5.3.

The set "prunes(S,G,rpt)" is the set of all interfaces on which the
router has received (*,G) joins and (S,G,rpt) prunes.

prunes(S,G,rpt) =
    { all interfaces I such that
      DownstreamJPState(S,G,rpt,I) is Prune or PruneTmp }

DownstreamJPState(S,G,rpt,I) is the state of the finite state machine in
Section 4.5.4.

The set "lost_assert(*,G)" is the set of all interfaces on which the
router has received (*,G) joins but has lost a (*,G) assert.  The macro
lost_assert(*,G,I) is defined in Section 4.6.5.

lost_assert(*,G) =
    { all interfaces I such that
      lost_assert(*,G,I) == TRUE }

The set "lost_assert(S,G,rpt)" is the set of all interfaces on which the
router has received (*,G) joins but has lost an (S,G) assert.  The macro
lost_assert(S,G,rpt,I) is defined in Section 4.6.5.

lost_assert(S,G,rpt) =
    { all interfaces I such that
      lost_assert(S,G,rpt,I) == TRUE }

The set "lost_assert(S,G)" is the set of all interfaces on which the
router has received (S,G) joins but has lost an (S,G) assert.  The macro
lost_assert(S,G,I) is defined in Section 4.6.5.

lost_assert(S,G) =
    { all interfaces I such that
      lost_assert(S,G,I) == TRUE }



The following pseudocode macro definitions are also used in many places
in the specification.  Basically RPF' is the RPF neighbor towards an RP



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or source unless a PIM-Assert has overridden the normal choice of
neighbor.

  neighbor RPF'(*,G) {
      if ( I_Am_Assert_Loser(*, G, RPF_interface(RP(G))) ) {
           return AssertWinner(*, G, RPF_interface(RP(G)) )
      } else {
           return NBR( RPF_interface(RP(G)), MRIB.next_hop( RP(G) ) )
      }
  }


  neighbor RPF'(S,G,rpt) {
      if( I_Am_Assert_Loser(S, G, RPF_interface(RP(G)) ) ) {
           return AssertWinner(S, G, RPF_interface(RP(G)) )
      } else {
           return RPF'(*,G)
      }
  }


  neighbor RPF'(S,G) {
      if ( I_Am_Assert_Loser(S, G, RPF_interface(S) )) {
           return AssertWinner(S, G, RPF_interface(S) )
      } else {
           return NBR( RPF_interface(S), MRIB.next_hop( S ) )
      }
  }


RPF'(*,G) and RPF'(S,G) indicate the neighbor from which data packets
should be coming and to which joins should be sent on the RP tree and
SPT respectively.

RPF'(S,G,rpt) is basically RPF'(*,G) modified by the result of an
Assert(S,G) on RPF_interface(RP(G)).  In such a case, packets from S
will be originating from a different router than RPF'(*,G).  If we only
have active (*,G) Join state, we need to accept packets from
RPF'(S,G,rpt), and add a Prune(S,G,rpt) to the periodic Join(*,G)
messages that we send to RPF'(*,G) (See Section 4.5.8).

The function MRIB.next_hop( S ) returns an address of the next-hop PIM
neighbor toward the host S, as indicated by the current MRIB.  If S is
directly adjacent, then MRIB.next_hop( S ) returns NULL.  At the RP for
G, MRIB.next_hop( RP(G)) returns NULL.

The function NBR( I, A ) uses information gathered through PIM Hello
messages to map the IP address A of a directly connected PIM neighbor



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router on interface I to the primary IP address of the same router
(Section 4.3.4). The primary IP address of a neighbor is the address
that it uses as the source of its PIM Hello messages. Note that a
neighbor's IP address may be non-unique within the PIM neighbor database
due to scope issues. The address must however be unique amongst the
addresses of all the PIM neighbors on a specific interface.

I_Am_Assert_Loser(S, G, I) is true if the Assert state machine (in
Section 4.6.1) for (S,G) on Interface I is in "I am Assert Loser" state.

I_Am_Assert_Loser(*, G, I) is true if the Assert state machine (in
Section 4.6.2) for (*,G) on Interface I is in "I am Assert Loser" state.

4.2.  Data Packet Forwarding Rules

The PIM-SM packet forwarding rules are defined below in pseudocode.

     iif is the incoming interface of the packet.
     S is the source address of the packet.
     G is the destination address of the packet (group address).
     RP is the address of the Rendezvous Point for this group.
     RPF_interface(S) is the interface the MRIB indicates would be used
     to route packets to S.
     RPF_interface(RP) is the interface the MRIB indicates would be used
     to route packets to RP, except at the RP when it is the
     decapsulation interface (the "virtual" interface on which register
     packets are received).

First, we restart (or start) the Keepalive Timer if the source is on a
directly connected subnet.

Second, we check to see if the SPTbit should be set because we've now
switched from the RP tree to the SPT.

Next we check to see whether the packet should be accepted based on TIB
state and the interface that the packet arrived on.

If the packet should be forwarded using (S,G) state, we then build an
outgoing interface list for the packet.  If this list is not empty, then
we restart the (S,G) state Keepalive Timer.

If the packet should be forwarded using (*,*,RP) or (*,G) state, then we
just build an outgoing interface list for the packet. We also check if
we should initiate a switch to start receiving this source on a shortest
path tree.

Finally we remove the incoming interface from the outgoing interface
list we've created, and if the resulting outgoing interface list is not



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empty, we forward the packet out of those interfaces.

On receipt of data from S to G on interface iif:
 if( DirectlyConnected(S) == TRUE AND iif == RPF_interface(S) ) {
      set KeepaliveTimer(S,G) to Keepalive_Period
      # Note: a register state transition or UpstreamJPState(S,G)
      # transition may happen as a result of restarting
      # KeepaliveTimer, and must be dealt with here.
 }


 if( iif == RPF_interface(S) AND UpstreamJPState(S,G) == Joined AND
    inherited_olist(S,G) != NULL ) {
        set KeepaliveTimer(S,G) to Keepalive_Period
 }

 Update_SPTbit(S,G,iif)
 oiflist = NULL

 if( iif == RPF_interface(S) AND SPTbit(S,G) == TRUE ) {
    oiflist = inherited_olist(S,G)
 } else if( iif == RPF_interface(RP(G)) AND SPTbit(S,G) == FALSE) {
   oiflist = inherited_olist(S,G,rpt)
   CheckSwitchToSpt(S,G)
 } else {
    # Note: RPF check failed
    # A transition in an Assert FSM, may cause an Assert(S,G)
    # or Assert(*,G) message to be sent out interface iif.
    # See section 4.6 for details.
    if ( SPTbit(S,G) == TRUE AND iif is in inherited_olist(S,G) ) {
       send Assert(S,G) on iif
    } else if ( SPTbit(S,G) == FALSE AND
                iif is in inherited_olist(S,G,rpt) {
       send Assert(*,G) on iif
    }
 }

 oiflist = oiflist (-) iif
 forward packet on all interfaces in oiflist

This pseudocode employs several "macro" definitions:

DirectlyConnected(S) is TRUE if the source S is on any subnet that is
directly connected to this router (or for packets originating on this
router).

inherited_olist(S,G) and inherited_olist(S,G,rpt) are defined in Section
4.1.



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Basically inherited_olist(S,G) is the outgoing interface list for
packets forwarded on (S,G) state taking into account (*,*,RP) state,
(*,G) state, asserts, etc.

inherited_olist(S,G,rpt) is the outgoing interface list for packets
forwarded on (*,*,RP) or (*,G) state taking into account (S,G,rpt) prune
state, and asserts, etc.

Update_SPTbit(S,G,iif) is defined in Section 4.2.2.

CheckSwitchToSpt(S,G) is defined in Section 4.2.1.

UpstreamJPState(S,G) is the state of the finite state machine in Section
4.5.7.

Keepalive_Period is defined in Section 4.10.

Data triggered PIM-Assert messages sent from the above forwarding code
should be rate-limited in a implementation-dependent manner.


4.2.1.  Last-hop Switchover to the SPT

In Sparse-Mode PIM, last-hop routers join the shared tree towards the
RP. Once traffic from sources to joined groups arrives at a last-hop
router it has the option of switching to receive the traffic on a
shortest path tree (SPT).

The decision for a router to switch to the SPT is controlled as follows:

     void
     CheckSwitchToSpt(S,G) {
       if ( ( pim_include(*,G) (-) pim_exclude(S,G)
              (+) pim_include(S,G) != NULL )
            AND SwitchToSptDesired(S,G) ) {
              # Note: Restarting the KAT will result in the SPT switch
              set KeepaliveTimer(S,G) to Keepalive_Period
       }
     }


SwitchToSptDesired(S,G) is a policy function that is implementation
defined. An "infinite threshold" policy can be implemented making
SwitchToSptDesired(S,G) return false all the time.  A "switch on first
packet" policy can be implemented by making SwitchToSptDesired(S,G)
return true once a single packet has been received for the source and
group.




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4.2.2.  Setting and Clearing the (S,G) SPTbit

The (S,G) SPTbit is used to distinguish whether to forward on
(*,*,RP)/(*,G) or on (S,G) state.  When switching from the RP tree to
the source tree, there is a transition period when data is arriving due
to upstream (*,*,RP)/(*,G) state while upstream (S,G) state is being
established during which time a router should continue to forward only
on (*,*,RP)/(*,G) state.  This prevents temporary black-holes that would
be caused by sending a Prune(S,G,rpt) before the upstream (S,G) state
has finished being established.

Thus, when a packet arrives, the (S,G) SPTbit is updated as follows:

     void
     Update_SPTbit(S,G,iif) {
       if ( iif == RPF_interface(S)
             AND JoinDesired(S,G) == TRUE
             AND ( DirectlyConnected(S) == TRUE
                   OR RPF_interface(S) != RPF_interface(RP(G))
                   OR inherited_olist(S,G,rpt) == NULL
                   OR ( ( RPF'(S,G) == RPF'(*,G) ) AND
                        ( RPF'(S,G) != NULL ) )
                   OR ( I_Am_Assert_Loser(S,G,iif) ) {
          Set SPTbit(S,G) to TRUE
       }
     }

Additionally a router can set SPTbit(S,G) to TRUE in other cases, such
as when it receives an Assert(S,G) on RPF_interface(S) (see Section
4.6.1).

JoinDesired(S,G) is defined in Section 4.5.7, and indicates whether we
have the appropriate (S,G) Join state to wish to send a Join(S,G)
upstream.

Basically Update_SPTbit will set the SPTbit if we have the appropriate
(S,G) join state and the packet arrived on the correct upstream
interface for S, and one or more of the following conditions applies:

1.   The source is directly connected, in which case the switch to the
     SPT is a no-op.

2.   The RPF interface to S is different from the RPF interface to the
     RP.  The packet arrived on RPF_interface(S), and so the SPT must
     have been completed.

3.   No-one wants the packet on the RP tree.




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4.   RPF'(S,G) == RPF'(*,G).  In this case the router will never be able
     to tell if the SPT has been completed, so it should just switch
     immediately.

In the case where the RPF interface is the same for the RP and for S,
but RPF'(S,G) and RPF'(*,G) differ, then we wait for an Assert(S,G)
which indicates that the upstream router with (S,G) state believes the
SPT has been completed.  However item (3) above is needed because there
may not be any (*,G) state to trigger an Assert(S,G) to happen.

The SPTbit is cleared in the (S,G) upstream state machine (see Section
4.5.7) when JoinDesired(S,G) becomes FALSE.


4.3.  Designated Routers (DR) and Hello Messages

A shared-media LAN like Ethernet may have multiple PIM-SM routers
connected to it. A single one of these routers, the DR, will act on
behalf of directly connected hosts with respect to the PIM-SM protocol.
Because the distinction between LANs and point-to-point interfaces can
sometimes be blurred, and because routers may also have multicast host
functionality, the PIM-SM specification makes no distinction between the
two.  Thus DR election will happen on all interfaces, LAN or otherwise.

DR election is performed using Hello messages.  Hello messages are also
the way that option negotiation takes place in PIM, so that additional
functionality can be enabled, or parameters tuned.


4.3.1.  Sending Hello Messages

PIM Hello messages are sent periodically on each PIM-enabled interface.
They allow a router to learn about the neighboring PIM routers on each
interface.  Hello messages are also the mechanism used to elect a
Designated Router (DR), and to negotiate additional capabilities.  A
router must record the Hello information received from each PIM
neighbor.

Hello messages MUST be sent on all active interfaces, including physical
point-to-point links, and are multicast to the `ALL-PIM-ROUTERS' group
address (`224.0.0.13' for IPv4 and `ff02::d' for IPv6).

     We note that some implementations do not send Hello messages
     on point-to-point interfaces.  This is non-compliant behavior.
     A compliant PIM router MUST send Hello messages, even on
     point-to-point interfaces.





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A per interface Hello Timer (HT(I)) is used to trigger sending Hello
messages on each active interface.  When PIM is enabled on an interface
or a router first starts, the Hello Timer of that interface is set to a
random value between 0 and Triggered_Hello_Delay.  This prevents
synchronization of Hello messages if multiple routers are powered on
simultaneously.  After the initial randomized interval, Hello messages
must be sent every Hello_Period seconds.  The Hello Timer should not be
reset except when it expires.

Note that neighbors will not accept Join/Prune or Assert messages from a
router unless they have first heard a Hello message from that router.
Thus if a router needs to send a Join/Prune or Assert message on an
interface on which it has not yet sent a Hello message with the
currently configured IP address, then it MUST immediately send the
relevant Hello message without waiting for the Hello Timer to expire,
followed by the Join/Prune or Assert message.

The DR_Priority Option allows a network administrator to give preference
to a particular router in the DR election process by giving it a
numerically larger DR Priority.  The DR_Priority Option SHOULD be
included in every Hello message, even if no DR Priority is explicitly
configured on that interface.  This is necessary because priority-based
DR election is only enabled when all neighbors on an interface advertise
that they are capable of using the DR_Priority Option.  The default
priority is 1.

The Generation_Identifier (GenID) Option SHOULD be included in all Hello
messages.  The GenID option contains a randomly generated 32-bit value
that is regenerated each time PIM forwarding is started or restarted on
the interface, including when the router itself restarts.  When a Hello
message with a new GenID is received from a neighbor, any old Hello
information about that neighbor SHOULD be discarded and superseded by
the information from the new Hello message.  This may cause a new DR to
be chosen on that interface.

The LAN Prune Delay Option SHOULD be included in all Hello messages sent
on multi-access LANs. This option advertises a router's capability to
use values other than the default for the Propagation_Delay and
Override_Interval which affect the setting of the Prune-Pending,
Upstream Join and Override Timers (defined in Section 4.10).

The Address List Option advertises all the secondary addresses
associated with the source interface of the router originating the
message. The option MUST be included in all Hello messages if there are
secondary addresses associated with the source interface and MAY be
omitted if no secondary addresses exist.





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To allow new or rebooting routers to learn of PIM neighbors quickly,
when a Hello message is received from a new neighbor, or a Hello message
with a new GenID is received from an existing neighbor, a new Hello
message should be sent on this interface after a randomized delay
between 0 and Triggered_Hello_Delay.  This triggered message need not
change the timing of the scheduled periodic message.  If a router needs
to send a Join/Prune to the new neighbor or send an Assert message in
response to an Assert message from the new neighbor before this
randomized delay has expired, then it MUST immediately send the relevant
Hello message without waiting for the Hello Timer to expire, followed by
the Join/Prune or Assert message.  If it does not do this, then the new
neighbor will discard the Join/Prune or Assert message.

Before an interface goes down or changes primary IP address, a Hello
message with a zero HoldTime should be sent immediately (with the old IP
address if the IP address changed).  This will cause PIM neighbors to
remove this neighbor (or its old IP address) immediately.  After an
interface has changed its IP address, it MUST send a Hello message with
its new IP address.  If an interface changes one of its secondary IP
addresses, a Hello message with an updated Address_List option and a
non-zero HoldTime should be sent immediately.  This will cause PIM
neighbors to update this neighbor's list of secondary addresses
immediately.

4.3.2.  DR Election

When a PIM Hello message is received on interface I the following
information about the sending neighbor is recorded:

     neighbor.interface
          The interface on which the Hello message arrived.

     neighbor.primary_ip_address
          The IP address that the PIM neighbor used as the source
          address of the Hello message.

     neighbor.genid
          The Generation ID of the PIM neighbor.

     neighbor.dr_priority
          The DR Priority field of the PIM neighbor if it is present in
          the Hello message.

     neighbor.dr_priority_present
          A flag indicating if the DR Priority field was present in the
          Hello message.





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     neighbor.timeout
          A timer value to time out the neighbor state when it becomes
          stale.
          The Neighbor Liveness Timer (NLT(N,I)) is reset to
          Hello_Holdtime (from the Hello Holdtime option) whenever a
          Hello message is received containing a Holdtime option, or to
          Default_Hello_Holdtime if the Hello message does not contain
          the Holdtime option.

Neighbor state is deleted when the neighbor timeout expires.

The function for computing the DR on interface I is:

  host
  DR(I) {
      dr = me
      for each neighbor on interface I {
          if ( dr_is_better( neighbor, dr, I ) == TRUE ) {
              dr = neighbor
          }
      }
      return dr
  }


The function used for comparing DR "metrics" on interface I is:

  bool
  dr_is_better(a,b,I) {
      if( there is a neighbor n on I for which n.dr_priority_present
              is false ) {
          return a.primary_ip_address > b.primary_ip_address
      } else {
          return ( a.dr_priority > b.dr_priority ) OR
              ( a.dr_priority == b.dr_priority AND
                   a.primary_ip_address > b.primary_ip_address )
      }
  }

The trivial function I_am_DR(I) is defined to aid readability:

  bool
  I_am_DR(I) {
     return DR(I) == me
  }






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The DR Priority is a 32-bit unsigned number and the numerically larger
priority is always preferred.  A router's idea of the current DR on an
interface can change when a PIM Hello message is received, when a
neighbor times out, or when a router's own DR Priority changes.  If the
router becomes the DR or ceases to be the DR, this will normally cause
the DR Register state machine to change state.  Subsequent actions are
determined by that state machine.

     We note that some PIM implementations do not send Hello
     messages on point-to-point interfaces, and so cannot perform
     DR election on such interfaces.  This is non-compliant
     behavior.  DR election MUST be performed on ALL active PIM-SM
     interfaces.


4.3.3.  Reducing Prune Propagation Delay on LANs

In addition to the information recorded for the DR Election, the
following per neighbor information is obtained from the LAN Prune Delay
Hello option:

     neighbor.lan_prune_delay_present
          A flag indicating if the LAN Prune Delay option was present in
          the Hello message.

     neighbor.tracking_support
          A flag storing the value of the T bit in the LAN Prune Delay
          option if it is present in the Hello message. This indicates
          the neighbor's capability to disable Join message suppression.

     neighbor.propagation_delay
          The Propagation Delay field of the LAN Prune Delay option (if
          present) in the Hello message.

     neighbor.override_interval
          The Override_Interval field of the LAN Prune Delay option (if
          present) in the Hello message.

The additional state described above is deleted along with the DR
neighbor state when the neighbor timeout expires.

Just like the DR_Priority option, the information provided in the LAN
Prune Delay option is not used unless all neighbors on a link advertise
the option. The function below computes this state:







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  bool
  lan_delay_enabled(I) {
      for each neighbor on interface I {
          if ( neighbor.lan_prune_delay_present == false ) {
              return false
          }
      }
      return true
  }


The Propagation Delay inserted by a router in the LAN Prune Delay option
expresses the expected message propagation delay on the link and should
be configurable by the system administrator. It is used by upstream
routers to figure out how long they should wait for a Join override
message before pruning an interface.

PIM implementors should enforce a lower bound on the permitted values
for this delay to allow for scheduling and processing delays within
their router.  Such delays may cause received messages to be processed
later as well as triggered messages to be sent later than intended.
Setting this Propagation Delay to too low a value may result in
temporary forwarding outages because a downstream router will not be
able to override a neighbor's Prune message before the upstream neighbor
stops forwarding.

When all routers on a link are in a position to negotiate a different
than default Propagation Delay, the largest value from those advertised
by each neighbor is chosen. The function for computing the
Effective_Propagation_Delay of interface I is:

  time_interval
  Effective_Propagation_Delay(I) {
      if ( lan_delay_enabled(I) == false ) {
          return Propagation_delay_default
      }
      delay = Propagation_Delay(I)
      for each neighbor on interface I {
          if ( neighbor.propagation_delay > delay ) {
              delay = neighbor.propagation_delay
          }
      }
      return delay
  }


To avoid synchronization of override messages when multiple downstream
routers share a multi-access link, sending of such messages is delayed



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by a small random amount of time. The period of randomization should
represent the size of the PIM router population on the link.  Each
router expresses its view of the amount of randomization necessary in
the Override Interval field of the LAN Prune Delay option.

When all routers on a link are in a position to negotiate a different
than default Override Interval, the largest value from those advertised
by each neighbor is chosen. The function for computing the Effective
Override Interval of interface I is:

  time_interval
  Effective_Override_Interval(I) {
      if ( lan_delay_enabled(I) == false ) {
          return t_override_default
      }
      delay = Override_Interval(I)
      for each neighbor on interface I {
          if ( neighbor.override_interval > delay ) {
              delay = neighbor.override_interval
          }
      }
      return delay
  }


Although the mechanisms are not specified in this document, it is
possible for upstream routers to explicitly track the join membership of
individual downstream routers if Join suppression is disabled.  A router
can advertise its willingness to disable Join suppression by using the T
bit in the LAN Prune Delay Hello option. Unless all PIM routers on a
link negotiate this capability, explicit tracking and the disabling of
the Join suppression mechanism are not possible. The function for
computing the state of Suppression on interface I is:

  bool
  Suppression_Enabled(I) {
      if ( lan_delay_enabled(I) == false ) {
          return true
      }
      for each neighbor on interface I {
          if ( neighbor.tracking_support == false ) {
              return true
          }
      }
      return false
  }

Note that the setting of Suppression_Enabled(I) affects the value of



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t_suppressed (see Section 4.10).

4.3.4.  Maintaining Secondary Address Lists

Communication of a router's interface secondary addresses to its PIM
neighbors is necessary to provide the neighbors with a mechanism for
mapping next_hop information obtained through their MRIB to a primary
address that can be used as a destination for Join/Prune messages.  The
mapping is performed through the NBR macro.  The primary address of a
PIM neighbor is obtained from the source IP address used in its PIM
Hello messages. Secondary addresses are carried within the Hello message
in an Address List Hello option. The primary address of the source
interface of the router MUST NOT be listed within the Address List Hello
option.

In addition to the information recorded for the DR Election, the
following per neighbor information is obtained from the Address List
Hello option:

     neighbor.secondary_address_list
          The list of secondary addresses used by the PIM neighbor on
          the interface through which the Hello message was transmitted.

When processing a received PIM Hello message containing an Address List
Hello option, the list of secondary addresses in the message completely
replaces any previously associated secondary addresses for that
neighbor. If a received PIM Hello message does not contain an Address
List Hello option then all secondary addresses associated with the
neighbor must be deleted. If a received PIM Hello message contains an
Address List Hello option that includes the primary address of the
sending router in the list of secondary addresses (although this is not
expected) then the addresses listed in the message excluding the primary
address are used to update the associated secondary addresses for that
neighbor.

All the advertised secondary addresses in received Hello messages must
be checked against those previously advertised by all other PIM
neighbors on that interface. If there is a conflict and the same
secondary address was previously advertised by another neighbor then
only the most recently received mapping MUST be maintained and an error
message SHOULD be logged to the administrator in a rate limited manner.

Within one Address List Hello option, all the addresses MUST be of the
same address family.  It is not permitted to mix IPv4 and IPv6 addresses
within the same message.  In addition, the address family of the fields
in the message SHOULD be the same as the IP source and destination
addresses of the packet header.




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4.4.  PIM Register Messages

Overview

The Designated Router (DR) on a LAN or point-to-point link encapsulates
multicast packets from local sources to the RP for the relevant group
unless it recently received a Register-Stop message for that (S,G) or
(*,G) from the RP.  When the DR receives a Register-Stop message from
the RP, it starts a Register-Stop Timer to maintain this state.  Just
before the Register-Stop Timer expires, the DR sends a Null-Register
Message to the RP to allow the RP to refresh the Register-Stop
information at the DR.  If the Register-Stop Timer actually expires, the
DR will resume encapsulating packets from the source to the RP.


4.4.1.  Sending Register Messages from the DR

Every PIM-SM router has the capability to be a DR.  The state machine
below is used to implement Register functionality.  For the purposes of
specification, we represent the mechanism to encapsulate packets to the
RP as a Register-Tunnel interface, which is added to or removed from the
(S,G) olist.  The tunnel interface then takes part in the normal packet
forwarding rules as specified in Section 4.2.

If register state is maintained, it is maintained only for directly
connected sources, and is per-(S,G).  There are four states in the DR's
per-(S,G) Register state machine:

Join (J)
     The register tunnel is "joined" (the join is actually implicit, but
     the DR acts as if the RP has joined the DR on the tunnel
     interface).

Prune (P)
     The register tunnel is "pruned" (this occurs when a Register-Stop
     is received).

Join-Pending (JP)
     The register tunnel is pruned but the DR is contemplating adding it
     back.

NoInfo (NI)
     No information.  This is the initial state, and the state when the
     router is not the DR.

In addition, a Register-Stop Timer (RST) is kept if the state machine is
not in the NoInfo state.




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   Figure 1: Per-(S,G) register state machine at a DR in tabular form

+-----------++---------------------------------------------------------------+
|           ||                            Event                              |
|           ++-----------+------------+------------+------------+------------+
|Prev State ||Register-  | Could      | Could      | Register-  | RP changed |
|           ||Stop Timer | Register   | Register   | Stop       |            |
|           ||expires    | ->True     | ->False    | received   |            |
+-----------++-----------+------------+------------+------------+------------+
|NoInfo     ||-          | -> J state | -          | -          | -          |
|(NI)       ||           | add reg    |            |            |            |
|           ||           | tunnel     |            |            |            |
+-----------++-----------+------------+------------+------------+------------+
|           ||-          | -          | -> NI      | -> P state | -> J state |
|           ||           |            | state      |            |            |
|           ||           |            | remove reg | remove reg | update reg |
|Join (J)   ||           |            | tunnel     | tunnel;    | tunnel     |
|           ||           |            |            | set        |            |
|           ||           |            |            | Register-  |            |
|           ||           |            |            | Stop       |            |
|           ||           |            |            | Timer(*)   |            |
+-----------++-----------+------------+------------+------------+------------+
|           ||-> J state | -          | -> NI      | -> P state | -> J state |
|           ||           |            | state      |            |            |
|Join-      ||add reg    |            |            | set        | add reg    |
|Pending    ||tunnel     |            |            | Register-  | tunnel;    |
|(JP)       ||           |            |            | Stop       | cancel     |
|           ||           |            |            | Timer(*)   | Register-  |
|           ||           |            |            |            | Stop Timer |
+-----------++-----------+------------+------------+------------+------------+
|           ||-> JP      | -          | -> NI      | -          | -> J state |
|           ||state      |            | state      |            |            |
|           ||set        |            |            |            | add reg    |
|Prune (P)  ||Register-  |            |            |            | tunnel;    |
|           ||Stop       |            |            |            | cancel     |
|           ||Timer(**); |            |            |            | Register-  |
|           ||send Null- |            |            |            | Stop Timer |
|           ||Register   |            |            |            |            |
+-----------++-----------+------------+------------+------------+------------+

Notes:

(*) The Register-Stop Timer is set to a random value chosen uniformly
     from the interval ( 0.5 * Register_Suppression_Time, 1.5 *
     Register_Suppression_Time) minus Register_Probe_Time;

     Subtracting off Register_Probe_Time is a bit unnecessary because it
     is really small compared to Register_Suppression_Time, but was in



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     the old spec and is kept for compatibility.

