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Internet Engineering Task Force                                   PIM WG
INTERNET-DRAFT                                          Bill Fenner/AT&T
draft-ietf-pim-sm-v2-new-01.txt                       Mark Handley/ACIRI
                                                     Hugh Holbrook/Cisco
                                                   Isidor Kouvelas/Cisco
                                                        24 November 2000
                                                       Expires: May 2001


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



Status of this Document

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference material
or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

This document is a product of the IETF PIM WG.  Comments should be
addressed to the authors, or the WG's mailing list at
pim@catarina.usc.edu.

                                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



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     builds unidirectional shared trees rooted at a Rendezvous
     Point (RP) per group, and optionally creates shortest-path
     trees per source.

Note on PIM-SM status

PIM-SM v2 is currently widely implemented and deployed, but the existing
specification in RFC 2362 is insufficient to implement from, and is
incorrect in a number of aspects.  This document is a complete re-write
from RFC 2362, and is intended to obsolete RFC 2362.  The authors have
attempted to document current practice as far as possible, but a number
of cases have arisen where current practice is clearly incorrect,
typically leading to traffic being black-holed.  In these cases we
diverge from current practice, but always in a way that will
interoperate successfully with the legacy PIM v2 implementations that we
are aware of.



































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                           Table of Contents


1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . .   5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
 2.1. Definitions. . . . . . . . . . . . . . . . . . . . . . . . . .   5
 2.2. Pseudocode Notation. . . . . . . . . . . . . . . . . . . . . .   6
3. PIM-SM Protocol Overview. . . . . . . . . . . . . . . . . . . . .   7
4. Protocol Specification. . . . . . . . . . . . . . . . . . . . . .  12
 4.1. PIM Protocol State . . . . . . . . . . . . . . . . . . . . . .  12
  4.1.1. General Purpose State . . . . . . . . . . . . . . . . . . .  13
  4.1.2. (*,*,RP) State. . . . . . . . . . . . . . . . . . . . . . .  14
  4.1.3. (*,G) State . . . . . . . . . . . . . . . . . . . . . . . .  15
  4.1.4. (S,G) State . . . . . . . . . . . . . . . . . . . . . . . .  16
  4.1.5. (S,G,rpt) State . . . . . . . . . . . . . . . . . . . . . .  18
  4.1.6. State Summarization Macros. . . . . . . . . . . . . . . . .  19
 4.2. Data Packet Forwarding Rules . . . . . . . . . . . . . . . . .  23
  4.2.1. Setting and Clearing the (S,G) SPT bit. . . . . . . . . . .  25
 4.3. PIM Register Messages. . . . . . . . . . . . . . . . . . . . .  27
  4.3.1. Sending Register Messages from the DR . . . . . . . . . . .  27
  4.3.2. Receiving Register Messages at the RP . . . . . . . . . . .  29
 4.4. PIM Join/Prune Messages. . . . . . . . . . . . . . . . . . . .  31
  4.4.1. Receiving (*,*,RP) Join/Prune Messages. . . . . . . . . . .  31
  4.4.2. Receiving (*,G) Join/Prune Messages . . . . . . . . . . . .  34
  4.4.3. Receiving (S,G) Join/Prune Messages . . . . . . . . . . . .  38
  4.4.4. Receiving (S,G,rpt) Join/Prune Messages . . . . . . . . . .  42
  4.4.5. Sending (*,*,RP) Join/Prune Messages. . . . . . . . . . . .  47
  4.4.6. Sending (*,G) Join/Prune Messages . . . . . . . . . . . . .  52
  4.4.7. Sending (S,G) Join/Prune Messages . . . . . . . . . . . . .  56
  4.4.8. (S,G,rpt) Periodic Messages . . . . . . . . . . . . . . . .  61
  4.4.9. State Machine for (S,G,rpt) Triggered
  Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  62
 4.5. PIM Assert Messages. . . . . . . . . . . . . . . . . . . . . .  66
  4.5.1. (S,G) Assert Message State Machine. . . . . . . . . . . . .  66
  4.5.2. (*,G) Assert Message State Machine. . . . . . . . . . . . .  73
  4.5.3. Assert Metrics. . . . . . . . . . . . . . . . . . . . . . .  79
  4.5.4. AssertCancel Messages . . . . . . . . . . . . . . . . . . .  81
  4.5.5. Assert State Macros . . . . . . . . . . . . . . . . . . . .  81
 4.6. Designated Routers (DR) and Hello Messages . . . . . . . . . .  83
  4.6.1. Sending Hello Messages. . . . . . . . . . . . . . . . . . .  83
  4.6.2. DR Election . . . . . . . . . . . . . . . . . . . . . . . .  84
 4.7. PIM Bootstrap and RP Discovery . . . . . . . . . . . . . . . .  86
  4.7.1. Overview of RP Discovery. . . . . . . . . . . . . . . . . .  86
  4.7.2. Bootstrap Router Election and RP-Set
  Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . .  87
  4.7.3. Sending Candidate-RP-Advertisements . . . . . . . . . . . .  92
  4.7.4. Receiving Candidate-RP-Advertisements at
  the BSR and Creating the RP-Set. . . . . . . . . . . . . . . . . .  93



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  4.7.5. Receiving and Using the RP-Set. . . . . . . . . . . . . . .  94
 4.8. Source-Specific Multicast. . . . . . . . . . . . . . . . . . .  95
  4.8.1. Protocol Modifications for SSM destination
  addresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . .  95
  4.8.2. PIM-SSM-only Routers. . . . . . . . . . . . . . . . . . . .  96
 4.9. PIM Packet Formats . . . . . . . . . . . . . . . . . . . . . .  97
  4.9.1. Encoded Source and Group Address Formats. . . . . . . . . .  98
  4.9.2. Hello Message Format. . . . . . . . . . . . . . . . . . . . 101
  4.9.3. Register Message Format . . . . . . . . . . . . . . . . . . 104
  4.9.4. Register-Stop Message Format. . . . . . . . . . . . . . . . 105
  4.9.5. Join/Prune Message Format . . . . . . . . . . . . . . . . . 105
  4.9.6. Bootstrap Message Format. . . . . . . . . . . . . . . . . . 109
  4.9.7. Assert Message Format . . . . . . . . . . . . . . . . . . . 112
  4.9.8. Candidate-RP-Advertisement Format . . . . . . . . . . . . . 113
 4.10. PIM Timers. . . . . . . . . . . . . . . . . . . . . . . . . . 114
 4.11. Timer Values. . . . . . . . . . . . . . . . . . . . . . . . . 116
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 122
 5.1. PIM Address Family . . . . . . . . . . . . . . . . . . . . . . 122
 5.2. PIM Hello Options. . . . . . . . . . . . . . . . . . . . . . . 123
6. Security Considerations . . . . . . . . . . . . . . . . . . . . . 123
7. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 123
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 124
9. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
10. Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125



























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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.  This document is intended to obsolete RFC 2362, and to
correct a number of deficiencies that have been identified with the way
PIM-SM was previously specified.  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 and indicate
requirement levels for compliant PIM-SM implementations.

2.1.  Definitions

This specification uses a number of terms to refer to the roles of
routers participating in PIM-SM.  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.  If the LAN has directly connected hosts, then a
      single one of these routers, the DR, will act on behalf of those
      hosts with respect to the PIM-SM protocol.  A single DR is elected
      per LAN using a simple election process.





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MRIB  Multicast Routing Information Base.  This is the multicast         |
      topology table, which is typically derived from the unicast        |
      routing table, or routing protocols such as MBGP that carry        |
      multicast-specific topology information.  In PIM-SM this is used   |
      to make decisions regarding where to forward Join/Prune 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 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.

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.

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

NULL
    is the empty set or list.



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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 [1]. In any
event, the routes in the MRIB must represent a multicast-capable path to
each subnet.  The MRIB is used to determine the path that PIM control
messages such as Join messages take to get to the source subnet, and
data flows along the reverse path of the Join messages.  Thus, in
contrast to the unicast RIB where the routes give a path that data
packets take to get to each subnet, the MRIB gives reverse-path
information, and indicates the path that data packets would take from
each subnet to the router that has the MRIB.

Like all multicast routing protocols that implement the service model
from RFC 1112 [2], 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 be occur simultaneously.

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 [3], 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-



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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
  receivers that are close to the sender.  For some applications, this
  increased latency 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   |



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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, a receiver's 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 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



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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.


Multi-access Transit LANs

The overview so far has concerned itself with point-to-point 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.




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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 through a
bootstrap mechanism.

One router in each PIM domain is elected the Bootstrap Router (BSR)
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.





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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 the PIM Register generation and processing
  rules.

o Section 4.4 specifies the PIM Join/Prune generation and processing
  rules.

o Section 4.5 specifies the PIM Assert generation and processing rules.

o Designated Router (DR) election is specified in Section 4.6.

o Section 4.7 specifies the Bootstrap and 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.

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.



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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.

4.1.1.  General Purpose State

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

     Bootstrap State:

          o Bootstrap Router's IP Address

          o BSR Priority

          o Bootstrap Timer (BST)

     RP Set

     For each interface:

          Neighbor State:

               For each neighbor:

                    o Information from neighbor's Hello





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                    o Neighbor's Gen ID.

                    o Neighbor liveness timer (NLT)

          Designated Router (DR) State:

               o Designated Router's IP Address

               o DR's DR Priority

Bootstrap state is described in section 4.7, the RP Set is described in
section 4.7.5, and Designated Router state is described in section 4.6.

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),          |
                      "PrunePending" (PP)}                               |

                    o Prune Pending Timer (PPT)                          |

                    o Join/Prune Expiry Timer (ET)                       |

          Not interface specific:                                        |

               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       |
4.4.1.                                                                   |

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       |



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upstream neighbor towards the RP has rebooted, then it should re-        |
instantiate state by sending a Join(*,*,RP).  These mechanisms are       |
specified in Section 4.4.5.                                              |

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),
                      "PrunePending" (PP)}

                    o Prune Pending Timer (PPT)

                    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

                    o Assert winner's Assert Metric

          Not interface specific:

               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) 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.  This
information is used by the pim_include(*,G) macro described in section



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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
4.4.2. 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 4.4.6) 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 4.5.2.

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
4.7.5) 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
4.4.6.

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),
                      "PrunePending" (PP)}

                    o Prune Pending Timer (PPT)





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                    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

                    o Assert winner's Assert Metric

          Not interface specific:

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

               o Last RPF Neighbor towards S that was used

               o SPT bit (indicates (S,G) state is active)

               o (S,G) KeepAlive Timer (KAT)

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.  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
4.4.2. 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 4.4.7) 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 4.5.1.

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



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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 4.4.7.

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.

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"}

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

                    o State: One of {"NoInfo", "Pruned", "PrunePending"}

                    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 {"NotJoined(*,G)",
                      "NotPruned(S,G,rpt)", "Pruned(S,G,rpt)"}





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                    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.  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
4.4.4. 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
4.4.8.

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 4.4.9.

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.

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(*,G).                                                    |





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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) (+) immediate_olist(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 )                  |
       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(S,G,I) == FALSE )                  |
        OR AssertWinner(S,G,I) == me )                                   |
       AND  local_receiver_exclude(S,G,I) }                              |

The clause "local_receiver_include(S,G,I)" is true if the IGMP module or |
other local membership mechanism has determined that there are local     |
members on interface I that desire to receive traffic sent specifically  |



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by S to G.  "local_receiver_include(*,G,I)" is true if the IGMP module   |
or other local membership mechanism has determined that there are local  |
members on interface I that desire to receive all traffic sent to G.     |
"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 Joined or                    |
          PrunePending }                                                 |

DownstreamJPState(*,*,RP,I) is the state of the finite state machine in  |
section 4.4.1.                                                           |

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 Joined or PrunePending }

DownstreamJPState(*,G,I) is the state of the finite state machine in
section 4.4.2.

