[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 4601

Internet Engineering Task Force                                   PIM WG
INTERNET-DRAFT                                          Bill Fenner/AT&T
draft-ietf-pim-sm-v2-new-06.txt                        Mark Handley/ICIR
                                                     Hugh Holbrook/Cisco
                                                   Isidor Kouvelas/Cisco
                                                        10 December 2002
                                                      Expires: June 2003


         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



Fenner/Handley/Holbrook/Kouvelas                                [Page 1]

INTERNET-DRAFT             Expires: June 2003              December 2002


     or a separate multicast-capable routing information base.  It
     builds unidirectional shared trees rooted at a Rendezvous
     Point (RP) per group, and optionally creates shortest-path
     trees per source.















































Fenner/Handley/Holbrook/Kouvelas                                [Page 2]

INTERNET-DRAFT             Expires: June 2003              December 2002


                           Table of Contents


     1. Introduction. . . . . . . . . . . . . . . . . . . . . .   6
     2. Terminology . . . . . . . . . . . . . . . . . . . . . .   6
      2.1. Definitions. . . . . . . . . . . . . . . . . . . . .   6
      2.2. Pseudocode Notation. . . . . . . . . . . . . . . . .   7
     3. PIM-SM Protocol Overview. . . . . . . . . . . . . . . .   8
     4. Protocol Specification. . . . . . . . . . . . . . . . .  13
      4.1. PIM Protocol State . . . . . . . . . . . . . . . . .  13
       4.1.1. General Purpose State . . . . . . . . . . . . . .  14
       4.1.2. (*,*,RP) State. . . . . . . . . . . . . . . . . .  15
       4.1.3. (*,G) State . . . . . . . . . . . . . . . . . . .  16
       4.1.4. (S,G) State . . . . . . . . . . . . . . . . . . .  17
       4.1.5. (S,G,rpt) State . . . . . . . . . . . . . . . . .  19
       4.1.6. State Summarization Macros. . . . . . . . . . . .  20
      4.2. Data Packet Forwarding Rules . . . . . . . . . . . .  25
       4.2.1. Last hop switchover to the SPT. . . . . . . . . .  27
       4.2.2. Setting and Clearing the (S,G) SPT bit. . . . . .  27
      4.3. Designated Routers (DR) and Hello Messages . . . . .  29
       4.3.1. Sending Hello Messages. . . . . . . . . . . . . .  29
       4.3.2. DR Election . . . . . . . . . . . . . . . . . . .  31
       4.3.3. Reducing Prune Propagation Delay on LANs. . . . .  32
      4.4. PIM Register Messages. . . . . . . . . . . . . . . .  35
       4.4.1. Sending Register Messages from the DR . . . . . .  35
       4.4.2. Receiving Register Messages at the RP . . . . . .  39
      4.5. PIM Join/Prune Messages. . . . . . . . . . . . . . .  41
       4.5.1. Receiving (*,*,RP) Join/Prune Messages. . . . . .  42
       4.5.2. Receiving (*,G) Join/Prune Messages . . . . . . .  45
       4.5.3. Receiving (S,G) Join/Prune Messages . . . . . . .  49
       4.5.4. Receiving (S,G,rpt) Join/Prune Messages . . . . .  52
       4.5.5. Sending (*,*,RP) Join/Prune Messages. . . . . . .  58
       4.5.6. Sending (*,G) Join/Prune Messages . . . . . . . .  62
       4.5.7. Sending (S,G) Join/Prune Messages . . . . . . . .  66
       4.5.8. (S,G,rpt) Periodic Messages . . . . . . . . . . .  71
       4.5.9. State Machine for (S,G,rpt) Triggered
       Messages . . . . . . . . . . . . . . . . . . . . . . . .  72
      4.6. PIM Assert Messages. . . . . . . . . . . . . . . . .  76
       4.6.1. (S,G) Assert Message State Machine. . . . . . . .  76
       4.6.2. (*,G) Assert Message State Machine. . . . . . . .  84
       4.6.3. Assert Metrics. . . . . . . . . . . . . . . . . .  91
       4.6.4. AssertCancel Messages . . . . . . . . . . . . . .  92
       4.6.5. Assert State Macros . . . . . . . . . . . . . . .  93
      4.7. PIM Multicast Border Router Behavior . . . . . . . .  96
       4.7.1. Sources External to the PIM-SM Domain . . . . . .  96
       4.7.2. Sources Internal to the PIM-SM Domain . . . . . .  97
      4.8. PIM Bootstrap and RP Discovery . . . . . . . . . . .  98
       4.8.1. Group-to-RP Mapping . . . . . . . . . . . . . . .  99



Fenner/Handley/Holbrook/Kouvelas                                [Page 3]

INTERNET-DRAFT             Expires: June 2003              December 2002


       4.8.2. Hash Function . . . . . . . . . . . . . . . . . . 100
      4.9. Source-Specific Multicast. . . . . . . . . . . . . . 101
       4.9.1. Protocol Modifications for SSM destination
       addresses. . . . . . . . . . . . . . . . . . . . . . . . 102
       4.9.2. PIM-SSM-only Routers. . . . . . . . . . . . . . . 102
      4.10. PIM Packet Formats. . . . . . . . . . . . . . . . . 104
       4.10.1. Encoded Source and Group Address
       Formats. . . . . . . . . . . . . . . . . . . . . . . . . 105
       4.10.2. Hello Message Format . . . . . . . . . . . . . . 108
       4.10.3. Register Message Format. . . . . . . . . . . . . 110
       4.10.4. RegisterStop Message Format. . . . . . . . . . . 112
       4.10.5. Join/Prune Message Format. . . . . . . . . . . . 112
        4.10.5.1. Group Set Source List Rules . . . . . . . . . 115
        4.10.5.2. Group Set Fragmentation . . . . . . . . . . . 119
       4.10.6. Assert Message Format. . . . . . . . . . . . . . 119
      4.11. PIM Timers. . . . . . . . . . . . . . . . . . . . . 121
      4.12. Timer Values. . . . . . . . . . . . . . . . . . . . 122
     5. IANA Considerations . . . . . . . . . . . . . . . . . . 128
      5.1. PIM Address Family . . . . . . . . . . . . . . . . . 128
      5.2. PIM Hello Options. . . . . . . . . . . . . . . . . . 129
     6. Security Considerations . . . . . . . . . . . . . . . . 129
      6.1. Attacks based on forged messages . . . . . . . . . . 129
       6.1.1. Forged link-local messages. . . . . . . . . . . . 129
       6.1.2. Forged unicast messages . . . . . . . . . . . . . 130
      6.2. Non-cryptographic Authentication Mechanisms. . . . . 130
      6.3. Authentication using IPsec . . . . . . . . . . . . . 131
       6.3.1. Protecting link-local multicast messages. . . . . 131
       6.3.2. Protecting unicast messages . . . . . . . . . . . 132
        6.3.2.1. Register messages. . . . . . . . . . . . . . . 132
        6.3.2.2. Register Stop messages . . . . . . . . . . . . 132
      6.4. Denial of Service Attacks. . . . . . . . . . . . . . 133
     7. Authors' Addresses. . . . . . . . . . . . . . . . . . . 133
     8. Acknowledgments . . . . . . . . . . . . . . . . . . . . 134
     9. References. . . . . . . . . . . . . . . . . . . . . . . 134
     10. Index. . . . . . . . . . . . . . . . . . . . . . . . . 136