(**) The Register-Stop Timer is set to Register_Probe_Time.

The following actions are defined:

Add Register Tunnel

A Register-Tunnel virtual interface, VI, is created (if it doesn't
already exist) with its encapsulation target being RP(G).
DownstreamJPState(S,G,VI) is set to Join state, causing the tunnel
interface to be added to immediate_olist(S,G) and inherited_olist(S,G).

Remove Register Tunnel

VI is the Register-Tunnel virtual interface with encapsulation target of
RP(G). DownstreamJPState(S,G,VI) is set to NoInfo state, causing the
tunnel interface to be removed from immediate_olist(S,G) and
inherited_olist(S,G).  If DownstreamJPState(S,G,VI) is NoInfo for all
(S,G), then VI can be deleted.

Update Register Tunnel

This action occurs when RP(G) changes.

VI_old is the Register-Tunnel virtual interface with encapsulation
target old_RP(G).  A Register-Tunnel virtual interface, VI_new, is
created (if it doesn't already exist) with its encapsulation target
being new_RP(G).  DownstreamJPState(S,G,VI_old) is set to NoInfo state
and DownstreamJPState(S,G,VI_new) is set to Join state.  If
DownstreamJPState(S,G,VI_old) is NoInfo for all (S,G), then VI_old can
be deleted.

Note that we can not simply change the encapsulation target of VI_old
because not all groups using that encapsulation tunnel will have moved
to the same new RP.

CouldRegister(S,G)

The macro "CouldRegister" in the state machine is defined as:

  bool CouldRegister(S,G) {
     return ( I_am_DR( RPF_interface(S) ) AND
              KeepaliveTimer(S,G) is running AND
              DirectlyConnected(S) == TRUE )
  }





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Note that on reception of a packet at the DR from a directly connected
source, KeepaliveTimer(S,G) needs to be set by the packet forwarding
rules before computing CouldRegister(S,G) in the register state machine,
or the first packet from a source won't be registered.


Encapsulating data packets in the Register Tunnel

Conceptually, the Register Tunnel is an interface with a smaller MTU
than the underlying IP interface towards the RP.  IP fragmentation on
packets forwarded on the Register Tunnel is performed based upon this
smaller MTU.  The encapsulating DR may perform Path MTU Discovery to the
RP to determine the effective MTU of the tunnel.  Fragmentation for the
smaller MTU should take both the outer IP header and the PIM register
header overhead into account.  If a multicast packet is fragmented on
the way into the Register Tunnel, each fragment is encapsulated
individually so it contains IP, PIM, and inner IP headers.

In IPv6, the DR MUST perform Path MTU discovery, and an ICMP Packet Too
Big message MUST be sent by the encapsulating DR if it receives a packet
that will not fit in the effective MTU of the tunnel.  If the MTU
between the DR and the RP results in the effective tunnel MTU being
smaller than 1280 (the IPv6 minimum MTU), the DR MUST send Fragmentation
Required messages with an MTU value of 1280 and MUST fragment its PIM
register messages as required, using an IPv6 fragmentation header
between the outer IPv6 header and the PIM Register header.

The TTL of a forwarded data packet is decremented before it is
encapsulated in the Register Tunnel.  The encapsulating packet uses the
normal TTL that the router would use for any locally-generated IP
packet.

The IP ECN bits should be copied from the original packet to the IP
header of the encapsulating packet.  They SHOULD NOT be set
independently by the encapsulating router.

The Diffserv Code Point (DSCP) should be copied from the original packet
to the IP header of the encapsulating packet.  It MAY be set
independently by the encapsulating router, based upon static
configuration or traffic classification.  See [12] for more discussion
on setting the DSCP on tunnels.

Handling Register-Stop(*,G) Messages at the DR

An old RP might send a Register-Stop message with the source address set
to all-zeros.  This was the normal course of action in RFC 2362 when the
Register message matched against (*,G) state at the RP, and was defined
as meaning "stop encapsulating all sources for this group".  However,



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the behavior of such a Register-Stop(*,G) is ambiguous or incorrect in
some circumstances.

We specify that an RP should not send Register-Stop(*,G) messages, but
for compatibility, a DR should be able to accept one if it is received.

A Register-Stop(*,G) should be treated as a Register-Stop(S,G) for all
(S,G) Register state machines that are not in the NoInfo state.  A
router should not apply a Register-Stop(*,G) to sources that become
active after the Register-Stop(*,G) was received.









































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4.4.2.  Receiving Register Messages at the RP

When an RP receives a Register message, the course of action is decided
according to the following pseudocode:

packet_arrives_on_rp_tunnel( pkt ) {
    if( outer.dst is not one of my addresses ) {
        drop the packet silently.
        # Note: this may be a spoofing attempt
    }
    if( I_am_RP(G) AND outer.dst == RP(G) ) {
          sentRegisterStop = FALSE;
          if ( register.borderbit == TRUE ) {
               if ( PMBR(S,G) == unknown ) {
                    PMBR(S,G) = outer.src
               } else if ( outer.src != PMBR(S,G) ) {
                    send Register-Stop(S,G) to outer.src
                    drop the packet silently.
               }
          }
          if ( SPTbit(S,G) OR
           ( SwitchToSptDesired(S,G) AND ( inherited_olist(S,G) == NULL ))) {
            send Register-Stop(S,G) to outer.src
            sentRegisterStop = TRUE;
          }
          if ( SPTbit(S,G) OR SwitchToSptDesired(S,G) ) {
               if ( sentRegisterStop == TRUE ) {
                    set KeepaliveTimer(S,G) to RP_Keepalive_Period;
               } else {
                    set KeepaliveTimer(S,G) to Keepalive_Period;
               }
          }
          if( !SPTbit(S,G) AND ! pkt.NullRegisterBit ) {
               decapsulate and forward the inner packet to
               inherited_olist(S,G,rpt) # Note (+)
          }
    } else {
        send Register-Stop(S,G) to outer.src
        # Note (*)
    }
}


outer.dst is the IP destination address of the encapsulating header.

outer.src is the IP source address of the encapsulating header, i.e.,
the DR's address.




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I_am_RP(G) is true if the group-to-RP mapping indicates that this router
is the RP for the group.

Note (*): This may block traffic from S for Register_Suppression_Time if
     the DR learned about a new group-to-RP mapping before the RP did.
     However, this doesn't matter unless we figure out some way for the
     RP to also accept (*,G) joins when it doesn't yet realize that it
     is about to become the RP for G.  This will all get sorted out once
     the RP learns the new group-to-rp mapping.  We decided to do
     nothing about this and just accept the fact that PIM may suffer
     interrupted (*,G) connectivity following an RP change.

Note (+): Implementations are advised to not make this a special case,
     but to arrange that this path rejoin the normal packet forwarding
     path.  All of the appropriate actions from the "On receipt of data
     from S to G on interface iif" pseudocode in Section 4.2 should be
     performed.

KeepaliveTimer(S,G) is restarted at the RP when packets arrive on the
proper tunnel interface and the RP desires to switch to the SPT or the
SPTbit is already set.  This may cause the upstream (S,G) state machine
to trigger a join if the inherited_olist(S,G) is not NULL;

An RP should preserve (S,G) state that was created in response to a
Register message for at least ( 3 * Register_Suppression_Time ),
otherwise the RP may stop joining (S,G) before the DR for S has
restarted sending registers.  Traffic would then be interrupted until
the Register-Stop Timer expires at the DR.

Thus, at the RP, KeepaliveTimer(S,G) should be restarted to ( 3 *
Register_Suppression_Time + Register_Probe_Time ).

When forwarding a packet from the Register Tunnel, the TTL of the
original data packet is decremented after it is decapsulated.

The IP ECN bits should be copied from the IP header of the Register
packet to the decapsulated packet.

The Diffserv Code Point (DSCP) should be copied from the IP header of
the Register packet to the decapsulated packet.  The RP MAY retain the
DSCP of the inner packet, or re-classify the packet and apply a
different DSCP.  Scenarios where each of these might be useful are
discussed in [12].

4.5.  PIM Join/Prune Messages

A PIM Join/Prune message consists of a list of groups and a list of
Joined and Pruned sources for each group.  When processing a received



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Join/Prune message, each Joined or Pruned source for a Group is
effectively considered individually, and applies to one or more of the
following state machines.  When considering a Join/Prune message whose
Upstream Neighbor Address field addresses this router, (*,G) Joins and
Prunes can affect both the (*,G) and (S,G,rpt) downstream state
machines, while (*,*,RP), (S,G) and (S,G,rpt) Joins and Prunes can only
affect their respective downstream state machines.  When considering a
Join/Prune message whose Upstream Neighbor Address field addresses
another router, most Join or Prune messages could affect each upstream
state machine.

In general, a PIM Join/Prune message should only be accepted for
processing if it comes from a known PIM neighbor.  A PIM router hears
about PIM neighbors through PIM Hello messages.  If a router receives a
Join/Prune message from a particular IP source address and it has not
seen a PIM Hello message from that source address, then the Join/Prune
message SHOULD be discarded without further processing.  In addition, if
the Hello message from a neighbor was authenticated using IPsec AH (see
Section 6.3) then all Join/Prune messages from that neighbor MUST also
be authenticated using IPsec AH.

We note that some older PIM implementations incorrectly fail to send
Hello messages on point-to-point interfaces, so we also RECOMMEND that a
configuration option be provided to allow interoperation with such older
routers, but that this configuration option SHOULD NOT be enabled by
default.


4.5.1.  Receiving (*,*,RP) Join/Prune Messages

The per-interface state machine for receiving (*,*,RP) Join/Prune
Messages is given below.  There are three states:

     NoInfo (NI)
          The interface has no (*,*,RP) Join state and no timers
          running.

     Join (J)
          The interface has (*,*,RP) Join state which will cause the
          router to forward packets destined for any group handled by RP
          from this interface except if there is also (S,G,rpt) prune
          information (see Section 4.5.4) or the router lost an assert
          on this interface.

     Prune-Pending (PP)
          The router has received a Prune(*,*,RP) on this interface from
          a downstream neighbor and is waiting to see whether the prune
          will be overridden by another downstream router.  For



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          forwarding purposes, the Prune-Pending state functions exactly
          like the Join state.

In addition, the state machine uses two timers:

     ExpiryTimer (ET)
          This timer is restarted when a valid Join(*,*,RP) is received.
          Expiry of the ExpiryTimer causes the interface state to revert
          to NoInfo for this RP.

     Prune-Pending Timer (PPT)
          This timer is set when a valid Prune(*,*,RP) is received.
          Expiry of the Prune-Pending Timer causes the interface state
          to revert to NoInfo for this RP.

Figure 2: Downstream per-interface (*,*,RP) state machine in tabular form

+-------------++----------------------------------------------------------+
|             ||                          Event                           |
|             ++-------------+--------------+--------------+--------------+
|Prev State   ||Receive      | Receive      | Prune-       | Expiry Timer |
|             ||Join(*,*,RP) | Prune        | Pending      | Expires      |
|             ||             | (*,*,RP)     | Timer        |              |
|             ||             |              | Expires      |              |
+-------------++-------------+--------------+--------------+--------------+
|             ||-> J state   | -> NI state  | -            | -            |
|NoInfo (NI)  ||start Expiry |              |              |              |
|             ||Timer        |              |              |              |
+-------------++-------------+--------------+--------------+--------------+
|             ||-> J state   | -> PP state  | -            | -> NI state  |
|Join (J)     ||restart      | start Prune- |              |              |
|             ||Expiry Timer | Pending      |              |              |
|             ||             | Timer        |              |              |
+-------------++-------------+--------------+--------------+--------------+
|Prune-       ||-> J state   | -> PP state  | -> NI state  | -> NI state  |
|Pending (PP) ||restart      |              | Send Prune-  |              |
|             ||Expiry Timer |              | Echo(*,*,RP) |              |
+-------------++-------------+--------------+--------------+--------------+

The transition events "Receive Join(*,*,RP)" and "Receive Prune(*,*,RP)"
imply receiving a Join or Prune targeted to this router's primary IP
address on the received interface.  If the upstream neighbor address
field is not correct, these state transitions in this state machine must
not occur, although seeing such a packet may cause state transitions in
other state machines.

On unnumbered interfaces on point-to-point links, the router's address
should be the same as the source address it chose for the Hello message



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it sent over that interface.  However on point-to-point links we also
recommend that for backwards compatibility PIM Join/Prune messages with
a upstream neighbor address field of all zeros are also accepted.

Transitions from NoInfo State

When in NoInfo state, the following event may trigger a transition:

     Receive Join(*,*,RP)
          A Join(*,*,RP) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,*,RP) downstream state machine on interface I
          transitions to the Join state.  The Expiry Timer (ET) is
          started, and set to the HoldTime from the triggering
          Join/Prune message.

          Note that it is possible to receive a Join(*,*,RP) message for
          an RP that we do not have information telling us that it is an
          RP.  In the case of (*,*,RP) state, so long as we have a route
          to the RP, this will not cause a problem, and the transition
          should still take place.

Transitions from Join State

When in Join state, the following events may trigger a transition:

     Receive Join(*,*,RP)
          A Join(*,*,RP) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,*,RP) downstream state machine on interface I remains
          in Join state, and the Expiry Timer (ET) is restarted, set to
          maximum of its current value and the HoldTime from the
          triggering Join/Prune message.

     Receive Prune(*,*,RP)
          A Prune(*,*,RP) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,*,RP) downstream state machine on interface I
          transitions to the Prune-Pending state.  The Prune-Pending
          Timer is started; it is set to the J/P_Override_Interval(I) if
          the router has more than one neighbor on that interface;
          otherwise it is set to zero causing it to expire immediately.

     Expiry Timer Expires
          The Expiry Timer for the (*,*,RP) downstream state machine on



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          interface I expires.

          The (*,*,RP) downstream state machine on interface I
          transitions to the NoInfo state.

Transitions from Prune-Pending State

When in Prune-Pending state, the following events may trigger a
transition:

     Receive Join(*,*,RP)
          A Join(*,*,RP) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,*,RP) downstream state machine on interface I
          transitions to the Join state.  The Prune-Pending Timer is
          canceled (without triggering an expiry event).  The Expiry
          Timer is restarted, set to maximum of its current value and
          the HoldTime from the triggering Join/Prune message.

     Expiry Timer Expires
          The Expiry Timer for the (*,*,RP) downstream state machine on
          interface I expires.

          The (*,*,RP) downstream state machine on interface I
          transitions to the NoInfo state.

     Prune-Pending Timer Expires
          The Prune-Pending Timer for the (*,*,RP) downstream state
          machine on interface I expires.

          The (*,*,RP) downstream state machine on interface I
          transitions to the NoInfo state.  A PruneEcho(*,*,RP) is sent
          onto the subnet connected to interface I.

          The action "Send PruneEcho(*,*,RP)" is triggered when the
          router stops forwarding on an interface as a result of a
          prune.  A PruneEcho(*,*,RP) is simply a Prune(*,*,RP) message
          sent by the upstream router on a LAN with its own address in
          the Upstream Neighbor Address field.  Its purpose is to add
          additional reliability so that if a Prune that should have
          been overridden by another router is lost locally on the LAN,
          then the PruneEcho may be received and cause the override to
          happen.  A PruneEcho(*,*,RP) need not be sent on an interface
          that contains only a single PIM neighbor during the time this
          state machine was in Prune-Pending state.





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4.5.2.  Receiving (*,G) Join/Prune Messages

When a router receives a Join(*,G) it must first check to see whether
the RP in the message matches RP(G) (the router's idea of who the RP
is).  If the RP in the message does not match RP(G) the Join(*,G) should
be silently dropped.  (Note that other source list entries such as
(S,G,rpt) or (S,G) in the same Group Specific Set should still be
processed.)  If a router has no RP information (e.g. has not recently
received a BSR message) then it may choose to accept Join(*,G) and treat
the RP in the message as RP(G).  Received Prune(*,G) messages are
processed even if the RP in the message does not match RP(G).

The per-interface state machine for receiving (*,G) Join/Prune Messages
is given below.  There are three states:

     NoInfo (NI)
          The interface has no (*,G) Join state and no timers running.

     Join (J)
          The interface has (*,G) Join state which will cause the router
          to forward packets destined for G from this interface except
          if there is also (S,G,rpt) prune information (see Section
          4.5.4) or the router lost an assert on this interface.

     Prune-Pending (PP)
          The router has received a Prune(*,G) on this interface from a
          downstream neighbor and is waiting to see whether the prune
          will be overridden by another downstream router.  For
          forwarding purposes, the Prune-Pending state functions exactly
          like the Join state.

In addition, the state machine uses two timers:

     Expiry Timer (ET)
          This timer is restarted when a valid Join(*,G) is received.
          Expiry of the Expiry Timer causes the interface state to
          revert to NoInfo for this group.

     Prune-Pending Timer (PPT)
          This timer is set when a valid Prune(*,G) is received.  Expiry
          of the Prune-Pending Timer causes the interface state to
          revert to NoInfo for this group.









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 Figure 3: Downstream per-interface (*,G) state machine in tabular form

+-------------++---------------------------------------------------------+
|             ||                         Event                           |
|             ++-------------+--------------+-------------+--------------+
|Prev State   ||Receive      | Receive      | Prune-      | Expiry Timer |
|             ||Join(*,G)    | Prune(*,G)   | Pending     | Expires      |
|             ||             |              | Timer       |              |
|             ||             |              | Expires     |              |
+-------------++-------------+--------------+-------------+--------------+
|             ||-> J state   | -> NI state  | -           | -            |
|NoInfo (NI)  ||start Expiry |              |             |              |
|             ||Timer        |              |             |              |
+-------------++-------------+--------------+-------------+--------------+
|             ||-> J state   | -> PP state  | -           | -> NI state  |
|Join (J)     ||restart      | start Prune- |             |              |
|             ||Expiry Timer | Pending      |             |              |
|             ||             | Timer        |             |              |
+-------------++-------------+--------------+-------------+--------------+
|Prune-       ||-> J state   | -> PP state  | -> NI state | -> NI state  |
|Pending (PP) ||restart      |              | Send Prune- |              |
|             ||Expiry Timer |              | Echo(*,G)   |              |
+-------------++-------------+--------------+-------------+--------------+

The transition events "Receive Join(*,G)" and "Receive Prune(*,G)" imply
receiving a Join or Prune targeted to this router's primary IP address
on the received interface.  If the upstream neighbor address field is
not correct, these state transitions in this state machine must not
occur, although seeing such a packet may cause state transitions in
other state machines.

On unnumbered interfaces on point-to-point links, the router's address
should be the same as the source address it chose for the Hello message
it sent over that interface.  However on point-to-point links we also
recommend that for backwards compatibility PIM Join/Prune messages with
a upstream neighbor address field of all zeros are also accepted.

Transitions from NoInfo State

When in NoInfo state, the following event may trigger a transition:

     Receive Join(*,G)
          A Join(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,G) downstream state machine on interface I transitions
          to the Join state.  The Expiry Timer (ET) is started, and set
          to the HoldTime from the triggering Join/Prune message.



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Transitions from Join State

When in Join state, the following events may trigger a transition:

     Receive Join(*,G)
          A Join(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,G) downstream state machine on interface I remains in
          Join state, and the Expiry Timer (ET) is restarted, set to
          maximum of its current value and the HoldTime from the
          triggering Join/Prune message.

     Receive Prune(*,G)
          A Prune(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,G) downstream state machine on interface I transitions
          to the Prune-Pending state.  The Prune-Pending Timer is
          started; it is set to the J/P_Override_Interval(I) if the
          router has more than one neighbor on that interface; otherwise
          it is set to zero causing it to expire immediately.

     Expiry Timer Expires
          The Expiry Timer for the (*,G) downstream state machine on
          interface I expires.

          The (*,G) downstream state machine on interface I transitions
          to the NoInfo state.

Transitions from Prune-Pending State

When in Prune-Pending state, the following events may trigger a
transition:

     Receive Join(*,G)
          A Join(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (*,G) downstream state machine on interface I transitions
          to the Join state.  The Prune-Pending Timer is canceled
          (without triggering an expiry event).  The Expiry Timer is
          restarted, set to maximum of its current value and the
          HoldTime from the triggering Join/Prune message.

     Expiry Timer Expires
          The Expiry Timer for the (*,G) downstream state machine on
          interface I expires.



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          The (*,G) downstream state machine on interface I transitions
          to the NoInfo state.

     Prune-Pending Timer Expires
          The Prune-Pending Timer for the (*,G) downstream state machine
          on interface I expires.

          The (*,G) downstream state machine on interface I transitions
          to the NoInfo state.  A PruneEcho(*,G) is sent onto the subnet
          connected to interface I.

          The action "Send PruneEcho(*,G)" is triggered when the router
          stops forwarding on an interface as a result of a prune.  A
          PruneEcho(*,G) is simply a Prune(*,G) message sent by the
          upstream router on a LAN with its own address in the Upstream
          Neighbor Address field.  Its purpose is to add additional
          reliability so that if a Prune that should have been
          overridden by another router is lost locally on the LAN, then
          the PruneEcho may be received and cause the override to
          happen.  A PruneEcho(*,G) need not be sent on an interface
          that contains only a single PIM neighbor during the time this
          state machine was in Prune-Pending state.

4.5.3.  Receiving (S,G) Join/Prune Messages

The per-interface state machine for receiving (S,G) Join/Prune messages
is given below, and is almost identical to that for (*,G) messages.
There are three states:

     NoInfo (NI)
          The interface has no (S,G) Join state and no (S,G) timers
          running.

     Join (J)
          The interface has (S,G) Join state which will cause the router
          to forward packets from S destined for G from this interface
          if the (S,G) state is active (the SPTbit is set) except if the
          router lost an assert on this interface.

     Prune-Pending (PP)
          The router has received a Prune(S,G) on this interface from a
          downstream neighbor and is waiting to see whether the prune
          will be overridden by another downstream router.  For
          forwarding purposes, the Prune-Pending state functions exactly
          like the Join state.

In addition, there are two timers:




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     Expiry Timer (ET)
          This timer is set when a valid Join(S,G) is received.  Expiry
          of the Expiry Timer causes this state machine to revert to
          NoInfo state.

     Prune-Pending Timer (PPT)
          This timer is set when a valid Prune(S,G) is received.  Expiry
          of the Prune-Pending Timer causes this state machine to revert
          to NoInfo state.

 Figure 4: Downstream per-interface (S,G) state machine in tabular form

+-------------++---------------------------------------------------------+
|             ||                         Event                           |
|             ++-------------+--------------+-------------+--------------+
|Prev State   ||Receive      | Receive      | Prune-      | Expiry Timer |
|             ||Join(S,G)    | Prune(S,G)   | Pending     | Expires      |
|             ||             |              | Timer       |              |
|             ||             |              | Expires     |              |
+-------------++-------------+--------------+-------------+--------------+
|             ||-> J state   | -> NI state  | -           | -            |
|NoInfo (NI)  ||start Expiry |              |             |              |
|             ||Timer        |              |             |              |
+-------------++-------------+--------------+-------------+--------------+
|             ||-> J state   | -> PP state  | -           | -> NI state  |
|Join (J)     ||restart      | start Prune- |             |              |
|             ||Expiry Timer | Pending      |             |              |
|             ||             | Timer        |             |              |
+-------------++-------------+--------------+-------------+--------------+
|Prune-       ||-> J state   | -> PP state  | -> NI state | -> NI state  |
|Pending (PP) ||restart      |              | Send Prune- |              |
|             ||Expiry Timer |              | Echo(S,G)   |              |
+-------------++-------------+--------------+-------------+--------------+

The transition events "Receive Join(S,G)" and "Receive Prune(S,G)" imply
receiving a Join or Prune targeted to this router's primary IP address
on the received interface.  If the upstream neighbor address field is
not correct, these state transitions in this state machine must not
occur, although seeing such a packet may cause state transitions in
other state machines.

On unnumbered interfaces on point-to-point links, the router's address
should be the same as the source address it chose for the Hello message
it sent over that interface.  However on point-to-point links we also
recommend that for backwards compatibility PIM Join/Prune messages with
a upstream neighbor address field of all zeros are also accepted.





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Transitions from NoInfo State

When in NoInfo state, the following event may trigger a transition:

     Receive Join(S,G)
          A Join(S,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G) downstream state machine on interface I transitions
          to the Join state.  The Expiry Timer (ET) is started, and set
          to the HoldTime from the triggering Join/Prune message.

Transitions from Join State

When in Join state, the following events may trigger a transition:

     Receive Join(S,G)
          A Join(S,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G) downstream state machine on interface I remains in
          Join state, and the Expiry Timer (ET) is restarted, set to
          maximum of its current value and the HoldTime from the
          triggering Join/Prune message.

     Receive Prune(S,G)
          A Prune(S,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G) downstream state machine on interface I transitions
          to the Prune-Pending state.  The Prune-Pending Timer is
          started; it is set to the J/P_Override_Interval(I) if the
          router has more than one neighbor on that interface; otherwise
          it is set to zero causing it to expire immediately.

     Expiry Timer Expires
          The Expiry Timer for the (S,G) downstream state machine on
          interface I expires.

          The (S,G) downstream state machine on interface I transitions
          to the NoInfo state.

Transitions from Prune-Pending State

When in Prune-Pending state, the following events may trigger a
transition:





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     Receive Join(S,G)
          A Join(S,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G) downstream state machine on interface I transitions
          to the Join state.  The Prune-Pending Timer is canceled
          (without triggering an expiry event).  The Expiry Timer is
          restarted, set to maximum of its current value and the
          HoldTime from the triggering Join/Prune message.

     Expiry Timer Expires
          The Expiry Timer for the (S,G) downstream state machine on
          interface I expires.

          The (S,G) downstream state machine on interface I transitions
          to the NoInfo state.

     Prune-Pending Timer Expires
          The Prune-Pending Timer for the (S,G) downstream state machine
          on interface I expires.