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 Joined or PrunePending }

DownstreamJPState(S,G,I) is the state of the finite state machine in
section 4.4.3.

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,I) is Pruned or PruneTmp }

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 4.5.5.



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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 4.5.5.

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 4.5.5.

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
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 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)
      }
  }








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  neighbor RPF'(S,G) {
      if ( I_Am_Assert_loser(S, G, RPF_interface(S) )) {
           return AssertWinner(S, G, RPF_interface(S) )
      } else {
           return 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 4.4.8).                  |

The function MRIB.next_hop( S ) returns 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.                                     |

I_Am_Assert_loser(S, G, I) is true if the Assert start machine (in       |
section 4.5.1) for (S,G) on Interface I is in "I am Assert Loser" state. |

I_Am_Assert_loser(*, G, I) is true if the Assert start machine (in       |
section 4.5.2) 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.



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Second, we check to see if the SPT bit 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 refresh 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.                    |

Finally we remove the incoming interface from the outgoing interface
list we've created, and if the resulting outgoing interface list is not
empty, we forward the packet out of those interfaces.


On receipt on a data from S to G on interface iif:                       |

 if( DirectlyConnected(S) == TRUE ) {                                    |
      set KeepaliveTimer(S,G) to Keepalive_Period                        |
      # Note: register state transition may happen as a result           |
      # of restarting KeepaliveTimer, and must be dealt with here.       |
 }                                                                       |

 Update_SPTbit(S,G,iif)                                                  |

 if( iif == RPF_interface(S) AND UpstreamJPState(S,G) == Joined ) {      |
    oiflist = inherited_olist(S,G)                                       |
    if( oiflist != NULL ) {                                              |
        restart KeepaliveTimer(S,G)                                      |
    }                                                                    |
 } else if( iif == RPF_interface(RP) AND SPTbit(S,G) == FALSE) {         |
   oiflist = inherited_olist(S,G,rpt)                                    |
 } else {                                                                |
    # Note: RPF check failed                                             |
    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                             |




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This pseudocode employs several "macro" definitions:

directly_connected(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.

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 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 4.2.1.

UpstreamJPState(S,G) is the state of the finite state machine in section
4.4.7.

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.  Setting and Clearing the (S,G) SPT bit

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:











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     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)
                   OR inherited_olist(S,G,rpt) == NULL
                   OR RPF'(S,G) == RPF'(*,G) ) ) {
          Set SPTbit(S,G) to TRUE
       }
     }

Additionally a router sets SPTbit(S,G) to TRUE when it sees an           |
Assert(S,G) on RPF_interface(S).                                         |

JoinDesired(S,G) is defined in Section 4.4.7, 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 SPT bit 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.

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 SPT bit is cleared in the (S,G) upstream state machine (see Section  |
4.4.7) when JoinDesired(S,G) becomes FALSE.                              |







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4.3.  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 to the source.


4.3.1.  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 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.

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

In addition, a RegisterStop timer (RST) is kept if the state machine in
not in the No Info state.




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                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


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

In tabular form, the state-machine is:

+---------+-----------------------------------------------------------------+
|         |                             Event                               |
|         +------------+--------------+-------------+-----------+-----------+
Prev StateRegister-    CouldRegister  CouldRegister Register-   RP changed  |
|         Stop Timer   ->True         ->False       Stop        |           |
|         expires      |              |             received    |           |
+---------+------------+--------------+-------------+-----------+-----------+
No Info   +            +> J state     +             +           +           |
(NI)      |            add tunnel     |             |           |           |
+---------+------------+--------------+-------------+-----------+-----------+
|         +            +              +> NI state   +> P state  +> J state  |
|         |            |              remove tunnel remove      redirect    |
|         |            |              |             tunnel;     tunnel to   |
Join (J)  |            |              |             set         new RP;     |
|         |            |              |             Register-   stop        |
|         |            |              |             Stop        Register-   |
|         |            |              |             timer(*)    Stop timer  |
+---------+------------+--------------+-------------+-----------+-----------+
|         +> J state   +              +> NI state   +> P state  +> J state  |
|         add tunnel   |              remove tunnel set         redirect    |
Join      |            |              |             Register-   tunnel to   |
Pending   |            |              |             Stop        new RP;     |
(JP)      |            |              |             timer(*)    stop        |
|         |            |              |             |           Register-   |
|         |            |              |             |           Stop timer  |
+---------+------------+--------------+-------------+-----------+-----------+
|         +> JP state  +              +> NI state   +           +> J state  |
|         set          |              remove tunnel |           redirect    |
|         Register-    |              |             |           tunnel to   |
Prune (P) Stop         |              |             |           new RP;     |
|         timer(**);   |              |             |           stop        |
|         send null    |              |             |           Register-   |
|         register     |              |             |           Stop timer  |
+---------+------------+--------------+-------------+-----------+-----------+

Notes:

(*) The RegisterStopTimer is set to a random value chosen uniformly from
     the interval ( 0.5 * Register_Suppression_Time, 1.5 *



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     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 timeout, but was in the
old spec and is kept for compatibility.

(**) The RegisterStopTimer is set to register_probe_time.

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 )                             |
  }                                                                      |


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.


Handling RegisterStop(*,G) Messages at the DR

An RP MAY send a RegisterStop message with the source address set to
all-zeros.  This was the normal course of action in RFC 2326 when the
register message matched against (*,G) state at the RP, and was defined
as meaning "stop encapsulating all sources for this group".  However,
the behavior of such a RegisterStop(*,G) is ambiguous or incorrect in
some circumstances.

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

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










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4.3.2.  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 that this should not happen if the lower layer is working |
    }                                                                    |
    if( I_am_RP( G ) && outer.dst == RP(G) ) {                           |
        restart KeepaliveTimer(S,G)                                      |
        if(( inherited_olist(S,G) == NULL ) OR SPTbit(S,G)) {            |
            send RegisterStop(S,G) to outer.src                          |
        } else {                                                         |
            if( ! pkt.NullRegisterBit ) {                                |
                decapsulate and pass the inner packet to the normal      |
                forwarding path for forwarding on the (*,G) tree.        |
            }                                                            |
        }                                                                |
    } else {                                                             |
        send RegisterStop(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.

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.

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



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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 ).                       |

4.4.  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
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
PIM Destination field addresses this router, (*,*,RP) Joins and Prunes   |
can affect the (*,*,RP) and (S,G,rpt) downstream state machines, (*,G)   |
Joins and Prunes can affect both the (*,G) and (S,G,rpt) downstream
state machines, while (S,G) and (S,G,rpt) Joins and Prunes can only
affect their respective downstream state machines.  When considering a
Join/Prune message whose PIM Destination field addresses another router,
most Join or Prune messages could affect each upstream state machine.
(... it's possible to enumerate this ...) XXX

4.4.1.  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 us 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 4.4.4) or the router lost an assert on this       |
          interface.                                                     |

     PrunePending (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          |
          forwarding purposes, the PrunePending state functions exactly  |
          like the Join state.                                           |




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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 group.                                      |

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

                    +-----------------------------------+                |
                    | Figures omitted from text version |                |
                    +-----------------------------------+                |


          Figure 2: Downstream (*,*,RP) per-interface state-machine      |


In tabular form, the per-interface (*,*,RP) state-machine is:            |

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

The transition events "Receive Join(*,*,RP)" and "Receive Prune(*,*,RP)" |
imply receiving a Join or Prune targeted to this router's address on the |
received interface.  If the destination address is not correct, these    |
state transitions in this state machine must not occur, although seeing  |



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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 packet   |
it sent over that interface.  However on point-to-point links we also    |
recommend that PIM messages with a 0.0.0.0 destination address 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 IP          |
          destination set to the router's 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      |
          message.                                                       |

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 IP          |
          destination set to the router's address on I.                  |

          The (*,*,RP) downstream state machine on interface I remains   |
          in Join state, and the Expiry Timer (ET) is restarted, set to  |
          the HoldTime from the triggering Join message.                 |

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

          The (*,*,RP) downstream state machine on interface I           |
          transitions to the PrunePending state.  The PrunePending timer |
          is started; it is set to the J/P_Override_Interval 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  |
          interface I expires.                                           |





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

Transitions from PrunePending State                                      |

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

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

          The (*,*,RP) downstream state machine on interface I           |
          transitions to the Join state.  The PrunePending timer is      |
          canceled (without triggering an expiry event).  The Expiry     |
          Timer is restarted, and set to the HoldTime from the           |
          triggering Join 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.                               |

     PrunePending Timer Expires                                          |
          The PrunePending 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 to itself on a LAN.  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 a |
          point-to-point interface.                                      |


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

When a router receives a Join(*,G) or Prune(*,G) it must first check to
see whether the RP in the message matches RP(G) (the router's idea of



Fenner/Handley/Holbrook/Kouvelas               Section 4.4.2.  [Page 34]

INTERNET-DRAFT              Expires: May 2001              November 2000


who the RP is).  If the RP in the message does not match RP(G) the Join
or Prune should be silently dropped.  If a router has no RP information
(e.g. has not recently received a BSR message) then it may choose to
accept Join(*,G) or Prune(*,G) and treat the RP in the message as 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 us to
          forward packets destined for G from this interface except if
          there is also (S,G,rpt) prune information (see Section 4.4.4)
          or the router lost an assert on this interface.

     PrunePending (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 PrunePending 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(*,G) is received.
          Expiry of the ExpiryTimer causes the interface state to revert
          to NoInfo for this group.

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

                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


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









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In tabular form, the per-interface (*,G) state-machine is:

+-------------++--------------------------------------------------------+
|             ||                         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       |             |              |
+-------------++-------------+-------------+-------------+--------------+
|             ||-> J state   | -> PP state | -> NI state | -> NI state  |
|             ||restart      |             | Send Prune- |              |
|Prune        ||Expiry       |             | Echo(*,G)   |              |
|Pending (PP) ||Timer; stop  |             |             |              |
|             ||Prune        |             |             |              |
|             ||Pending      |             |             |              |
|             ||Timer        |             |             |              |
+-------------++-------------+-------------+-------------+--------------+

The transition events "Receive Join(*,G)" and "Receive Prune(*,G)" imply
receiving a Join or Prune targeted to this router's address on the
received interface.  If the destination address 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 packet
it sent over that interface.  However on point-to-point links we also
recommend that PIM messages with a 0.0.0.0 destination address 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 IP destination |
          set to the router's address on I.                              |




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          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 message.              |

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 IP destination |
          set to the router's address on I.                              |

          The (*,G) downstream state machine on interface I remains in   |
          Join state, and the Expiry Timer (ET) is restarted, set to the |
          HoldTime from the triggering Join message.                     |

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

          The (*,G) downstream state machine on interface I transitions  |
          to the PrunePending state.  The PrunePending timer is started; |
          it is set to the J/P_Override_Interval 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 PrunePending State                                      |

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

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

          The (*,G) downstream state machine on interface I transitions  |
          to the Join state.  The PrunePending timer is canceled         |
          (without triggering an expiry event).  The Expiry Timer is     |
          restarted, and set to the HoldTime from the triggering Join    |
          message.                                                       |




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     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.                                           |

     PrunePending Timer Expires                                          |
          The PrunePending 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 to itself on a LAN.  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 a point-to-point
          interface.