                            List of Figures


     Figure 1. Per-(S,G) register state-machine at a DR . . . .  36
     Figure 2. Downstream (*,*,RP) per-interface
     state-machine. . . . . . . . . . . . . . . . . . . . . . .  42
     Figure 3. Downstream (*,G) per-interface
     state-machine. . . . . . . . . . . . . . . . . . . . . . .  46
     Figure 4. Downstream per-interface (S,G)
     state-machine. . . . . . . . . . . . . . . . . . . . . . .  50



Fenner/Handley/Holbrook/Kouvelas                                [Page 4]

INTERNET-DRAFT             Expires: June 2003              December 2002


     Figure 5. Downstream per-interface (S,G,rpt)
     state-machine. . . . . . . . . . . . . . . . . . . . . . .  53
     Figure 6. Upstream (*,*,RP) state-machine. . . . . . . . .  58
     Figure 7. Upstream (*,G) state-machine . . . . . . . . . .  62
     Figure 8. Upstream (S,G) state-machine . . . . . . . . . .  67
     Figure 9. Upstream (S,G,rpt) state-machine for trig-
     gered messages . . . . . . . . . . . . . . . . . . . . . .  72
     Figure 10. Per-interface (S,G) Assert
     State-machine. . . . . . . . . . . . . . . . . . . . . . .  78
     Figure 11. (*,G) Assert State-machine. . . . . . . . . . .  85









































Fenner/Handley/Holbrook/Kouvelas                                [Page 5]

INTERNET-DRAFT             Expires: June 2003              December 2002


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 interface (LAN or otherwise) using a simple election process.





Fenner/Handley/Holbrook/Kouvelas                  Section 2.1.  [Page 6]

INTERNET-DRAFT             Expires: June 2003              December 2002


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, the MRIB is
      used to decide where to send Join/Prune messages.  A secondary
      function of the MRIB is to provide routing metrics for destination
      addresses, these metrics are used when sending and processing
      Assert messages.

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

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

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

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

Downstream
      Away from the root of the tree.

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.



Fenner/Handley/Holbrook/Kouvelas                  Section 2.2.  [Page 7]

INTERNET-DRAFT             Expires: June 2003              December 2002


NULL
    is the empty set or list.

In addition we use C-like syntax:

=   denotes assignment of a variable.

==  denotes a comparison for equality.

!=  denotes a comparison for inequality.

Braces { and } are used for grouping.


3.  PIM-SM Protocol Overview

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

PIM relies on an underlying topology-gathering protocol to populate a
routing table with routes.  This routing table is called the MRIB or
Multicast Routing Information Base.  The routes in this table may be
taken directly from the unicast routing table, or it may be different
and provided by a separate routing protocol such as MBGP [1]. Regardless
of how it is created, the primary role of the MRIB in the PIM protocol
is to provide the next hop router along a multicast-capable path to each
destination subnet.  The MRIB is used to determine the next hop neighbor
to which any PIM Join/Prune message is sent.  Data flows along the
reverse path of the Join messages.  Thus, in contrast to the unicast RIB
which specifies the next hop that a data packet would take to get to
some subnet, the MRIB gives reverse-path information, and indicates the
path that a multicast data packet would take from its origin subnet to
the router that has the MRIB.

Like all multicast routing protocols that implement the service model
from RFC 1112 [3], PIM-SM must be able to route data packets from
sources to receivers without either the sources or receivers knowing a-
priori of the existence of the others.  This is essentially done in
three phases, although as senders and receivers may come and go at any
time, all three phases may 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 [6] or MLD [4], but other mechanisms might also serve this purpose.
One of the receiver's local routers is elected as the Designated Router



Fenner/Handley/Holbrook/Kouvelas                    Section 3.  [Page 8]

INTERNET-DRAFT             Expires: June 2003              December 2002


(DR) for that subnet.  On receiving the receiver's expression of
interest, the DR then sends a PIM Join message towards the RP for that
multicast group.  This Join message is known as a (*,G) Join because it
joins group G for all sources to that group.  The (*,G) Join travels
hop-by-hop towards the RP for the group, and in each router it passes
through, multicast tree state for group G is instantiated.  Eventually
the (*,G) Join either reaches the RP, or reaches a router that already
has (*,G) Join state for that group.  When many receivers join the
group, their Join messages converge on the RP, and form a distribution
tree for group G that is rooted at the RP.  This is known as the RP Tree
(RPT), and is also known as the shared tree because it is shared by all
sources sending to that group.  Join messages are resent periodically so
long as the receiver remains in the group.  When all receivers on a
leaf-network leave the group, the DR will send a PIM (*,G) Prune message
towards the RP for that multicast group. However if the Prune message is
not sent for any reason, the state will eventually time out.

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

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


Phase Two: Register Stop

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

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

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



Fenner/Handley/Holbrook/Kouvelas                    Section 3.  [Page 9]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

While the RP is in the process of joining the source-specific tree for
S, the data packets will continue being encapsulated to the RP.  When
packets from S also start to arrive natively at the the RP, the RP will
be receiving two copies of each of these packets.  At this point, the RP
starts to discard the encapsulated copy of these packets, and it sends a
RegisterStop 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 router on the receiver's LAN, typically the
DR, may optionally initiate a transfer from the shared tree to a source-
specific shortest-path tree (SPT).  To do this, it issues an (S,G) Join
towards S.  This instantiates 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



Fenner/Handley/Holbrook/Kouvelas                   Section 3.  [Page 10]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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


Source-specific Joins

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

The range of multicast addresses from 232.0.0.0 to 232.255.255.255 is
currently set aside for source-specific multicast in IPv4.  For groups
in this range, receivers should only issue source-specific IGMPv3 joins.
If a PIM router receives a non-source-specific join for a group in this
range, it should ignore it, as described in Section 4.9.

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



Fenner/Handley/Holbrook/Kouvelas                   Section 3.  [Page 11]

INTERNET-DRAFT             Expires: June 2003              December 2002


  entries regarding how to reach the RP.  Both paths on the RP tree will
  be set up, causing two copies of all the shared tree traffic to appear
  on the LAN.

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

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

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

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

RP Discovery

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

One dynamic way to do this is to use the Bootstrap Router (BSR)
mechanism [7]. One router in each PIM domain is elected the Bootstrap
Router through a simple election process.  All the routers in the domain
that are configured to be candidates to be RPs periodically unicast
their candidacy to the BSR.  From the candidates, the BSR picks an RP-
set, and periodically announces this set in a Bootstrap message.
Bootstrap messages are flooded hop-by-hop throughout the domain until
all routers in the domain know the RP-Set.