          The (S,G) downstream state machine on interface I transitions
          to the NoInfo state.  A PruneEcho(S,G) is sent onto the subnet
          connected to interface I.

          The action "Send PruneEcho(S,G)" is triggered when the router
          stops forwarding on an interface as a result of a prune.  A
          PruneEcho(S,G) is simply a Prune(S,G) message sent by the
          upstream router on a LAN with its own address in the Upstream
          Neighbor Address field.  Its purpose is to add additional
          reliability so that if a Prune that should have been
          overridden by another router is lost locally on the LAN, then
          the PruneEcho may be received and cause the override to
          happen.  A PruneEcho(S,G) need not be sent on an interface
          that contains only a single PIM neighbor during the time this
          state machine was in Prune-Pending state.

4.5.4.  Receiving (S,G,rpt) Join/Prune Messages

The per-interface state machine for receiving (S,G,rpt) Join/Prune
messages is given below.  There are five states:

     NoInfo (NI)
          The interface has no (S,G,rpt) Prune state and no (S,G,rpt)
          timers running.

     Prune (P)
          The interface has (S,G,rpt) Prune state which will cause the



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          router not to forward packets from S destined for G from this
          interface even though the interface has active (*,G) Join
          state.

     Prune-Pending (PP)
          The router has received a Prune(S,G,rpt) on this interface
          from a downstream neighbor and is waiting to see whether the
          prune will be overridden by another downstream router.  For
          forwarding purposes, the Prune-Pending state functions exactly
          like the NoInfo state.

     PruneTmp (P')
          This state is a transient state which for forwarding purposes
          behaves exactly like the Prune state.  A (*,G) Join has been
          received (which may cancel the (S,G,rpt) Prune).  As we parse
          the Join/Prune message from top to bottom, we first enter this
          state if the message contains a (*,G) Join.  Later in the
          message we will normally encounter an (S,G,rpt) prune to
          reinstate the Prune state.  However if we reach the end of the
          message without encountering such a (S,G,rpt) prune, then we
          will revert to NoInfo state in this state machine.

          As no time is spent in this state, no timers can expire.

     Prune-Pending-Tmp (PP')
          This state is a transient state which is identical to P'
          except that it is associated with the PP state rather than the
          P state.  For forwarding purposes, PP' behaves exactly like PP
          state.

In addition, there are two timers:

     Expiry Timer (ET)
          This timer is set when a valid Prune(S,G,rpt) is received.
          Expiry of the Expiry Timer causes this state machine to revert
          to NoInfo state.

     Prune-Pending Timer (PPT)
          This timer is set when a valid Prune(S,G,rpt) is received.
          Expiry of the Prune-Pending Timer causes this state machine to
          move on to Prune state.










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Figure 5: Downstream per-interface (S,G,rpt) state machine in tabular form

+----------++----------------------------------------------------------------+
|          ||                             Event                              |
|          ++----------+-----------+-----------+---------+---------+---------+
|Prev      ||Receive   | Receive   | Receive   | End of  | Prune-  | Expiry  |
|State     ||Join(*,G) | Join      | Prune     | Message | Pending | Timer   |
|          ||          | (S,G,rpt) | (S,G,rpt) |         | Timer   | Expires |
|          ||          |           |           |         | Expires |         |
+----------++----------+-----------+-----------+---------+---------+---------+
|          ||-         | -         | -> PP     | -       | -       | -       |
|          ||          |           | state     |         |         |         |
|          ||          |           | start     |         |         |         |
|NoInfo    ||          |           | Prune-    |         |         |         |
|(NI)      ||          |           | Pending   |         |         |         |
|          ||          |           | Timer;    |         |         |         |
|          ||          |           | start     |         |         |         |
|          ||          |           | Expiry    |         |         |         |
|          ||          |           | Timer     |         |         |         |
+----------++----------+-----------+-----------+---------+---------+---------+
|          ||-> P'     | -> NI     | -> P      | -       | -       | -> NI   |
|          ||state     | state     | state     |         |         | state   |
|Prune (P) ||          |           | restart   |         |         |         |
|          ||          |           | Expiry    |         |         |         |
|          ||          |           | Timer     |         |         |         |
+----------++----------+-----------+-----------+---------+---------+---------+
|Prune-    ||-> PP'    | -> NI     | -         | -       | -> P    | -       |
|Pending   ||state     | state     |           |         | state   |         |
|(PP)      ||          |           |           |         |         |         |
+----------++----------+-----------+-----------+---------+---------+---------+
|          ||-         | -         | -> P      | -> NI   | -       | -       |
|PruneTmp  ||          |           | state     | state   |         |         |
|(P')      ||          |           | restart   |         |         |         |
|          ||          |           | Expiry    |         |         |         |
|          ||          |           | Timer     |         |         |         |
+----------++----------+-----------+-----------+---------+---------+---------+
|          ||-         | -         | -> PP     | -> NI   | -       | -       |
|Prune-    ||          |           | state     | state   |         |         |
|Pending-  ||          |           | restart   |         |         |         |
|Tmp (PP') ||          |           | Expiry    |         |         |         |
|          ||          |           | Timer     |         |         |         |
+----------++----------+-----------+-----------+---------+---------+---------+

The transition events "Receive Join(S,G,rpt)", "Receive Prune(S,G,rpt)",
and "Receive Join(*,G)" imply receiving a Join or Prune targeted to this
router's primary IP address on the received interface.  If the upstream
neighbor address field is not correct, these state transitions in this
state machine must not occur, although seeing such a packet may cause



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state transitions in other state machines.

On unnumbered interfaces on point-to-point links, the router's address
should be the same as the source address it chose for the Hello message
it sent over that interface.  However on point-to-point links we also
recommend that PIM Join/Prune messages with a upstream neighbor address
field of all zeros are also accepted.

Transitions from NoInfo State

When in NoInfo (NI) state, the following event may trigger a transition:

     Receive Prune(S,G,rpt)
          A Prune(S,G,rpt) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G,rpt) downstream state machine on interface I
          transitions to the Prune-Pending state.  The Expiry Timer (ET)
          is started, and set to the HoldTime from the triggering
          Join/Prune message.  The Prune-Pending Timer is started; it is
          set to the J/P_Override_Interval(I) if the router has more
          than one neighbor on that interface; otherwise it is set to
          zero causing it to expire immediately.

Transitions from Prune-Pending State

When in Prune-Pending (PP) state, the following events may trigger a
transition:

     Receive Join(*,G)
          A Join(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G,rpt) downstream state machine on interface I
          transitions to Prune-Pending-Tmp state whilst the remainder of
          the compound Join/Prune message containing the Join(*,G) is
          processed.

     Receive Join(S,G,rpt)
          A Join(S,G,rpt) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G,rpt) downstream state machine on interface I
          transitions to NoInfo state.  ET and PPT are canceled.

     Prune-Pending Timer Expires
          The Prune-Pending Timer for the (S,G,rpt) downstream state
          machine on interface I expires.



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          The (S,G,rpt) downstream state machine on interface I
          transitions to the Prune state.

Transitions from Prune State

When in Prune (P) state, the following events may trigger a transition:

     Receive Join(*,G)
          A Join(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G,rpt) downstream state machine on interface I
          transitions to PruneTmp state whilst the remainder of the
          compound Join/Prune message containing the Join(*,G) is
          processed.

     Receive Join(S,G,rpt)
          A Join(S,G,rpt) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G,rpt) downstream state machine on interface I
          transitions to NoInfo state.  ET and PPT are canceled.

     Receive Prune(S,G,rpt)
          A Prune(S,G,rpt) is received on interface I with its Upstream
          Neighbor Address set to the router's primary IP address on I.

          The (S,G,rpt) downstream state machine on interface I remains
          in Prune state.  The Expiry Timer (ET) is restarted, set to
          maximum of its current value and the HoldTime from the
          triggering Join/Prune message.

     Expiry Timer Expires
          The Expiry Timer for the (S,G,rpt) downstream state machine on
          interface I expires.

          The (S,G,rpt) downstream state machine on interface I
          transitions to the NoInfo state.

Transitions from Prune-Pending-Tmp State

When in Prune-Pending-Tmp (PP') state and processing a compound
Join/Prune message, the following events may trigger a transition:

     Receive Prune(S,G,rpt)
          The compound Join/Prune message contains a Prune(S,G,rpt).





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          The (S,G,rpt) downstream state machine on interface I
          transitions back to the Prune-Pending state.  The Expiry Timer
          (ET) is restarted, set to maximum of its current value and the
          HoldTime from the triggering Join/Prune message.

     End of Message
          The end of the compound Join/Prune message is reached.

          The (S,G,rpt) downstream state machine on interface I
          transitions to the NoInfo state.  ET and PPT are canceled.

Transitions from PruneTmp State

When in PruneTmp (P') state and processing a compound Join/Prune
message, the following events may trigger a transition:

     Receive Prune(S,G,rpt)
          The compound Join/Prune message contains a Prune(S,G,rpt).

          The (S,G,rpt) downstream state machine on interface I
          transitions back to the Prune state.  The Expiry Timer (ET) is
          restarted, set to maximum of its current value and the
          HoldTime from the triggering Join/Prune message.

     End of Message
          The end of the compound Join/Prune message is reached.

          The (S,G,rpt) downstream state machine on interface I
          transitions to the NoInfo state.  ET is canceled.

Notes:

Receiving a Prune(*,G) does not affect the (S,G,rpt) downstream state
machine.

Receiving a Join(*,*,RP) does not affect the (S,G,rpt) downstream state
machine.  If a router has originated Join(*,*,RP) and pruned a source
off it using Prune(S,G,rpt), then to receive that source again it should
explicitly re-join using Join(S,G,rpt) or Join(*,G).  In some LAN
topologies it is possible for a router sending a new Join(*,*,RP) to
have to wait as much as a Join/Prune Interval before noticing that it
needs to override a neighbor's pre-existing Prune(S,G,rpt).  This is
considered acceptable, as (*,*,RP) state is intended to be used only in
long-lived and persistent scenarios.







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4.5.5.  Sending (*,*,RP) Join/Prune Messages

The per-interface state machines for (*,*,RP) hold join state from
downstream PIM routers.  This state then determines whether a router
needs to propagate a Join(*,*,RP) upstream towards the RP.

If a router wishes to propagate a Join(*,*,RP) upstream, it must also
watch for messages on its upstream interface from other routers on that
subnet, and these may modify its behavior.  If it sees a Join(*,*,RP) to
the correct upstream neighbor, it should suppress its own Join(*,*,RP).
If it sees a Prune(*,*,RP) to the correct upstream neighbor, it should
be prepared to override that prune by sending a Join(*,*,RP) almost
immediately.  Finally, if it sees the Generation ID (see Section 4.3) of
the correct upstream neighbor change, it knows that the upstream
neighbor has lost state, and it should be prepared to refresh the state
by sending a Join(*,*,RP) almost immediately.

In addition, if the MRIB changes to indicate that the next hop towards
the RP has changed, the router should prune off from the old next hop,
and join towards the new next hop.

The upstream (*,*,RP) state machine contains only two states:

Not Joined
     The downstream state machines and local membership information do
     not indicate that the router needs to join the (*,*,RP) tree for
     this RP.

Joined
     The downstream state machines and local membership information
     indicate that the router should join the (*,*,RP) tree for this RP.

In addition, one timer JT(*,*,RP) is kept which is used to trigger the
sending of a Join(*,*,RP) to the upstream next hop towards the RP,
NBR(RPF_interface(RP), MRIB.next_hop(RP)).
















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       Figure 6: Upstream (*,*,RP) state machine in tabular form

+--------------------++-------------------------------------------------+
|                    ||                      Event                      |
|  Prev State        ++-------------------------+-----------------------+
|                    ||   JoinDesired           |    JoinDesired        |
|                    ||   (*,*,RP) ->True       |    (*,*,RP) ->False   |
+--------------------++-------------------------+-----------------------+
|                    ||   -> J state            |    -                  |
|  NotJoined (NJ)    ||   Send Join(*,*,RP);    |                       |
|                    ||   Set Join Timer to     |                       |
|                    ||   t_periodic            |                       |
+--------------------++-------------------------+-----------------------+
|  Joined (J)        ||   -                     |    -> NJ state        |
|                    ||                         |    Send Prune         |
|                    ||                         |    (*,*,RP); Cancel   |
|                    ||                         |    Join Timer         |
+--------------------++-------------------------+-----------------------+

In addition, we have the following transitions which occur within the
Joined state:

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+-------------------+--------------------+------------------------------+
| Timer Expires     |  See               |   See                        |
|                   |  Join(*,*,RP)      |   Prune(*,*,RP)              |
|                   |  to MRIB.          |   to MRIB.                   |
|                   |  next_hop(RP)      |   next_hop(RP)               |
+-------------------+--------------------+------------------------------+
| Send              |  Increase Join     |   Decrease Join              |
| Join(*,*,RP);     |  Timer to          |   Timer to                   |
| Set Join Timer    |  t_joinsuppress    |   t_override                 |
| to t_periodic     |                    |                              |
+-------------------+--------------------+------------------------------+
















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+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+-----------------------------------+-----------------------------------+
|    NBR(RPF_interface(RP),         |       MRIB.next_hop(RP) GenID     |
|    MRIB.next_hop(RP))             |       changes                     |
|    changes                        |                                   |
+-----------------------------------+-----------------------------------+
|    Send Join(*,*,RP) to new       |       Decrease Join Timer to      |
|    next hop; Send                 |       t_override                  |
|    Prune(*,*,RP) to old           |                                   |
|    next hop; set Join Timer       |                                   |
|    to t_periodic                  |                                   |
+-----------------------------------+-----------------------------------+

This state machine uses the following macro:

  bool JoinDesired(*,*,RP) {
     if immediate_olist(*,*,RP) != NULL
         return TRUE
     else
         return FALSE
  }

JoinDesired(*,*,RP) is true when the router has received (*,*,RP) Joins
from any downstream interface.  Note that although JoinDesired is true,
the router's sending of a Join(*,*,RP) message may be suppressed by
another router sending a Join(*,*,RP) onto the upstream interface.

Transitions from NotJoined State

When the upstream (*,*,RP) state machine is in NotJoined state, the
following event may trigger a state transition:

     JoinDesired(*,*,RP) becomes True
          The downstream state for (*,*,RP) has changed so that at least
          one interface is in immediate_olist(*,*,RP), making
          JoinDesired(*,*,RP) become True.

          The upstream (*,*,RP) state machine transitions to Joined
          state.  Send Join(*,*,RP) to the appropriate upstream
          neighbor, which is NBR(RPF_interface(RP), MRIB.next_hop(RP)).
          Set the Join Timer (JT) to expire after t_periodic seconds.

Transitions from Joined State

When the upstream (*,*,RP) state machine is in Joined state, the
following events may trigger state transitions:




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     JoinDesired(*,*,RP) becomes False
          The downstream state for (*,*,RP) has changed so no interface
          is in immediate_olist(*,*,RP), making JoinDesired(*,*,RP)
          become False.

          The upstream (*,*,RP) state machine transitions to NotJoined
          state.  Send Prune(*,*,RP) to the appropriate upstream
          neighbor, which is NBR(RPF_interface(RP), MRIB.next_hop(RP)).
          Cancel the Join Timer (JT).

     Join Timer Expires
          The Join Timer (JT) expires, indicating time to send a
          Join(*,*,RP)

          Send Join(*,*,RP) to the appropriate upstream neighbor, which
          is NBR(RPF_interface(RP), MRIB.next_hop(RP)).  Restart the
          Join Timer (JT) to expire after t_periodic seconds.

     See Join(*,*,RP) to MRIB.next_hop(RP)
          This event is only relevant if RPF_interface(RP) is a shared
          medium.  This router sees another router on RPF_interface(RP)
          send a Join(*,*,RP) to NBR(RPF_interface(RP),
          MRIB.next_hop(RP)).  This causes this router to suppress its
          own Join.

          The upstream (*,*,RP) state machine remains in Joined state.

          Let t_joinsuppress be the minimum of t_suppressed and the
          HoldTime from the Join/Prune message triggering this event.
          If the Join Timer is set to expire in less than t_joinsuppress
          seconds, reset it so that it expires after t_joinsuppress
          seconds.  If the Join Timer is set to expire in more than
          t_joinsuppress seconds, leave it unchanged.

     See Prune(*,*,RP) to MRIB.next_hop(RP)
          This event is only relevant if RPF_interface(RP) is a shared
          medium.  This router sees another router on RPF_interface(RP)
          send a Prune(*,*,RP) to NBR(RPF_interface(RP),
          MRIB.next_hop(RP)).  As this router is in Joined state, it
          must override the Prune after a short random interval.

          The upstream (*,*,RP) state machine remains in Joined state.
          If the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.
          If the Join Timer is set to expire in less than t_override
          seconds, leave it unchanged.





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     NBR(RPF_interface(RP), MRIB.next_hop(RP)) changes
          A change in the MRIB routing base causes the next hop towards
          the RP to change.

          The upstream (*,*,RP) state machine remains in Joined state.
          Send Join(*,*,RP) to the new upstream neighbor which is the
          new value of NBR(RPF_interface(RP), MRIB.next_hop(RP)).  Send
          Prune(*,*,RP) to the old upstream neighbor, which is the old
          value of NBR(RPF_interface(RP), MRIB.next_hop(RP)).  Set the
          Join Timer (JT) to expire after t_periodic seconds.

     MRIB.next_hop(RP) GenID changes
          The Generation ID of the router that is MRIB.next_hop(RP)
          changes.  This normally means that this neighbor has lost
          state, and so the state must be refreshed.

          The upstream (*,*,RP) state machine remains in Joined state.
          If the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.

4.5.6.  Sending (*,G) Join/Prune Messages

The per-interface state machines for (*,G) hold join state from
downstream PIM routers.  This state then determines whether a router
needs to propagate a Join(*,G) upstream towards the RP.

If a router wishes to propagate a Join(*,G) upstream, it must also watch
for messages on its upstream interface from other routers on that
subnet, and these may modify its behavior.  If it sees a Join(*,G) to
the correct upstream neighbor, it should suppress its own Join(*,G).  If
it sees a Prune(*,G) to the correct upstream neighbor, it should be
prepared to override that prune by sending a Join(*,G) almost
immediately.  Finally, if it sees the Generation ID (see Section 4.3) of
the correct upstream neighbor change, it knows that the upstream
neighbor has lost state, and it should be prepared to refresh the state
by sending a Join(*,G) almost immediately.

If a (*,G) Assert occurs on the upstream interface, and this changes
this router's idea of the upstream neighbor, it should be prepared to
ensure that the Assert winner is aware of downstream routers by sending
a Join(*,G) almost immediately.

In addition, if the MRIB changes to indicate that the next hop towards
the RP has changed, and either the upstream interface changes or there
is no Assert winner on the upstream interface, the router should prune
off from the old next hop, and join towards the new next hop.





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The upstream (*,G) state machine only contains two states:

Not Joined
     The downstream state machines indicate that the router does not
     need to join the RP tree for this group.

Joined
     The downstream state machines indicate that the router should join
     the RP tree for this group.

In addition, one timer JT(*,G) is kept which is used to trigger the
sending of a Join(*,G) to the upstream next hop towards the RP,
RPF'(*,G).






































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         Figure 7: Upstream (*,G) state machine in tabular form

+--------------------++-------------------------------------------------+
|                    ||                      Event                      |
|  Prev State        ++------------------------+------------------------+
|                    ||   JoinDesired(*,G)     |    JoinDesired(*,G)    |
|                    ||   ->True               |    ->False             |
+--------------------++------------------------+------------------------+
|                    ||   -> J state           |    -                   |
|  NotJoined (NJ)    ||   Send Join(*,G);      |                        |
|                    ||   Set Join Timer to    |                        |
|                    ||   t_periodic           |                        |
+--------------------++------------------------+------------------------+
|  Joined (J)        ||   -                    |    -> NJ state         |
|                    ||                        |    Send Prune(*,G);    |
|                    ||                        |    Cancel Join Timer   |
+--------------------++------------------------+------------------------+

In addition, we have the following transitions which occur within the
Joined state:

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+-----------------+-----------------+-----------------+-----------------+
|Timer Expires    | See Join(*,G)   | See Prune(*,G)  | RPF'(*,G)       |
|                 | to RPF'(*,G)    | to RPF'(*,G)    | changes due to  |
|                 |                 |                 | an Assert       |
+-----------------+-----------------+-----------------+-----------------+
|Send             | Increase Join   | Decrease Join   | Decrease Join   |
|Join(*,G); Set   | Timer to        | Timer to        | Timer to        |
|Join Timer to    | t_joinsuppress  | t_override      | t_override      |
|t_periodic       |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+----------------------------------+------------------------------------+
|    RPF'(*,G) changes not         |       RPF'(*,G) GenID changes      |
|    due to an Assert              |                                    |
+----------------------------------+------------------------------------+
|    Send Join(*,G) to new         |       Decrease Join Timer to       |
|    next hop; Send                |       t_override                   |
|    Prune(*,G) to old next        |                                    |
|    hop; Set Join Timer to        |                                    |
|    t_periodic                    |                                    |
+----------------------------------+------------------------------------+





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This state machine uses the following macro:

  bool JoinDesired(*,G) {
     if (immediate_olist(*,G) != NULL OR
         (JoinDesired(*,*,RP(G)) AND
          AssertWinner(*, G, RPF_interface(RP(G))) != NULL))
         return TRUE
     else
         return FALSE
  }

JoinDesired(*,G) is true when the router has forwarding state that would
cause it to forward traffic for G using shared tree state.  Note that
although JoinDesired is true, the router's sending of a Join(*,G)
message may be suppressed by another router sending a Join(*,G) onto the
upstream interface.

Transitions from NotJoined State

When the upstream (*,G) state machine is in NotJoined state, the
following event may trigger a state transition:

     JoinDesired(*,G) becomes True
          The macro JoinDesired(*,G) becomes True, e.g., because the
          downstream state for (*,G) has changed so that at least one
          interface is in immediate_olist(*,G).

          The upstream (*,G) state machine transitions to Joined state.
          Send Join(*,G) to the appropriate upstream neighbor, which is
          RPF'(*,G).  Set the Join Timer (JT) to expire after t_periodic
          seconds.

Transitions from Joined State

When the upstream (*,G) state machine is in Joined state, the following
events may trigger state transitions:

     JoinDesired(*,G) becomes False
          The macro JoinDesired(*,G) becomes False, e.g., because the
          downstream state for (*,G) has changed so no interface is in
          immediate_olist(*,G).

          The upstream (*,G) state machine transitions to NotJoined
          state.  Send Prune(*,G) to the appropriate upstream neighbor,
          which is RPF'(*,G).  Cancel the Join Timer (JT).

     Join Timer Expires
          The Join Timer (JT) expires, indicating time to send a



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          Join(*,G)

          Send Join(*,G) to the appropriate upstream neighbor, which is
          RPF'(*,G).  Restart the Join Timer (JT) to expire after
          t_periodic seconds.

     See Join(*,G) to RPF'(*,G)
          This event is only relevant if RPF_interface(RP(G)) is a
          shared medium.  This router sees another router on
          RPF_interface(RP(G)) send a Join(*,G) to RPF'(*,G).  This
          causes this router to suppress its own Join.

          The upstream (*,G) state machine remains in Joined state.

          Let t_joinsuppress be the minimum of t_suppressed and the
          HoldTime from the Join/Prune message triggering this event.
          If the Join Timer is set to expire in less than t_joinsuppress
          seconds, reset it so that it expires after t_joinsuppress
          seconds.  If the Join Timer is set to expire in more than
          t_joinsuppress seconds, leave it unchanged.

     See Prune(*,G) to RPF'(*,G)
          This event is only relevant if RPF_interface(RP(G)) is a
          shared medium.  This router sees another router on
          RPF_interface(RP(G)) send a Prune(*,G) to RPF'(*,G).  As this
          router is in Joined state, it must override the Prune after a
          short random interval.

          The upstream (*,G) state machine remains in Joined state.  If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.
          If the Join Timer is set to expire in less than t_override
          seconds, leave it unchanged.

     RPF'(*,G) changes due to an Assert
          The current next hop towards the RP changes due to an
          Assert(*,G) on the RPF_interface(RP(G)).

          The upstream (*,G) state machine remains in Joined state.  If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.
          If the Join Timer is set to expire in less than t_override
          seconds, leave it unchanged.

     RPF'(*,G) changes not due to an Assert
          An event occurred which caused the next hop towards the RP for
          G to change.  This may be caused by a change in the MRIB
          routing database or the group-to-RP mapping.  Note that this



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          transition does not occur if an Assert is active and the
          upstream interface does not change.

          The upstream (*,G) state machine remains in Joined state.
          Send Join(*,G) to the new upstream neighbor which is the new
          value of RPF'(*,G).  Send Prune(*,G) to the old upstream
          neighbor, which is the old value of RPF'(*,G). Use the new
          value of RP(G) in the Prune(*,G) message or all-zeros if RP(G)
          becomes unknown (old value of RP(G) may be used instead to
          improve behavior in routers implementing older versions of
          this spec).  Set the Join Timer (JT) to expire after
          t_periodic seconds.

     RPF'(*,G) GenID changes
          The Generation ID of the router that is RPF'(*,G) changes.
          This normally means that this neighbor has lost state, and so
          the state must be refreshed.

          The upstream (*,G) state machine remains in Joined state. If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.

4.5.7.  Sending (S,G) Join/Prune Messages

The per-interface state machines for (S,G) hold join state from
downstream PIM routers.  This state then determines whether a router
needs to propagate a Join(S,G) upstream towards the source.

If a router wishes to propagate a Join(S,G) upstream, it must also watch
for messages on its upstream interface from other routers on that
subnet, and these may modify its behavior.  If it sees a Join(S,G) to
the correct upstream neighbor, it should suppress its own Join(S,G).  If
it sees a Prune(S,G), Prune(S,G,rpt), or Prune(*,G) to the correct
upstream neighbor towards S, it should be prepared to override that
prune by scheduling a Join(S,G) to be sent almost immediately.  Finally,
if it sees the Generation ID of its upstream neighbor change, it knows
that the upstream neighbor has lost state, and it should refresh the
state by scheduling a Join(S,G) to be sent almost immediately.

If a (S,G) Assert occurs on the upstream interface, and this changes the
this router's idea of the upstream neighbor, it should be prepared to
ensure that the Assert winner is aware of downstream routers by
scheduling a Join(S,G) to be sent almost immediately.

In addition, if MRIB changes cause the next hop towards the source to
change, and either the upstream interface changes or there is no Assert
winner on the upstream interface, the router should send a prune to the
old next hop, and a join to the new next hop.



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The upstream (S,G) state machine only contains two states:

Not Joined
     The downstream state machines and local membership information do
     not indicate that the router needs to join the shortest-path tree
     for this (S,G).

Joined
     The downstream state machines and local membership information
     indicate that the router should join the shortest-path tree for
     this (S,G).