4.4.3.  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 us 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.

     PrunePending (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 PrunePending state functions exactly
          like the Join state.




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In addition there are two timers:

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

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

                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


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


In tabular form, the state machine is:

+-------------++--------------------------------------------------------+
|             ||                         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       |             |              |
+-------------++-------------+-------------+-------------+--------------+
|             ||-> J state   | -> PP state | -> NI state | -> NI state  |
|             ||restart      |             | Send Prune- |              |
|Prune        ||Expiry       |             | Echo(S,G)   |              |
|Pending (PP) ||Timer; stop  |             |             |              |
|             ||Prune        |             |             |              |
|             ||Pending      |             |             |              |
|             ||Timer        |             |             |              |
+-------------++-------------+-------------+-------------+--------------+




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The transition events "Receive Join(S,G)" and "Receive Prune(S,G)" imply
receiving a Join or Prune targeted to this router's address on the
received interface.  If the destination address 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 packet
it sent over that interface.  However on point-to-point links we also    |
recommend that PIM messages with a 0.0.0.0 destination address are also  |
accepted.

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 IP destination |
          set to the router's 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 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 IP destination |
          set to the router's 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 the |
          HoldTime from the triggering Join message.                     |

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

          The (S,G) downstream state machine on interface I transitions  |
          to the PrunePending state.  The PrunePending timer is started; |
          it is set to the J/P_Override_Interval 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     |



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          interface I expires.                                           |

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

Transitions from PrunePending State                                      |

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

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

          The (S,G) downstream state machine on interface I transitions  |
          to the Join state.  The PrunePending timer is canceled         |
          (without triggering an expiry event).  The Expiry Timer is     |
          restarted, and set to the HoldTime from the triggering Join    |
          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.                                           |

     PrunePending Timer Expires                                          |
          The PrunePending 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 to itself on a LAN.  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 a point-to-point
          interface.







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4.4.4.  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 us
          not to forward packets from S destined for G from this
          interface even though the interface has active (*,G) Join
          state.  When interface I is in this state, the macro
          prune(S,G,rpt,I) returns true.

     PrunePending (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 PrunePending 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 re-
          instate 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.

     PrunePendingTmp (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:

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



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

                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


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








































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In tabular form, the state machine is:

+-------+---------------------------------------------------------------+
|       |                            Event                              |
|       +----------------+----------+---------+--------+-------+--------+
|Prev   |Receive         |Receive   Receive   |End of  |Prune  |Expiry  |
|State  |Join(*,G)       |Join      Prune     |Message |Pending|Timer   |
|       |or              |(S,G,rpt) (S,G,rpt) |        |Timer  |Expires |
|       |Join(*,*,RP(G)) |          |         |        |Expires|        |
+-------+----------------+----------+---------+--------+-------+--------+
|       |-               |-         +> PP     |-       |n/a    |n/a     |
|       |                |          state     |        |       |        |
|       |                |          start     |        |       |        |
|       |                |          Prune     |        |       |        |
|No Info|                |          Pending   |        |       |        |
|(NI)   |                |          Timer;    |        |       |        |
|       |                |          start     |        |       |        |
|       |                |          Expiry    |        |       |        |
|       |                |          Timer     |        |       |        |
|       |                |          Timer     |        |       |        |
+-------+----------------+----------+---------+--------+-------+--------+
|       |-> P' state     |-> NI     +> P      |-       |n/a    |-> NI   |
|Pruned |                |state     state     |        |       |state   |
|(P)    |                |          restart   |        |       |        |
|       |                |          Expiry    |        |       |        |
|       |                |          Timer     |        |       |        |
+-------+----------------+----------+---------+--------+-------+--------+
|Prune  |-> PP' state    |-> NI     +         |-       |-> P   |n/a     |
|Pending|                |state     |         |        |state  |        |
|(PP)   |                |          |         |        |       |        |
+-------+----------------+----------+---------+--------+-------+--------+
|       |error           |error     +> P      |-> NI   |n/a    |n/a     |
|Temp.  |                |          state     |state   |       |        |
|Pruned |                |          restart   |        |       |        |
|(P')   |                |          Expiry    |        |       |        |
|       |                |          Timer     |        |       |        |
+-------+----------------+----------+---------+--------+-------+--------+
|Temp.  |error           |error     +> PP     |-> NI   |n/a    |n/a     |
|Prune  |                |          state     |state   |       |        |
|Pending|                |          restart   |        |       |        |
|(PP')  |                |          Expiry    |        |       |        |
|       |                |          Timer     |        |       |        |
+-------+----------------+----------+---------+--------+-------+--------+

The transition events "Receive Join(S,G,rpt)", "Receive Prune(S,G,rpt)", |
"Receive Join(*,G)" and "Receive Join(*,*,RP(G))" imply receiving a Join |
or Prune targeted to this router's address on the received interface.    |
If the destination address is not correct, these state transitions in



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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 packet
it sent over that interface.  However on point-to-point links we also    |
recommend that PIM messages with a 0.0.0.0 destination address 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 IP        |
          destination set to the router's address on I.                  |

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

Transitions from PrunePending State                                      |

When in PrunePending (PP) state, the following events may trigger a      |
transition:                                                              |

     Receive Join(*,G) or Join(*,*,RP(G))                                |
          A Join(*,*,RP(G)) or Join(*,G) is received on interface I with |
          its IP destination set to the router's address on I.           |

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

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

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

     PrunePending Timer Expires                                          |
          The PrunePending Timer for the (S,G,rpt) downstream state      |



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          machine on interface I expires.                                |

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

Transitions from Pruned State                                            |

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

     Receive Join(*,G) or Join(*,*,RP(G))                                |
          A Join(*,*,RP(G)) or Join(*,G) is received on interface I with |
          its IP destination set to the router's address on I.           |

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

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

          The (S,G,rpt) downstream state machine on interface I remains  |
          in Pruned state.  The Expiry Timer (ET) is restarted, set to   |
          the HoldTime from the triggering Join 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.  ET and PPT are canceled.     |

Transitions from Temp. PrunePending State                                |

When in Temp. PrunePending (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 PrunePending state.  The Expiry Timer  |
          (ET) is restarted, set to the HoldTime from the 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 Temp. Pruned State                                      |

When in Temp. Pruned (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 Pruned state.  The Expiry Timer (ET)   |
          is restarted, set to the HoldTime from the 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.     |

Notes:                                                                   |

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

The HoldTime from the Join/Prune message must be larger than the
J/P_Override_Interval.

4.4.5.  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   |



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be prepared to override that prune by sending a Join(*,*,RP) almost      |
immediately.  Finally, if it sees the Generation ID (see Section 4.6) 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 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 would like   |
     to join the RP tree for this group.                                 |

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,       |
MRIB.next_hop(RP).                                                       |

                    +-----------------------------------+                |
                    | Figures omitted from text version |                |
                    +-----------------------------------+                |


                  Figure 6: Upstream (*,*,RP) state-machine              |





















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In tabular form, the state machine is:                                   |

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

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             |      |to             |            ||
|                   |MRIB.next_hop(RP)|    |MRIB.next_hop(RP)|          ||
+-------------------+----------------------+----------------------------+|
|Send             | |Increase Timer to  |  |Decrease Timer to  |        ||
|Join(*,*,RP);    | |t_suppressed       |  |t_override         |        ||
|Set Timer to     | |                      |                            ||
|t_periodic       | |                      |                            ||
+-------------------+----------------------+----------------------------+|

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






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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 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:                          |

     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 MRIB.next_hop(RP).  Cancel the Join Timer   |
          (JT).                                                          |

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




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          Send Join(*,*,RP) to the appropriate upstream neighbor, which  |
          is 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 MRIB.next_hop(RP).  This causes this    |
          router to suppress its own Join.                               |

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

     Topology Change wrt MRIB.next_hop(RP)                               |
          A route changed in the routing base stored in the MRIB so that |
          the next hop towards the RP is a different neighbor from       |
          before.                                                        |

          The upstream (*,*,RP) state machine remains in Joined state.   |
          Send Prune(*,*,RP) to the old upstream neighbor, which is the  |
          old value of MRIB.next_hop(RP).  Send Join(*,*,RP) to the new  |
          upstream neighbor which is the new value of 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. |



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4.4.6.  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 4.6) 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.

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 (*,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 would like
     to 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).                                                               |

                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


                   Figure 7: Upstream (*,G) state-machine










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In tabular form, the state machine is:

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

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         |
+-----------------+-----------------+-----------------+-----------------+
|Send             | Increase Timer  | Decrease Timer  | Decrease Timer  |
|Join(*,G); Set   | to              | to t_override   | to t_override   |
|Timer to         | t_suppressed    |                 |                 |
|t_periodic       |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+----------------------------------+------------------------------------+
|    topology change wrt           |       RPF'(*,G) GenID changes      |
|    MRIB.next_hop(RP)             |                                    |
+----------------------------------+------------------------------------+
|    Send Join(*,G) to new         |       Decrease Timer to            |
|    next hop; Send                |       t_override                   |
|    Prune(*,G) to old next        |                                    |
|    hop; set Timer to             |                                    |
|    t_periodic                    |                                    |
+----------------------------------+------------------------------------+







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This state machine uses the following macro:

  bool JoinDesired(*,G) {
     if immediate_olist(*,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 downstream state for (*,G) has changed so that at least
          one interface is in immediate_olist(*,G), making
          JoinDesired(*,G) become True.

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

          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
          Join(*,G)





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          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.  If
          the Join Timer is set to expire in less than t_suppressed
          seconds, reset it so that it expires after t_suppressed
          seconds.  If the Join Timer is set to expire in more than
          t_suppressed 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
          The current net hop towards the RP changes due 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.

     Topology Change wrt MRIB.next_hop(RP)
          A route changed in the routing base stored in the MRIB so that
          the next hop towards the RP is a different neighbor from
          before.

          The upstream (*,G) state machine remains in Joined state.
          Send Prune(*,G) to the old upstream neighbor, which is the old
          value of RPF'(*,G).  Send Join(*,G) to the new upstream
          neighbor which is the new value of RPF(*,G). Note that the



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          Join goes to RPF(*,G) and not RPF'(*,G) even if the new
          neighbor is on the same interface as the old one because the
          routing change may cause the assert state to be incorrect. 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.


4.4.7.  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.

In addition if MRIB changes cause the next hop towards the source to
change, the router should send a prune to the old next hop, and a join
to the new next hop.