Fenner/Handley/Holbrook/Kouvelas                   Section 3.  [Page 12]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

4.  Protocol Specification

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

o Section 4.1 details the protocol state stored.

o Section 4.2 specifies the data packet forwarding rules.

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

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

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

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

o Section 4.8 specifies the RP discovery mechanisms.

o The subset of PIM required to support Source-Specific Multicast, PIM-
  SSM, is described in Section 4.9.

o PIM packet formats are specified in Section 4.10.

o A summary of PIM-SM timers and their default values is given in
  Section 4.11.

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.



Fenner/Handley/Holbrook/Kouvelas                 Section 4.1.  [Page 13]

INTERNET-DRAFT             Expires: June 2003              December 2002


This is actually an abstract state definition, which is needed in order
to specify the router's behavior.  A PIM-SM implementation is free to
hold whatever internal state it requires, and will still be conformant
with this specification so long as it results in the same externally
visible protocol behavior as an abstract router that holds the following
state.

We divide TIB state into four sections:

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

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

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

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

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

4.1.1.  General Purpose State

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

     For each interface:

          o Override Interval

          o Propagation Delay

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

          Neighbor State:

            For each neighbor:




Fenner/Handley/Holbrook/Kouvelas               Section 4.1.1.  [Page 14]

INTERNET-DRAFT             Expires: June 2003              December 2002


                 o Information from neighbor's Hello

                 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

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

4.1.2.  (*,*,RP) State

For every RP a router keeps the following state:

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

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

                    o State: One of {"NoInfo" (NI), "Join" (J),
                      "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
4.5.1.

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,



Fenner/Handley/Holbrook/Kouvelas               Section 4.1.2.  [Page 15]

INTERNET-DRAFT             Expires: June 2003              December 2002


then we need to trigger a new Join(*,*,RP) to the new upstream neighbor
and a Prune(*,*,RP) to the old upstream neighbor.  Similarly, if a
router detects through a changed GenID in a Hello message that the
upstream neighbor towards the RP has rebooted, then it should re-
instantiate state by sending a Join(*,*,RP).  These mechanisms are
specified in Section 4.5.5.

4.1.3.  (*,G) State

For every group G a router keeps the following state:

     (*,G) state:
          For each interface:

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

               PIM (*,G) Join/Prune State:

                    o State: One of {"NoInfo" (NI), "Join" (J),
                      "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 or MLD) running on that interface.  It need not be kept if this
router is not the DR on that interface unless this router won a (*,G)



Fenner/Handley/Holbrook/Kouvelas               Section 4.1.3.  [Page 16]

INTERNET-DRAFT             Expires: June 2003              December 2002


assert on this interface for this group, although implementations may
optionally keep this state in case they become the DR or assert winner.
We recommend storing this information if possible, as it reduces latency
converging to stable operating conditions after a failure causing a
change of DR.  This information is used by the pim_include(*,G) macro
described in section 4.1.6.

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

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

The upstream (*,G) Join/Prune 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
4.8) then state must be torn down and rebuilt for groups whose RP
changes.

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

4.1.4.  (S,G) State

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

     (S,G) state:

          For each interface:

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

               PIM (S,G) Join/Prune State:





Fenner/Handley/Holbrook/Kouvelas               Section 4.1.4.  [Page 17]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

                    o Prune Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

               (S,G) Assert Winner State

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

                    o Assert Timer (AT)

                    o Assert winner's IP Address

                    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.  However, we recommend storing this information if
possible, as it reduces latency converging to stable operating
conditions after a failure causing a change of DR.  This information is
used by the pim_include(S,G) macro described in section 4.1.6.

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.1.4.  [Page 18]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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:




Fenner/Handley/Holbrook/Kouvelas               Section 4.1.5.  [Page 19]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

                    o Override Timer (OT)

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

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

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

4.1.6.  State Summarization Macros

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

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.





Fenner/Handley/Holbrook/Kouvelas               Section 4.1.6.  [Page 20]

INTERNET-DRAFT             Expires: June 2003              December 2002


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).

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) =



Fenner/Handley/Holbrook/Kouvelas               Section 4.1.6.  [Page 21]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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 Join or PrunePending }

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.1.6.  [Page 22]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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

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

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

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



The following pseudocode macro definitions are also used in many places
in the specification.  Basically RPF' is the RPF neighbor towards an RP
or source unless a PIM-Assert has overridden the normal choice of
neighbor.











Fenner/Handley/Holbrook/Kouvelas               Section 4.1.6.  [Page 23]

INTERNET-DRAFT             Expires: June 2003              December 2002


  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)
      }
  }


  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 4.5.8).

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 4.6.1) for (S,G) on Interface I is in "I am Assert Loser" state.

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.1.6.  [Page 24]

INTERNET-DRAFT             Expires: June 2003              December 2002


4.2.  Data Packet Forwarding Rules

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

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

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

Second, we check to see if the 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 restart the (S,G) state keepalive timer.

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

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















Fenner/Handley/Holbrook/Kouvelas                 Section 4.2.  [Page 25]

INTERNET-DRAFT             Expires: June 2003              December 2002


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)
 oiflist = NULL

 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)
   CheckSwitchToSpt(S,G)
 } 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

This pseudocode employs several "macro" definitions:

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

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

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.



Fenner/Handley/Holbrook/Kouvelas                 Section 4.2.  [Page 26]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

Keepalive_Period is defined in Section 4.11.

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


4.2.1.  Last hop switchover to the SPT

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

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


     void
     CheckSwitchToSpt(S,G) {
       if ( ( pim_include(*,G) (-) pim_exclude(S,G)
              (+) pim_include(S,G) != NULL )
            AND SwitchToSptDesired(S,G) ) {
              restart KeepAliveTimer(S,G);
       }
     }


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


4.2.2.  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



Fenner/Handley/Holbrook/Kouvelas               Section 4.2.2.  [Page 27]

INTERNET-DRAFT             Expires: June 2003              December 2002


on (*,*,RP)/(*,G) state.  This prevents temporary black-holes that would
be caused by sending a Prune(S,G,rpt) before the upstream (S,G) state
has finished being established.

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


     void
     Update_SPTbit(S,G,iif) {
       if ( iif == RPF_interface(S)
             AND JoinDesired(S,G) == TRUE
             AND ( DirectlyConnected(S) == TRUE
                   OR RPF_interface(S) != RPF_interface(RP)
                   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 receives an
Assert(S,G) on RPF_interface(S).

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

Basically Update_SPTbit will set the 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.



Fenner/Handley/Holbrook/Kouvelas               Section 4.2.2.  [Page 28]

INTERNET-DRAFT             Expires: June 2003              December 2002


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


4.3.  Designated Routers (DR) and Hello Messages

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

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


4.3.1.  Sending Hello Messages

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

Hello messages MUST be sent on all active interfaces, including physical
point-to-point links, and are multicast to address 224.0.0.13 (the ALL-
PIM-ROUTERS group).