In addition, one timer JT(S,G) is kept which is used to trigger the
sending of a Join(S,G) to the upstream next hop towards S, RPF'(S,G).

         Figure 8: Upstream (S,G) state machine in tabular form

+--------------------+--------------------------------------------------+
|                    |                      Event                       |
|  Prev State        +-------------------------+------------------------+
|                    |   JoinDesired(S,G)      |   JoinDesired(S,G)     |
|                    |   ->True                |   ->False              |
+--------------------+-------------------------+------------------------+
|  NotJoined (NJ)    |   -> J state            |   -                    |
|                    |   Send Join(S,G);       |                        |
|                    |   Set Join Timer to     |                        |
|                    |   t_periodic            |                        |
+--------------------+-------------------------+------------------------+
|  Joined (J)        |   -                     |   -> NJ state          |
|                    |                         |   Send Prune(S,G);     |
|                    |                         |   Set SPTbit(S,G) to   |
|                    |                         |   FALSE; Cancel Join   |
|                    |                         |   Timer                |
+--------------------+-------------------------+------------------------+

















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In addition, we have the following transitions which occur within the
Joined state:

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+-----------------+-----------------+------------------+----------------+
| Timer Expires   | See Join(S,G)   |  See Prune(S,G)  | See Prune      |
|                 | to RPF'(S,G)    |  to RPF'(S,G)    | (S,G,rpt) to   |
|                 |                 |                  | RPF'(S,G)      |
+-----------------+-----------------+------------------+----------------+
| Send            | Increase Join   |  Decrease Join   | Decrease Join  |
| Join(S,G); Set  | Timer to        |  Timer to        | Timer to       |
| Join Timer to   | t_joinsuppress  |  t_override      | t_override     |
| t_periodic      |                 |                  |                |
+-----------------+-----------------+------------------+----------------+

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+-----------------+-----------------+-----------------+-----------------+
| See Prune(*,G)  | RPF'(S,G)       |  RPF'(S,G)      | RPF'(S,G)       |
| to RPF'(S,G)    | changes not     |  GenID changes  | changes due to  |
|                 | due to an       |                 | an Assert       |
|                 | Assert          |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Decrease Join   | Send Join(S,G)  |  Decrease Join  | Decrease Join   |
| Timer to        | to new next     |  Timer to       | Timer to        |
| t_override      | hop; Send       |  t_override     | t_override      |
|                 | Prune(S,G) to   |                 |                 |
|                 | old next hop;   |                 |                 |
|                 | Set Join Timer  |                 |                 |
|                 | to t_periodic   |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

This state machine uses the following macro:

  bool JoinDesired(S,G) {
      return( immediate_olist(S,G) != NULL
              OR ( KeepaliveTimer(S,G) is running
                   AND inherited_olist(S,G) != NULL ) )
  }

JoinDesired(S,G) is true when the router has forwarding state that would
cause it to forward traffic for G using source tree state.  The source
tree state can either be as a result of active source-specific join
state, or the (S,G) Keepalive Timer and active non-source-specific
state. Note that although JoinDesired is true, the router's sending of a
Join(S,G) message may be suppressed by another router sending a
Join(S,G) onto the upstream interface.



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Transitions from NotJoined State

When the upstream (S,G) state machine is in NotJoined state, the
following event may trigger a state transition:

     JoinDesired(S,G) becomes True
          The macro JoinDesired(S,G) becomes True, e.g., because the
          downstream state for (S,G) has changed so that at least one
          interface is in inherited_olist(S,G).

          The upstream (S,G) state machine transitions to Joined state.
          Send Join(S,G) to the appropriate upstream neighbor, which is
          RPF'(S,G).  Set the Join Timer (JT) to expire after t_periodic
          seconds.

Transitions from Joined State

When the upstream (S,G) state machine is in Joined state, the following
events may trigger state transitions:

     JoinDesired(S,G) becomes False
          The macro JoinDesired(S,G) becomes False, e.g., because the
          downstream state for (S,G) has changed so no interface is in
          inherited_olist(S,G).

          The upstream (S,G) state machine transitions to NotJoined
          state.  Send Prune(S,G) to the appropriate upstream neighbor,
          which is RPF'(S,G).  Cancel the Join Timer (JT), and set
          SPTbit(S,G) to FALSE.

     Join Timer Expires
          The Join Timer (JT) expires, indicating time to send a
          Join(S,G)

          Send Join(S,G) to the appropriate upstream neighbor, which is
          RPF'(S,G).  Restart the Join Timer (JT) to expire after
          t_periodic seconds.

     See Join(S,G) to RPF'(S,G)
          This event is only relevant if RPF_interface(S) is a shared
          medium.  This router sees another router on RPF_interface(S)
          send a Join(S,G) to RPF'(S,G).  This causes this router to
          suppress its own Join.

          The upstream (S,G) state machine remains in Joined state.

          Let t_joinsuppress be the minimum of t_suppressed and the
          HoldTime from the Join/Prune message triggering this event.



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          If the Join Timer is set to expire in less than t_joinsuppress
          seconds, reset it so that it expires after t_joinsuppress
          seconds.  If the Join Timer is set to expire in more than
          t_joinsuppress seconds, leave it unchanged.

     See Prune(S,G) to RPF'(S,G)
          This event is only relevant if RPF_interface(S) is a shared
          medium.  This router sees another router on RPF_interface(S)
          send a Prune(S,G) to RPF'(S,G).  As this router is in Joined
          state, it must override the Prune after a short random
          interval.

          The upstream (S,G) state machine remains in Joined state.  If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.

     See Prune(S,G,rpt) to RPF'(S,G)
          This event is only relevant if RPF_interface(S) is a shared
          medium.  This router sees another router on RPF_interface(S)
          send a Prune(S,G,rpt) to RPF'(S,G).  If the upstream router is
          an RFC 2362 compliant PIM router, then the Prune(S,G,rpt) will
          cause it to stop forwarding.  For backwards compatibility,
          this router should override the prune so that forwarding
          continues.

          The upstream (S,G) state machine remains in Joined state.  If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.

     See Prune(*,G) to RPF'(S,G)
          This event is only relevant if RPF_interface(S) is a shared
          medium.  This router sees another router on RPF_interface(S)
          send a Prune(*,G) to RPF'(S,G).  If the upstream router is an
          RFC 2362 compliant PIM router, then the Prune(*,G) will cause
          it to stop forwarding.  For backwards compatibility, this
          router should override the prune so that forwarding continues.

          The upstream (S,G) state machine remains in Joined state.  If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.

     RPF'(S,G) changes due to an Assert
          The current next hop towards S changes due to an Assert(S,G)
          on the RPF_interface(S).

          The upstream (S,G) state machine remains in Joined state.  If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.



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          If the Join Timer is set to expire in less than t_override
          seconds, leave it unchanged.

     RPF'(S,G) changes not due to an Assert
          An event occurred which caused the next hop towards S to
          change.  Note that this transition does not occur if an Assert
          is active and the upstream interface does not change.

          The upstream (S,G) state machine remains in Joined state.
          Send Join(S,G) to the new upstream neighbor which is the new
          value of RPF'(S,G).  Send Prune(S,G) to the old upstream
          neighbor, which is the old value of RPF'(S,G).  Set the Join
          Timer (JT) to expire after t_periodic seconds.

     RPF'(S,G) GenID changes
          The Generation ID of the router that is RPF'(S,G) changes.
          This normally means that this neighbor has lost state, and so
          the state must be refreshed.

          The upstream (S,G) state machine remains in Joined state. If
          the Join Timer is set to expire in more than t_override
          seconds, reset it so that it expires after t_override seconds.

4.5.8.  (S,G,rpt) Periodic Messages

(S,G,rpt) Joins and Prunes are (S,G) Joins or Prunes sent on the RP tree
with the RPT bit set, either to modify the results of (*,G) Joins, or to
override the behavior of other upstream LAN peers.  The next section
describes the rules for sending triggered messages.  This section
describes the rules for including a Prune(S,G,rpt) message with a
Join(*,G).

When a router is going to send a Join(*,G), it should use the following
pseudocode, for each (S,G) for which it has state, to decide whether to
include a Prune(S,G,rpt) in the compound Join/Prune message:
















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  if( SPTbit(S,G) == TRUE ) {
      # Note: If receiving (S,G) on the SPT, we only prune off the
      # shared tree if the RPF neighbors differ.
       if( RPF'(*,G) != RPF'(S,G) ) {
           add Prune(S,G,rpt) to compound message
       }
  } else if ( inherited_olist(S,G,rpt) == NULL ) {
    #  Note: all (*,G) olist interfaces received RPT prunes for (S,G).
    add Prune(S,G,rpt) to compound message
  } else if ( RPF'(*,G) != RPF'(S,G,rpt) {
    # Note: we joined the shared tree, but there was an (S,G) assert and
    # the source tree RPF neighbor is different.
    add Prune(S,G,rpt) to compound message
  }


Note that Join(S,G,rpt) is not normally sent as a periodic message, but
only as a triggered message.


4.5.9.  State Machine for (S,G,rpt) Triggered Messages

The state machine for (S,G,rpt) triggered messages is required per-(S,G)
when there is (*,G) or (*,*,RP) join state at a router, and the router
or any of its upstream LAN peers wishes to prune S off the RP tree.

There are three states in the state machine.  One of the states is when
there is neither (*,G) nor (*,*,RP(G)) join state at this router.  If
there is (*,G) or (*,*,RP(G)) join state at the router, then the state
machine must be at one of the other two states. The three states are:


Pruned(S,G,rpt)
     (*,G) or (*,*,RP(G)) Joined, but (S,G,rpt) pruned

NotPruned(S,G,rpt)
     (*,G) or (*,*,RP(G)) Joined, and (S,G,rpt) not pruned

RPTNotJoined(G)
     neither (*,G) nor (*,*,RP(G)) has been joined.

In addition, there is an (S,G,rpt) Override Timer, OT(S,G,rpt), which is
used to delay triggered Join(S,G,rpt) messages to prevent implosions of
triggered messages.







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Figure 9: Upstream (S,G,rpt) state machine for triggered messages in
                              tabular form

+---------------++-------------------------------------------------------------+
|               ||                           Event                             |
|               ++---------------+---------------+--------------+--------------+
|Prev State     || PruneDesired  | PruneDesired  | RPTJoin      | inherited_   |
|               || (S,G,rpt)     | (S,G,rpt)     | Desired(G)   | olist        |
|               || ->True        | ->False       | ->False      | (S,G,rpt)    |
|               ||               |               |              | ->non-NULL   |
+---------------++---------------+---------------+--------------+--------------+
|RPTNotJoined   || -> P state    | -             | -            | -> NP state  |
|(G) (NJ)       ||               |               |              |              |
+---------------++---------------+---------------+--------------+--------------+
|Pruned         || -             | -> NP state   | -> NJ state  | -            |
|(S,G,rpt) (P)  ||               | Send Join     |              |              |
|               ||               | (S,G,rpt)     |              |              |
+---------------++---------------+---------------+--------------+--------------+
|NotPruned      || -> P state    | -             | -> NJ state  | -            |
|(S,G,rpt)      || Send Prune    |               | Cancel OT    |              |
|(NP)           || (S,G,rpt);    |               |              |              |
|               || Cancel OT     |               |              |              |
+---------------++---------------+---------------+--------------+--------------+
Additionally, we have the following transitions within the
NotPruned(S,G,rpt) state which are all used for prune override behavior.

+-----------------------------------------------------------------------+
|                     In NotPruned(S,G,rpt) State                       |
+-----------+--------------+--------------+--------------+--------------+
|Override   | See Prune    | See Join     | See Prune    | RPF'         |
|Timer      | (S,G,rpt) to | (S,G,rpt) to | (S,G) to     | (S,G,rpt) -> |
|expires    | RPF'         | RPF'         | RPF'         | RPF' (*,G)   |
|           | (S,G,rpt)    | (S,G,rpt)    | (S,G,rpt)    |              |
+-----------+--------------+--------------+--------------+--------------+
|Send Join  | OT = min(OT, | Cancel OT    | OT = min(OT, | OT = min(OT, |
|(S,G,rpt); | t_override)  |              | t_override)  | t_override)  |
|Leave OT   |              |              |              |              |
|unset      |              |              |              |              |
+-----------+--------------+--------------+--------------+--------------+

Note that the min function in the above state machine considers a non-
running timer to have an infinite value (e.g. min(not-running,
t_override) = t_override).








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This state machine uses the following macros:

  bool RPTJoinDesired(G) {
    return (JoinDesired(*,G) OR JoinDesired(*,*,RP(G)))
  }


RPTJoinDesired(G) is true when the router has forwarding state that
would cause it to forward traffic for G using either (*,G) or (*,*,RP)
shared tree state.

  bool PruneDesired(S,G,rpt) {
       return ( RPTJoinDesired(G) AND
                ( inherited_olist(S,G,rpt) == NULL
                  OR (SPTbit(S,G)==TRUE
                      AND (RPF'(*,G) != RPF'(S,G)) )))
  }


PruneDesired(S,G,rpt) can only be true if RPTJoinDesired(G) is true.  If
RPTJoinDesired(G) is true, then PruneDesired(S,G,rpt) is true if either
there are no outgoing interfaces that S would be forwarded on, or if the
router has active (S,G) forwarding state but RPF'(*,G) != RPF'(S,G).

The state machine contains the following transition events:

See Join(S,G,rpt) to RPF'(S,G,rpt)
     This event is only relevant in the "Not Pruned" state.

     The router sees a Join(S,G,rpt) from someone else to RPF'(S,G,rpt),
     which is the correct upstream neighbor.  If we're in "NotPruned"
     state and the (S,G,rpt) Override Timer is running, then this is
     because we have been triggered to send our own Join(S,G,rpt) to
     RPF'(S,G,rpt).  Someone else beat us to it, so there's no need to
     send our own Join.

     The action is to cancel the Override Timer.

See Prune(S,G,rpt) to RPF'(S,G,rpt)
     This event is only relevant in the "NotPruned" state.

     The router sees a Prune(S,G,rpt) from someone else to to
     RPF'(S,G,rpt), which is the correct upstream neighbor.  If we're in
     the "NotPruned" state, then we want to continue to receive traffic
     from S destined for G, and that traffic is being supplied by
     RPF'(S,G,rpt).  Thus we need to override the Prune.





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     The action is to set the (S,G,rpt) Override Timer to the randomized
     prune-override interval, t_override.  However if the Override Timer
     is already running, we only set the timer if doing so would set it
     to a lower value.  At the end of this interval, if no-one else has
     sent a Join, then we will do so.

See Prune(S,G) to RPF'(S,G,rpt)
     This event is only relevant in the "NotPruned" state.

     This transition and action are the same as the above transition and
     action, except that the Prune does not have the RPT bit set.  This
     transition is necessary to be compatible with routers implemented
     from RFC2362 that don't maintain separate (S,G) and (S,G,rpt)
     state.

The (S,G,rpt) prune Override Timer expires
     This event is only relevant in the "NotPruned" state.

     When the Override Timer expires, we must send a Join(S,G,rpt) to
     RPF'(S,G,rpt) to override the Prune message that caused the timer
     to be running.  We only send this if RPF'(S,G,rpt) equals RPF'(*,G)
     - if this were not the case, then the Join might be sent to a
     router that does not have (*,G) or (*,*,RP(G)) Join state, and so
     the behavior would not be well defined.  If RPF'(S,G,rpt) is not
     the same as RPF'(*,G), then it may stop forwarding S.  However, if
     this happens, then the router will send an AssertCancel(S,G), which
     would then cause RPF'(S,G,rpt) to become equal to RPF'(*,G) (see
     below).

RPF'(S,G,rpt) changes to become equal to RPF'(*,G)
     This event is only relevant in the "NotPruned" state.

     RPF'(S,G,rpt) can only be different from RPF'(*,G) if an (S,G)
     Assert has happened, which means that traffic from S is arriving on
     the SPT, and so Prune(S,G,rpt) will have been sent to RPF'(*,G).
     When RPF'(S,G,rpt) changes to become equal to RPF'(*,G), we need to
     trigger a Join(S,G,rpt) to RPF'(*,G) to cause that router to start
     forwarding S again.

     The action is to set the (S,G,rpt) Override Timer to the randomized
     prune-override interval t_override.  However if the timer is
     already running, we only set the timer if doing so would set it to
     a lower value.  At the end of this interval, if no-one else has
     sent a Join, then we will do so.

PruneDesired(S,G,rpt)->TRUE
     See macro above.  This event is relevant in the "NotPruned" and
     "RPTNotJoined(G)" states.



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     The router wishes to receive traffic for G, but does not wish to
     receive traffic from S destined for G.  This causes the router to
     transition into the Pruned state.

     If the router was previously in NotPruned state, then the action is
     to send a Prune(S,G,rpt) to RPF'(S,G,rpt), and to cancel the
     Override Timer.  If the router was previously in RPTNotJoined(G)
     state, then there is no need to trigger an action in this state
     machine because sending a Prune(S,G,rpt) is handled by the rules
     for sending the Join(*,G) or Join(*,*,RP).

PruneDesired(S,G,rpt)->FALSE
     See macro above.  This transition is only relevant in the "Pruned"
     state.

     If the router is in the Pruned(S,G,rpt) state, and
     PruneDesired(S,G,rpt) changes to FALSE, this could be because the
     router no longer has RPTJoinDesired(G) true, or it now wishes to
     receive traffic from S again.  If it is the former, then this
     transition should not happen, but instead the
     "RPTJoinDesired(G)->FALSE" transition should happen. Thus this
     transition should be interpreted as "PruneDesired(S,G,rpt)->FALSE
     AND RPTJoinDesired(G)==TRUE"

     The action is to send a Join(S,G,rpt) to RPF'(S,G,rpt).

RPTJoinDesired(G)->FALSE
     This event is relevant in the "Pruned" and "NotPruned" states.

     The router no longer wishes to receive any traffic destined for G
     on the RP Tree.  This causes a transition to the RPTNotJoined(G)
     state, and the Override Timer is canceled if it was running.  Any
     further actions are handled by the appropriate upstream state
     machine for (*,G) or (*,*,RP).

inherited_olist(S,G,rpt) becomes non-NULL
     This transition is only relevant in the RPTNotJoined(G) state.

     The router has joined the RP tree (handled by the (*,G) or (*,*,RP)
     upstream state machine as appropriate), and wants to receive
     traffic from S.  This does not trigger any events in this state
     machine, but causes a transition to the NotPruned(S,G,rpt) state.

4.5.10.  Background: (*,*,RP) and (S,G,rpt) Interaction

In sections 4.5.8 and 4.5.9 the mechanisms for sending periodic and
triggered (S,G,rpt) messages are described.  The astute reader will note
that periodic Prune(S,G,rpt) messages are only sent in PIM Join/Prune



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messages containing a Join(*,G), whereas it is possible for a triggered
Prune(S,G,rpt) message to be sent when the router has no (*,G) join
state.  This may seem like a contradiction, but in fact it is
intentional, and is a side effect of not optimizing (*,*,RP) behavior.

We first note that reception of a Join(*,*,RP) by itself does not cancel
(S,G,rpt) prune state on that interface, whereas receiving a Join(*,G)
by itself does cancel (S,G,rpt) prune state on that interface.
Similarly, reception of a Prune(*,G) on an interface with (*,*,RP) join
state does not by itself prevent forwarding of G using the (*,*,RP)
state - this is because a Prune(*,G) only serves to cancel (*,G) join
state.  Conceptually (*,*,RP) state functions "above" the normal (*,G)
and (S,G) mechanisms, and so neither Join(*,*,RP) or Prune(*,*,RP)
messages affect any other state.

The upshot of this is that to prevent forwarding (S,G) on (*,*,RP)
state, a Prune(S,G,rpt) must be used.

We also note that for historical reasons there is no Assert(*,*,RP)
message, so any forwarding contention is resolved using Assert(*,G)
messages.

We now need to consider the interaction between (*,*,RP) state and (*,G)
state.  If there is a need for an assert between two upstream routers on
a LAN, we need to ensure that the correct thing happens for all
combinations of (*,*,RP) and (*,G) forwarding state.  As there is no
Assert(*,*,RP) message, no router can tell whether the assert winner has
(*,*,RP) state or (*,G) state.  Thus a downstream router has to treat
the two the same and send its periodic Prune(S,G,rpt) messages to
RPF'(*,G).

To avoid needing to specify all the complex override rules between
(*,*,RP), (*,G) and (S,G,rpt), we simply require that to prune (S,G) off
the (*,*,RP) tree, a Join(*,G) must also be sent.

If a router is receiving on (*,*,RP) state, and has not yet had (*,G)
state instantiated, it may still need to send a triggered Join(S,G,rpt)
to override a Prune(S,G,rpt) that it sees directed to RPF'(*,G) on its
upstream interface.  Hence triggered (S,G,rpt) messages may be sent when
JoinDesired(*,G) is false but JoinDesired(*,*,RP) is true.

Finally we note that there is an unoptimized case when the upstream
router on a LAN already has (*,G) join and (S,G,rpt) prune state caused
by an existing downstream router.  If at this time a new Join(*,*,RP) is
sent to the upstream router from a different downstream router, this
will not override the (S,G,rpt) prune state at the upstream router.  The
override will not occur until the next time the original downstream
router resends its Prune(S,G,rpt).  This case was considered to be not



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worth optimizing, as (*,*,RP) state is generally very long lived, and so
any minor delays in getting traffic to a new PMBR seem unimportant.


4.6.  PIM Assert Messages

Where multiple PIM routers peer over a shared LAN it is possible for
more than one upstream router to have valid forwarding state for a
packet, which can lead to packet duplication (see Section 3 "Multi-
access LANs").  PIM does not attempt to prevent this from occurring.
Instead it detects when this has happened and elects a single forwarder
amongst the upstream routers to prevent further duplication.  This
election is performed using PIM Assert messages.  Assert messages are
also received by downstream routers on the LAN, and these cause
subsequent Join/Prune messages to be sent to the upstream router that
won the Assert.

In general, a PIM Assert message should only be accepted for processing
if it comes from a known PIM neighbor.  A PIM router hears about PIM
neighbors through PIM Hello messages.  If a router receives an Assert
message from a particular IP source address and it has not seen a PIM
Hello message from that source address, then the Assert message SHOULD
be discarded without further processing.  In addition, if the Hello
message from a neighbor was authenticated using the IPsec Authentication
Header (AH) (see Section 6.3) then all Assert messages from that
neighbor MUST also be authenticated using IPsec AH.

We note that some older PIM implementations incorrectly fail to send
Hello messages on point-to-point interfaces, so we also RECOMMEND that a
configuration option be provided to allow interoperation with such older
routers, but that this configuration option SHOULD NOT be enabled by
default.

4.6.1.  (S,G) Assert Message State Machine

The (S,G) Assert state machine for interface I is shown in Figure 10.
There are three states:

NoInfo (NI)
     This router has no (S,G) assert state on interface I.

I am Assert Winner (W)
     This router has won an (S,G) assert on interface I.  It is now
     responsible for forwarding traffic from S destined for G out of
     interface I.  Irrespective of whether it is the DR for I, while a
     router is the assert winner, it is also responsible for forwarding
     traffic onto I on behalf of local hosts on I that have made
     membership requests that specifically refer to S (and G).



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I am Assert Loser (L)
     This router has lost an (S,G) assert on interface I.  It must not
     forward packets from S destined for G onto interface I.  If it is
     the DR on I, it is no longer responsible for forwarding traffic
     onto I to satisfy local hosts with membership requests that
     specifically refer to S and G.

In addition, there is also an Assert Timer (AT) that is used to time out
asserts on the assert losers and to re-send asserts on the assert
winner.









































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  Figure 10: Per-interface (S,G) Assert State machine in tabular form

+-----------------------------------------------------------------------+
|                         In NoInfo (NI) State                          |
+---------------+-------------------+------------------+----------------+
| Receive       |  Receive Assert   |  Data arrives    |  Receive       |
| Inferior      |  with RPTbit      |  from S to G on  |  Acceptable    |
| Assert with   |  set and          |  I and           |  Assert with   |
| RPTbit clear  |  CouldAssert      |  CouldAssert     |  RPTbit clear  |
| and           |  (S,G,I)          |  (S,G,I)         |  and AssTrDes  |
| CouldAssert   |                   |                  |  (S,G,I)       |
| (S,G,I)       |                   |                  |                |
+---------------+-------------------+------------------+----------------+
| -> W state    |  -> W state       |  -> W state      |  -> L state    |
| [Actions A1]  |  [Actions A1]     |  [Actions A1]    |  [Actions A6]  |
+---------------+-------------------+------------------+----------------+

+-----------------------------------------------------------------------+
|                   In I Am Assert Winner (W) State                     |
+----------------+------------------+-----------------+-----------------+
| Assert Timer   |   Receive        |  Receive        |   CouldAssert   |
| Expires        |   Inferior       |  Preferred      |   (S,G,I) ->    |
|                |   Assert         |  Assert         |   FALSE         |
+----------------+------------------+-----------------+-----------------+
| -> W state     |   -> W state     |  -> L state     |   -> NI state   |
| [Actions A3]   |   [Actions A3]   |  [Actions A2]   |   [Actions A4]  |
+----------------+------------------+-----------------+-----------------+

+-------------------------------------------------------------------------+
|             In I Am Assert Loser (L) State                              |
+-------------+--------------+--------------+--------------+--------------+
|Receive      | Receive      | Receive      | Assert Timer | Current      |
|Preferred    | Acceptable   | Inferior     | Expires      | Winner's     |
|Assert       | Assert with  | Assert or    |              | GenID        |
|             | RPTbit clear | Assert       |              | Changes or   |
|             | from Current | Cancel from  |              | NLT Expires  |
|             | Winner       | Current      |              |              |
|             |              | Winner       |              |              |
+-------------+--------------+--------------+--------------+--------------+
|-> L state   | -> L state   | -> NI state  | -> NI state  | -> NI state  |
|[Actions A2] | [Actions A2] | [Actions A5] | [Actions A5] | [Actions A5] |
+-------------+--------------+--------------+--------------+--------------+









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+-----------------------------------------------------------------------+
|                    In I Am Assert Loser (L) State                     |
+----------------+-----------------+-------------------+----------------+
| AssTrDes       |  my_metric ->   |   RPF_interface   |  Receive       |
| (S,G,I) ->     |  better than    |   (S) stops       |  Join(S,G) on  |
| FALSE          |  winner's       |   being I         |  interface I   |
|                |  metric         |                   |                |
+----------------+-----------------+-------------------+----------------+
| -> NI state    |  -> NI state    |   -> NI state     |  -> NI State   |
| [Actions A5]   |  [Actions A5]   |   [Actions A5]    |  [Actions A5]  |
+----------------+-----------------+-------------------+----------------+

Note that for reasons of compactness, "AssTrDes(S,G,I)" is used in the
state machine table to refer to AssertTrackingDesired(S,G,I).