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

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

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




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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 toward S, RPF'(S,G).     |

                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


                   Figure 8: Upstream (S,G) state-machine


In tabular form, the state machine is:

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






















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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 Timer  | Decrease Timer  | Decrease Timer  |
|Join(S,G); Set   | to t_suppr      | to t_override   | to t_override   |
|Timer to         |                 |                 |                 |
|t_periodic       |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

+-----------------------------------------------------------------------+
|                         In Joined (J) State                           |
+----------------------+-------------------------+----------------------+
| See Prune(*,G) to    |   topology change       |  RPF'(S,G) GenID     |
| RPF'(S,G)            |   wrt                   |  changes             |
|                      |   MRIB.next_hop(S)      |                      |
+----------------------+-------------------------+----------------------+
| Decrease Timer to    |   Send Join(S,G) to     |  Decrease Timer to   |
| t_override           |   new next hop; Send    |  t_override          |
|                      |   Prune(S,G) to old     |                      |
|                      |   next hop; Set         |                      |
|                      |   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 downstream state for (S,G) has changed so that at least    |
          one interface is in inherited_olist(S,G), making               |
          JoinDesired(S,G) become True.                                  |

          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 downstream state for (S,G) has changed so no interface is  |
          in inherited_olist(S,G), making JoinDesired(S,G) become False. |

          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).               |

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




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     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                                                   |
          The current net hop towards the RP changes due 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. |
          If the Join Timer is set to expire in less than t_override     |
          seconds, leave it unchanged.                                   |

     Topology Change wrt MRIB.next_hop(S)                                |
          A route changed in the routing base stored in the MRIB so that |



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          the next hop towards S is a different neighbor from before.    |

          The upstream (S,G) state machine remains in Joined state.      |
          Send Prune(S,G) to the old upstream neighbor, which is the old |
          value of RPF'(S,G).  Send Join(S,G) to the new upstream        |
          neighbor which is the new value of RPF(S,G). Note that the     |
          Join goes to RPF(S,G) and not RPF'(S,G) even if the new        |
          neighbor is on the same interface as the old one because the   |
          routing change may cause the assert state to be incorrect. 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. |

4.4.8.  (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 an 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:

  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 sent 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
  }




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


4.4.9.  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:                          |


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 not 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.                                                      |

                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+


      Figure 9: Upstream (S,G,rpt) state-machine for triggered messages

















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In tabular form, the state machine is:

+-------------++---------------------------------------------------------------+
|             ||                            Event                              |
|             ++-------------+-------------+------------------+----------------+
|Prev State   |PruneDesired  |PruneDesired |RPTJoinDesired(G) |inherited_olist |
|             |(S,G,rpt)     |(S,G,rpt)    |->False           |(S,G,rpt)       |
|             |->True        |->False      |                  |->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    |             |                  |                |
|(NP)         |(S,G,rpt);    |             |                  |                |
|             |Stop OT timer |             |                  |                |
+-------------++-------------+-------------+------------------+----------------+
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                       |
+------------+--------------+---------------+------------+--------------+
|OT timer    |See Prune     | See Join      |See Prune   | RPF'         |
|expires     |(S,G,rpt) to  | (S,G,rpt) to  |(S,G) to    | (S,G,rpt) -> |
|            |RPF'          | RPF'          |RPF'        | RPF' (*,G)   |
|            |(S,G,rpt)     | (S,G,rpt)     |(S,G,rpt)   |              |
+------------+--------------+---------------+------------+--------------+
|Send Join   |OT timer =    | stop OT       |OT timer =  | OT timer =   |
|(S,G,rpt);  |min(timer,    | timer         |min(timer,  | min(timer,   |
|Stop OT     |t_po)         |               |t_po)       | t_po)        |
|timer       |              |               |            |              |
+------------+--------------+---------------+------------+--------------+

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_po) =   |
t_po).                                                                   |










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This state machine uses the following macros:                            |

  bool RPTJoinDesired(G) {                                               |
    return (JoinDesired(*,G) || 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) time to the randomized prune-    |
     override interval.  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 existing routers 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.  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.





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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).  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
     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.  Any 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.  PIM Assert Messages

4.5.1.  (S,G) Assert Message State Machine

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





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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).

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 a assert timer (AT) that is used to time out
asserts on the assert losers and to resend asserts on the assert winner.

                 +-----------------------------------+
                 | Figures omitted from text version |
                 +-----------------------------------+


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
























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In tabular form the state machine is:

+-----------------------------------------------------------------------+
|                         In NoInfo (NI) State                          |
+---------------+-------------------+------------------+----------------+
| Receive       |  Receive Assert   |  Data arrives    |  Receive       |
| Inferior      |  with RPTbit      |  from S to G on  |  Preferred     |
| 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                     |
+-----------------+-----------------+------------------+----------------+
| Timer Expires   |  Receive        |   Receive        |  CouldAssert   |
|                 |  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          |  Timer Expires  |  AssTrDes       |
| Preferred     |  Inferior         |                 |  (S,G,I) ->     |
| Assert        |  Assert from      |                 |  FALSE          |
|               |  Current Winner   |                 |                 |
+---------------+-------------------+-----------------+-----------------+
| -> L state    |  -> NI state      |  -> NI state    |  -> NI state    |
| [Actions A2]  |  [Actions A5]     |  [Actions A5]   |  [Actions A5]   |
+---------------+-------------------+-----------------+-----------------+












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+-----------------------------------------------------------------------+
|                    In I Am Assert Loser (L) State                     |
+----------------+-----------------+-----------------+------------------+
| my_metric ->   | RPF interface   |  Receive        |  Receive Assert  |
| better than    | stops being I   |  Join(S,G) on   |  from Current    |
| winner's       |                 |  interface I    |  Winner          |
| metric         |                 |                 |                  |
+----------------+-----------------+-----------------+------------------+
| -> NI state    | -> NI state     |  -> NI State    |  -> L state      |
| [Actions A5]   | [Actions A5]    |  [Actions A5]   |  [Actions A2]    |
+----------------+-----------------+-----------------+------------------+


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 "inferior assert" is one with a worse metric than                |
     my_assert_metric(S,G,I).                                            |

     The state machine uses the following macros:

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



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          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 Preferred 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 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 Winner State

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

     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 timer (Action A3 below).  Note that the assert
          winner's 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
          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) which could cause transitions in the upstream |
          (S,G) state machine.

     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 "cancelling assert" with an infinite metric.



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Transitions from 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 Inferior Assert 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).  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.

     Timer Expires
          The (S,G) assert timer expires.  We transition to NoInfo
          state, deleting the (S,G) assert information.

     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 routing metrics have changed so that now my assert metric
          for (S,G) is better than the metric we have stored for current
          assert winner.  We transition to NoInfo state, delete this
          (S,G) assert state, 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 changed away from interface I
          Interface I used to be the RPF interface for S, and now it is
          not.  We transition to NoInfo state, delete this (S,G) assert
          state.

     Receive Join(S,G)
          We receive a Join(S,G) directed to my IP address in interface
          I.  The action is to transition to NoInfo state, and delete
          this (S,G) assert state, 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



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          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 timer to (Assert_Time - Assert_Override_Interval)
          Store self as AssertWinner

     A2:  Store new assert winner                                        |
          Set timer to Assert_Time

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

     A4:  Send AssertCancel(S,G)
          Delete assert info

     A5:  Delete assert info

     A6:  Store new assert winner
          Set timer to Assert_Time
          If I is RPF_interface(S) Set SPTbit(S,G) to TRUE.

4.5.2.  (*,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 resend asserts on the assert winner.

It is important to note that no transition occurs in the (*,G) state     |
machine as a result of receiving an assert message if the (S,G) assert
state machine for the relevant S and G is not in the "NoInfo" state.

                 +-----------------------------------+
                 | Figures omitted from text version |
                 +-----------------------------------+


                 Figure 11: (*,G) Assert State-machine






































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In tabular form the state machine is:

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

+-----------------------------------------------------------------------+
|                   In I Am Assert Winner (W) State                     |
+-----------------+-----------------+------------------+----------------+
| Timer Expires   |  Receive        |   Receive        |  CouldAssert   |
|                 |  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          |  Timer Expires  |  AssTrDes       |
| Preferred     |  Inferior         |                 |  (*,G,I) ->     |
| Assert        |  Assert from      |                 |  FALSE          |
|               |  Current Winner   |                 |                 |
+---------------+-------------------+-----------------+-----------------+
| -> L state    |  -> NI state      |  -> NI state    |  -> NI state    |
| [Actions A2]  |  [Actions A5]     |  [Actions A5]   |  [Actions A5]   |
+---------------+-------------------+-----------------+-----------------+

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




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The state machine uses the following macros:

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

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

AssertTrackingDesired(*,G,I) =                                           |
    CouldAssert(*,G) 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 "inferior assert" is one with a worse metric than                |
     my_assert_metric(S,G).                                              |

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:                    |

     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



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          Actions A1 (below).

     Receive Preferred 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 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:                                                                   |

     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 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).

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

     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 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).







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Transitions from 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:                                                                   |

     Receive Preferred Assert
          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 Inferior Assert 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).  We transition to NoInfo
          state, delete this (*,G) assert state, 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:                                                             |

     Timer Expires
          The (*,G) assert timer expires.  We transition to NoInfo state
          and delete this (*,G) assert info.

     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.

     My metric becomes better than the assert winner's metric
          My routing metrics have 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, 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 changed away from 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.                                                  |

     Receive Join(*,G) or Join(*,*,RP(G))                                |
          We receive a Join(*,G) or a Join(*,*,RP(G)) directed to my IP  |



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          address in interface I.  The action is to transition to NoInfo |
          state, and delete this (*,G) assert state, 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 timer to (Assert_Time - Assert_Override_Interval)
          Store self as AssertWinner(*,G)

     A2:  Store new AssertWinner(*,G)                                    |
          Set timer to assert_time

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

     A4:  Send AssertCancel(*,G)
          Delete assert info

     A5:  Delete assert info


4.5.3.  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 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,G,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
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,infinity}
  }







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4.5.4.  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
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 typically will name RP(G) as the source as it cannot name an
appropriate S.

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.                               |

4.5.5.  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) == I ) {                                      |
       return FALSE                                                      |
    } else {                                                             |
       return ( AssertWinner(S,G,I) != me )                              |
    }                                                                    |
  }                                                                      |



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




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


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

Rationale for Assert Rules                                               |

The following is a summary of the rules for sending and reacting to      |
asserts.  It is not intended to be definitive (the state machines and    |
pseudocode provide the definitive behavior).  Instead it provides some   |
rationale for the behavior.                                              |

1.   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.  Normal suppression and override    |
     rules apply.                                                        |

     This guarantees that all requested traffic will continue to arrive. |
     This doesn't allow switching back to the "normal" RPF neighbor      |
     until the assert times out, which it won't while data is flowing if |
     we are implementing rule 8.

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

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

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

     Same rationale as (2)

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

     Same rationale as (1).

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




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     This avoids keeping state alive on (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 might be
     confusing and could be interpreted as being undefined although
     technically the current spec says to drop such a join.

6.   An assert loser that receives a Join(S,G) directed to it cancels
     the (S,G) assert timer.

7.   An assert loser that receives a Join(*,G) or a Join(*,*,RP(G))      |
     directed to it 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.                                    |

     Rules 7 and 8 help convergence during topology changes.

8.   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) entry.  This  |
     rule does not apply to (S,G,rpt).                                   |

     This allow switching back to the shared tree after the last SPT     |
     router on the lan leaves.  We don't want RPT downstream routers to
     keep SPT state alive.

9.   [Optionally] re-assert before timing out.

     This prevents periodic duplicates.

10.  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).

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


4.6.  Designated Routers (DR) and Hello Messages


4.6.1.  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).  A router must record the Hello information
received from each PIM neighbor.

Hello messages are sent periodically on each PIM-enabled interface.
Hello messages are multicast to address 224.0.0.13 (the ALL-PIM-ROUTERS



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group).  Hello messages must be sent on all active interfaces, including
physical point-to-point links.  When PIM is enabled on an interface or a |
router first starts, the hello timer is set to a random value between 0  |
and Hello_Period to prevent 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.  A single hello timer is used to trigger sending Hello messages
on all active interfaces.  The hello timer should not be reset except
when it expires.

The DR Election 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 Election Priority.  The DR Election Priority
Option SHOULD be included in every Hello message, even if no DR election
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 Election
Priority Option.  The default priority is 1.