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

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.3.1.  [Page 29]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

The LAN_Prune_Delay Option SHOULD be included in all Hello messages sent
on multi-access LANs. This option advertises a router's capability to
use values other than the default for the Propagation_Delay and
Override_Interval which affect the setting of the Prune Pending,
Upstream Join and Override Timers (defined in section 4.11).

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

Before an interface goes down or changes IP address, a Hello message
with a zero HoldTime should be sent immediately (with the old IP address
if the IP address changed).  This will cause PIM neighbors to remove
this neighbor (or its old IP address) immediately.



Fenner/Handley/Holbrook/Kouvelas               Section 4.3.1.  [Page 30]

INTERNET-DRAFT             Expires: June 2003              December 2002


4.3.2.  DR Election

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

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

     neighbor.ip_address
          The IP address of the PIM neighbor.

     neighbor.genid
          The Generation ID of the PIM neighbor.

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

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

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

Neighbor state is deleted when the neighbor timeout expires.

The function for computing the DR on interface I is:

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






Fenner/Handley/Holbrook/Kouvelas               Section 4.3.2.  [Page 31]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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


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
on an interface can change when a PIM-Hello message is received, when a
neighbor times out, or when a router's own DR priority changes.  If the
router becomes the DR or ceases to be the DR, this will normally cause
the DR Register state-machine to change state.  Subsequent actions are
determined by that state-machine.

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


4.3.3.  Reducing Prune Propagation Delay on LANs

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

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.3.3.  [Page 32]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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


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

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

When all routers on a link are in a position to negotiate a different
than default Propagation Delay, the largest value from those advertised



Fenner/Handley/Holbrook/Kouvelas               Section 4.3.3.  [Page 33]

INTERNET-DRAFT             Expires: June 2003              December 2002


by each neighbor is chosen. The function for computing the Propagation
Delay of interface I is:

  time_interval
  Propagation_Delay(I) {
      if ( lan_delay_enabled(I) == false ) {
          return LAN_delay_default
      }
      delay = 0
      for each neighbor on interface I {
          if ( neighbor.lan_delay > delay ) {
              delay = neighbor.lan_delay
          }
      }
      return delay
  }


To avoid synchronization of override messages when multiple downstream
routers share a multi-access link, sending of such messages is delayed
by a small random amount of time. The period of randomization should
represent the size of the PIM router population on the link.  Each
router expresses its view of the amount of randomization necessary in
the Override Delay field of the LAN Prune Delay option.

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

  time_interval
  Override_Interval(I) {
      if ( lan_delay_enabled(I) == false ) {
          return t_override_default
      }
      delay = 0
      for each neighbor on interface I {
          if ( neighbor.override_interval > delay ) {
              delay = neighbor.override_interval
          }
      }
      return delay
  }


Although the mechanisms are not specified in this document, it is
possible for upstream routers to explicitly track the join membership of
individual downstream routers if Join suppression is disabled.  A router



Fenner/Handley/Holbrook/Kouvelas               Section 4.3.3.  [Page 34]

INTERNET-DRAFT             Expires: June 2003              December 2002


can advertise its willingness to disable Join suppression by using the T
bit in the LAN Prune Delay Hello option. Unless all PIM routers on a
link negotiate this capability, explicit tracking and the disabling of
the Join suppression mechanism are not possible. The function for
computing the state of Suppression on interface I is:

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

Note that the setting of Suppression_Enabled(I) affects the value of
t_suppressed (see section 4.11).

4.4.  PIM Register Messages

Overview

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


4.4.1.  Sending Register Messages from the DR

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.4.1.  [Page 35]

INTERNET-DRAFT             Expires: June 2003              December 2002


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.






























Fenner/Handley/Holbrook/Kouvelas               Section 4.4.1.  [Page 36]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

+-----------++------------------------------------------------------------------------------------------+
|           ||                                          Event                                           |
|           ++------------------+------------------+----------------------+--------------+--------------+
|Prev State ||Register-Stop     |Could-Register    | Could-Register       |Register-     |RP changed    |
|           ||Timer expires     |->True            | ->False              |Stop          |              |
|           ||                  |                  |                      |received      |              |
+-----------++------------------+------------------+----------------------+--------------+--------------+
|No Info    ||-                 |-> J state        | -                    |-             |-             |
|(NI)       ||                  |add reg tunnel    |                      |              |              |
+-----------++------------------+------------------+----------------------+--------------+--------------+
|           ||-                 |-                 | -> NI state          |-> P state    |-> J state    |
|           ||                  |                  | remove reg tunnel    |remove        |update reg    |
|           ||                  |                  |                      |tunnel;       |tunnel        |
|Join (J)   ||                  |                  |                      |set           |              |
|           ||                  |                  |                      |Register-     |              |
|           ||                  |                  |                      |Stop          |              |
|           ||                  |                  |                      |timer(*)      |              |
+-----------++------------------+------------------+----------------------+--------------+--------------+
|           ||-> J state        |-                 | -> NI state          |-> P state    |-> J state    |
|Join       ||add reg tunnel    |                  | remove reg tunnel    |set           |add reg       |
|Pending    ||                  |                  |                      |Register-     |tunnel;       |
|(JP)       ||                  |                  |                      |Stop          |cancel        |
|           ||                  |                  |                      |timer(*)      |Register-     |
|           ||                  |                  |                      |              |Stop timer    |
+-----------++------------------+------------------+----------------------+--------------+--------------+
|           ||-> JP state       |-                 | -> NI state          |-             |-> J state    |
|           ||set Register-     |                  | remove reg tunnel    |              |add reg       |
|Prune (P)  ||Stop              |                  |                      |              |tunnel;       |
|           ||timer(**);        |                  |                      |              |cancel        |
|           ||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 *
     Register_Suppression_Time) minus Register_Probe_Time;

     Subtracting off Register_Probe_Time is a bit unnecessary because it
     is really small compared to Register_Suppression_Time, but was in
     the old spec and is kept for compatibility.

(**) The RegisterStopTimer is set to Register_Probe_Time.





Fenner/Handley/Holbrook/Kouvelas               Section 4.4.1.  [Page 37]

INTERNET-DRAFT             Expires: June 2003              December 2002


The following actions are defined:

Add Register Tunnel

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

Remove Register Tunnel

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

Update Register Tunnel

This action occurs when RP(G) changes.

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

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

CouldRegister(S,G)

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

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


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.



Fenner/Handley/Holbrook/Kouvelas               Section 4.4.1.  [Page 38]

INTERNET-DRAFT             Expires: June 2003              December 2002


Encapsulating data packets in the Register Tunnel

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

In IPv6, an ICMP Fragmentation Required message may be sent by the
encapsulating DR.

Just like any forwarded packet, the TTL of the original data packet is
decremented before it is encapsulated in the Register Tunnel.