Terminology:
     A "preferred assert" is one with a better metric than the current
     winner.

     An "acceptable assert" is one that has a better metric than
     my_assert_metric(S,G,I).  An assert is never considered acceptable
     if its metric is infinite.

     An "inferior assert" is one with a worse metric than
     my_assert_metric(S,G,I).  An assert is never considered inferior if
     my_assert_metric(S,G,I) is infinite.

The state machine uses the following macros:

CouldAssert(S,G,I) =
     SPTbit(S,G)==TRUE
     AND (RPF_interface(S) != I)
     AND (I in ( ( joins(*,*,RP(G)) (+) joins(*,G) (-) prunes(S,G,rpt) )
                 (+) ( pim_include(*,G) (-) pim_exclude(S,G) )
                 (-) lost_assert(*,G)
                 (+) joins(S,G) (+) pim_include(S,G) ) )

CouldAssert(S,G,I) is true for downstream interfaces which would be in
the inherited_olist(S,G) if (S,G) assert information was not taken into
account.











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AssertTrackingDesired(S,G,I) =
     (I in ( ( joins(*,*,RP(G)) (+) joins(*,G) (-) prunes(S,G,rpt) )
             (+) ( pim_include(*,G) (-) pim_exclude(S,G) )
             (-) lost_assert(*,G)
             (+) joins(S,G) ) )
     OR (local_receiver_include(S,G,I) == TRUE
         AND (I_am_DR(I) OR (AssertWinner(S,G,I) == me)))
     OR ((RPF_interface(S) == I) AND (JoinDesired(S,G) == TRUE))
     OR ((RPF_interface(RP(G)) == I) AND (JoinDesired(*,G) == TRUE)
         AND (SPTbit(S,G) == FALSE))

AssertTrackingDesired(S,G,I) is true on any interface in which an (S,G)
assert might affect our behavior.

The first three lines of AssertTrackingDesired account for (*,G) join
and local membership information received on I that might cause the
router to be interested in asserts on I.

The 4th line accounts for (S,G) join information received on I that
might cause the router to be interested in asserts on I.

The 5th and 6th lines account for (S,G) local membership information on
I. Note that we can't use the pim_include(S,G) macro since it uses
lost_assert(S,G,I) and would result in the router forgetting that it
lost an assert if the only reason it was interested was local
membership. The AssertWinner(S,G,I) check forces an assert winner to
keep on being responsible for forwarding as long as local receivers are
present. Removing this check would make the assert winner give up
forwarding as soon as the information that originally caused it to
forward went away and the task of forwarding for local receivers would
revert back to the DR.

The last three lines account for the fact that a router must keep track
of assert information on upstream interfaces in order to send joins and
prunes to the proper neighbor.

Transitions from NoInfo State

When in NoInfo state, the following events may trigger transitions:

     Receive Inferior Assert with RPTbit cleared AND
          CouldAssert(S,G,I)==TRUE
          An assert is received for (S,G) with the RPT bit cleared that
          is inferior to our own assert metric. The RPT bit cleared
          indicates that the sender of the assert had (S,G) forwarding
          state on this interface.  If the assert is inferior to our
          metric, then we must also have (S,G) forwarding state (i.e.
          CouldAssert(S,G,I)==TRUE) as (S,G) asserts beat (*,G) asserts,



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          and so we should be the assert winner.  We transition to the
          "I am Assert Winner" state, and perform Actions A1 (below).

     Receive Assert with RPTbit set AND CouldAssert(S,G,I)==TRUE
          An assert is received for (S,G) on I with the RPT bit set
          (it's a (*,G) assert).  CouldAssert(S,G,I) is TRUE only if we
          have (S,G) forwarding state on this interface, so we should be
          the assert winner.  We transition to the "I am Assert Winner"
          state, and perform Actions A1 (below).

     An (S,G) data packet arrives on interface I, AND
          CouldAssert(S,G,I)==TRUE
          An (S,G) data packet arrived on an downstream interface which
          is in our (S,G) outgoing interface list.  We optimistically
          assume that we will be the assert winner for this (S,G), and
          so we transition to the "I am Assert Winner" state, and
          perform Actions A1 (below) which will initiate the assert
          negotiation for (S,G).

     Receive Acceptable Assert with RPT bit clear AND
          AssertTrackingDesired(S,G,I)==TRUE
          We're interested in (S,G) Asserts, either because I is a
          downstream interface for which we have (S,G) or (*,G)
          forwarding state, or because I is the upstream interface for S
          and we have (S,G) forwarding state.  The received assert has a
          better metric than our own, so we do not win the Assert.  We
          transition to "I am Assert Loser" and perform actions A6
          (below).

Transitions from "I am Assert Winner" State

When in "I am Assert Winner" state, the following events trigger
transitions:

     Assert Timer Expires
          The (S,G) Assert Timer expires.  As we're in the Winner state,
          then we must still have (S,G) forwarding state that is
          actively being kept alive.  We re-send the (S,G) Assert and
          restart the Assert Timer (Action A3 below).  Note that the
          assert winner's Assert Timer is engineered to expire shortly
          before timers on assert losers; this prevents unnecessary
          thrashing of the forwarder and periodic flooding of duplicate
          packets.

     Receive Inferior Assert
          We receive an (S,G) assert or (*,G) assert mentioning S that
          has a worse metric than our own.  Whoever sent the assert is
          in error, and so we re-send an (S,G) Assert, and restart the



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          Assert Timer (Action A3 below).

     Receive Preferred Assert
          We receive an (S,G) assert that has a better metric than our
          own.  We transition to "I am Assert Loser" state and perform
          actions A2 (below).  Note that this may affect the value of
          JoinDesired(S,G) and PruneDesired(S,G,rpt) which could cause
          transitions in the upstream (S,G) or (S,G,rpt) state machines.

     CouldAssert(S,G,I) -> FALSE
          Our (S,G) forwarding state or RPF interface changed so as to
          make CouldAssert(S,G,I) become false.  We can no longer
          perform the actions of the assert winner, and so we transition
          to NoInfo state and perform actions A4 (below).  This includes
          sending a "canceling assert" with an infinite metric.

Transitions from "I am Assert Loser" State

When in "I am Assert Loser" state, the following transitions can occur:

     Receive Preferred Assert
          We receive an assert that is better than that of the current
          assert winner.  We stay in Loser state, and perform actions A2
          below.

     Receive Acceptable Assert with RPTbit clear from Current Winner
          We receive an assert from the current assert winner that is
          better than our own metric for this (S,G) (although the metric
          may be worse than the winner's previous metric).  We stay in
          Loser state, and perform actions A2 below.

     Receive Inferior Assert or Assert Cancel from Current Winner
          We receive an assert from the current assert winner that is
          worse than our own metric for this group (typically the
          winner's metric became worse or because it is an assert
          cancel).  We transition to NoInfo state, deleting the (S,G)
          assert information and allowing the normal PIM Join/Prune
          mechanisms to operate.  Usually we will eventually re-assert
          and win when data packets from S have started flowing again.

     Assert Timer Expires
          The (S,G) Assert Timer expires.  We transition to NoInfo
          state, deleting the (S,G) assert information (action A5
          below).

     Current Winner's GenID Changes or NLT Expires
          The Neighbor Liveness Timer associated with the current winner
          expires or we receive a Hello message from the current winner



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          reporting a different GenID from the one it previously
          reported.  This indicates that the current winner's interface
          or router has gone down (and may have come back up), and so we
          must assume it no longer knows it was the winner. We
          transition to the NoInfo state, deleting this (S,G) assert
          information (action A5 below).

     AssertTrackingDesired(S,G,I)->FALSE
          AssertTrackingDesired(S,G,I) becomes FALSE.  Our forwarding
          state has changed so that (S,G) Asserts on interface I are no
          longer of interest to us.  We transition to the NoInfo state,
          deleting the (S,G) assert information.

     My metric becomes better than the assert winner's metric
          my_assert_metric(S,G,I) has changed so that now my assert
          metric for (S,G) is better than the metric we have stored for
          current assert winner.  This might happen the underlying
          routing metric changes, or when CouldAssert(S,G,I) becomes
          true; for example, when SPTbit(S,G) becomes true.  We
          transition to NoInfo state, delete this (S,G) assert state
          (action A5 below), and allow the normal PIM Join/Prune
          mechanisms to operate.  Usually we will eventually re-assert
          and win when data packets from S have started flowing again.

     RPF_interface(S) stops being interface I
          Interface I used to be the RPF interface for S, and now it is
          not.  We transition to NoInfo state, deleting this (S,G)
          assert state (action A5 below).

     Receive Join(S,G) on Interface I
          We receive a Join(S,G) that has the Upstream Neighbor Address
          field set to my primary IP address on interface I.  The action
          is to transition to NoInfo state, and delete this (S,G) assert
          state (action A5 below), and allow the normal PIM Join/Prune
          mechanisms to operate.  If whoever sent the Join was in error,
          then the normal assert mechanism will eventually re-apply and
          we will lose the assert again.  However whoever sent the
          assert may know that the previous assert winner has died, and
          so we may end up being the new forwarder.

(S,G) Assert State machine Actions

     A1:  Send Assert(S,G)
          Set Assert Timer to (Assert_Time - Assert_Override_Interval)
          Store self as AssertWinner(S,G,I)
          Store spt_assert_metric(S,I) as AssertWinnerMetric(S,G,I)





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     A2:  Store new assert winner as AssertWinner(S,G,I) and assert
          winner metric as AssertWinnerMetric(S,G,I).
          Set Assert Timer to Assert_Time

     A3:  Send Assert(S,G)
          Set Assert Timer to (Assert_Time - Assert_Override_Interval)

     A4:  Send AssertCancel(S,G)
          Delete assert info (AssertWinner(S,G,I) and
          AssertWinnerMetric(S,G,I) will then return their default
          values).

     A5:  Delete assert info (AssertWinner(S,G,I) and
          AssertWinnerMetric(S,G,I) will then return their default
          values).

     A6:  Store new assert winner as AssertWinner(S,G,I) and assert
          winner metric as AssertWinnerMetric(S,G,I).
          Set Assert Timer to Assert_Time
          If (I is RPF_interface(S)) AND (UpstreamJPState(S,G) == true)
          set SPTbit(S,G) to TRUE.

Note that some of these actions may cause the value of JoinDesired(S,G),
PruneDesired(S,G,rpt), or RPF'(S,G) to change, which could cause further
transitions in other state machines.

4.6.2.  (*,G) Assert Message State Machine

The (*,G) Assert state machine for interface I is shown in Figure 11.
There are three states:

NoInfo (NI)
     This router has no (*,G) assert state on interface I.

I am Assert Winner (W)
     This router has won an (*,G) assert on interface I.  It is now
     responsible for forwarding traffic destined for G onto interface I
     with the exception of traffic for which it has (S,G) "I am Assert
     Loser" state.  Irrespective of whether it is the DR for I, it is
     also responsible for handling the membership requests for G from
     local hosts on I.

I am Assert Loser (L)
     This router has lost an (*,G) assert on interface I.  It must not
     forward packets for G onto interface I with the exception of
     traffic from sources for which is has (S,G) "I am Assert Winner"
     state.  If it is the DR, it is no longer responsible for handling
     the membership requests for group G from local hosts on I.



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In addition, there is also an Assert Timer (AT) that is used to time out
asserts on the assert losers and to re-send asserts on the assert
winner.

When an Assert message is received with a source address other than
zero, a PIM implementation must first match it against the possible
events in the (S,G) assert state machine and process any transitions and
actions, before considering whether the Assert message matches against
the (*,G) assert state machine.

It is important to note that NO TRANSITION CAN OCCUR in the (*,G) state
machine as a result of receiving an Assert message unless the (S,G)
assert state machine for the relevant S and G is in the "NoInfo" state
after the (S,G) state machine has processed the message. Also NO
TRANSITION CAN OCCUR in the (*,G) state machine as a result of receiving
an assert message if that message triggers any change of state in the
(S,G) state machine.  Obviously when the source address in the received
message is set to zero an (S,G) state machine for the S and G does not
exist and can be assumed to be in the "NoInfo" state.

For example, if both the (S,G) and (*,G) assert state machines where in
the NoInfo state when an Assert message arrives, and the message causes
the (S,G) state machine to transition to either "W" or "L" state, then
the assert would not be processed by the (*,G) assert state machine.

Another example: if the (S,G) assert state machine is in "L" state when
an assert message is received, and the assert metric in the message is
worse than my_assert_metric(S,G,I), then the (S,G) assert state machine
will transition to NoInfo state.  In such a case if the (*,G) assert
state machine were in NoInfo state, it might appear that it would
transition to "W" state, but this is not the case because this message
already triggered a transition in the (S,G) assert state machine.



















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  Figure 11: Per-interface (*,G) Assert State machine in tabular form

+-----------------------------------------------------------------------+
|                         In NoInfo (NI) State                          |
+-----------------------+-----------------------+-----------------------+
| Receive Inferior      |  Data arrives for G   |   Receive Acceptable  |
| Assert with RPTbit    |  on I and             |   Assert with RPTbit  |
| set and               |  CouldAssert          |   set and AssTrDes    |
| CouldAssert(*,G,I)    |  (*,G,I)              |   (*,G,I)             |
+-----------------------+-----------------------+-----------------------+
| -> W state            |  -> W state           |   -> L state          |
| [Actions A1]          |  [Actions A1]         |   [Actions A2]        |
+-----------------------+-----------------------+-----------------------+

+-----------------------------------------------------------------------+
|                   In I Am Assert Winner (W) State                     |
+----------------+------------------+-----------------+-----------------+
| Assert Timer   |   Receive        |  Receive        |   CouldAssert   |
| Expires        |   Inferior       |  Preferred      |   (*,G,I) ->    |
|                |   Assert         |  Assert         |   FALSE         |
+----------------+------------------+-----------------+-----------------+
| -> W state     |   -> W state     |  -> L state     |   -> NI state   |
| [Actions A3]   |   [Actions A3]   |  [Actions A2]   |   [Actions A4]  |
+----------------+------------------+-----------------+-----------------+

+-------------------------------------------------------------------------+
|             In I Am Assert Loser (L) State                              |
+-------------+--------------+--------------+--------------+--------------+
|Receive      | Receive      | Receive      | Assert Timer | Current      |
|Preferred    | Acceptable   | Inferior     | Expires      | Winner's     |
|Assert with  | Assert from  | Assert or    |              | GenID        |
|RPTbit set   | Current      | Assert       |              | Changes or   |
|             | Winner with  | Cancel from  |              | NLT Expires  |
|             | RPTbit set   | Current      |              |              |
|             |              | Winner       |              |              |
+-------------+--------------+--------------+--------------+--------------+
|-> L state   | -> L state   | -> NI state  | -> NI state  | -> NI state  |
|[Actions A2] | [Actions A2] | [Actions A5] | [Actions A5] | [Actions A5] |
+-------------+--------------+--------------+--------------+--------------+












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+-----------------------------------------------------------------------+
|          In I Am Assert Loser (L) State                               |
+----------------+----------------+------------------+------------------+
| AssTrDes       | my_metric ->   |  RPF_interface   |  Receive         |
| (*,G,I) ->     | better than    |  (RP(G)) stops   |  Join(*,G) or    |
| FALSE          | Winner's       |  being I         |  Join            |
|                | metric         |                  |  (*,*,RP(G)) on  |
|                |                |                  |  Interface I     |
+----------------+----------------+------------------+------------------+
| -> NI state    | -> NI state    |  -> NI state     |  -> NI State     |
| [Actions A5]   | [Actions A5]   |  [Actions A5]    |  [Actions A5]    |
+----------------+----------------+------------------+------------------+


The state machine uses the following macros:

CouldAssert(*,G,I) =
    ( I in ( joins(*,*,RP(G)) (+) joins(*,G)
             (+) pim_include(*,G)) )
    AND (RPF_interface(RP(G)) != I)

CouldAssert(*,G,I) is true on downstream interfaces for which we have
(*,*,RP(G)) or (*,G) join state, or local members that requested any
traffic destined for G.

AssertTrackingDesired(*,G,I) =
    CouldAssert(*,G,I)
    OR (local_receiver_include(*,G,I)==TRUE
        AND (I_am_DR(I) OR AssertWinner(*,G,I) == me))
    OR (RPF_interface(RP(G)) == I AND RPTJoinDesired(G))

AssertTrackingDesired(*,G,I) is true on any interface on which an (*,G)
assert might affect our behavior.

Note that for reasons of compactness, "AssTrDes(*,G,I)" is used in the
state machine table to refer to AssertTrackingDesired(*,G,I).

Terminology:
     A "preferred assert" is one with a better metric than the current
     winner.

     An "acceptable assert" is one that has a better metric than
     my_assert_metric(*,G,I).  An assert is never considered acceptable
     if its metric is infinite.

     An "inferior assert" is one with a worse metric than
     my_assert_metric(*,G,I).  An assert is never considered inferior if
     my_assert_metric(*,G,I) is infinite.



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Transitions from NoInfo State

When in NoInfo state, the following events trigger transitions, but only
if the (S,G) assert state machine is in NoInfo state before and after
consideration of the received message:

     Receive Inferior Assert with RPTbit set AND
          CouldAssert(*,G,I)==TRUE
          An Inferior (*,G) assert is received for G on Interface I.  If
          CouldAssert(*,G,I) is TRUE, then I is our downstream
          interface, and we have (*,G) forwarding state on this
          interface, so we should be the assert winner.  We transition
          to the "I am Assert Winner" state, and perform Actions A1
          (below).

     A data packet destined for G arrives on interface I, AND
          CouldAssert(*,G,I)==TRUE
          A data packet destined for G arrived on a downstream interface
          which is in our (*,G) outgoing interface list.  We therefore
          believe we should be the forwarder for this (*,G), and so we
          transition to the "I am Assert Winner" state, and perform
          Actions A1 (below).

     Receive Acceptable Assert with RPT bit set AND
          AssertTrackingDesired(*,G,I)==TRUE
          We're interested in (*,G) Asserts, either because I is a
          downstream interface for which we have (*,G) forwarding state,
          or because I is the upstream interface for RP(G) and we have
          (*,G) forwarding state.  We get a (*,G) Assert that has a
          better metric than our own, so we do not win the Assert.  We
          transition to "I am Assert Loser" and perform actions A2
          (below).

Transitions from "I am Assert Winner" State

When in "I am Assert Winner" state, the following events trigger
transitions, but only if the (S,G) assert state machine is in NoInfo
state before and after consideration of the received message:

     Receive Inferior Assert
          We receive a (*,G) assert that has a worse metric than our
          own.  Whoever sent the assert has lost, and so we re-send a
          (*,G) Assert, and restart the Assert Timer (Action A3 below).

     Receive Preferred Assert
          We receive a (*,G) assert that has a better metric than our
          own.  We transition to "I am Assert Loser" state and perform
          actions A2 (below).



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When in "I am Assert Winner" state, the following events trigger
transitions:

     Assert Timer Expires
          The (*,G) Assert Timer expires.  As we're in the Winner state,
          then we must still have (*,G) forwarding state that is
          actively being kept alive.  To prevent unnecessary thrashing
          of the forwarder and periodic flooding of duplicate packets,
          we re-send the (*,G) Assert, and restart the Assert Timer
          (Action A3 below).

     CouldAssert(*,G,I) -> FALSE
          Our (*,G) forwarding state or RPF interface changed so as to
          make CouldAssert(*,G,I) become false.  We can no longer
          perform the actions of the assert winner, and so we transition
          to NoInfo state and perform actions A4 (below).

Transitions from "I am Assert Loser" State

When in "I am Assert Loser" state, the following events trigger
transitions, but only if the (S,G) assert state machine is in NoInfo
state before and after consideration of the received message:

     Receive Preferred Assert with RPTbit set
          We receive a (*,G) assert that is better than that of the
          current assert winner.  We stay in Loser state, and perform
          actions A2 below.

     Receive Acceptable Assert from Current Winner with RPTbit set
          We receive a (*,G) assert from the current assert winner that
          is better than our own metric for this group (although the
          metric may be worse than the winner's previous metric).  We
          stay in Loser state, and perform actions A2 below.

     Receive Inferior Assert or Assert Cancel from Current Winner
          We receive an assert from the current assert winner that is
          worse than our own metric for this group (typically because
          the winner's metric became worse or is now an assert cancel).
          We transition to NoInfo state, delete this (*,G) assert state
          (action A5), and allow the normal PIM Join/Prune mechanisms to
          operate.  Usually we will eventually re-assert and win when
          data packets for G have started flowing again.

When in "I am Assert Loser" state, the following events trigger
transitions:

     Assert Timer Expires
          The (*,G) Assert Timer expires.  We transition to NoInfo state



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          and delete this (*,G) assert info (action A5).

     Current Winner's GenID Changes or NLT Expires
          The Neighbor Liveness Timer associated with the current winner
          expires or we receive a Hello message from the current winner
          reporting a different GenID from the one it previously
          reported.  This indicates that the current winner's interface
          or router has gone down (and may have come back up), and so we
          must assume it no longer knows it was the winner. We
          transition to the NoInfo state, deleting the (*,G) assert
          information (action A5).

     AssertTrackingDesired(*,G,I)->FALSE
          AssertTrackingDesired(*,G,I) becomes FALSE.  Our forwarding
          state has changed so that (*,G) Asserts on interface I are no
          longer of interest to us.  We transition to NoInfo state and
          delete this (*,G) assert info (action A5).

     My metric becomes better than the assert winner's metric
          My routing metric, rpt_assert_metric(G,I), has changed so that
          now my assert metric for (*,G) is better than the metric we
          have stored for current assert winner.  We transition to
          NoInfo state, and delete this (*,G) assert state (action A5),
          and allow the normal PIM Join/Prune mechanisms to operate.
          Usually we will eventually re-assert and win when data packets
          for G have started flowing again.

     RPF_interface(RP(G)) stops being interface I
          Interface I used to be the RPF interface for RP(G), and now it
          is not.  We transition to NoInfo state, and delete this (*,G)
          assert state (action A5).

     Receive Join(*,G) or Join(*,*,RP(G)) on interface I
          We receive a Join(*,G) or a Join(*,*,RP(G)) that has the
          Upstream Neighbor Address field set to my primary IP address
          on interface I.  The action is to transition to NoInfo state,
          and delete this (*,G) assert state (action A5), and allow the
          normal PIM Join/Prune mechanisms to operate.  If whoever sent
          the Join was in error, then the normal assert mechanism will
          eventually re-apply and we will lose the assert again.
          However whoever sent the assert may know that the previous
          assert winner has died, and so we may end up being the new
          forwarder.

(*,G) Assert State machine Actions

     A1:  Send Assert(*,G)
          Set Assert Timer to (Assert_Time - Assert_Override_Interval)



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          Store self as AssertWinner(*,G,I).
          Store rpt_assert_metric(G,I) as AssertWinnerMetric(*,G,I).

     A2:  Store new assert winner as AssertWinner(*,G,I) and assert
          winner metric as AssertWinnerMetric(*,G,I).
          Set Assert Timer to Assert_Time

     A3:  Send Assert(*,G)
          Set Assert Timer to (Assert_Time - Assert_Override_Interval)

     A4:  Send AssertCancel(*,G)
          Delete assert info (AssertWinner(*,G,I) and
          AssertWinnerMetric(*,G,I) will then return their default
          values).

     A5:  Delete assert info (AssertWinner(*,G,I) and
          AssertWinnerMetric(*,G,I) will then return their default
          values).

Note that some of these actions may cause the value of JoinDesired(*,G)
or RPF'(*,G)) to change, which could cause further transitions in other
state machines.


4.6.3.  Assert Metrics

Assert metrics are defined as:

  struct assert_metric {
    rpt_bit_flag;
    metric_preference;
    route_metric;
    ip_address;
  };


When comparing assert_metrics, the rpt_bit_flag, metric_preference, and
route_metric field are compared in order, where the first lower value
wins.  If all fields are equal, the primary IP address of the router
that sourced the Assert message is used as a tie-breaker, with the
highest IP address winning.

An assert metric for (S,G) to include in (or compare against) an Assert
message sent on interface I should be computed using the following
pseudocode:






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  assert_metric
  my_assert_metric(S,G,I) {
      if( CouldAssert(S,G,I) == TRUE ) {
          return spt_assert_metric(S,I)
      } else if( CouldAssert(*,G,I) == TRUE ) {
          return rpt_assert_metric(G,I)
      } else {
          return infinite_assert_metric()
      }
  }


spt_assert_metric(S,I) gives the assert metric we use if we're sending
an assert based on active (S,G) forwarding state:

  assert_metric
  spt_assert_metric(S,I) {
     return {0,MRIB.pref(S),MRIB.metric(S),my_ip_address(I)}
  }


rpt_assert_metric(G,I) gives the assert metric we use if we're sending
an assert based only on (*,G) forwarding state:

  assert_metric
  rpt_assert_metric(G,I) {
      return {1,MRIB.pref(RP(G)),MRIB.metric(RP(G)),my_ip_address(I)}
  }


MRIB.pref(X) and MRIB.metric(X) are the routing preference and routing
metrics associated with the route to a particular (unicast) destination
X, as determined by the MRIB.  my_ip_address(I) is simply the router's
primary IP address that is associated with the local interface I.

infinite_assert_metric() gives the assert metric we need to send an
assert but don't match either (S,G) or (*,G) forwarding state:

  assert_metric
  infinite_assert_metric() {
       return {1,infinity,infinity,0}
  }


4.6.4.  AssertCancel Messages

An AssertCancel message is simply an RPT Assert message but with
infinite metric.  It is sent by the assert winner when it deletes the



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forwarding state that had caused the assert to occur.  Other routers
will see this metric, and it will cause any other router that has
forwarding state to send its own assert, and to take over forwarding.

An AssertCancel(S,G) is an infinite metric assert with the RPT bit set
that names S as the source.

An AssertCancel(*,G) is an infinite metric assert with the RPT bit set
and the source set to zero.

AssertCancel messages are simply an optimization.  The original Assert
timeout mechanism will allow a subnet to eventually become consistent;
the AssertCancel mechanism simply causes faster convergence.  No special
processing is required for an AssertCancel message, since it is simply
an Assert message from the current winner.