The Generation Identifier (GenID) Option SHOULD be included in all Hello
messages.  The generation ID 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.

When an interface goes down or changes IP address, a Hello message with  |
a zero Hold Time 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.                            |

4.6.2.  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.ip_address
          The IP address of the PIM neighbor.

     neighbor.genid
          The Generation ID of the PIM neighbor.





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     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.

     neighbor.timeout
          A timer to time out the neighbor state when it becomes stale.
          This is reset to Hello Holdtime whenever a Hello message is
          received, or to the value specified in the message, if the
          hold time option is used.

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.ip_address > b.ip_address                             |
      } else {                                                           |
          return ( a.dr_priority > b.dr_priority ) OR                    |
              ( a.dr_priority == b.dr_priority AND                       |
                   a.ip_address > b.ip_address )                         |
      }                                                                  |
  }                                                                      |


The DR election priority is a 32-bit unsigned number and the numerically
larger priority is always preferred.  A router's idea of the current DR



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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.


4.7.  PIM Bootstrap and RP Discovery

To obtain the RP information, all routers within a PIM domain collect
Bootstrap messages. Bootstrap messages are sent hop-by-hop within the
domain; the domain's bootstrap router (BSR) is responsible for
originating the Bootstrap messages. Bootstrap messages are used to carry
out a dynamic BSR election when needed and to distribute RP information
in steady state.

A domain in this context is a contiguous set of routers that all
implement PIM and are configured to operate within a common boundary
defined by PIM Multicast Border Routers (PMBRs). PMBRs connect each PIM
domain to the rest of the internet.

Routers use a set of available RPs (called the RP-Set) distributed in
Bootstrap messages to get the proper Group to RP mapping. The following
paragraphs give an overview of this process. The mechanism is specified
in Sections 4.7.2 and 4.7.4.

4.7.1.  Overview of RP Discovery

A small set of routers from a domain are configured as candidate
bootstrap routers (C-BSRs) and, through a simple election mechanism, a
single BSR is selected for that domain. A set of routers within a domain
are also configured as candidate RPs (C-RPs); typically these will be
the same routers that are configured as C-BSRs.  Candidate RPs
periodically unicast Candidate-RP-Advertisement messages (C-RP-Advs) to
the BSR of that domain, advertising their willingness to be an RP. A C-
RP-Adv message includes the address of the advertising C-RP, as well as
an optional list of group addresses and a mask length fields, indicating
the group prefix(es) for which the candidacy is advertised. The BSR then
includes a set of these Candidate-RPs (the RP-Set), along with the
corresponding group prefixes, in Bootstrap messages it periodically
originates.  Bootstrap messages are distributed hop-by-hop throughout
the domain.

All the PIM routers in the domain receive and store Bootstrap messages
originated by the BSR.  When a DR gets a indication of local membership
from IGMP or a data packet from a directly connected host, for a group
for which it has no forwarding state, the DR uses a hash function to map
the group address to one of the C-RPs whose group-prefix includes the



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group (see Section 4.7.5 ).  The DR then sends a Join message towards
that RP if the local host joined the group, or it Register-encapsulates
and unicasts the data packet to the RP if the local host sent a packet
to the group.

A Bootstrap message indicates liveness of the RPs included therein.  If
an RP is included in the message, then it is tagged as `up' at the
routers; while RPs not included in the message are removed from the list
of RPs over which the hash algorithm acts. Each router continues to use
the contents of the most recently received Bootstrap message from the
BSR until it receives a new Bootstrap message.

If a PIM domain becomes partitioned, each area separated from the old
BSR will elect its own BSR, which will distribute an RP-Set containing
RPs that are reachable within that partition. When the partition heals,
another election will occur automatically and only one of the BSRs will
continue to send out Bootstrap messages. As is expected at the time of a
partition or healing, some disruption in packet delivery may occur. This
time will be on the order of the region's round-trip time and the
bootstrap router timeout value.

4.7.2.  Bootstrap Router Election and RP-Set Distribution

For simplicity, bootstrap messages (BSMs) are used in both the BSR
election and the RP-Set distribution mechanisms.

The state-machine for bootstrap messages depends on whether or not a
router has been configured to be a Candidate-BSR.  The state-machine for
a C-BSR is given below, followed by the state-machine for a router that
is not configured to be a C-BSR.

Candidate-BSR State Machine


                 +-----------------------------------+
                 | Figures omitted from text version |
                 +-----------------------------------+


              Figure 12: State-machine for a candidate BSR


In tabular form this state machine is:








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+-------------------++--------------------------------------------------+
|                   ||                      Event                       |
|  Prev State       ++------------------------+-------------------------+
|                   ||   Receive Preferred    |    BS Timer Expires     |
|                   ||   BSM                  |                         |
+-------------------++------------------------+-------------------------+
|                   ||   -> C-BSR state       |    -> P-BSR state       |
|  Candidate BSR    ||   Forward BSM; Set     |    Set BS Timer to      |
|  (C-BSR)          ||   BS Timer to BS       |    rand_override        |
|                   ||   Timeout              |                         |
+-------------------++------------------------+-------------------------+
|                   ||   -> C-BSR state       |    -> E-BSR state       |
|  Pending BSR      ||   Forward BSM; Set     |    Originate BSM; Set   |
|  (P-BSR)          ||   BS Timer to BS       |    BS Timer to BS       |
|                   ||   Timeout              |    Period               |
+-------------------++------------------------+-------------------------+
|                   ||   -> C-BSR state       |    -> E-BSR state       |
|  Elected BSR      ||   Forward BSM; Set     |    Originate BSM; Set   |
|  (E-BSR)          ||   BS Timer to BS       |    BS Timer to BS       |
|                   ||   Timeout              |    Period               |
+-------------------++------------------------+-------------------------+
A candidate-BSR may be in one of three states:

Candidate-BSR (C-BSR)
     The router is a candidate to be a BSR, but currently another router
     is the preferred BSR.

Pending-BSR (P-BSR)
     The router is a candidate to be a BSR.  Currently no other router
     is the preferred BSR, but this router is not yet the BSR.  For
     comparisons with incoming BS messages, the router treats itself as
     the BSR.  This is a temporary state that prevents rapid thrashing
     of the choice of BSR during BSR election.

Elected-BSR (E-BSR)
     The router is the elected bootstrap router and it must perform all
     the BSR functions.

On startup, the initial state is "Pending-BSR", and the BS Timer is
initialized to the BS Timeout value.

In addition, there is a single timer - the bootstrap timer (BS Timer) -
that is used to time out old bootstrap router information, and used in
the election process to terminate P-BSR state.







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State-machine for Non-Candidate-BSR Routers


                 +-----------------------------------+
                 | Figures omitted from text version |
                 +-----------------------------------+


     Figure 13: State-machine for a router not configured as C-BSR

In tabular form this state machine is:

+-----------------------+-----------------------------------------------+
|                       |                    Event                      |
|Prev State             +----------------+----------------+-------------+
|                       | Receive        | Receive BSM    |BS Timer     |
|                       | Preferred BSM  |                |Expires      |
+-----------------------+----------------+----------------+-------------+
|                       | -> AP State    | -> AP State    |-            |
|                       | Forward BSM;   | Forward BSM;   |             |
|Accept Any (AA)        | Store RP-Set;  | Store RP-Set;  |             |
|                       | Set BS Timer   | Set BS Timer   |             |
|                       | to BS Timeout  | to BS Timeout  |             |
+-----------------------+----------------+----------------+-------------+
|                       | -> AP State    | -              |-> AA State  |
|                       | Forward BSM;   |                |             |
|Accept Preferred (AP)  | Store RP-Set;  |                |             |
|                       | Set BS Timer   |                |             |
|                       | to BS Timeout  |                |             |
+-----------------------+----------------+----------------+-------------+
A router that is not a candidate-BSR may be in one of two states:

Accept Any (AA)
     The router does not know of an active BSR, and will accept the
     first bootstrap message it sees as giving the new BSR's identity
     and the RP-Set.  If the router has an RP-Set cached from an
     obsolete bootstrap message, it continues to use it.

Accept Preferred (AP)
     The router knows the identity of the current BSR, and is using the
     RP-Set provided by that BSR.  Only bootstrap messages from that BSR
     or from a C-BSR with higher weight than the current BSR will be
     accepted.

On startup, the initial state is "Accept Any".

In addition, there is a single timer - the bootstrap timer (BS Timer)
that is used to time out old bootstrap router information.



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Bootstrap Message Processing Checks

When a bootstrap message is received, the following initial checks must
be performed:

if (BSM.dst_ip_address == ALL-PIM-ROUTERS group) {
  if ( BSM.src_ip_address != RPF_neighbor(BSM.BSR_ip_address) ) {
     drop the BS message silently
  }
} else if (BSM.dst_ip_address is one of my addresses) {
  if ( (BSR state != Accept Any)
       OR (DirectlyConnected(BSM.src_ip_address) == FALSE) ) {
     #the packet was unicast, but this wasn't
     #a quick refresh on startup
     drop the BS message silently
  }
} else {
  drop the BS message silently
}

Basically, the packet must have been sent to the ALL-PIM-ROUTERS group
by the correct upstream router towards the BSR that originated the BS
message, or the router must have no BSR state (it just restarted) and
have received the BS message by unicast from a directly connected
neighbor.


BS State-machine Transition Events

If the bootstrap message passes the initial checks above without being
discarded, then it may cause a state transition event in one of the
above state-machines.  For both candidate and non-candidate BSRs, the
following transition events are defined:

     Receive Preferred BSM
          A bootstrap message is received from a BSR that has greater
          than or equal weight than the current BSR.  In a router is in
          P-BSR state, then it uses its own weight as that of the
          current BSR.

          The weighting for a BSR is the concatenation in fixed-
          precision unsigned arithmetic of the BSR priority field from
          the bootstrap message and the IP address of the BSR from the
          bootstrap message (with the BSR priority taking the most-
          significant bits and the IP address taking the least
          significant bits).





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     Receive BSM
          A bootstrap message is received, regardless of BSR weight.

BS State-machine Actions

The state-machines specify actions that include setting the BS timer to
the following values:

     BS Period
          The periodic interval with which bootstrap messages are
          normally sent.  The default value is 60 seconds.

     BS Timeout
          The interval after which bootstrap router state is timed out
          if no bootstrap message from that router has been heard.  The
          default value is 2.5 times the BS Period, which is 150
          seconds.

     Randomized Override Interval
          The randomized interval during which a router avoids sending a
          bootstrap message while it waits to see if another router has
          a higher bootstrap weight.  This interval is to reduce control
          message overhead during BSR election.  The following
          pseudocode is proposed as an efficient implementation of this
          "randomized" value:

          Delay = 5 + 2 * log_2(1 + bestPriority - myPriority)
                  + AddrDelay


          where myPriority is the Candidate-BSR's configured priority,
          and bestPriority equals:

          bestPriority = Max(storedPriority, myPriority)

          and AddrDelay is given by the following:

          if ( bestPriority == myPriority) {
              AddrDelay = log_2(bestAddr - myAddr) / 16
          } else {
              AddrDelay = 2 - (myAddr / 2^31)
          }


          where myAddr is the Candidate-BSR's address, and bestAddr is
          the stored BSR's address.





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In addition to setting the timer, the following actions may be triggered
by state-changes in the state-machines:

     Forward BSM
          The bootstrap message is forwarded out of all multicast-
          capable interfaces except the interface it was received on.
          The source IP address of the message is the forwarding
          router's IP address on the interface the message is being
          forwarded from, the destination address is ALL-PIM-ROUTERS,
          and the TTL of the message is set to 1.