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

The Diffserv Code Point (DSCP) should be copied from the original packet
to the IP header of the encapsulating packet.  It MAY be set
independently by the encapsulating router, based upon static
configuration or traffic classification.  See [2] for more discussion on
setting the DSCP on tunnels.

Handling RegisterStop(*,G) Messages at the DR

An old RP might 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.







Fenner/Handley/Holbrook/Kouvelas               Section 4.4.2.  [Page 39]

INTERNET-DRAFT             Expires: June 2003              December 2002


4.4.2.  Receiving Register Messages at the RP

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

packet_arrives_on_rp_tunnel( pkt ) {
    if( outer.dst is not one of my addresses ) {
        drop the packet silently.
        # note 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;



Fenner/Handley/Holbrook/Kouvelas               Section 4.4.2.  [Page 40]

INTERNET-DRAFT             Expires: June 2003              December 2002


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 RegisterStop timer expires at the DR.

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

Just like any forwarded packet, the TTL of the original data packet is
decremented after it is decapsulated from the Register Tunnel.

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

The Diffserv Code Point (DSCP) should be copied from the IP header of
the Register packet to the decapsulated packet.  The RP MAY retain the
DSCP of the inner packet, or re-classify the packet and apply a
different DSCP.  Scenarios where each of these might be useful are
discussed in [2].

4.5.  PIM Join/Prune Messages

A PIM Join/Prune message consists of a list of groups and a list of
Joined and Pruned sources for each group.  When processing a received
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, (*,G) Joins and Prunes can
affect both the (*,G) and (S,G,rpt) downstream state machines, while
(*,*,RP), (S,G) and (S,G,rpt) Joins and Prunes can only affect their
respective downstream state machines.  When considering a Join/Prune
message whose PIM Destination field addresses another router, most Join
or Prune messages could affect each upstream state machine.

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

We note that some older PIM implementations incorrectly fail to send
Hello messages on point-to-point interfaces, so we also RECOMMEND that a
configuration option be provided to allow interoperation with such older



Fenner/Handley/Holbrook/Kouvelas                 Section 4.5.  [Page 41]

INTERNET-DRAFT             Expires: June 2003              December 2002


routers, but that this configuration option SHOULD NOT be enabled by
default.


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

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

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

     Join (J)
          The interface has (*,*,RP) Join state which will cause 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 4.5.4) 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.

In addition the state-machine uses two timers:

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

     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 RP.













Fenner/Handley/Holbrook/Kouvelas               Section 4.5.1.  [Page 42]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

+-------------++---------------------------------------------------------+
|             ||                         Event                           |
|             ++-------------+-------------+--------------+--------------+
|Prev State   ||Receive      | Receive     | Prune        | Expiry Timer |
|             ||Join(*,*,RP) | Prune       | Pending      | Expires      |
|             ||             | (*,*,RP)    | Timer        |              |
|             ||             |             | Expires      |              |
+-------------++-------------+-------------+--------------+--------------+
|             ||-> J state   | -> NI state | -            | -            |
|NoInfo (NI)  ||start Expiry |             |              |              |
|             ||Timer        |             |              |              |
+-------------++-------------+-------------+--------------+--------------+
|             ||-> J state   | -> PP state | -            | -> NI state  |
|Join (J)     ||restart      | start Prune |              |              |
|             ||Expiry Timer | Pending     |              |              |
|             ||             | Timer       |              |              |
+-------------++-------------+-------------+--------------+--------------+
|             ||-> J state   | -> PP state | -> NI state  | -> NI state  |
|             ||restart      |             | Send Prune-  |              |
|Prune        ||Expiry       |             | Echo(*,*,RP) |              |
|Pending (PP) ||Timer;       |             |              |              |
|             ||cancel Prune |             |              |              |
|             ||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
such a packet may cause state transitions in other state machines.

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












Fenner/Handley/Holbrook/Kouvelas               Section 4.5.1.  [Page 43]

INTERNET-DRAFT             Expires: June 2003              December 2002


Transitions from NoInfo State

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

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

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

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

Transitions from Join State

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

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

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

     Receive Prune(*,*,RP)
          A Prune(*,*,RP) is received on interface I with its Upstream
          Neighbor Address set to the router's 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(I) if the
          router has more than one neighbor on that interface; otherwise
          it is set to zero causing it to expire immediately.

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.1.  [Page 44]

INTERNET-DRAFT             Expires: June 2003              December 2002


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 Upstream
          Neighbor Address 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, set to maximum of its current value and
          the HoldTime from the triggering Join/Prune message.

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

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

     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 on a LAN with its own address in
          the Upstream Neighbor Address field.  Its purpose is to add
          additional reliability so that if a Prune that should have
          been overridden by another router is lost locally on the LAN,
          then the PruneEcho may be received and cause the override to
          happen.  A PruneEcho(*,*,RP) need not be sent on an interface
          containing only one PIM neighbor.


4.5.2.  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
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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.2.  [Page 45]

INTERNET-DRAFT             Expires: June 2003              December 2002


(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 4.5.4)
          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.


















Fenner/Handley/Holbrook/Kouvelas               Section 4.5.2.  [Page 46]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

+-------------++--------------------------------------------------------+
|             ||                         Event                          |
|             ++-------------+-------------+-------------+--------------+
|Prev State   ||Receive      | Receive     | Prune       | Expiry Timer |
|             ||Join(*,G)    | Prune(*,G)  | Pending     | Expires      |
|             ||             |             | Timer       |              |
|             ||             |             | Expires     |              |
+-------------++-------------+-------------+-------------+--------------+
|             ||-> J state   | -> NI state | -           | -            |
|NoInfo (NI)  ||start Expiry |             |             |              |
|             ||Timer        |             |             |              |
+-------------++-------------+-------------+-------------+--------------+
|             ||-> J state   | -> PP state | -           | -> NI state  |
|Join (J)     ||restart      | start Prune |             |              |
|             ||Expiry Timer | Pending     |             |              |
|             ||             | Timer       |             |              |
+-------------++-------------+-------------+-------------+--------------+
|             ||-> J state   | -> PP state | -> NI state | -> NI state  |
|             ||restart      |             | Send Prune- |              |
|Prune        ||Expiry       |             | Echo(*,G)   |              |
|Pending (PP) ||Timer;       |             |             |              |
|             ||cancel 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 message
it sent over that interface.  However on point-to-point links we also
recommend that PIM messages with a destination address of all zeros are
also accepted.

Transitions from NoInfo State

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

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




Fenner/Handley/Holbrook/Kouvelas               Section 4.5.2.  [Page 47]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

Transitions from Join State

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

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

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

     Receive Prune(*,G)
          A Prune(*,G) is received on interface I with its Upstream
          Neighbor Address set to the router's 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(I) if the router has
          more than one neighbor on that interface; otherwise it is set
          to zero causing it to expire immediately.

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

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

Transitions from 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 Upstream
          Neighbor Address 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, set to maximum of its current value and the
          HoldTime from the triggering Join/Prune message.