4.6.5.  Assert State Macros

The macros lost_assert(S,G,rpt,I), lost_assert(S,G,I), and
lost_assert(*,G,I) are used in the olist computations of Section 4.1,
and are defined as:

  bool lost_assert(S,G,rpt,I) {
    if ( RPF_interface(RP(G)) == I  OR
         ( RPF_interface(S) == I AND SPTbit(S,G) == TRUE ) ) {
       return FALSE
    } else {
       return ( AssertWinner(S,G,I) != NULL AND
                AssertWinner(S,G,I) != me )
    }
  }


  bool lost_assert(S,G,I) {
    if ( RPF_interface(S) == I ) {
       return FALSE
    } else {
       return ( AssertWinner(S,G,I) != NULL AND
                AssertWinner(S,G,I) != me  AND
                (AssertWinnerMetric(S,G,I) is better
                   than spt_assert_metric(S,I) )
    }
  }


Note: the term "AssertWinnerMetric(S,G,I) is better than
spt_assert_metric(S,I)" is required to correctly handle the transition
phase when a router has (S,G) join state, but has not yet set the SPT



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bit.  In this case it needs to ignore the assert state if it will win
the assert once the SPTbit is set.

  bool lost_assert(*,G,I) {
    if ( RPF_interface(RP(G)) == I ) {
       return FALSE
    } else {
       return ( AssertWinner(*,G,I) != NULL AND
                AssertWinner(*,G,I) != me )
    }
  }


AssertWinner(S,G,I) is the IP source address of the Assert(S,G) packet
that won an Assert.

AssertWinner(*,G,I) is the IP source address of the Assert(*,G) packet
that won an Assert.

AssertWinnerMetric(S,G,I) is the Assert metric of the Assert(S,G) packet
that won an Assert.

AssertWinnerMetric(*,G,I) is the Assert metric of the Assert(*,G) packet
that won an Assert.

AssertWinner(S,G,I) defaults to NULL and AssertWinnerMetric(S,G,I)
defaults to Infinity when in the NoInfo state.

Summary of Assert Rules and Rationale

This section summarizes the key rules for sending and reacting to
asserts and the rationale for these rules.  This section is not intended
to be and should not be treated as a definitive specification of
protocol behavior.  The state machines and pseudocode should be
consulted for that purpose.  Rather, this section is intended to
document important aspects of a the Assert protocol behavior and to
provide information that may prove helpful to the reader in
understanding and implementing this part of the protocol.

1.   Behavior: Downstream neighbors send Join(*,G) and Join(S,G)
     periodic messages to the appropriate RPF' neighbor, i.e., the RPF
     neighbor as modified by the assert process.  They are not always
     sent to the RPF neighbor as indicated by the MRIB.  Normal
     suppression and override rules apply.

     Rationale: By sending the periodic and triggered Join messages to
     the RPF' neighbor instead of to the RPF neighbor, the downstream
     router avoids re-triggering the Assert process with every Join.  A



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     side effect of sending Joins to the Assert winner is that traffic
     will not switch back to the "normal" RPF neighbor until the Assert
     times out.  This will not happen until data stops flowing, if item
     8 below is implemented.

2.   Behavior: The assert winner for (*,G) acts as the local DR for
     (*,G) on behalf of IGMP/MLD members.

     Rationale: This is required to allow a single router to merge PIM
     and IGMP/MLD joins and leaves.  Without this, overrides don't work.

3.   Behavior: The assert winner for (S,G) acts as the local DR for
     (S,G) on behalf of IGMPv3 members.

     Rationale: Same rationale as for 2.

4.   Behavior: (S,G) and (*,G) prune overrides are sent to the RPF'
     neighbor and not to the regular RPF neighbor.

     Rationale: Same as for 1.

5.   Behavior: An (S,G,rpt) prune override is not sent (at all) if
     RPF'(S,G,rpt) != RPF'(*,G).

     Rationale: This avoids keeping state alive on the (S,G) tree when
     only (*,G) downstream members are left.  Also, it avoids sending
     (S,G,rpt) joins to a router that is not on the (*,G) tree.  This
     behavior might be confusing although this specification does
     indicate that such a join should be dropped.

6.   Behavior: An assert loser that receives a Join(S,G) with an
     Upstream Neighbor Address that is its primary IP address on that
     interface cancels the (S,G) Assert Timer.

     Rationale: This is necessary in order to have rapid convergence in
     the event that the downstream router that initially sent a join to
     the prior Assert winner has undergone a topology change.

7.   Behavior: An assert loser that receives a Join(*,G) or a
     Join(*,*,RP(G)) with an Upstream Neighbor Address that is its
     primary IP address on that interface cancels the (*,G) Assert Timer
     and all (S,G) assert timers that do not have corresponding
     Prune(S,G,rpt) messages in the compound Join/Prune message.

     Rationale: Same as 6.

8.   Behavior: An assert winner for (*,G) or (S,G) sends a canceling
     assert when it is about to stop forwarding on a (*,G) or an (S,G)



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     entry.  This behavior does not apply to (S,G,rpt).

     Rationale: This allows switching back to the shared tree after the
     last SPT router on the LAN leaves.  Doing this prevents downstream
     routers on the shared tree from keeping SPT state alive.

9.   Behavior: Re-send the assert messages before timing out an assert.
     (This behavior is optional.)

     Rationale: This prevents the periodic duplicates that would
     otherwise occur each time that an assert times out and is then re-
     established.

10.  Behavior: When RPF'(S,G,rpt) changes to be the same as RPF'(*,G) we
     need to trigger a Join(S,G,rpt) to RPF'(*,G).

     Rationale: This allows switching back to the RPT after the last SPT
     member leaves.


4.7.  PIM Bootstrap and RP Discovery

For correct operation, every PIM router within a PIM domain must be able
to map a particular multicast group address to the same RP.  If this is
not the case then black holes may appear, where some receivers in the
domain cannot receive some groups.  A domain in this context is a
contiguous set of routers that all implement PIM and are configured to
operate within a common boundary.

A notable exception to this is where a PIM domain is broken up into
multiple administrative scope regions - these are regions where a border
has been configured so that a range of multicast groups will not be
forwarded across that border.  For more information on Administratively
Scoped IP Multicast, see RFC 2365.  The modified criteria for admin-
scoped regions are that the region is convex with respect to forwarding
based on the MRIB, and that all PIM routers within the scope region map
scoped groups to the same RP within that region.

This specification does not mandate the use of a single mechanism to
provide routers with the information to perform the group-to-RP mapping.
Currently four mechanisms are possible, and all four have associated
problems:

Static Configuration
     A PIM router MUST support the static configuration of group-to-RP
     mappings.  Such a mechanism is not robust to failures, but does at
     least provide a basic interoperability mechanism.




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Embedded-RP
     Embedded-RP defines an address allocation policy in which the
     address of the Rendezvous Point (RP) is encoded in an IPv6
     multicast group address [17].

Cisco's Auto-RP
     Auto-RP uses a PIM Dense-Mode multicast group to announce group-to-
     RP mappings from a central location.  This mechanism is not useful
     if PIM Dense-Mode is not being run in parallel with PIM Sparse-
     Mode, and was only intended for use with PIM Sparse-Mode Version 1.
     No standard specification currently exists.

BootStrap Router (BSR)
     RFC 2362 specifies a bootstrap mechanism based around the automatic
     election of a bootstrap router (BSR).  Any router in the domain
     that is configured to be a possible RP reports its candidacy to the
     BSR, and then a domain-wide flooding mechanism distributes the
     BSR's chosen set of RPs throughout the domain.  As specified in RFC
     2362, BSR is flawed in its handling of admin-scoped regions that
     are smaller than a PIM domain, but the mechanism does work for
     global-scoped groups.

As far as PIM-SM is concerned, the only important requirement is that
all routers in the domain (or admin scope zone for scoped regions)
receive the same set of group-range-to-RP mappings.  This may be
achieved through the use of any of these mechanisms, or through
alternative mechanisms not currently specified.

It must be operationally ensured that any RP address configured, learned
or advertised is reachable from all routers in the PIM domain.


4.7.1.  Group-to-RP Mapping

Using one of the mechanisms described above, a PIM router receives one
or more possible group-range-to-RP mappings.  Each mapping specifies a
range of multicast groups (expressed as a group and mask) and the RP to
which such groups should be mapped.  Each mapping may also have an
associated priority.  It is possible to receive multiple mappings all of
which might match the same multicast group - this is the common case
with BSR.  The algorithm for performing the group-to-RP mapping is as
follows:

1.   Perform longest match on group-range to obtain a list of RPs.

2.   From this list of matching RPs, find the one with highest priority.
     Eliminate any RPs from the list that have lower priorities.




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3.   If only one RP remains in the list, use that RP.

4.   If multiple RPs are in the list, use the PIM hash function to
     choose one.

Thus if two or more group-range-to-RP mappings cover a particular group,
the one with the longest mask is the mapping to use.  If the mappings
have the same mask length, then the one with the highest priority is
chosen.  If there is more than one matching entry with the same longest
mask and the priorities are identical, then a hash function (see Section
4.7.2) is applied to choose the RP.

This algorithm is invoked by a DR when it needs to determine an RP for a
given group, e.g. upon reception of a packet or IGMP/MLD membership
indication for a group for which the DR does not know the RP.  It is
invoked by any router that has (*,*,RP) state when a packet is received
for which there is no corresponding (S,G) or (*,G) entry.  Furthermore,
the mapping function is invoked by all routers upon receiving a (*,G) or
(*,*,RP) Join/Prune message.

Note that if the set of possible group-range-to-RP mappings changes,
each router will need to check whether any existing groups are affected.
This may, for example, cause a DR or acting DR to re-join a group, or
cause it to re-start register encapsulation to the new RP.

     Implementation note: the bootstrap mechanism described in RFC
     2362 omitted step (1) above.  However of the implementations
     we are aware of, approximately half performed step (1) anyway.
     It should be noted that implementations of BSR that omit step
     1 will not correctly interoperate with implementations of this
     specification when used with the BSR mechanism described in
     [11].


4.7.2.  Hash Function

The hash function is used by all routers within a domain, to map a group
to one of the RPs from the matching set of group-range-to-RP mappings
(this set all have the same longest mask length and same highest
priority). The algorithm takes as input the group address, and the
addresses of the candidate RPs from the mappings, and gives as output
one RP address to be used.

The protocol requires that all routers hash to the same RP within a
domain (except for transients). The following hash function must be used
in each router:





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1.   For RP addresses in the matching group-range-to-RP mappings,
     compute a value:

     Value(G,M,C(i))=
      (1103515245 * ((1103515245 * (G&M)+12345) XOR C(i)) + 12345) mod 2^31


     where C(i) is the RP address and M is a hash-mask.  If BSR is being
     used, the hash-mask is given in the Bootstrap messages.  If BSR is
     not being used, the alternative mechanism that supplies the group-
     range-to-RP mappings may supply the value, or else it defaults to a
     mask with the most significant 30 bits being one for IPv4 and the
     most significant 126 bits being one for IPv6.  The hash-mask allows
     a small number of consecutive groups (e.g., 4) to always hash to
     the same RP. For instance, hierarchically-encoded data can be sent
     on consecutive group addresses to get the same delay and fate-
     sharing characteristics.

     For address families other than IPv4, a 32-bit digest to be used as
     C(i) and G must first be derived from the actual RP or group
     address.  Such a digest method must be used consistently throughout
     the PIM domain. For IPv6 addresses, we recommend using the
     equivalent IPv4 address for an IPv4-compatible address, and the
     exclusive-or of each 32-bit segment of the address for all other
     IPv6 addresses.  For example, the digest of the IPv6 address
     3ffe:b00:c18:1::10 would be computed as 0x3ffe0b00 ^ 0x0c180001 ^
     0x00000000 ^ 0x00000010, where ^ represents the exclusive-or
     operation.

2.   The candidate RP with the highest resulting hash value is then the
     RP chosen by this Hash Function.  If more than one RP has the same
     highest hash value, the RP with the highest IP address is chosen.


4.8.  Source-Specific Multicast

The Source-Specific Multicast (SSM) service model [6] can be implemented
with a strict subset of the PIM-SM protocol mechanisms.  Both regular IP
Multicast and SSM semantics can coexist on a single router and both can
be implemented using the PIM-SM protocol.  A range of multicast
addresses, currently 232.0.0.0/8 in IPv4 and FF3x::/32 for IPv6, is
reserved for SSM, and the choice of semantics is determined by the
multicast group address in both data packets and PIM messages.

4.8.1.  Protocol Modifications for SSM destination addresses

The following rules override the normal PIM-SM behavior for a multicast
address G in the SSM range:



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o A router MUST NOT send a (*,G) Join/Prune message for any reason.

o A router MUST NOT send an (S,G,rpt) Join/Prune message for any reason.

o A router MUST NOT send a Register message for any packet that is
  destined to an SSM address.

o A router MUST NOT forward packets based on (*,G) or (S,G,rpt) state.
  The (*,G) and (S,G,rpt) -related state summarization macros are NULL
  for any SSM address, for the purposes of packet forwarding.

o A router acting as an RP MUST NOT forward any Register-encapsulated
  packet that has an SSM destination address.

The last two rules are present to deal with "legacy" routers unaware of
SSM that may be sending (*,G) and (S,G,rpt) Join/Prunes, or Register
messages for SSM destination addresses.

Additionally:

o A router MAY be configured to advertise itself as a Candidate RP for
  an SSM address.  If so, it SHOULD respond with a Register-Stop message
  to any Register message containing a packet destined for an SSM
  address.

o A router MAY optimize out the creation and maintenance of (S,G,rpt)
  and (*,G) state for SSM destination addresses -- this state is not
  needed for SSM packets.

4.8.2.  PIM-SSM-only Routers

An implementor may choose to implement only the subset of PIM Sparse-
Mode that provides SSM forwarding semantics.

A PIM-SSM-only router MUST implement the following portions of this
specification:


o     Upstream (S,G) state machine (Section 4.5.7)

o     Downstream (S,G) state machine (Section 4.5.3)

o     (S,G) Assert state machine (Section 4.6.1)

o     Hello messages, neighbor discovery and DR election (Section 4.3)

o     Packet forwarding rules (Section 4.2)




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A PIM-SSM-only router does not need to implement the following protocol
elements:


o     Register state machine (Section 4.4)

o     (*,G), (S,G,rpt) and (*,*,RP) Downstream state machines (Sections
  4.5.2, 4.5.4, and 4.5.1)

o     (*,G), (S,G,rpt), and (*,*,RP) Upstream state machines (Sections
  4.5.6, 4.5.8, and 4.5.5)

o     (*,G) Assert state machine (Section 4.6.2)

o     Bootstrap RP Election (Section 4.7)

o     Keepalive Timer

o     SptBit (Section 4.2.2)

The Keepalive Timer should be treated as always running and SptBit
should be treated as being always set for an SSM address.  Additionally,
the Packet forwarding rules of Section 4.2 can be simplified in a PIM-
SSM-only router:

    if( iif == RPF_interface(S) AND UpstreamJPState(S,G) == Joined ) {
        oiflist = inherited_olist(S,G)
    } else if( iif is in inherited_olist(S,G) ) {
        send Assert(S,G) on iif
    }

    oiflist = oiflist (-) iif
    forward packet on all interfaces in oiflist

This is nothing more than the reduction of the normal PIM-SM forwarding
rule, with all (S,G,rpt) and (*,G) clauses replaced with NULL.

4.9.  PIM Packet Formats

This section describes the details of the packet formats for PIM control
messages.

All PIM control messages have IP protocol number 103.

PIM messages are either unicast (e.g.  Registers and Register-Stop), or
multicast with TTL 1 to the `ALL-PIM-ROUTERS' group (e.g. Join/Prune,
Asserts, etc.).  The source address used for unicast messages is a
domain-wide reachable address; the source address used for multicast



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messages is the link-local address of the interface on which the message
is being sent.

The IPv4 `ALL-PIM-ROUTERS' group is `224.0.0.13'.  The IPv6 `ALL-PIM-
ROUTERS' group is `ff02::d'.

The PIM header common to all PIM messages is:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Ver
     PIM Version number is 2.

Type Types for specific PIM messages.  PIM Types are:


Message Type                          Destination
---------------------------------------------------------------------------
0 = Hello                             Multicast to ALL-PIM-ROUTERS
1 = Register                          Unicast to RP
2 = Register-Stop                     Unicast to source of Register packet
3 = Join/Prune                        Multicast to ALL-PIM-ROUTERS
4 = Bootstrap                         Multicast to ALL-PIM-ROUTERS
5 = Assert                            Multicast to ALL-PIM-ROUTERS
6 = Graft (used in PIM-DM only)       Unicast to RPF'(S)
7 = Graft-Ack (used in PIM-DM only)   Unicast to source of Graft packet
8 = Candidate-RP-Advertisement        Unicast to Domain's BSR


Reserved
     Set to zero on transmission.  Ignored upon receipt.


Checksum
     The checksum is a standard IP checksum, i.e.  the 16-bit one's
     complement of the one's complement sum of the entire PIM message,
     excluding the "Multicast data packet" section of the Register
     message.  For computing the checksum, the checksum field is zeroed.
     If the packet's length is not an integral number of 16-bit words,
     the packet is padded with a trailing byte of zero before performing
     the checksum.





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     For IPv6, the checksum also includes the IPv6 "pseudo-header", as
     specified in RFC 2460, Section 8.1 [5]. This "pseudo-header" is
     prepended to the PIM header for the purposes of calculating the
     checksum.  The "Upper-Layer Packet Length" in the pseudo-header is
     set to the length of the PIM message, except in Register messages
     where it is set to the length of the PIM register header (8).  The
     Next Header value used in the pseudo-header is 103.

If a message is received with an unrecognized PIM Ver or Type field or a
message's destination does not correspond to the table above, it MUST be
discarded and an error message SHOULD be logged to the administrator in
a rate limited manner.


4.9.1.  Encoded Source and Group Address Formats


Encoded-Unicast address

An Encoded-Unicast address takes the following format:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Addr Family  | Encoding Type |     Unicast Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...


Addr Family
     The PIM address family of the `Unicast Address' field of this
     address.

     Values of 0-127 are as assigned by the IANA for Internet Address
     Families in [7]. Values 128-250 are reserved to be assigned by the
     IANA for PIM-specific Address Families.  Values 251 though 255 are
     designated for private use.  As there is no assignment authority
     for this space, collisions should be expected.

Encoding Type
     The type of encoding used within a specific Address Family.  The
     value `0' is reserved for this field, and represents the native
     encoding of the Address Family.


Unicast Address
     The unicast address as represented by the given Address Family and
     Encoding Type.




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Encoded-Group address

Encoded-Group addresses take the following format:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Addr Family  | Encoding Type |B| Reserved  |Z|  Mask Len     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                Group multicast Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...


Addr Family
     described above.


Encoding Type
     described above.


[B]idirectional PIM
     indicates the group range should use Bidirectional PIM [13]. For
     PIM-SM defined in this specification, this bit MUST be zero.


Reserved
     Transmitted as zero. Ignored upon receipt.


Admin Scope [Z]one
     indicates the group range is an admin scope zone.  This is used in
     the Bootstrap Router Mechanism [11] only.  For all other purposes,
     this bit is set to zero and ignored on receipt.


Mask Len
     The Mask length field is 8 bits. The value is the number of
     contiguous one bits left justified used as a mask which, combined
     with the group address, describes a range of groups. It is less
     than or equal to the address length in bits for the given Address
     Family and Encoding Type. If the message is sent for a single group
     then the Mask length must equal the address length in bits for the
     given Address Family and Encoding Type.  (e.g. 32 for IPv4 native
     encoding, 128 for IPv6 native encoding).






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Group multicast Address
     Contains the group address.


Encoded-Source address

Encoded-Source address takes the following format:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Family   | Encoding Type | Rsrvd   |S|W|R|  Mask Len     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Source Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...


Addr Family
     described above.


Encoding Type
     described above.


Reserved
     Transmitted as zero, ignored on receipt.


S    The Sparse bit is a 1 bit value, set to 1 for PIM-SM.  It is used
     for PIM version 1 compatibility.


W    The WC (or WildCard) bit is a 1 bit value for use with PIM
     Join/Prune messages (see Section 4.9.5.1 ).


R    The RPT (or Rendezvous Point Tree) bit is a 1 bit value for use
     with PIM Join/Prune messages (see Section 4.9.5.1 ). If the WC bit
     is 1, the RPT bit MUST be 1.


Mask Len
     The mask length field is 8 bits. The value is the number of
     contiguous one bits left justified used as a mask which, combined
     with the Source Address, describes a source subnet. The mask length
     MUST be equal to the mask length in bits for the given Address
     Family and Encoding Type (32 for IPv4 native and 128 for IPv6



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     native).  A router SHOULD ignore any messages received with any
     other mask length.


Source Address
     The source address.


4.9.2.  Hello Message Format

It is sent periodically by routers on all interfaces.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          OptionType           |         OptionLength          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          OptionValue                          |
|                              ...                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          OptionType           |         OptionLength          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          OptionValue                          |
|                              ...                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described in Section 4.9.

OptionType
     The type of the option given in the following OptionValue field.


OptionLength
     The length of the OptionValue field in bytes.


OptionValue
     A variable length field, carrying the value of the option.





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     The Option fields may contain the following values:

     o OptionType 1: Holdtime

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 1             |         Length = 2            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Holdtime             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Holdtime is the amount of time a receiver must keep the neighbor
       reachable, in seconds. If the Holdtime is set to `0xffff', the
       receiver of this message never times out the neighbor. This may
       be used with dial-on-demand links, to avoid keeping the link up
       with periodic Hello messages.

       Hello messages with a Holdtime value set to `0' are also sent by
       a router on an interface about to go down or changing IP address
       (see Section 4.3.1). These are effectively goodbye messages and
       the receiving routers should immediately time out the neighbor
       information for the sender.

     o OptionType 2: LAN Prune Delay

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 2             |          Length = 4           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |T|      Propagation_Delay      |      Override_Interval        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       The LAN Prune Delay option is used to tune the prune propagation
       delay on multi-access LANs.  The T bit specifies the ability of
       the sending router to disable joins suppression.
       Propagation_Delay and Override_Interval are time intervals in
       units of milliseconds.  A router originating a LAN Prune Delay
       option on interface I sets the Propagation_Delay field to the
       configured value of Propagation_Delay(I) and the value of the
       Override_Interval field to the value of Override_Interval(I).  On
       a receiving router the values of the fields are used to tune the
       value of the Effective_Override_Interval(I) and its derived timer
       values. Section 4.3.3 describes how these values affect the
       behavior of a router.





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     o OptionType 3 to 16: reserved to be defined in future versions of
       this document.

     o OptionType 18: deprecated and should not be used.

     o OptionType 19: DR Priority

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 19            |          Length = 4           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         DR Priority                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       DR Priority is a 32-bit unsigned number and should be considered
       in the DR election as described in Section 4.3.2.

     o OptionType 20: Generation ID

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 20            |          Length = 4           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Generation ID                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Generation ID is a random 32-bit value for the interface on which
       the Hello message is sent.  The Generation ID is regenerated
       whenever PIM forwarding is started or restarted on the interface.

     o OptionType 24: Address List

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 24            |      Length = <Variable>      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Secondary Address 1 (Encoded-Unicast format)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                      ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Secondary Address N (Encoded-Unicast format)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       The contents of the Address List Hello option are described in
       Section 4.3.4. All addresses within a single Address List must



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       belong to the same address family.

     OptionTypes 17 thru 65000 are assigned by the IANA.  OptionTypes
     65001 through 65535 are reserved for Private Use, as defined in
     [9].
     Unknown options MUST be ignored, and MUST NOT prevent a neighbor
     relationship from being formed.  The "Holdtime" option MUST be
     implemented; the "DR Priority" and "Generation ID" options SHOULD
     be implemented. The "Address List" option MUST be implemented for
     IPv6.


4.9.3.  Register Message Format

A Register message is sent by the DR or a PMBR to the RP when a
multicast packet needs to be transmitted on the RP-tree.  The IP source
address is set to the address of the DR, the destination address to the
RP's address.  The IP TTL of the PIM packet is the system's normal
unicast TTL.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B|N|                       Reserved2                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
.                     Multicast data packet                     .
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described in Section 4.9. Note that in order to reduce
     encapsulation overhead, the checksum for Registers is done only on
     first 8 bytes of the packet, including the PIM header and the next
     4 bytes, excluding the data packet portion. For interoperability
     reasons, a message carrying a checksum calculated over the entire
     PIM Register message should also be accepted.  When calculating the
     checksum, the IPv6 pseudoheader "Upper-Layer Packet Length" is set
     to 8.


B    The Border bit. If the router is a DR for a source that it is
     directly connected to, it sets the B bit to 0. If the router is a
     PMBR for a source in a directly connected cloud, it sets the B bit
     to 1.



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N    The Null-Register bit. Set to 1 by a DR that is probing the RP
     before expiring its local Register-Suppression Timer. Set to 0
     otherwise.


Reserved2
     Transmitted as zero, ignored on receipt.


Multicast data packet
     The original packet sent by the source.  This packet must be of the
     same address family as the encapsulating PIM packet, e.g. an IPv6
     data packet must be encapsulated in an IPv6 PIM packet.  Note that
     the TTL of the original packet is decremented before encapsulation,
     just like any other packet that is forwarded.  In addition, the RP
     decrements the TTL after decapsulating, before forwarding the
     packet down the shared tree.

     For (S,G) Null-Registers, the Multicast data packet portion
     contains a dummy IP header with S as the source address, G as the
     destination address.  When generating an IPv4 Null-Register
     message, the fields in the dummy IPv4 header SHOULD be filled in
     according to the following table.  Other IPv4 header fields may
     contain any value that is valid for that field.

     Field                  Value
     ---------------------------------------
     IP Version             4
     Header Length          5
     Checksum               Header checksum
     Fragmentation offset   0
     More Fragments         0
     Total Length           20
     IP Protocol            103 (PIM)

     On receipt of an (S,G) Null-Register, if the Header Checksum field
     is non-zero, the recipient SHOULD check the checksum and discard
     null registers that have a bad checksum.  The recipient SHOULD NOT
     check the value of any individual fields; a correct IP header
     checksum is sufficient.  If the Header Checksum field is zero, the
     recipient MUST NOT check the checksum.

     With IPv6, an implementation generates a dummy IP header followed
     by a dummy PIM header with values according to the following table
     in addition to the source and group.  Other IPv6 header fields may
     contain any value that is valid for that field.





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     Header Field   Value
     --------------------------------------
     IP Version     6
     Next Header    103 (PIM)
     Length         4
     PIM Version    0
     PIM Type       0
     PIM Reserved   0
     PIM Checksum   PIM checksum including
                    IPv6 "pseudo-header";
                    see Section 4.9

     On receipt of an IPv6 (S,G) Null-Register, if the dummy PIM header
     is present, the recipient SHOULD check the checksum and discard
     Null-Registers that have a bad checksum.


4.9.4.  Register-Stop Message Format

A Register-Stop is unicast from the RP to the sender of the Register
message.  The IP source address is the address to which the register was
addressed.  The IP destination address is the source address of the
register message.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Group Address (Encoded-Group format)              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Source Address (Encoded-Unicast format)            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described in Section 4.9.

Group Address
     The group address from the multicast data packet in the Register.
     Format described in Section 4.9.1. Note that for Register-Stops the
     Mask Len field contains the full address length * 8 (e.g. 32 for
     IPv4 native encoding), if the message is sent for a single group.


Source Address
     The host address of the source from the multicast data packet in
     the register.  The format for this address is given in the Encoded-



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     Unicast address in Section 4.9.1. A special wild card value
     consisting of an address field of all zeroes can be used to
     indicate any source.