     Originate BSM
          A new bootstrap message is constructed by the BSR, giving the
          BSR's address and BSR priority, and containing the BSR's
          chosen RP-Set.  The message is forwarded out of all multicast-
          capable interfaces.  The IP source address of the message is
          the forwarding router's IP address on the interface the
          message is being forwarded from, the destination address is
          ALL-PIM-ROUTERS, and the TTL of the message is set to 1.

     Store RP Set
          The RP-Set from the received bootstrap message is stored and
          used by the router to decide the RP for each group that the
          router has state for.  Storing this RP Set may cause other
          state-transitions to occur in the router.  The BSR's IP
          address and priority from the received bootstrap message are
          also stored to be used to decide if future bootstrap messages
          are preferred.

In addition to the above state-machine actions, a DR also unicasts a
stored copy of the Bootstrap message to each new PIM neighbor, i.e.,
after the DR receives the neighbor's first Hello message.  It does so
even if the new neighbor becomes the DR.

4.7.3.  Sending Candidate-RP-Advertisements

Every C-RP periodically unicasts a C-RP-Adv to the BSR for that domain
to inform the BSR of the C-RP's willingness to function as an RP.  The
interval for sending these messages is subject to local configuration at
the C-RP, but must be smaller than the HoldTime in the C-RP-Adv.

A Candidate-RP-Advertisement carries a list of group address and group
mask field pairs.  This enables the C-RP router to limit the
advertisement to certain prefixes or scopes of groups.  If the C-RP
becomes an RP, it may enforce this scope acceptance when receiving
Registers or Join/Prune messages.  C-RPs should normally send C-RP-Adv
messages with the `Priority' field set to `0'.




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4.7.4.  Receiving Candidate-RP-Advertisements at the BSR and Creating
the RP-Set

Upon receiving a C-RP-Adv, if the router is not the elected BSR, it
silently ignores the message.

If the router is the BSR, then it adds the RP address to its local pool
of candidate RPs.  For each C-RP, the BSR holds the following
information:

     IP address
          The IP address of the C-RP.

     Group Prefix and Mask list
          The list of group prefixes and group masks from the C-RP
          advertisement.

     HoldTime
          The HoldTime from the C-RP-Adv message.  This is included
          later in the RP-set information in the Bootstrap Message.

     C-RP Expiry Timer
          The C-RP-Expiry Timer is used to time out the C-RP when the
          BSR fails to receive C-RP-Advertisements from it.  The expiry
          timer is initialized to the HoldTime from the RP's C-RP-Adv,
          and is reset to the HoldTime whenever a C-RP-Adv is received
          from that C-RP.

     C-RP Priority
          Do we store this?

When the C-RP Expiry Timer expires, the C-RP is removed from the pool of
available C-RPs.

The BSR uses the pool of C-RPs to construct the RP-Set which is included
in Bootstrap Messages and sent to all the routers in the PIM domain.
The BSR may apply a local policy to limit the number of Candidate RPs
included in the Bootstrap message.  The BSR may override the prefix
indicated in a C-RP-Adv unless the `Priority' field from the C-RP-Adv is
not zero.

The Bootstrap message is subdivided into sets of group-prefix,RP-
Count,RP-addresses.  For each RP-address, the corresponding HoldTime is
included in the "RP-HoldTime" field.  The format of the Bootstrap
message allows `semantic fragmentation', if the length of the original
Bootstrap message exceeds the packet maximum boundaries. However, we
recommend against configuring a large number of routers as C-RPs, to
reduce the semantic fragmentation required.



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4.7.5.  Receiving and Using the RP-Set

When a router receives and stores a new RP-Set, it checks if each of the
RPs referred to by existing state (i.e., by (*,G), (*,*,RP), or
(S,G,rpt) entries) is in the new RP-Set.

If an RP is not in the new RP-set, that RP is considered unreachable and
the hash algorithm (see below) is re-performed for each group with
locally active state that previously hashed to that RP. This will cause
those groups to be distributed among the remaining RPs.

If the new RP-Set contains a RP that was not previously in the RP-Set,
the hash value of the new RP is calculated for each group covered by the
new C-RP's Group-prefix.  Any group for which the new RP's hash value is
greater than hash value of the group's previous RP is switched over to
the new RP.

Hash Function

The hash function is used by all routers within a domain, to map a group
to one of the C-RPs from the RP-Set. For a particular group, G, the hash
function uses only those C-RPs whose Group-prefix covers G.  The
algorithm takes as input the group address, and the addresses of the
Candidate RPs, 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:

1    For RP addresses in the RP-Set, whose Group-prefix is the longest
     that covers G, select the RPs with the highest priority (i.e.
     lowest `Priority' value), and 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 included in
     Bootstrap messages.  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) must first be derived from the actual RP address. Such a
     digest method must be used consistently throughout the PIM domain.
     For IPv6 addresses, we recommend using the equivalent IPv4 address



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     for an IPv4-compatible address, and the CRC-32 checksum [7] of all
     other IPv6 addresses.

2    From the RPs with the highest priority (i.e.  lowest `Priority'
     value), the candidate with the highest resulting hash value is then
     chosen as the RP for that group, and its identity and hash value
     are stored with the entry created.

     Ties between RPs having the same hash value and priority, are
     broken in advantage of the highest address.

The hash function algorithm is invoked by a DR, upon reception of a
packet, or IGMP membership indication, for a group, for which the DR has
no entry. 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 hash function is invoked by all routers upon
receiving a (*,G) or (*,*,RP) Join/Prune message.

4.8.  Source-Specific Multicast

The Source-Specific Multicast (SSM) service model [9] 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, 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 reserved range:                                     |

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.                            |





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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 4.4.7)                       |

o     Downstream (S,G) state machine (Section 4.4.3)                     |

o     (S,G) Assert state machine (Section 4.5.1)                         |

o     Hello messages, neighbor discovery and DR election (Section 4.6)   |

o     Packet forwarding rules (Section 4.2)                              |

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


o     Register state machine (Section 4.3)                               |

o     (*,G), (S,G,rpt) and (*,*,RP) Downstream state machines (Sections  |
  4.4.2, 4.4.4, and 4.4.1)                                               |

o     (*,G), (S,G,rpt), and (*,*,RP) Upstream state machines (Sections   |
  4.4.6, 4.4.8, and 4.4.5)                                               |

o     (*,G) Assert state machine (Section 4.5.2)                         |




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o     Bootstrap RP Election (Section 4.7)                                |

o     Keepalive Timer                                                    |

o     SptBit (Section 4.2.1)                                             |

The KeepaliveTimer 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.                    |

Basically, PIM messages are either unicast (e.g.  Registers and
Register-Stop), or multicast with TTL 1 to `ALL-PIM-ROUTERS' group
`224.0.0.13' (e.g. Join/Prune, Asserts, etc.).

 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:





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               0 = Hello
               1 = Register
               2 = Register-Stop
               3 = Join/Prune
               4 = Bootstrap
               5 = Assert
               6 = Graft (used in PIM-DM only)
               7 = Graft-Ack (used in PIM-DM only)
               8 = Candidate-RP-Advertisement


Reserved
     Set to zero on transmission.  Ignored upon receipt.


Checksum
     The checksum is standard IP checksum, i.e.  the 16-bit one's
     complement of the one's complement sum of the entire PIM message,
     excluding the data portion in the Register message.  For computing
     the checksum, the checksum field is zeroed.


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 [4]. 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



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     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.


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 |   Reserved    |  Mask Len     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                Group multicast Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...


Addr Family
     described above.


Encoding Type
     described above.


Reserved
     Transmitted as zero. Ignored upon 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 and 128 for IPv6 native encoding).


Group multicast Address
     Contains the group address.




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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. If 1, the join or  prune |
     applies to the (*,G) or (*,*,RP) entry. If 0, the join or prune     |
     applies to the (S,G) entry where S is Source Address.  Joins and    |
     prunes sent towards the RP must have this bit set.                  |


R    The RPT-bit is a 1 bit value. If 1, the information about (S,G) is  |
     sent towards the RP.  If 0, the information must be sent toward S,  |
     where S is the Source Address.                                      |


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 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 source then the Mask length must equal the address length  |
     in bits for the given Address Family and Encoding Type. In version



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     2 of PIM, it is strongly recommended that this field be set to 32
     for IPv4 native encoding.


Source Address
     The source address.                                                 |


Represented in the form of < WC-bit >< RPT-bit >< Mask length >< Source  |
address >:                                                               |

A source address could be a host IPv4 native encoding address :          |

 < 0 >< 0 >< 32 >< 192.1.1.17 >                                          |

A source address could be the RP's IP address :                          |

 < 1 >< 1 >< 32 >< 131.108.13.111 >                                      |

A source address could be an IP address to prune from the RP-tree :      |

 < 0 >< 1 >< 32 >< 192.1.1.16 >                                          |





























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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 above.


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.

     The Option fields may contain the following values:

     o OptionType 1: Hold Time                                           |








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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  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
       |          Type = 1             |         Length = 2            | |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
       |         Hold Time             |                                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                 |

       Hold Time 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.  Furthermore, if the Holdtime is
       set to `0', the information is timed out immediately.

     o OptionType 2 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 4.6.2.                 |

     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.





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     OptionTypes 17 thru 65000 are assigned by the IANA.  OptionTypes    |
     65001 through 65535 are reserved for Private Use, as defined in
     [5].
     Unknown options may be ignored.  The "Hold Time" option MUST be     |
     implemented; the "DR Priority" and "Generation ID" options SHOULD   |
     be implemented.                                                     |

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. Source address
is set to the address of the DR, destination address is to the RP's
address.

 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|                       Reserved                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
.                      Multicast data packet                     .
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described above. Note that the checksum for Registers is done only
     on first 8 bytes of 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 be accepted.                            |

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.


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.


Multicast data packet
     The original packet sent by the source.  This packet must be the of |
     the same address family as the encapsulating PIM packet, e.g. an    |



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     IPv6 data packet must be encapsulated in an IPv6 PIM packet.        |

     For (S,G) null Registers, the Multicast data packet portion
     contains only a dummy header with S as the source address, G as the
     destination address, and a data length of zero.


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 above.


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                                                           |
     Host address of source from multicast data packet in register.  The |
     format for this address is given in the Encoded-Unicast address in  |
     section 4.9.1. A special wild card value (0's), can be used to      |
     indicate any source.  XXX note that "(0's)" doesn't really describe |
     what the rest of the field in encoded-unicast-address should be     |

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



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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 above.


Unicast Upstream Neighbor Address
     The address of the RPF or upstream neighbor.  The format for this
     address is given in the Encoded-Unicast address in section 4.9.1.

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 never times out the oif. This may be used with dial-   |
     on-demand links, to avoid keeping the link up with periodic         |
     Join/Prune messages.  Furthermore, if the Holdtime is set to `0',   |
     the information is timed out immediately.


Number of Groups
     The number of multicast group sets contained in the message.


Multicast group address
     For format description see Section 4.9.1. A wild card group in the  |
     (*,*,RP) join is represented for IPv4 by a 224.0.0.0 in the group   |
     address field and `4' in the mask length field. A (*,*,RP) join     |
     also has the WC-bit and the RPT-bit set.


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.  If the Join/Prune message
     boundary exceeds the maximum packet size, then the join and prune
     lists for the same group must be included in the same packet.