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.2.  [Page 48]

INTERNET-DRAFT             Expires: June 2003              December 2002


     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 on a LAN with its own address in the Upstream
          Neighbor Address field.  Its purpose is to add additional
          reliability so that if a Prune that should have been
          overridden by another router is lost locally on the LAN, then
          the PruneEcho may be received and cause the override to
          happen.  A PruneEcho(*,G) need not be sent on an interface
          containing only one PIM neighbor.

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

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

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

     Join (J)
          The interface has (S,G) Join state which will cause 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.



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.3.  [Page 49]

INTERNET-DRAFT             Expires: June 2003              December 2002


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 this state machine to revert to
          NoInfo state.

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

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

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

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 message



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.3.  [Page 50]

INTERNET-DRAFT             Expires: June 2003              December 2002


it sent over that interface.  However on point-to-point links we also
recommend that PIM messages with a destination address of all zeros 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 Upstream
          Neighbor Address 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/Prune message.

Transitions from Join State

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

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

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

     Receive Prune(S,G)
          A Prune(S,G) is received on interface I with its Upstream
          Neighbor Address set to the router's 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(I) if the router has
          more than one neighbor on that interface; otherwise it is set
          to zero causing it to expire immediately.

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

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






Fenner/Handley/Holbrook/Kouvelas               Section 4.5.3.  [Page 51]

INTERNET-DRAFT             Expires: June 2003              December 2002


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 Upstream
          Neighbor Address 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, set to maximum of its current value and the
          HoldTime from the triggering Join/Prune message.

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

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

     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 on a LAN with its own address in the Upstream
          Neighbor Address field.  Its purpose is to add additional
          reliability so that if a Prune that should have been
          overridden by another router is lost locally on the LAN, then
          the PruneEcho may be received and cause the override to
          happen.  A PruneEcho(S,G) need not be sent on an interface
          containing only one PIM neighbor.

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

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.4.  [Page 52]

INTERNET-DRAFT             Expires: June 2003              December 2002


          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.

     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.





Fenner/Handley/Holbrook/Kouvelas               Section 4.5.4.  [Page 53]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.4.  [Page 54]

INTERNET-DRAFT             Expires: June 2003              December 2002


occur, although seeing such a packet may cause state transitions in
other state machines.

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

Transitions from NoInfo State

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

     Receive Prune(S,G,rpt)
          A Prune(S,G,rpt) is received on interface I with its Upstream
          Neighbor Address set to the router's 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/Prune message.  The PrunePending timer is started; it is
          set to the J/P_Override_Interval(I) if the router has more
          than one neighbor on that interface; otherwise it is set to
          zero causing it to expire immediately.

Transitions from PrunePending State

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

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

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.4.  [Page 55]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

     Receive Prune(S,G,rpt)
          A Prune(S,G,rpt) is received on interface I with its Upstream
          Neighbor Address set to the router's 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
          maximum of its current value and the HoldTime from the
          triggering Join/Prune message.

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

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

Transitions from PrunePendingTmp State

When in PrunePendingTmp (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).



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.4.  [Page 56]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

Transitions from PruneTmp State

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

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

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

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

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

Notes:

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

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







Fenner/Handley/Holbrook/Kouvelas               Section 4.5.4.  [Page 57]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

Not Joined
     The downstream state-machines indicate that the router does not
     need to join the (*,*,RP) tree for this RP.

Joined
     The downstream state-machines indicate that the router would like
     to join the (*,*,RP) tree for this RP.

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

















Fenner/Handley/Holbrook/Kouvelas               Section 4.5.5.  [Page 58]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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




Fenner/Handley/Holbrook/Kouvelas               Section 4.5.5.  [Page 59]

INTERNET-DRAFT             Expires: June 2003              December 2002


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)




Fenner/Handley/Holbrook/Kouvelas               Section 4.5.5.  [Page 60]

INTERNET-DRAFT             Expires: June 2003              December 2002


          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.

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

     See Prune(*,*,RP) to MRIB.next_hop(RP)
          This event is only relevant if RPF_interface(RP) is a shared
          medium.  This router sees another router on RPF_interface(RP)
          send a Prune(*,*,RP) to 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.

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

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.5.5.  [Page 61]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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).













Fenner/Handley/Holbrook/Kouvelas               Section 4.5.6.  [Page 62]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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




Fenner/Handley/Holbrook/Kouvelas               Section 4.5.6.  [Page 63]

INTERNET-DRAFT             Expires: June 2003              December 2002


This state machine uses the following macro:

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

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

Transitions from NotJoined State

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

     JoinDesired(*,G) becomes True
          The 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)



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.6.  [Page 64]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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

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

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

     MRIB.next_hop(RP(G)) changes
          An event occurred which caused the next hop towards the RP for
          G to change.  This may be caused by a change in the MRIB
          routing database or by the installation of a different RP-to-
          group mapping.  Note that this transition should occur even if
          RPF'(*,G) is not equal to the new next hop towards RP(G),



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.6.  [Page 65]

INTERNET-DRAFT             Expires: June 2003              December 2002


          because it may be that the new neighbor is a better path to
          RP(G) than RPF'(*,G); this transition ensures that the better
          path is discovered even if an assert occurred previously.

          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 MRIB.next_hop(RP(G)). Note
          that the Join goes to MRIB.next_hop(RP(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.

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

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

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

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:





Fenner/Handley/Holbrook/Kouvelas               Section 4.5.7.  [Page 66]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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



















Fenner/Handley/Holbrook/Kouvelas               Section 4.5.7.  [Page 67]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

This state machine uses the following macro:

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

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






Fenner/Handley/Holbrook/Kouvelas               Section 4.5.7.  [Page 68]

INTERNET-DRAFT             Expires: June 2003              December 2002


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), and set
          SPTbit(S,G) to FALSE.

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

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

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

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

          Let t_joinsuppress be the minimum of t_suppressed and the
          HoldTime from the Join/Prune message triggering this event.
          If the Join Timer is set to expire in less than t_joinsuppress



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.7.  [Page 69]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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

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

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.7.  [Page 70]

INTERNET-DRAFT             Expires: June 2003              December 2002


          seconds, leave it unchanged.

     MRIB.next_hop(S) changes
          A change in the routing base stored in the MRIB causes the
          next hop towards S to change.

          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 MRIB.next_hop(S).  Note
          that the Join goes to MRIB.next_hop(S) 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 MRIB.next_hop(S) to have
          a better path to S than RPF'(S,G); sending to MRIB.next_hop(S)
          ensures that this is discovered.  Set the Join Timer (JT) to
          expire after t_periodic seconds.

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

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

4.5.8.  (S,G,rpt) Periodic Messages

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













Fenner/Handley/Holbrook/Kouvelas               Section 4.5.8.  [Page 71]

INTERNET-DRAFT             Expires: June 2003              December 2002


  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
  }


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


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

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

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


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.