4.9.5.  Join/Prune Message Format

A Join/Prune message is sent by routers towards upstream sources and
RPs.  Joins are sent to build shared trees (RP trees) or source trees
(SPT). Prunes are sent to prune source trees when members leave groups
as well as sources that do not use the shared tree.








































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 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Upstream Neighbor Address (Encoded-Unicast format)     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Reserved     | Num groups    |          Holdtime             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Multicast Group Address 1 (Encoded-Group format)      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Number of Joined Sources    |   Number of Pruned Sources    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Joined Source Address 1 (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             .                                 |
|                             .                                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Joined Source Address n (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Pruned Source Address 1 (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             .                                 |
|                             .                                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Pruned Source Address n (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           .                                   |
|                           .                                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Multicast Group Address m (Encoded-Group format)      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Number of Joined Sources    |   Number of Pruned Sources    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Joined Source Address 1 (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             .                                 |
|                             .                                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Joined Source Address n (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Pruned Source Address 1 (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             .                                 |
|                             .                                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Pruned Source Address n (Encoded-Source format)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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PIM Version, Type, Reserved, Checksum
     Described in Section 4.9.

Unicast Upstream Neighbor Address
     The address of the upstream neighbor that is the target of the
     message.  The format for this address is given in the Encoded-
     Unicast address in Section 4.9.1. For IPv6 the source address used
     for multicast messages is the link-local address of the interface
     on which the message is being sent.  For IPv4, the source address
     is the primary address associated with that interface.


Reserved
     Transmitted as zero, ignored on receipt.


Holdtime
     The amount of time a receiver must keep the Join/Prune state alive,
     in seconds.  If the Holdtime is set to `0xffff', the receiver of
     this message should hold the state until canceled by the
     appropriate canceling Join/Prune message, or timed out according to
     local policy.  This may be used with dial-on-demand links, to avoid
     keeping the link up with periodic Join/Prune messages.

     Note that the HoldTime must be larger than the
     J/P_Override_Interval(I).


Number of Groups
     The number of multicast group sets contained in the message.


Multicast group address
     For format description see Section 4.9.1.

Number of Joined Sources
     Number of join source addresses listed for a given group.


Join Source Address 1 .. n
     This list contains the sources that the sending router will forward
     multicast datagrams for if received on the interface this message
     is sent on.

     See Encoded-Source-Address format in Section 4.9.1.

Number of Pruned Sources
     Number of prune source addresses listed for a group.



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Prune Source Address 1 .. n
     This list contains the sources that the sending router does not
     want to forward multicast datagrams for when received on the
     interface this message is sent on.


Within one PIM Join/Prune message, all the Multicast Group Addresses,
Joined Source addresses and Pruned Source addresses MUST be of the same
address family.  It is NOT PERMITTED to mix IPv4 and IPv6 addresses
within the same message.  In addition, the address family of the fields
in the message SHOULD be the same as the IP source and destination
addresses of the packet.  This permits maximum implementation
flexibility for dual-stack IPv4/IPv6 routers.  If a router receives a
message with mixed family addresses, it SHOULD only process the
addresses which are of the same family as the unicast upstream neighbor
address.


4.9.5.1.  Group Set Source List Rules

As described above, Join / Prune messages are composed of one or more
group sets. Each set contains two source lists, the Join Sources and the
Prune Sources. This section describes the different types of group sets
and source list entries that can exist in a Join / Prune message.

There are two valid group set types:


Wildcard Group Set
     The wildcard group set is represented by the entire multicast range
     - the beginning of the multicast address range in the group address
     field and the prefix length of the multicast address range in the
     mask length field of the Multicast Group Address, i.e.,
     `224.0.0.0/4' for IPv4 or `ff00::/8' for IPv6.  Each Join / Prune
     message SHOULD contain at most one wildcard group set.  Each
     wildcard group set may contain one or more (*,*,RP) source list
     entries in either the Join or Prune lists.

     A (*,*,RP) source list entry may only exist in a wildcard group
     set.  When added to a Join source list, this type of source entry
     expresses the router's interest in receiving traffic for all groups
     mapping to the specified RP. When added to a Prune source list a
     (*,*,RP) entry expresses the router's interest to stop receiving
     such traffic.  Note that as indicated by the Join/Prune state
     machines, such a Join or Prune will NOT override Join/Prune state
     created using a Group-Specific Set (see below).

     (*,*,RP) source list entries have the Source-Address set to the



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     address of the RP, the Source-Address Mask-Len set to the full
     length of the IP address and both the WC and RPT bits of the
     Source-Address set to 1.


Group Specific Set
     A Group Specific Set is represented by a valid IP multicast address
     in the group address field and the full length of the IP address in
     the mask length field of the Multicast Group Address.  Each Join /
     Prune message SHOULD NOT contain more than one group specific set
     for the same IP multicast address.  Each group specific set may
     contain (*,G), (S,G,rpt) and (S,G) source list entries in the Join
     or Prune lists.

     (*,G)
          The (*,G) source list entry is used in Join / Prune messages
          sent towards the RP for the specified group. It expresses
          interest (or lack of) in receiving traffic sent to the group
          through the Rendezvous-Point shared tree. There may only be
          one such entry in both the Join and Prune lists of a group
          specific set.

          (*,G) source list entries have the Source-Address set to the
          address of the RP for group G, the Source-Address Mask-Len set
          to the full length of the IP address and have both the WC and
          RPT bits of the Encoded-Source-Address set.


     (S,G,rpt)
          The (S,G,rpt) source list entry is used in Join / Prune
          messages sent towards the RP for the specified group. It
          expresses interest (or lack of) in receiving traffic through
          the shared tree sent by the specified source to this group.
          For each source address the entry may exist in only one of the
          Join and Prune source lists of a group specific set but not
          both.

          (S,G,rpt) source list entries have the Source-Address set to
          the address of the source S, the Source-Address Mask-Len set
          to the full length of the IP address and have the WC bit clear
          and the RPT bit set in the Encoded-Source-Address.


     (S,G)
          The (S,G) source list entry is used in Join / Prune messages
          sent towards the specified source. It expresses interest (or
          lack of) in receiving traffic through the shortest path tree
          sent by the source to the specified group. For each source



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          address the entry may exist in only one of the Join and Prune
          source lists of a group specific set but not both.

          (S,G) source list entries have the Source-Address set to the
          address of the source S, the Source-Address Mask-Len set to
          the full length of the IP address and have both the WC and RPT
          bits of the Encoded-Source-Address cleared.

The rules described above are sufficient to prevent invalid combinations
of source list entries in group-specific sets.  There are however a
number of combinations that have a valid interpretation but which are
not generated by the protocol as described in this specification:

o Combining a (*,G) Join and a (S,G,rpt) Join entry in the same message
  is redundant as the (*,G) entry covers the information provided by the
  (S,G,rpt) entry.

o The same applies for a (*,G) Prunes and (S,G,rpt) Prunes.

o The combination of a (*,G) Prune and a (S,G,rpt) Join is also not
  generated. (S,G,rpt) Joins are only sent when the router is receiving
  all traffic for a group on the shared tree and it wishes to indicate a
  change for the particular source. As a (*,G) prune indicates that the
  router no longer wishes to receive shared tree traffic, the (S,G,rpt)
  Join would be meaningless.

o As Join / Prune messages are targeted to a single PIM neighbor,
  including both a (S,G) Join and a (S,G,rpt) Prune in the same message
  is usually redundant. The (S,G) Join informs the neighbor that the
  sender wishes to receive the particular source on the shortest path
  tree. It is therefore unnecessary for the router to say that it no
  longer wishes to receive it on the shared tree. However, there is a
  valid interpretation for this combination of entries. A downstream
  router may have to instruct its upstream to only start forwarding a
  specific source once it has started receiving the source on the
  shortest-path tree.

o The combination of a (S,G) Prune and a (S,G,rpt) Join could possibly
  be used by a router to switch from receiving a particular source on
  the shortest-path tree back to receiving it on the shared tree
  (provided that the RPF neighbor for the shortest-path and shared trees
  is common). However Sparse-Mode PIM does not provide a mechanism for
  explicitly switching back to the shared tree.








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The rules are summarized in the tables below.

+----------++------+-------+-----------+-----------+-------+-------+
|          ||Join  | Prune | Join      | Prune     | Join  | Prune |
|          ||(*,G) | (*,G) | (S,G,rpt) | (S,G,rpt) | (S,G) | (S,G) |
+----------++------+-------+-----------+-----------+-------+-------+
|Join      ||-     | no    | ?         | yes       | yes   | yes   |
|(*,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Prune     ||no    | -     | ?         | ?         | yes   | yes   |
|(*,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Join      ||?     | ?     | -         | no        | yes   | ?     |
|(S,G,rpt) ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Prune     ||yes   | ?     | no        | -         | yes   | ?     |
|(S,G,rpt) ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Join      ||yes   | yes   | yes       | yes       | -     | no    |
|(S,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Prune     ||yes   | yes   | ?         | ?         | no    | -     |
|(S,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+


+---------------++--------------+----------------+------------+
|               ||Join (*,*,RP) | Prune (*,*,RP) | all others |
+---------------++--------------+----------------+------------+
|Join (*,*,RP)  ||-             | no             | yes        |
+---------------++--------------+----------------+------------+
|Prune (*,*,RP) ||no            | -              | yes        |
+---------------++--------------+----------------+------------+
|all others     ||yes           | yes            | see above  |
+---------------++--------------+----------------+------------+


yes  Allowed and expected.


no   Combination is not allowed by the protocol and MUST NOT be
     generated by a router.  A router MAY accept these messages but the
     result is undefined.  An error message MAY be logged to the
     administrator in a rate limited manner.


?    Combination not expected by the protocol, but well-defined. A
     router MAY accept it but SHOULD NOT generate it.



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The order of source list entries in a group set source list is not
important, except where limited by the packet format itself.


4.9.5.2.  Group Set Fragmentation

When building a Join / Prune for a particular neighbor, a router should
try and include in the message as much of the information it needs to
convey to the neighbor as possible.  This implies adding one group set
for each multicast group that has information pending transmission and
within each set including all relevant source list entries.

On a router with a large amount of multicast state the number of entries
that must be included may result in packets that are larger than the
maximum IP packet size. In most such cases the information may be split
into multiple messages.

There is an exception with group sets that contain a (*,G) Join source
list entry. The group set expresses the router's interest in receiving
all traffic for the specified group on the shared tree and it MUST
include an (S,G,rpt) Prune source list entry for every source that the
router does not wish to receive. This list of (S,G,rpt) Prune source-
list entries MUST not be split in multiple messages.

If only N (S,G,rpt) Prune entries fit into a maximum-sized Join / Prune
message, but the router has more than N (S,G,rpt) Prunes to add, then
the router MUST choose to include the first N (numerically smallest in
network byte order) IP addresses.


4.9.6.  Assert Message Format

The Assert message is used to resolve forwarder conflicts between
routers on a link. It is sent when a multicast data packet is received
on an interface that the router would normally forward that packet.
Assert messages may also be sent in response to an Assert message from
another router.














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 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Group Address (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Source Address (Encoded-Unicast format)            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|                      Metric Preference                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Metric                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described in Section 4.9.

Group Address
     The group address for which the router wishes to resolve the
     forwarding conflict.  This is an Encoded-Group address, as
     specified in Section 4.9.1.

Source Address
     Source address for which the router wishes to resolve the
     forwarding conflict. The source address MAY be set to zero for
     (*,G) asserts (see below).  The format for this address is given in
     Encoded-Unicast-Address in Section 4.9.1.

R    RPT-bit is a 1 bit value. The RPT-bit is set to 1 for Assert(*,G)
     messages and 0 for Assert(S,G) messages.


Metric Preference
     Preference value assigned to the unicast routing protocol that
     provided the route to the multicast source or Rendezvous-Point.


Metric
     The unicast routing table metric associated with the route used to
     reach the multicast source or Rendezvous-Point. The metric is in
     units applicable to the unicast routing protocol used.


Assert messages can be sent to resolve a forwarding conflict for all
traffic to given group or for a specific source and group.





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Assert(S,G)
     Source specific asserts are sent by routers forwarding a specific
     source on the shortest-path tree (SPTbit is TRUE). (S,G) Asserts
     have the Group-Address field set to the group G and the Source-
     Address field set to the source S. The RPT-bit is set to 0, the
     Metric-Preference is set to MRIB.pref(S) and the Metric is set to
     MRIB.metric(S).

Assert(*,G)
     Group specific asserts are sent by routers forwarding data for the
     group and source(s) under contention on the shared tree. (*,G)
     asserts have the Group-Address field set to the group G. For data
     triggered Asserts the Source-Address field MAY be set to the IP
     source address of the data packet that triggered the Assert and is
     set to zero otherwise.  The RPT-bit is set to 1, the Metric-
     Preference is set to MRIB.pref(RP(G)) and the Metric is set to
     MRIB.metric(RP(G)).

4.10.  PIM Timers

PIM-SM maintains the following timers, as discussed in Section 4.1. All
timers are countdown timers - they are set to a value and count down to
zero, at which point they typically trigger an action.  Of course they
can just as easily be implemented as count-up timers, where the absolute
expiry time is stored and compared against a real-time clock, but the
language in this specification assumes that they count downwards to
zero.


Global Timers

Per interface (I):

     Hello Timer: HT(I)

     Per neighbor (N):

          Neighbor Liveness Timer: NLT(N,I)

     Per active RP (RP):

          (*,*,RP) Join Expiry Timer: ET(*,*,RP,I)

          (*,*,RP) Prune-Pending Timer: PPT(*,*,RP,I)

     Per Group (G):





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          (*,G) Join Expiry Timer: ET(*,G,I)

          (*,G) Prune-Pending Timer: PPT(*,G,I)

          (*,G) Assert Timer: AT(*,G,I)

          Per Source (S):

               (S,G) Join Expiry Timer: ET(S,G,I)

               (S,G) Prune-Pending Timer: PPT(S,G,I)

               (S,G) Assert Timer: AT(S,G,I)

               (S,G,rpt) Prune Expiry Timer: ET(S,G,rpt,I)

               (S,G,rpt) Prune-Pending Timer: PPT(S,G,rpt,I)

Per active RP (RP):

     (*,*,RP) Upstream Join Timer: JT(*,*,RP)

Per Group (G):

     (*,G) Upstream Join Timer: JT(*,G)

     Per Source (S):

          (S,G) Upstream Join Timer: JT(S,G)

          (S,G) Keepalive Timer: KAT(S,G)

          (S,G,rpt) Upstream Override Timer: OT(S,G,rpt)

At the DRs or relevant Assert Winners only:

     Per Source,Group pair (S,G):

          Register-Stop Timer: RST(S,G)

4.11.  Timer Values

When timers are started or restarted, they are set to default values.
This section summarizes those default values.

Note that protocol events or configuration may change the default value
of a timer on a specific interface. When timers are initialized in this
document the value specific to the interface in context must be used.



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Some of the timers listed below (Prune-Pending, Upstream Join, Upstream
Override) can be set to values which depend on the settings of the
Propagation_Delay and Override_Interval of the corresponding interface.
The default values for these are given below.

Variable Name: Propagation_Delay(I)


+-------------------------------+---------------+-----------------------+
|  Value Name                   |   Value       |   Explanation         |
+-------------------------------+---------------+-----------------------+
|  Propagation_delay_default    |   0.5 secs    |   Expected            |
|                               |               |   propagation delay   |
|                               |               |   over the local      |
|                               |               |   link.               |
+-------------------------------+---------------+-----------------------+

The default value of the Propagation_delay_default is chosen to be
relatively large to provide compatibility with older PIM
implementations.

Variable Name: Override_Interval(I)


+--------------------------+-----------------+--------------------------+
|  Value Name              |    Value        |    Explanation           |
+--------------------------+-----------------+--------------------------+
|  t_override_default      |    2.5 secs     |    Default delay         |
|                          |                 |    interval over         |
|                          |                 |    which to randomize    |
|                          |                 |    when scheduling a     |
|                          |                 |    delayed Join          |
|                          |                 |    message.              |
+--------------------------+-----------------+--------------------------+

Timer Name: Hello Timer (HT(I))


+----------------------+---------+---------------------------------------+
|Value Name            | Value   | Explanation                           |
+----------------------+---------+---------------------------------------+
|Hello_Period          | 30 secs | Periodic interval for Hello messages. |
+----------------------+---------+---------------------------------------+
|Triggered_Hello_Delay | 5 secs  | Randomized interval for initial Hello |
|                      |         | message on bootup or triggered Hello  |
|                      |         | message to a rebooting neighbor.      |
+----------------------+---------+---------------------------------------+




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At system power-up, the timer is initialized to rand(0,
Triggered_Hello_Delay) to prevent synchronization.  When a new or
rebooting neighbor is detected, a responding Hello is sent within
rand(0, Triggered_Hello_Delay).

Timer Name: Neighbor Liveness Timer (NLT(N,I))


+--------------------------+-----------------------+--------------------+
| Value Name               |  Value                |  Explanation       |
+--------------------------+-----------------------+--------------------+
| Default_Hello_Holdtime   |  3.5 * Hello_Period   |  Default holdtime  |
|                          |                       |  to keep neighbor  |
|                          |                       |  state alive       |
+--------------------------+-----------------------+--------------------+
| Hello_Holdtime           |  from message         |  Holdtime from     |
|                          |                       |  Hello Message     |
|                          |                       |  Holdtime option.  |
+--------------------------+-----------------------+--------------------+

The Holdtime in a Hello Message should be set to (3.5 * Hello_Period),
giving a default value of 105 seconds.

Timer Names: Expiry Timer (ET(*,*,RP,I), ET(*,G,I), ET(S,G,I),
ET(S,G,rpt,I))


+----------------+-----------------+------------------------------------+
| Value Name     |  Value          |  Explanation                       |
+----------------+-----------------+------------------------------------+
| J/P_HoldTime   |  from message   |  Holdtime from Join/Prune Message  |
+----------------+-----------------+------------------------------------+

See details of JT(*,G) for the Holdtime that is included in Join/Prune
Messages.
















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Timer Names: Prune-Pending Timer (PPT(*,*,RP,I), PPT(*,G,I), PPT(S,G,I),
PPT(S,G,rpt,I))


+---------------------------+---------------------+---------------------+
|Value Name                 | Value               | Explanation         |
+---------------------------+---------------------+---------------------+
|J/P_Override_Interval(I)   | Default:            | Short period after  |
|                           | Effective_          | a join or prune to  |
|                           | Propagation_        | allow other         |
|                           | Delay(I) +          | routers on the LAN  |
|                           | EffectiveOverride_  | to override the     |
|                           | Interval(I)         | join or prune       |
+---------------------------+---------------------+---------------------+

Note that both the Effective_Propagation_Delay(I) and the
Effective_Override_Interval(I) are interface specific values that may
change when Hello messages are received (see section 4.3.3).

Timer Names: Assert Timer (AT(*,G,I), AT(S,G,I))


+---------------------------+----------------------+--------------------+
| Value Name                |  Value               | Explanation        |
+---------------------------+----------------------+--------------------+
| Assert_Override_Interval  |  Default: 3 secs     | Short interval     |
|                           |                      | before an assert   |
|                           |                      | times out where    |
|                           |                      | the assert winner  |
|                           |                      | resends an Assert  |
|                           |                      | message            |
+---------------------------+----------------------+--------------------+
| Assert_Time               |  Default: 180 secs   | Period after last  |
|                           |                      | assert before      |
|                           |                      | assert state is    |
|                           |                      | timed out          |
+---------------------------+----------------------+--------------------+

Note that for historical reasons, the Assert message lacks a Holdtime
field.  Thus changing the Assert Time from the default value is not
recommended.










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Timer Names: Upstream Join Timer (JT(*,*,RP), JT(*,G), JT(S,G))


+-------------+--------------------+-------------------------------------+
|Value Name   | Value              | Explanation                         |
+-------------+--------------------+-------------------------------------+
|t_periodic   | Default: 60 secs   | Period between Join/Prune Messages  |
+-------------+--------------------+-------------------------------------+
|t_suppressed | rand(1.1 *         | Suppression period when someone     |
|             | t_periodic, 1.4 *  | else sends a J/P message so we      |
|             | t_periodic) when   | don't need to do so.                |
|             | Suppression_       |                                     |
|             | Enabled(I) is      |                                     |
|             | true, 0 otherwise  |                                     |
+-------------+--------------------+-------------------------------------+
|t_override   | rand(0, Effective_ | Randomized delay to prevent         |
|             | Override_          | response implosion when sending a   |
|             | Interval(I))       | join message to override someone    |
|             |                    | else's Prune message.               |
+-------------+--------------------+-------------------------------------+

t_periodic may be set to take into account such things as the configured
bandwidth and expected average number of multicast route entries for the
attached network or link (e.g., the period would be longer for lower-
speed links, or for routers in the center of the network that expect to
have a larger number of entries). If the Join/Prune-Period is modified
during operation, these changes should be made relatively infrequently
and the router should continue to refresh at its previous Join/Prune-
Period for at least Join/Prune-Holdtime, in order to allow the upstream
router to adapt.

The holdtime specified in a Join/Prune message should be set to (3.5 *
t_periodic).

t_override depends on the Effective_Override_Interval of the upstream
interface which may change when Hello messages are received.

t_suppressed depends on the Suppression State of the upstream interface
(Section 4.3.3) and becomes zero when suppression is disabled.












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Timer Name: Upstream Override Timer (OT(S,G,rpt))


+---------------+---------------------------+---------------------------+
| Value Name    | Value                     |  Explanation              |
+---------------+---------------------------+---------------------------+
| t_override    | see Upstream Join Timer   |  see Upstream Join Timer  |
+---------------+---------------------------+---------------------------+

The upstream Override Timer is only ever set to t_override; this value
is defined in the section on Upstream Join Timers.

Timer Name: Keepalive Timer (KAT(S,G))


+-----------------------+------------------------+----------------------+
| Value Name            |  Value                 |  Explanation         |
+-----------------------+------------------------+----------------------+
| Keepalive_Period      |  Default: 210 secs     |  Period after last   |
|                       |                        |  (S,G) data packet   |
|                       |                        |  during which (S,G)  |
|                       |                        |  Join state will be  |
|                       |                        |  maintained even in  |
|                       |                        |  the absence of      |
|                       |                        |  (S,G) Join          |
|                       |                        |  messages.           |
+-----------------------+------------------------+----------------------+
| RP_Keepalive_Period   |  ( 3 * Register_       |  As                  |
|                       |  Suppression_Time )    |  Keepalive_Period,   |
|                       |  + Register_           |  but at the RP when  |
|                       |  Probe_Time            |  a Register-Stop is  |
|                       |                        |  sent.               |
+-----------------------+------------------------+----------------------+
The normal keepalive period for the KAT(S,G) defaults to 210 seconds.
However at the RP, the keepalive period must be at least the
Register_Suppression_Time or the RP may time out the (S,G) state before
the next Null-Register arrives.  Thus the KAT(S,G) is set to
max(Keepalive_Period, RP_Keepalive_Period) when a Register-Stop is sent.













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Timer Name: Register-Stop Timer (RST(S,G))


+----------------------------+--------------------+---------------------+
|Value Name                  | Value              | Explanation         |
+----------------------------+--------------------+---------------------+
|Register_Suppression_Time   | Default: 60 secs   | Period during       |
|                            |                    | which a DR stops    |
|                            |                    | sending Register-   |
|                            |                    | encapsulated data   |
|                            |                    | to the RP after     |
|                            |                    | receiving a         |
|                            |                    | Register-Stop       |
|                            |                    | message.            |
+----------------------------+--------------------+---------------------+
|Register_Probe_Time         | Default: 5 secs    | Time before RST     |
|                            |                    | expires when a DR   |
|                            |                    | may send a Null-    |
|                            |                    | Register to the RP  |
|                            |                    | to cause it to re-  |
|                            |                    | send a Register-    |
|                            |                    | Stop message.       |
+----------------------------+--------------------+---------------------+
If the the Register_Suppression_Time or the Register_Probe_Time are
configured to values other than the defaults it MUST be ensured that the
value of the Register_Probe_Time is less than half the value of the
Register_Suppression_Time to prevent a possible negative value in the
setting of the Register-Stop Timer.

5.  IANA Considerations

5.1.  PIM Address Family

The PIM Address Family field was chosen to be 8 bits as a tradeoff
between packet format and use of the IANA assigned numbers.  Since when
the PIM packet format was designed only 15 values were assigned for
Address Families, and large numbers of new Address Family values were
not envisioned, 8 bits seemed large enough.  However, the IANA assigns
Address Families in a 16-bit field.  Therefore, the PIM Address Family
is allocated as follows:

     Values 0 through 127 are designated to have the same meaning as
     IANA-assigned Address Family Numbers [7].

     Values 128 through 250 are designated to be assigned for PIM by the
     IANA based upon IESG Approval, as defined in [9].





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     Values 251 through 255 are designated for Private Use, as defined
     in [9].

5.2.  PIM Hello Options

Values 17 through 65000 are to be assigned by the IANA.  Since the space
is large, they may be assigned as First Come First Served as defined in
[9]. Such assignments are valid for one year, and may be renewed.
Permanent assignments require a specification (see "Specification
Required" in [9].)

6.  Security Considerations

This section describes various possible security concerns related to the
PIM-SM protocol, including a description of how to use IPsec to secure
the protocol.  The reader is referred to [15] and [16] for a further
discussion of PIM-SM and multicast security.  The IPsec authentication
header [8] MAY be used to provide data integrity protection and
groupwise data origin authentication of PIM protocol messages.
Authentication of PIM messages can protect against unwanted behaviors
caused by unauthorized or altered PIM messages.

6.1.  Attacks based on forged messages

The extent of possible damage depends on the type of counterfeit
messages accepted.  We next consider the impact of possible forgeries,
including forged link-local (Join/Prune, Hello, and Assert) and forged
unicast (Register and Register-Stop) messages.

6.1.1.  Forged link-local messages

Join/Prune, Hello, and Assert messages are all sent to the link-local
ALL_PIM_ROUTERS multicast addresses, and thus are not forwarded by a
compliant router.  A forged message of this type can only reach a LAN if
it was sent by a local host or if it was allowed onto the LAN by a
compromised or non-compliant router.

1.   A forged Join/Prune message can cause multicast traffic to be
     delivered to links where there are no legitimate requesters,
     potentially wasting bandwidth on that link.  A forged leave message
     on a multi-access LAN is generally not a significant attack in PIM,
     because any legitimately joined router on the LAN would override
     the leave with a join before the upstream router stops forwarding
     data to the LAN.

2.    By forging a Hello message, an unauthorized router can cause
     itself to be elected as the designated router on a LAN.  The
     designated router on a LAN is (in the absence of asserts)



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     responsible for forwarding traffic to that LAN on behalf of any
     local members.  The designated router is also responsible for
     register-encapsulating to the RP any packets that are originated by
     hosts on the LAN.  Thus, the ability of local hosts to send and
     receive multicast traffic may be compromised by a forged Hello
     message.