4.9.6.  Bootstrap Message Format

The Bootstrap messages are multicast to `ALL-PIM-ROUTERS' group, out all
interfaces having PIM neighbors (excluding the one over which the
message was received).  Bootstrap messages are sent with TTL value of 1.
Bootstrap messages originate at the BSR, and are forwarded by
intermediate routers.

A bootstrap message is divided up into `semantic fragments', if the
original message exceeds the maximum packet size boundaries.  XXX Define |
semantic fragmentation!                                                  |
The format of a single `fragment' is given below:                        |































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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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Fragment Tag          | Hash Mask len | BSR-priority  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             BSR Address (Encoded-Unicast format)              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address 1 (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Count 1    | Frag RP Cnt 1 |         Reserved              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 1 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP1 Holdtime         | RP1 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 2 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP2 Holdtime         | RP2 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address m (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RPm Holdtime         | RPm Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address 2 (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address n (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Count n    | Frag RP Cnt n |          Reserved             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 1 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP1 Holdtime         | RP1 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 2 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP2 Holdtime         | RP2 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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|             RP Address m (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RPm Holdtime         | RPm Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described above.


Fragment Tag
     A randomly generated number, acts to distinguish the fragments
     belonging to different Bootstrap messages; fragments belonging to
     same Bootstrap message carry the same `Fragment Tag'.


Hash Mask len
     The length (in bits) of the mask to use in the hash function. For
     IPv4 we recommend a value of 30. For IPv6 we recommend a value of
     126.


BSR priority
     Contains the BSR priority value of the included BSR.  This field is
     considered as a high order byte when comparing BSR addresses.


Unicast BSR Address
     The address of the bootstrap router for the domain.  The format for
     this address is given in the Encoded-Unicast address in 4.9.1.

Group Address 1..n
     The group prefix (address and mask) with which the Candidate RPs
     are associated.  Format described in section 4.9.1.

RP Count 1..n
     The number of Candidate RP addresses included in the whole
     Bootstrap message for the corresponding group prefix. A router does
     not replace its old RP-Set for a given group prefix until/unless it
     receives `RP-Count' addresses for that prefix; the addresses could
     be carried over several fragments.  If only part of the RP-Set for
     a given group prefix was received, the router discards it, without
     updating that specific group prefix's RP-Set.


Frag RP Cnt 1..m
     The number of Candidate RP addresses included in this fragment of
     the Bootstrap message, for the corresponding group prefix. The



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     `Frag RP-Cnt' field facilitates parsing of the RP-Set for a given
     group prefix, when carried over more than one fragment.


RP address 1..m
     The address of the Candidate RPs, for the corresponding group
     prefix.  The format for these addresses is given in the Encoded-
     Unicast address in section 4.9.1.

RP1..m Holdtime
     The Holdtime for the corresponding RP.  This field is copied from
     the `Holdtime' field of the associated RP stored at the BSR.


RP1..m Priority
     The `Priority' of the corresponding RP and Encoded-Group Address.
     This field is copied from the `Priority' field stored at the BSR    |
     when receiving a Candidate-RP-Advertisement.  The highest priority  |
     is `0' (i.e. the lower the value of the `Priority' field, the       |
     better).  Note that the priority is per RP per Group Address.       |

4.9.7.  Assert Message Format

The Assert message is sent when a multicast data packet is received on
an outgoing interface corresponding to the (S,G) or (*,G) associated
with the source.

 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 above.


Group Address
     The group address to which the data packet was addressed, and which |



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     triggered the Assert.  This is an Encoded-Group address, as         |
     specified in 4.9.1.                                                 |

Source Address
     Source address from multicast datagram that triggered the Assert
     packet to be sent. The format for this address is given in Encoded-
     Unicast-Address in section 4.9.1.

R    RPT-bit is a 1 bit value. If the multicast datagram that triggered
     the Assert packet is routed down the RP tree, then the RPT-bit is
     1; if the multicast datagram is routed down the SPT, it is 0.


Metric Preference
     Preference value assigned to the unicast routing protocol that
     provided the route to Host address.


Metric
      The unicast routing table metric. The metric is in units
     applicable to the unicast routing protocol used.


4.9.8.  Candidate-RP-Advertisement Format

Candidate-RP-Advertisements are periodically unicast from the C-RPs to
the BSR.

 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Cnt    |   Priority    |           Holdtime            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address (Encoded-Unicast format)               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address 1 (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address n (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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PIM Version, Type, Reserved, Checksum
     Described above.


Prefix Cnt
     The number of encoded group addresses included in the message;
     indicating the group prefixes for which the C-RP is advertising. A  |
     Prefix Cnt of `0' implies all multicast groups, e.g. for IPv4 a     |
     prefix of 224.0.0.0 with mask length of 4.  If the C-RP is not      |
     configured with Group-prefix information, the C-RP puts a default
     value of `0' in this field.


Priority
     The `Priority' of the included RP, for the corresponding Encoded-
     Group Address (if any).  highest priority is `0' (i.e. the lower
     the value of the `Priority' field, the higher the priority). This
     field is stored at the BSR upon receipt along with the RP address
     and corresponding Encoded-Group Address.


Holdtime
     The amount of time the advertisement is valid. This field allows
     advertisements to be aged out.


RP Address
     The address of the interface to advertise as a Candidate RP.  The
     format for this address is given in the Encoded-Unicast address in
     section 4.9.1.

Group Address-1..n
     The group prefixes for which the C-RP is advertising.  Format
     described in Encoded-Group-Address in section 4.9.1.

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.







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Global Timers

     Bootstrap Timer: BST

     Hello Timer: HT

Per interface (I):

     Per neighbor (N):

          Neighbor liveness Timer: NLT(N,I)

     Per active RP (RP):

          (*,*,RP) Join Expiry Timer: ET(*,*,RP,I)

          (*,*,RP) PrunePending Timer: PPT(*,*,RP,I)

     Per Group (G):

          (*,G) Join Expiry Timer: ET(*,G,I)

          (*,G) PrunePending Timer: PPT(*,G,I)

          (*,G) Assert Timer: AT(*,G,I)

          Per Source (S):

               (S,G) Join Expiry Timer: ET(S,G,I)

               (S,G) PrunePending 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) PrunePending 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)






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     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 Bootstrap Router only:

     Per Candidate RP (C):

          C-RP Expiry Timer: CET(C)

At the C-RPs only:

     C-RP Advertisement Timer: CRPT

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.























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Timer Name: Bootstrap Timer (BST)


+----------------------+------------------------+-----------------------+
| Value Name           |  Value                 |   Explanation         |
+----------------------+------------------------+-----------------------+
| BS Period            |  Default: 60 secs      |   Period between      |
|                      |                        |   bootstrap messages  |
+----------------------+------------------------+-----------------------+
| BS Timeout           |  2 * BS_Period + 10    |   Period after last   |
|                      |  seconds               |   BS message before   |
|                      |                        |   BSR is timed out    |
|                      |                        |   and election        |
|                      |                        |   begins              |
+----------------------+------------------------+-----------------------+
| BS randomized        |  rand(0, 5.0 secs)     |   Suppression period  |
| override interval    |                        |   in BSR election to  |
|                      |                        |   prevent thrashing   |
+----------------------+------------------------+-----------------------+

Timer Name: Hello Timer (HT)


+----------------+------------+-----------------------------------------+
| Value Name     |  Value     |  Explanation                            |
+----------------+------------+-----------------------------------------+
| Hello_Period   |  30 sec    |  Periodic interval for hello messages.  |
+----------------+------------+-----------------------------------------+

Hello messages are sent on every active interface once every
Hello_Period seconds.  At system power-up, the timer is initialized to   |
rand(0,Hello_Period) to prevent synchronization.                         |

Timer Name: Neighbor Liveness Timer (NLT(N,I))


+-------------------+-----------------+---------------------------------+
| Value Name        |  Value          |   Explanation                   |
+-------------------+-----------------+---------------------------------+
| Hello Holdtime    |  from message   |   Hold Time from Hello Message  |
+-------------------+-----------------+---------------------------------+

The Holdtime in a Hello Message should be set to (3.5 * Hello_Period),
giving a default value of 105 seconds.







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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   |  Hold Time from Join/Prune Message  |
+----------------+----------------+-------------------------------------+

See details of JT(*,G) for the Hold Time that is included in Join/Prune
Messages.

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    |  Default: 3 secs   |   Short period after  |
|                          |                    |   a join or prune to  |
|                          |                    |   allow other         |
|                          |                    |   routers on the LAN  |
|                          |                    |   to override the     |
|                          |                    |   join or prune       |
+--------------------------+--------------------+-----------------------+

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          |
+---------------------------+----------------------+--------------------+





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Note that for historical reasons, the Assert message lacks a Holdtime
field.  Thus changing the Assert Time from the default value is not
recommended.

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)         |don't need to do so.                |
+-------------+--------------------+------------------------------------+
|t_override   |rand(0, 0.9 * J/P   |Randomized delay to prevent         |
|             |Override Interval)  |response implosion when sending a   |
|             |                    |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.

0.9 * J/P Override Interval is really an attempt to estimate the true    |
desired max value of t_override, which is the J/P Override Interval      |
minus the local network's propagation delay.  If the network's           |
propagation delay is actually known, the value (J/P Override Interval -  |
propagation delay) may be used instead.                                  |

The holdtime specified in a Join/Prune message should be set to (3.5 *   |
t_periodic).











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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                  |
|                       |  Period Suppression    |  Keepalive_Period,   |
|                       |  ) + Register Probe    |  but at the RP when  |
|                       |  Time                  |  a RegisterStop 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).


Timer Name: Upstream Override Timer (OT(S,G,rpt))


+------------------+--------------------------+-------------------------+
|  Value Name      |   Value                  |    Explanation          |
+------------------+--------------------------+-------------------------+
|  t_po            |   rand(0, 0.9 *          |    Randomized delay     |
|                  |   Join/Prune             |    to prevent           |
|                  |   Override Interval)     |    response implosion   |
|                  |                          |    when sending a       |
|                  |                          |    join message to      |
|                  |                          |    override someone     |
|                  |                          |    else's prune         |
|                  |                          |    message.             |
+------------------+--------------------------+-------------------------+

As with t_override, the network's propagation delay may be used if       |
known.  XXX t_po and t_override seem to be the same thing???             |





Fenner/Handley/Holbrook/Kouvelas               Section 4.11.  [Page 120]

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Timer Name: C-RP Expiry Timer (CET(R))


+----------------+------------------+-----------------------------------+
| Value Name     |  Value           |  Explanation                      |
+----------------+------------------+-----------------------------------+
| C-RP Timeout   |  from message    |  Hold time from C-RP-Adv message  |
+----------------+------------------+-----------------------------------+

C-RP Advertisement messages are sent periodically with period C-RP-Adv-
Period.  C-RP-Adv-Period defaults to 60 seconds.  The holdtime to be
specified in a C-RP-Adv message should be set to (2.5 * C-RP-Adv-Period
).