Fenner/Handley/Holbrook/Kouvelas               Section 4.5.9.  [Page 72]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

+--------------++------------------------------------------------------------------+
|              ||                              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)    |                   |                 |
+--------------++-------------+--------------+-------------------+-----------------+
|              ||-> P state   | -            | -> NJ state       | -               |
|NotPruned     ||Send Prune   |              | Cancel OT timer   |                 |
|(S,G,rpt)     ||(S,G,rpt);   |              |                   |                 |
|(NP)          ||Cancel 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 =    |Cancel OT     |OT timer =   | OT timer =   |
|(S,G,rpt);  |min(timer,    |timer         |min(timer,   | min(timer,   |
|Cancel OT   |t_override)   |              |t_override)  | t_override)  |
|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_override) = t_override).








Fenner/Handley/Holbrook/Kouvelas               Section 4.5.9.  [Page 73]

INTERNET-DRAFT             Expires: June 2003              December 2002


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.





Fenner/Handley/Holbrook/Kouvelas               Section 4.5.9.  [Page 74]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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

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

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.5.9.  [Page 75]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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

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

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

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









Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 76]

INTERNET-DRAFT             Expires: June 2003              December 2002


4.6.  PIM Assert Messages

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

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

4.6.1.  (S,G) Assert Message State Machine

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

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

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

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.



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 77]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

+-----------------------------------------------------------------------+
|                         In NoInfo (NI) State                          |
+---------------+-------------------+------------------+----------------+
| Receive       |  Receive Assert   |  Data arrives    |  Receive       |
| Inferior      |  with RPTbit      |  from S to G on  |  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      | Receive      | Timer        | Current      |
|Preferred    | Acceptable   | Inferior     | Expires      | Winner's     |
|Assert       | Assert from  | Assert from  |              | GenID        |
|             | Current      | Current      |              | changes      |
|             | Winner       | Winner       |              |              |
+-------------+--------------+--------------+--------------+--------------+
|-> L state   | -> L state   | -> NI state  | -> NI state  | -> NI state  |
|[Actions A2] | [Actions A2] | [Actions A5] | [Actions A5] | [Actions A5] |
+-------------+--------------+--------------+--------------+--------------+











Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 78]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

     An "acceptable assert" is one that has a better metric than
     my_assert_metric(S,G,I).

     An "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(*,*,RP(G)) (+) joins(*,G) (-) prunes(S,G,rpt) )
                 (+) ( pim_include(*,G) (-) pim_exclude(S,G) )
                 (-) lost_assert(*,G)
                 (+) joins(S,G) (+) pim_include(S,G) ) )

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














Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 79]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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

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

Transitions from NoInfo State

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 80]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

     Receive 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 A6
          (below).

Transitions from "I am Assert 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).



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 81]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

Transitions from "I am Assert Loser" State

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

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

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

     Receive Inferior Assert 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 (action A5
          below).

     Current Winner's GenID Changes
          We receive a Hello message from the current winner reporting a
          different GenID from the one it previously reported.  This
          indicates that the current winner's interface or router has
          gone down and come back up, and so we must assume it no longer



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 82]

INTERNET-DRAFT             Expires: June 2003              December 2002


          knows it was the winner. We transition to the NoInfo state,
          deleting this (S,G) assert information (action A5 below).

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

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

     RPF interface 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, deleting this (S,G)
          assert state (action A5 below).

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

(S,G) Assert State-machine Actions

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

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.6.1.  [Page 83]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

     A6:  Store new assert winner as AssertWinner(S,G,I) and assert
          winner metric as AssertWinnerMetric(S,G,I).
          Set timer to Assert_Time
          If I is RPF_interface(S) set SPTbit(S,G) to TRUE.

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

4.6.2.  (*,G) Assert Message State Machine

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

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

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

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

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.





Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 84]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

It is important to note that NO TRANSITION CAN OCCUR in the (*,G) state
machine as a result of receiving an Assert message unless the (S,G)
assert state machine for the relevant S and G is in the "NoInfo" state
after the (S,G) state machine has processed the message.  Also NO
TRANSITION CAN OCCUR in the (*,G) state machine as a result of receiving
an assert message if that message triggers any change of state in the
(S,G) state machine.

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

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


























Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 85]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

+-----------------------------------------------------------------------+
|                         In NoInfo (NI) State                          |
+-----------------------+-----------------------+-----------------------+
| Receive Inferior      |  Data arrives for G   |   Receive Preferred   |
| Assert with RPTbit    |  and CouldAssert      |   Assert with RPTbit  |
| set and               |  (*,G,I)              |   set and AssTrDes    |
| CouldAssert(*,G,I)    |                       |   (*,G,I)             |
+-----------------------+-----------------------+-----------------------+
| -> W state            |  -> W state           |   -> L 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      | Receive      | Timer        | Current      |
|Preferred    | Acceptable   | Inferior     | Expires      | Winner's     |
|Assert       | Assert from  | Assert from  |              | GenID        |
|             | Current      | Current      |              | Changes      |
|             | Winner       | Winner       |              |              |
+-------------+--------------+--------------+--------------+--------------+
|-> L state   | -> L state   | -> NI state  | -> NI state  | -> NI state  |
|[Actions A2] | [Actions A2] | [Actions A5] | [Actions A5] | [Actions A5] |
+-------------+--------------+--------------+--------------+--------------+

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 86]

|               |                 |                 |                   |
|               |                 |                 |                   |
|               |                 |                 |                   |
INTERNET-DRAFT  |          Expires: June 2003       |      December 2002|
|               |                 |                 |                   |
|               |                 |                 |                   |
+---------------+-----------------+-----------------+-------------------+


The state machine uses the following macros:

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

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

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

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

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

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

     An "acceptable assert" is one that has a better metric than
     my_assert_metric(S,G,I).

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 87]

INTERNET-DRAFT             Expires: June 2003              December 2002


          (below).

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

     Receive 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 "I am Assert Winner" State

When in "I am Assert Winner" state, the following events trigger
transitions, but only if the (S,G) assert state machine is in NoInfo
state:

     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).





Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 88]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

Transitions from "I am Assert Loser" State

When in "I am Assert Loser" state, the following events trigger
transitions, but only if the (S,G) assert state machine is in NoInfo
state:

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

     Receive Inferior Assert 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 (action A5), and allow
          the normal PIM Join/Prune mechanisms to operate.  Usually we
          will eventually re-assert and win when data packets for G have
          started flowing again.

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

     Timer Expires
          The (*,G) assert timer expires.  We transition to NoInfo state
          and delete this (*,G) assert info (action A5).

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 89]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

(*,G) Assert State-machine Actions

     A1:  Send Assert(*,G)
          Set timer to (Assert_Time - Assert_Override_Interval)
          Store self as AssertWinner(*,G,I).
          Store rpt_assert_metric(G,I) as AssertWinnerMetric(*,G,I).

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

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

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.2.  [Page 90]

INTERNET-DRAFT             Expires: June 2003              December 2002


          AssertWinnerMetric(*,G,I) will then return their default
          values).