3.   By forging an Assert message on a multi-access LAN, an attacker
     could cause the legitimate designated forwarder to stop forwarding
     traffic to the LAN.  Such a forgery would prevent any hosts
     downstream of that LAN from receiving traffic.

6.1.2.  Forged unicast messages

Register messages and  Register-Stop messages are forwarded by
intermediate routers to their destination using normal IP forwarding.
Without data origin authentication, an attacker who is located anywhere
in the network may be able to forge a Register or Register-Stop message.
We consider the effect of a forgery of each of these messages next.

1.   By forging a Register message, an attacker can cause the RP to
     inject forged traffic onto the shared multicast tree.

2.   By forging a Register-stop message, an attacker can prevent a
     legitimate DR from Registering packets to the RP.  This can prevent
     local hosts on that LAN from sending multicast packets.

The above two PIM messages are not changed by intermediate routers and
need only be examined by the intended receiver.  Thus these messages can
be authenticated end-to-end, using AH.  Attacks on Register and
Register-Stop messages do not apply to a PIM-SSM-only implementation, as
these messages are not required for PIM-SSM.

6.2.  Non-cryptographic Authentication Mechanisms

A PIM router SHOULD provide an option to limit the set of neighbors from
which it will accept Join/Prune, Assert, and Hello messages.  Either
static configuration of IP addresses or an IPsec security association
may be used.  Furthermore, a PIM router SHOULD NOT accept protocol
messages from a router from which it has not yet received a valid Hello
message.

A Designated Router MUST NOT register-encapsulate a packet and send it
to the RP unless the source address of the packet is a legal address for
the subnet on which the packet was received.  Similarly, a Designated
Router SHOULD NOT accept a Register-Stop packet whose IP source address
is not a valid RP address for the local domain.




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An implementation SHOULD provide a mechanism to allow an RP to restrict
the range of source addresses from which it accepts Register-
encapsulated packets.

All options that restrict the range of addresses from which packets are
accepted MUST default to allowing all packets.

6.3.  Authentication using IPsec

The IPsec [8] transport mode using the Authentication Header (AH) is the
recommended method to prevent the above attacks against PIM.  The
specific AH authentication algorithm and parameters, including the
choice of authentication algorithm and the choice of key, are configured
by the network administrator.  When IPsec authentication is used, a PIM
router should reject (drop without processing) any unauthorized PIM
protocol messages.

To use IPsec, the administrator of a PIM network configures each PIM
router with one or more Security Associations and associated SPI(s) that
are used by senders to authenticate PIM protocol messages and are used
by receivers to authenticate received PIM protocol messages.  This
document does not describe protocols for establishing Security
Associations.  It assumes that manual configuration of Security
Associations is performed, but it does not preclude the use of a
negotiation protocol such as The Internet Key Exchange [14] to establish
Security Associations.

IPsec [8] provides protection against replayed unicast and multicast
messages.  The anti-replay option for IPsec SHOULD be enabled on all
security associations.

The following sections describe the Security Associations required to
protect PIM protocol messages.

6.3.1.  Protecting link-local multicast messages

The network administrator defines a Security Association (SA) and
Security Parameters Index (SPI) that is to be used to authenticate all
link-local PIM protocol messages (Hello, Join/Prune, and Assert) on each
link in a PIM domain.

IPsec [8] allows (but does not require) there to be different Security
Policy Databases (SPD) for each router interface.  If available, it may
be desirable to configure the Security Policy Database at a PIM router
such that all incoming and outgoing Join/Prune, Assert, and Hello
packets use a different SA for each incoming or outgoing interface.





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6.3.2.  Protecting unicast messages

IPsec can also be used to provide data origin authentication and data
integrity protection for the Register and Register-Stop unicast
messages.

6.3.2.1.  Register messages

The Security Policy Database at every PIM router is configured to select
a Security Association to use when sending PIM Register packets to each
rendezvous point.

In the most general mode of operation, the Security Policy Database at
each DR is configured to select a unique SA and SPI for traffic sent to
each RP.  This allows each DR to have a different authentication
algorithm and key to talk to the RP.  However, this creates a daunting
key management and distribution problem for the network administrator.
Therefore, it may be preferable in PIM domains where all Designated
Routers are under a single administrative control, to use the same
authentication algorithm parameters (including the key) for all
Registered packets in a domain, regardless of who is the RP and
regardless of who is the DR.

In this "single shared key" mode of operation, the network administrator
must choose an SPI for each DR that will be used to send it PIM protocol
packets.  The Security Policy Database at every DR is configured to
select a Security Association (including the authentication algorithm,
authentication parameters, and this SPI) when sending Register messages
to this RP.

By using a single authentication algorithm and associated parameters,
the key distribution problem is simplified.  Note however, that this
method has the property that, in order to change the authentication
method or authentication key used, all routers in the domain must be
updated.

6.3.2.2.  Register-Stop messages

Similarly, the Security Policy Database at each Rendezvous Point should
be configured to choose a Security Association to use when sending
Register-Stop messages.  Because Register-Stop messages are unicast to
the destination DR, a different Security Association and a potentially
unique SPI is required for each DR.

In order to simplify the management problem, it may be acceptable to use
the same authentication algorithm and authentication parameters,
regardless of the sending RP and regardless of the destination DR.
Although a unique Security Association is needed for each DR, the same



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authentication algorithm and authentication algorithm parameters (secret
key) can be shared by all DRs and by all RPs.


6.4.  Denial of Service Attacks

There are a number of possible denial of service attacks against PIM
that can be caused by generating false PIM protocol messages or even by
generating data false traffic.  Authenticating PIM protocol traffic
prevents some, but not all of these attacks.  Two of the possible
attacks include:

-    Sending packets to many different group addresses quickly can be a
     denial of service attack in and of itself.  This will cause many
     register-encapsulated packets, loading the DR, the RP, and the
     routers between the DR and the RP.

-    Forging Join messages can cause a multicast tree to get set up.  A
     large number of forged joins can consume router resources and
     result in denial of service.

-    The (*,*,RP) forwarding model has some unique security concerns.
     In particular, a (*,*,RP) join presents a possibility for a denial
     of service attack by causing all traffic in the domain to flow to
     the PMBR issuing the join.  (*,*,RP) behavior is included here
     primarily for backwards compatibility with prior revisions of the
     spec.  However, the implementation of (*,*,RP) and PMBR is
     optional.  When using (*,*,RP), the security concerns should be
     carefully considered.

7.  Authors' Addresses

     Bill Fenner
     AT&T Labs - Research
     75 Willow Road
     Menlo Park, CA 94025
     fenner@research.att.com


     Mark Handley
     Department of Computer Science
     University College London
     Gower Street
     London WC1E 6BT
     United Kingdom
     M.Handley@cs.ucl.ac.uk





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     Hugh Holbrook
     Arastra, Inc.
     P.O. Box 10905
     Palo Alto, CA 94303
     holbrook@arastra.com


     Isidor Kouvelas
     Cisco Systems
     170 W. Tasman Drive
     San Jose, CA 95134
     kouvelas@cisco.com



8.  Acknowledgments

PIM-SM was designed over many years by a large group of people,
including ideas, comments, and corrections from Deborah Estrin, Dino
Farinacci, Ahmed Helmy, David Thaler, Steve Deering, Van Jacobson, C.
Liu, Puneet Sharma, Liming Wei, Tom Pusateri, Tony Ballardie, Scott
Brim, Jon Crowcroft, Paul Francis, Joel Halpern, Horst Hodel, Polly
Huang, Stephen Ostrowski, Lixia Zhang, Girish Chandranmenon, Brian
Haberman, Hal Sandick, Mike Mroz, Garry Kump, Pavlin Radoslavov, Mike
Davison, James Huang, Christopher Thomas Brown, and James Lingard.

Thanks are due to the American Licorice Company, for its obscure but
possibly essential role in the creation of this document.

9.  Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.

[2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan,
     "Internet Group Management Protocol, Version 3", RFC 3376, October
     2002.

[3] Deering, S., "Host extensions for IP multicasting", STD 5, RFC 1112,
     August 1989.

[4] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
     Discovery (MLD) for IPv6", RFC 2710, October 1999.

[5] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
     Specification", RFC 2460, December 1998.





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[6] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", draft-
     ietf-ssm-arch, work in progress.

[7] IANA, "Address Family Numbers", linked from
     http://www.iana.org/numbers.html

[8] Kent, S. and K. Seo, "Security Architecture for the Internet
     Protocol", RFC 4301, December 2005.

[9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
     Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

10.  Informative References

[10] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol
     Extensions for BGP-4", draft-ietf-idr-rfc2858bis, work in progress.

[11] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas, "Bootstrap
     Router (BSR) Mechanism for PIM Sparse Mode", draft-ietf-pim-sm-bsr,
     work in progress.

[12] Black, D., "Differentiated Services and Tunnels", RFC 2983, October
     2000.

[13] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bi-
     directional Protocol Independent Multicast", draft-ietf-pim-bidir,
     work in progress.

[14] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC
     2409, November 1998.

[15] P. Savola, R. Lehtonen, D. Meyer, "PIM-SM Multicast Routing
     Security Issues and Enhancements", draft-savola-mboned-
     mroutesec-00.txt, work in progress.

[16] P. Savola, J. Lingard, "Last-hop Threats to Protocol Independent
     Multicast (PIM)" draft-savola-pim-lasthop-threats-01.txt, work in
     progress.

[17] P. Savola, B. Haberman, "Embedding the Rendezvous Point (RP)
     Address in an IPv6 Multicast Address" draft-ietf-mboned-embeddedrp,
     work in progress.

[18] Thaler, D., "Interoperability Rules for Multicast Routing
     Protocols", RFC 2715, October 1999.






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11.  Appendix A: PIM Multicast Border Router Behavior

In some cases PIM-SM domains will interconnect with non-PIM multicast
domains.  In these cases, the border routers of the PIM domain speak
PIM-SM on some interfaces and speak other multicast routing protocols on
other interfaces.  Such routers are termed PIM Multicast Border Routers
or PMBRs.  In general, RFC 2715 [18] provides rules for interoperability
between different multicast routing protocols.  In this section we
specify how PMBRs differ from regular PIM-SM routers.

From the point of view of PIM-SM, a PMBR has two tasks:

o To ensure that traffic from sources outside the PIM-SM domain reaches
  receivers inside the domain.

o To ensure that traffic from sources inside the PIM-SM domain reaches
  receivers outside the domain.

We note that multiple PIM-SM domains are sometimes connected together
using protocols such as MSDP, which provides information about active
external sources, but does not follow RFC 2715.  In such cases the
domains are not connected via PMBRs because Join(S,G) messages traverse
the border between domains.  A PMBR is required when no PIM messages can
traverse the border.

11.1.  Sources External to the PIM-SM Domain

A PMBR needs to ensure that traffic from multicast sources external to
the PIM-SM domain reaches receivers inside the domain.  The PMBR will
follow the rules in RFC 2715, such that traffic from external sources
reaches the PMBR itself.

According to RFC 2715, the PIM-SM component of the PMBR will receive an
(S,G) Creation event when data from an (S,G) data packet from an
external source first reaches the PMBR.  If RPF_interface(S) is an
interface in the PIM-SM domain, the packet cannot be originated into the
PIM domain at this router, and the PIM-SM component of the PMBR will not
process the packet.  Otherwise the PMBR will then act exactly as if it
were the DR for this source (see Section 4.4.1), with the following
modifications:

o The Border-bit is set in all PIM Register message sent for these
  sources.

o DirectlyConnected(S) is treated as being TRUE for these sources.

o The PIM-SM forwarding rule "iif == RPF_interface(S)" is relaxed to be
  TRUE if iif is any interface that is not part of the PIM-SM component



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  of the PMBR (see Section 4.2).

11.2.  Sources Internal to the PIM-SM Domain

A PMBR needs to ensure that traffic from sources inside the PIM-SM
domain reaches receivers outside the domain.  Using terminology from RFC
2715, there are two possible scenarios for this:

o Another component of the PMBR is a wildcard receiver.  In this case
  the PIM-SM component of the PMBR must ensure that traffic from all
  internal sources reaches the PMBR until it is informed otherwise.

  Note that certain profiles of PIM-SM, e.g., PIM-SSM, PIM-SM with
  Embedded RP, cannot interoperate with a neighboring wildcard receiver
  domain.

o No other component of the PMBR is a wildcard receiver.  In this case
  the PMBR will receive explicit information as to which groups or
  (source,group) pairs the external domains wish to receive.

In the former case, the PMBR will need to send a Join(*,*,RP) to all the
active RPs in the PIM-SM domain.  It may also send a Join(*,*,RP) to all
the candidate RPs in the PIM-SM domain.  This will cause all traffic in
the domain to reach the PMBR.  The PMBR may then act as if it were a DR
with directly connected receivers, and trigger the transition to a
shortest path tree (see Section 4.2.1).

In the latter case, the PMBR will not need to send Join(*,*,RP)
messages.  However the PMBR will still need to act as a DR with directly
connected receivers on behalf of the external receivers in terms of
being able to switch to the shortest-path tree for internally-reached
sources.

According to RFC 2715, the PIM-SM component of the PMBR may receive a
number of alerts generated by events in the external routing components.
To implement the above behavior, one reasonable way to map these alerts
into PIM-SM state as follows:

o When a PIM-SM component receives an (S,G) Prune alert, it sets
  local_receiver_include(S,G,I) to FALSE for the discard interface.

o When a PIM-SM component receives a (*,G) Prune alert, it sets
  local_receiver_include(*,G,I) to FALSE for the discard interface.

o When a PIM-SM component receives an (S,G) Join alert, it sets
  local_receiver_include(S,G,I) to TRUE for the discard interface.





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o When a PIM-SM component receives a (*,G) Join alert, it sets
  local_receiver_include(*,G,I) to TRUE for the discard interface.

o When a PIM-SM component receives a (*,*) Join alert, it sets
  DownstreamJPState(*,*,RP,I) to Join state on the discard interface for
  all RPs in the PIM-SM domain.

o When a PIM-SM component receives a (*,*) Prune alert, then it sets
  DownstreamJPState(*,*,RP,I) to NoInfo state on the discard interface
  for all RPs in the PIM-SM domain.

We refer above to the discard interface because the macros and state
machines are interface-specific, but we need to have PIM state that is
not associated with any actual PIM-SM interface. Implementors are free
to implement this in any reasonable manner.

Note that these state changes will then cause additional PIM-SM state
machine transitions in the normal way.

These rules are however not sufficient to allow pruning off the (*,*,RP)
tree.  Some additional rules provide guidance as to one way this may be
done:

o If the PMBR has joined on the (*,*,RP) tree, then it should set
  DownstreamJPState(*,G,I) to JOIN on the discard interface for all
  active groups.

o If the router receives a (S,G) prune alert it will need to set
  DownstreamJPState(S,G,rpt,I) to PRUNE on the discard interface.

o If the router receives a (*,G) prune alert, it will need to set
  DownstreamJPState(S,G,rpt,I) to PRUNE on the discard interface for all
  active sources sending to G.

The rationale for this is that there is no way in PIM-SM to prune
traffic off the (*,*,RP) tree, except by Joining the (*,G) tree and then
pruning each source individually.














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12.  Index
Address_List . . . . . . . . . . . . . . . . . . . . . . . . . . . .  31
Assert(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . .27,127
Assert(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . . .27,127
AssertCancel(*,G). . . . . . . . . . . . . . . . . . . . . . . . . 97,99
AssertCancel(S,G). . . . . . . . . . . . . . . . . . . . . . . .79,90,99
AssertTimer(*,G,I) . . . . . . . . . . . . . . . . . . . . .17,25,91,131
AssertTimer(S,G,I) . . . . . . . . . . . . . . . . . . . . .18,25,83,131
AssertTrackingDesired(*,G,I) . . . . . . . . . . . . . . . . . .93,94,96
AssertTrackingDesired(S,G,I) . . . . . . . . . . . . . . . . 85,85,87,89
AssertWinner(*,G,I). . . . . . . . . . . . . . . . . .17,23,25,93,97,100
AssertWinner(S,G,I). . . . . . . . . . . . . . . . 18,23,25,85,89,99,100
AssertWinnerMetric(*,G,I). . . . . . . . . . . . . . . . . . . 17,97,100
AssertWinnerMetric(S,G,I). . . . . . . . . . . . . . . . . . . 18,89,100
assert_metric. . . . . . . . . . . . . . . . . . . . . . . . . . . .  97
Assert_Override_Interval . . . . . . . . . . . . . . . . . . . 89,96,131
Assert_Time. . . . . . . . . . . . . . . . . . . . . . . . . . 89,96,131
AT(*,G,I). . . . . . . . . . . . . . . . . . . . . . . .17,25,91,128,131
AT(S,G,I). . . . . . . . . . . . . . . . . . . . . . . .18,25,83,128,131
CheckSwitchToSpt(S,G). . . . . . . . . . . . . . . . . . . . . . . 27,28
CouldAssert(*,G,I) . . . . . . . . . . . . . . . . . . . .91,93,94,95,98
CouldAssert(S,G,I) . . . . . . . . . . . . . . . . . . 83,85,87,88,89,98
CouldRegister(S,G) . . . . . . . . . . . . . . . . . . . . . . . . 38,40
Default_Hello_Holdtime . . . . . . . . . . . . . . . . . . . . . . .  33
DirectlyConnected(S) . . . . . . . . . . . . . . . . . . 27,27,29,40,142
DownstreamJPState(*,*,RP,I). . . . . . . . . . . . . . . . . . . .23,144
DownstreamJPState(*,G,I) . . . . . . . . . . . . . . . . . . . . . .  23
DownstreamJPState(S,G,I) . . . . . . . . . . . . . . . . . . . . . 24,40
DownstreamJPState(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . .  24
DR(I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  33
dr_is_better(a,b,I). . . . . . . . . . . . . . . . . . . . . . . . 33,33
DR_Priority. . . . . . . . . . . . . . . . . . . . . . . . . . .31,32,33
Effective_Override_Interval(I) . . . . . . . . . . . . . . . .36,113,131
Effective_Propagation_Delay(I) . . . . . . . . . . . . . . . . . .35,131
ET(*,*,RP,I) . . . . . . . . . . . . . . . . . . . . . . . 15,46,127,130
ET(*,G,I). . . . . . . . . . . . . . . . . . . . . . . . . 17,49,128,130
ET(S,G,I). . . . . . . . . . . . . . . . . . . . . . . . . 18,53,128,130
ET(S,G,rpt,I). . . . . . . . . . . . . . . . . . . . . .21,56,58,128,130
GenID. . . . . . . . . . . . . . . . . . . 16,18,20,31,63,67,70,72,83,91
Hash_Function. . . . . . . . . . . . . . . . . . . . . . . . . . .13,105
Hello_Holdtime . . . . . . . . . . . . . . . . . . . . . . . . . .33,130
Hello_Period . . . . . . . . . . . . . . . . . . . . . . . . . . .31,129
HT(I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31,129
IGMP . . . . . . . . . . . . . . . . . . . . . . . . . 7,9,17,23,101,104
immediate_olist(*,*,RP). . . . . . . . . . . . . . . . . . . . . . 22,63
immediate_olist(*,G) . . . . . . . . . . . . . . . . . . . . . . . 22,68
immediate_olist(S,G) . . . . . . . . . . . . . . . . . . . . . .22,40,72
infinite_assert_metric() . . . . . . . . . . . . . . . . . . . . . .  98



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inherited_olist(S,G) . . . . . . . . . . . . . . . 22,27,40,43,72,85,107
inherited_olist(S,G,rpt) . . . . . . . . . . . . . . . 22,27,29,76,78,80
I_Am_Assert_Loser(*,G,I) . . . . . . . . . . . . . . . . . . . . . .  25
I_Am_Assert_Loser(S,G,I) . . . . . . . . . . . . . . . . . . . . . .  25
I_am_DR(I) . . . . . . . . . . . . . . . . . . . . . . . .23,33,40,85,93
I_am_RP(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43,44
J/P_Holdtime . . . . . . . . . . . . . .47,50,54,58,64,69,74,120,130,132
J/P_Override_Interval(I) . . . . . . . . . . . . . . 47,51,54,58,120,131
JoinDesired(*,*,RP). . . . . . . . . . . . . . . . . . . . . . . . 63,77
JoinDesired(*,G) . . . . . . . . . . . . . . . . . . . . .17,68,77,85,97
JoinDesired(S,G) . . . . . . . . . . . . . . . . . . . 19,29,72,85,88,90
joins(*,*,RP(G)) . . . . . . . . . . . . . . . . . . . . . . . . . .  22
joins(*,*,RP). . . . . . . . . . . . . . . . . . . . . . . . 22,23,85,93
joins(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . 22,23,85,93
joins(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . . .22,24,85
JT(*,*,RP) . . . . . . . . . . . . . . . . . . . . . . . . 16,61,128,132
JT(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . 17,66,128,132
JT(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . 19,71,128,132
KAT(S,G) . . . . . . . . . . . . . . . .19,26,27,28,40,43,72,107,128,133
KeepaliveTimer(S,G). . . . . . . . . 19,26,27,27,28,40,43,72,107,128,133
Keepalive_Period . . . . . . . . . . . . . . . . . . . . . . . . .27,133
lan_delay_enabled(I) . . . . . . . . . . . . . . . . . . . . . . . 35,36
LAN_Prune_Delay. . . . . . . . . . . . . . . . . . . . . . . . . . .  31
local_receiver_exclude(S,G,I). . . . . . . . . . . . . . . . . . . .  23
local_receiver_include(*,G,I). . . . . . . . . . . . . . . . . 23,93,143
local_receiver_include(S,G,I). . . . . . . . . . . . . . . . . . . 23,85
local_receiver_include(S,G,I). . . . . . . . . . . . . . . . . . . . 143
lost_assert(*,G) . . . . . . . . . . . . . . . . . . . . . . . .22,24,85
lost_assert(*,G,I) . . . . . . . . . . . . . . . . . . . . . . 23,24,100
lost_assert(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . 22,24
lost_assert(S,G,I) . . . . . . . . . . . . . . . . . . . . . . .23,24,99
lost_assert(S,G,rpt) . . . . . . . . . . . . . . . . . . . . . . . .  24
lost_assert(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . . . . 24,99
MBGP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,8
MFIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,14
MLD. . . . . . . . . . . . . . . . . . . . . . . . . . 7,9,17,23,101,104
MRIB . . . . . . . . . . . . . . .7,8,12,16,20,25,61,65,65,75,98,102,127
MRIB.next_hop(host). . . . . . . . . . . . . . . . . . . . . 25,25,61,63
my_assert_metric(*,G,I). . . . . . . . . . . . . . . . . . . . . . .  93
my_assert_metric(S,G,I). . . . . . . . . . . . . . . . . . . 85,89,91,98
NBR(Interface,IP_address). . . . . . . . . . . . . . . . .26,37,61,63,65
NLT(N,I) . . . . . . . . . . . . . . . . . . . . . . . . . 15,33,127,130
OT(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . 21,76,128,133
Override_Interval(I) . . . . . . . . . . . . . . 15,31,34,36,113,129,131
packet_arrives_on_rp_tunnel(pkt) . . . . . . . . . . . . . . . . . .  43
pim_exclude(S,G) . . . . . . . . . . . . . . . . . . . . . . 22,23,28,85
pim_include(*,G) . . . . . . . . . . . . . . . . . . . 17,22,23,28,85,93
pim_include(S,G) . . . . . . . . . . . . . . . . . . . . .19,22,23,28,85



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PPT(*,*,RP,I). . . . . . . . . . . . . . . . . . . . . . . 15,46,127,131
PPT(*,G,I) . . . . . . . . . . . . . . . . . . . . . . . . 16,49,128,131
PPT(S,G,I) . . . . . . . . . . . . . . . . . . . . . . . . 18,53,128,131
PPT(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . . .21,56,58,128,131
Propagation_Delay(I) . . . . . . . . . . . . . . . . . . . 31,35,129,131
Propagation_delay_default. . . . . . . . . . . . . . . . . . . . .35,129
PruneDesired(S,G,rpt). . . . . . . . . . . . . . . . . . . . 78,79,88,90
prunes(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . .22,24,85
Register-Stop(*,G) . . . . . . . . . . . . . . . . . . . . . . . . .  41
Register-Stop(S,G) . . . . . . . . . . . . . . . . . . . . . . . . .  43
Register-StopTimer(S,G). . . . . . . . . . . . . . . . . . 38,39,128,133
Register_Probe_Time. . . . . . . . . . . . . . . . . . . . . . 39,44,133
Register_Suppression_Time. . . . . . . . . . . . . . . . . . . 39,44,133
RP(G). . . . . . . . . . . . . . 6,22,25,40,43,49,68,76,85,93,98,101,127
RPF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
RPF'(*,G). . . . . . . . . . . . . . . . . . 25,29,66,67,70,76,77,97,100
RPF'(S,G). . . . . . . . . . . . . . . . . . . . . 25,29,71,76,77,90,100
RPF'(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . .25,76,78,101
RPF_interface. . . . . . . . . . . . . . . . . . . . . . . . . . . .  93
RPF_interface(host). . . . . . . . 25,27,29,40,68,69,74,85,93,99,107,142
RPTJoinDesired(G). . . . . . . . . . . . . . . . . . . . . . . .77,80,93
rpt_assert_metric(G,I) . . . . . . . . . . . . . . . . . . . . . . 96,98
RST(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . 38,39,128,133
SPTbit(S,G). . . . . . . . . .20,27,29,43,52,73,76,78,85,85,89,90,99,107
spt_assert_metric(S,I) . . . . . . . . . . . . . . . . . . . . .89,98,99
SSM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,105
Suppression_Enabled(I) . . . . . . . . . . . . . . . . . . . . . .36,132
SwitchToSptDesired(S,G). . . . . . . . . . . . . . . . . . . . .28,28,43
TIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,14,26
Triggered_Hello_Delay. . . . . . . . . . . . . . . . . . . . . 31,32,129
t_joinsuppress . . . . . . . . . . . . . . . . . . . . . .63,64,67,69,74
t_override . . . . . . . . . . . . . . . . . . . . . 63,67,72,77,132,133
t_override_default . . . . . . . . . . . . . . . . . . . . . . . .36,129
t_periodic . . . . . . . . . . . . . . . . . . . . . . . . .63,67,72,132
t_suppressed . . . . . . . . . . . . . . . . . . . . .37,64,69,72,74,132
Update_SPTbit(S,G,iif) . . . . . . . . . . . . . . . . . . . . . . 27,29
UpstreamJPState(S,G) . . . . . . . . . . . . . . . . . . . . . . .27,107














Fenner/Handley/Holbrook/Kouvelas                 Section 12.  [Page 147]

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