Timer Name: C-RP Advertisement Timer (CRPT)                              |

+--------------------+------------------------+-------------------------+|
| Value Name         |  Value                 |   Explanation           ||
+--------------------+------------------------+-------------------------+|
| C-RP-Adv-Period    |  Default: 60 seconds   |   Period with which  |  ||
|                    |                        |   periodic C-RP      |  ||
|                    |                        |   Advertisements are |  ||
|                    |                        |   sent to BSR        |  ||
+--------------------+------------------------+-------------------------+|


























Fenner/Handley/Holbrook/Kouvelas               Section 4.11.  [Page 121]

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Timer Name: Register Stop Timer (RST(S,G))


+---------------------------+----------------------+--------------------+
|Value Name                 |Value                 | Explanation        |
+---------------------------+----------------------+--------------------+
|Register Suppression Time  |Default: 60 seconds   | Period during      |
|                           |                      | which a DR stops   |
|                           |                      | sending Register-  |
|                           |                      | encapsulated data  |
|                           |                      | to the RP after    |
|                           |                      | receiving a        |
|                           |                      | RegisterStop       |
+---------------------------+----------------------+--------------------+
|Register Probe Time        |Default: 5 seconds    | Time before RST    |
|                           |                      | expires when a DR  |
|                           |                      | may send a Null-   |
|                           |                      | Register to the RP |
|                           |                      | to cause it to     |
|                           |                      | resend a           |
|                           |                      | RegisterStop       |
|                           |                      | message.           |
+---------------------------+----------------------+--------------------+

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 [4].

     Values 128 through 250 are designated to be assigned by the IANA
     based upon IESG Approval, as defined in [5]. XXX note: is the IESG
     OK with this?

     Values 251 through 255 are designated for Private Use, as defined
     in [5].





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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  |
[5]. Such assignments are valid for one year, and may be renewed.
Permanent assignments require a specification (see "Specification
Required" in [5].)

6.  Security Considerations

All PIM control messages MAY use IPsec [6] to address security concerns.
The authentication methods are addressed in a companion document [7].
Keys may be distributed as described in [8].

XXX This probably needs more.

7.  Authors' Addresses

     Bill Fenner
     AT&T Labs - Research
     75 Willow Road
     Menlo Park, CA 94025
     fenner@research.att.com


     Mark Handley
     ACIRI/ICSI
     1947 Center St, Suite 600
     Berkeley, CA 94708
     mjh@aciri.org


     Hugh Holbrook
     Cisco Systems
     170 W. Tasman Drive
     San Jose, CA 95134
     holbrook@cisco.com


     Isidor Kouvelas
     Cisco Systems
     170 W. Tasman Drive
     San Jose, CA 95134
     kouvelas@cisco.com







Fenner/Handley/Holbrook/Kouvelas                  Section 7.  [Page 123]

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8.  Acknowledgments

PIM-SM was designed over many years by a large group of people,
including ideas 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
and Girish Chandranmenon.

Thanks are due to the American Licorice Company, for its obscure but
possibly essential role in the creation of this document.

9.  References

[1] T. Bates , R. Chandra , D. Katz , Y. Rekhter, "Multiprotocol
     Extensions for BGP-4", RFC 2283

[2] S.E. Deering, "Host extensions for IP multicasting", RFC 1112, Aug
     1989.

[3] W. Fenner, "Internet Group Management Protocol, Version 2", RFC
     2236.

[4] IANA, "Address Family Numbers", linked from
     http://www.iana.org/numbers.html

[5] T. Narten , H. Alvestrand, "Guidelines for Writing an IANA
     Considerations Section in RFCs", RFC 2434.

[6] S. Kent, R. Atkinson, "Security Architecture for the Internet
     Protocol.", RFC 2401.

[7] L. Wei, "Authenticating PIM version 2 messages", draft-ietf-pim-
     v2-auth-01.txt, work in progress.

[8] T. Hardjono, B. Cain, "Simple Key Management Protocol for PIM",
     draft-ietf-pim-simplekmp-01.txt, work in progress.

[9] H. Holbrook, B. Cain, "Source-Specific Multicast for IP", draft-
     holbrook-ssm-00.txt, work in progress.











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10.  Index
AssertCancel(*,G). . . . . . . . . . . . . . . . . . . . . . . . . .  79
AssertTimer(*,G,I) . . . . . . . . . . . . . . . . . . . . .15,22,74,118
AssertTimer(S,G,I) . . . . . . . . . . . . . . . . . . . . .17,22,67,118
AssertTrackingDesired(*,G,I) . . . . . . . . . . . . . . . . . . . .  76
AssertTrackingDesired(S,G,I) . . . . . . . . . . . . . . . . . . . .  69
AssertWinner(*,G,I). . . . . . . . . . . . . . . . . . . . . . . . 20,22
AssertWinner(S,G,I). . . . . . . . . . . . . . . . . . . . . . .20,22,81
assert_metric. . . . . . . . . . . . . . . . . . . . . . . . . . . .  79
Assert_Override_Interval . . . . . . . . . . . . . . . . . . . 73,79,118
Assert_Time. . . . . . . . . . . . . . . . . . . . . . . . . . 73,79,118
AT(*,G,I). . . . . . . . . . . . . . . . . . . . . . . . . .15,22,74,118
AT(S,G,I). . . . . . . . . . . . . . . . . . . . . . . . . .17,22,67,118
BST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
BS_Period. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
BS_randomized_override_interval. . . . . . . . . . . . . . . . . . . 117
BS_Timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
BS_Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
C-RP-Adv-Period. . . . . . . . . . . . . . . . . . . . . . . . . . . 121
C-RP-Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
C-RP_Timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
CET(R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
CouldAssert(*,G,I) . . . . . . . . . . . . . . . . . . . . . . . . .  76
CouldAssert(S,G,I) . . . . . . . . . . . . . . . . . . . . . . . . 69,69
CouldRegister(S,G) . . . . . . . . . . . . . . . . . . . . . . . . .  29
DirectlyConnected(S) . . . . . . . . . . . . . . . . . . . . . .25,26,29
DownstreamJPState(*,*,RP,I). . . . . . . . . . . . . . . . . . . . .  21
DownstreamJPState(*,G,I) . . . . . . . . . . . . . . . . . . . . . .  21
DownstreamJPState(S,G,I) . . . . . . . . . . . . . . . . . . . . . .  21
DR(I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  85
dr_is_better(a,b,I). . . . . . . . . . . . . . . . . . . . . . . . .  85
ET(*,*,RP,I) . . . . . . . . . . . . . . . . . . . . . . . . . 14,32,118
ET(*,G,I). . . . . . . . . . . . . . . . . . . . . . . . . . . 15,35,118
ET(S,G,I). . . . . . . . . . . . . . . . . . . . . . . . . . . 17,39,118
ET(S,G,rpt,I). . . . . . . . . . . . . . . . . . . . . . . . . 18,42,118
Hash_Function. . . . . . . . . . . . . . . . . . . . . . . . . . . .  94
Hello_Holdtime . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Hello_Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
HT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
immediate_olist(*,*,RP). . . . . . . . . . . . . . . . . . . . . . 20,49
immediate_olist(*,G) . . . . . . . . . . . . . . . . . . . . . . . 20,53
immediate_olist(S,G) . . . . . . . . . . . . . . . . . . . . . .20,58,80
infinite_assert_metric() . . . . . . . . . . . . . . . . . . . . . .  80
inherited_olist(S,G) . . . . . . . . . . . . . . . . . . .20,25,30,58,69
inherited_olist(S,G,rpt) . . . . . . . . . . . . . .20,25,26,62,64,66,80
I_am_DR(I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,29
I_am_RP(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
J/P_HoldTime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118



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J/P_Override_Interval. . . . . . . . . . . . . . . . . . 33,37,40,45,118
Join(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
join(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  69
JoinDesired(*,*,RP). . . . . . . . . . . . . . . . . . . . . . . . 49,63
JoinDesired(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . 53,63
JoinDesired(S,G) . . . . . . . . . . . . . . . . . . . . . . . .26,58,69
joins(*,*,RP). . . . . . . . . . . . . . . . . . . . . . . . . . . 21,76
joins(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . . .21,69,76
joins(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
JT(*,*,RP) . . . . . . . . . . . . . . . . . . . . . . . . . . 14,48,119
JT(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . 15,52,119
JT(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . 17,57,119
KAT(S,G) . . . . . . . . . . . . . . . . . . . . . . .17,25,29,30,58,119
KeepaliveTimer(S,G). . . . . . . . . . . . . . . . . .17,25,29,30,58,119
Keepalive_Period . . . . . . . . . . . . . . . . . . . . . . . . . . 119
local_receiver_exclude(S,G,I). . . . . . . . . . . . . . . . . . . .  20
local_receiver_include(*,G,I). . . . . . . . . . . . . . . . . . . .  20
local_receiver_include(S,G,I). . . . . . . . . . . . . . . . . . . .  20
lost_assert(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . .  22
lost_assert(*,G,I) . . . . . . . . . . . . . . . . . . . . . 20,22,69,82
lost_assert(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . .  22
lost_assert(S,G,I) . . . . . . . . . . . . . . . . . . . . . . .20,22,82
lost_assert(S,G,rpt) . . . . . . . . . . . . . . . . . . . . . . . .  22
lost_assert(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . . . . 22,81
MBGP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
MRIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
MRIB.next_hop(host). . . . . . . . . . . . . . . . . . . . . . . . .  22
my_assert_metric(S,G,I). . . . . . . . . . . . . . . . . . . . . . .  80
NLT(N,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14,117
OT(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . . . . .19,120
packet_arrives_on_rp_tunnel(pkt) . . . . . . . . . . . . . . . . . .  30
pim_exclude(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . .  20
pim_exclude(S,G,I) . . . . . . . . . . . . . . . . . . . . . . . . .  69
pim_include(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . 20,76
pim_include(*,G,I) . . . . . . . . . . . . . . . . . . . . . . . . .  69
pim_include(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . 20,69
PPT(*,*,RP,I). . . . . . . . . . . . . . . . . . . . . . . . . 14,32,118
PPT(*,G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . 15,35,118
PPT(S,G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . 16,39,118
PPT(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . . . . . . 18,43,118
PruneDesired(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . 64,65
prunes(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . . . 21,69
RegisterStop . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
RegisterStop(*,G). . . . . . . . . . . . . . . . . . . . . . . . . .  29
RegisterStop(S,G). . . . . . . . . . . . . . . . . . . . . . . . . .  30
RegisterStop_timer . . . . . . . . . . . . . . . . . . . . . . . . .  27
Register_Probe_Time. . . . . . . . . . . . . . . . . . . . . . 29,31,122
Register_Suppression_Time. . . . . . . . . . . . . . . . . 29,31,120,122



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RP(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22,76,76
RPF'(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . .22,26,62
RPF'(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . . .23,26,62
RPF'(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . . .22,62,64
RPF_interface. . . . . . . . . . . . . . . . . . . . . . . . . . . .  76
RPF_interface(host). . . . . . . . . . . . . . . . .22,25,26,29,69,76,81
RPTJoinDesired(G). . . . . . . . . . . . . . . . . . . . . . . .63,66,76
rpt_assert_metric(G,I) . . . . . . . . . . . . . . . . . . . . . . .  80
RST(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27,122
SPTbit(S,G). . . . . . . . . . . . . . . . . . . . . . . .25,26,30,62,80
spt_assert_metric(S,I) . . . . . . . . . . . . . . . . . . . . . . .  80
SSM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  95
t_override . . . . . . . . . . . . . . . . . . . . . . . . . . 49,53,119
t_periodic . . . . . . . . . . . . . . . . . . . . . . . . . . 49,53,119
t_po . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63,120
t_suppressed . . . . . . . . . . . . . . . . . . . . . . . . . 49,53,119
Update_SPTbit(S,G,iif) . . . . . . . . . . . . . . . . . . . . . . .  26
UpstreamJPState(S,G) . . . . . . . . . . . . . . . . . . . . . . . .  25

































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