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

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


4.6.3.  Assert Metrics

Assert metrics are defined as:

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


When comparing assert_metrics, the rpt_bit_flag, metric_preference, and
route_metric field are compared in order, where the first lower value
wins.  If all fields are equal, the 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:


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






Fenner/Handley/Holbrook/Kouvelas               Section 4.6.3.  [Page 91]

INTERNET-DRAFT             Expires: June 2003              December 2002


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,0}
  }


4.6.4.  AssertCancel Messages

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





Fenner/Handley/Holbrook/Kouvelas               Section 4.6.4.  [Page 92]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

4.6.5.  Assert State Macros

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

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


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


Note: the term "AssertWinnerMetric(S,G,I) is better than
spt_assert_metric(S,I)" is required to correctly handle the transition
phase when a router has (S,G) join state, but has not yet set the SPT
bit.  In this case it needs to ignore the assert state if it will win
the assert once the SPT bit is set.











Fenner/Handley/Holbrook/Kouvelas               Section 4.6.5.  [Page 93]

INTERNET-DRAFT             Expires: June 2003              December 2002


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


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

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

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

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

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

Summary of Assert Rules and Rationale

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

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

     Rationale: By sending the periodic and triggered Join messages to
     the RPF' neighbor instead of to the RPF neighbor, the downstream
     router avoids re-triggering the Assert process with every Join.  A
     side effect of sending Joins to the Assert winner is that traffic
     will not switch back to the "normal" RPF neighbor until the Assert
     times out.  This will not happen until data stops flowing, if item



Fenner/Handley/Holbrook/Kouvelas               Section 4.6.5.  [Page 94]

INTERNET-DRAFT             Expires: June 2003              December 2002


     8 below is implemented.

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

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

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

     Rationale: Same rationale as for 2.

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

     Rationale: Same as for 1.

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

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

6.   Behavior: An assert loser that receives a Join(S,G) with an
     Upstream Neighbor Address that is one of its addresses on that
     interface cancels the (S,G) assert timer.

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

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

     Rationale: Same as 6.

8.   Behavior: An assert winner for (*,G) or (S,G) sends a canceling
     assert when it is about to stop forwarding on a (*,G) or an (S,G)
     entry.  This behavior does not apply to (S,G,rpt).





Fenner/Handley/Holbrook/Kouvelas               Section 4.6.5.  [Page 95]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

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


4.7.  PIM Multicast Border Router Behavior

In some cases PIM-SM domains will interconnect with non-PIM domains.  In
these cases, the border routers of the PIM domain speak PIM-SM on some
interfaces and speak other multicast routing protocols on other
interfaces.  Such routers are termed PIM Multicast Border Routers or
PMBRs.  In general, RFC 2715 [13] provides rules for interoperability
between different multicast routing protocols.  In this section we
specify how PMBRs differ from regular PIM-SM routers.

>From the point of view of PIM-SM, a PMBR has two tasks:

o To ensure that traffic from sources outside the PIM-SM domain reaches
  receivers inside the domain.

o To ensure that traffic from sources inside the PIM-SM domain reaches
  receives outside the domain.

We note that multiple PIM-SM domains are sometimes connected together
using protocols such as MSDP, which provides information about active
external sources, but does not follow RFC 2715.  In such cases the
domains are not connected via PMBRs because Join(S,G) messages traverse
the border between domains.  A PMBR is required when no PIM messages can
traverse the border; typically this is because the routing protocol in
the neighboring domain is not PIM-SM.

4.7.1.  Sources External to the PIM-SM Domain

A PMBR needs to ensure that traffic from multicast sources external to
the PIM-SM domain reaches receivers inside the domain.  The PMBR will



Fenner/Handley/Holbrook/Kouvelas               Section 4.7.1.  [Page 96]

INTERNET-DRAFT             Expires: June 2003              December 2002


follow the rules in RFC 2715, such that traffic from external sources
reaches the PMBR itself.

According to RFC 2715, the PIM-SM component of the PMBR will receive an
(S,G) Creation event when data from an (S,G) data packet from an
external source first reaches the PMBR.  If RPF_interface(S) is not an
interface in the PIM-SM domain, the packet cannot be originated into the
PIM domain at this router, and the PIM-SM component of the PMBR will not
process the packet.  Otherwise the PMBR will then act exactly as if it
were the DR for this source (see section 4.4.1 with the following
modifications:

o The Border-bit is set in all PIM Register message sent for these
  sources.

o DirectlyConnected(S) is treated as being TRUE for these sources.

o The PIM-SM forwarding rule "iif == RPF_interface(S)" is relaxed to be
  TRUE if iif is any interface that is not part of the PIM-SM component
  of the PMBR (see section 4.2).

4.7.2.  Sources Internal to the PIM-SM Domain

A PMBR needs to ensure that traffic from sources inside the PIM-SM
domain reaches receivers outside the domain.  Using terminology from RFC
2715, there are two possible scenarios for this:

o Another component of the PMBR is a wildcard receiver.  In this case
  the PIM-SM component of the PMBR must ensure that traffic from all
  internal sources reaches the PMBR until it is informed otherwise.

o No other component of the PMBR is a wildcard receiver.  In this case
  the PMBR will receive explicit information as to which groups or
  (source,group) pairs the external domains wish to receive.

In the former case, the PMBR will need to issue send a Join(*,*,RP) to
all the RPs in the PIM-SM domain.  This will cause all traffic in the
domain to reach the PMBR.  The PMBR may then act as if it were a DR with
directly connected receivers, and trigger the transition to a shortest
path tree (see section 4.2.1).

In the latter case, the PMBR will not need to send Join(*,*,RP)
messages.  However the PMBR will still need to act as a DR with directly
connected receivers on behalf of the external receivers in terms of
being able to switch to the shortest-path tree for internally-reached
sources.





Fenner/Handley/Holbrook/Kouvelas               Section 4.7.2.  [Page 97]

INTERNET-DRAFT             Expires: June 2003              December 2002


According to RFC 2715, the PIM-SM component of the PMBR may receive a
number of alerts generated by events in the external routing components.
To implement the above behavior, one reasonable way to map these alerts
into PIM-SM state as follows:

o When a PIM-SM component receives an (S,G) Prune alert, it sets
  local_receiver_include(S,G,I) to FALSE for the discard interface.

o When a PIM-SM component receives a (*,G) Prune alert, it sets
  local_receiver_include(*,G,I) to FALSE for the discard interface.

o When a PIM-SM component receives an (S,G) Join alert, it sets
  local_receiver_include(S,G,I) to TRUE for the discard interface.

o When a PIM-SM component receives a (*,G) Join alert, it sets
  local_receiver_include(*,G,I) to TRUE for the discard interface.

o When a PIM-SM component receives a (*,*) Join alert, it sets
  DownstreamJPState(*,*,RP,I) to Join state on the discard interface for
  all RPs in the PIM-SM domain.

o When a PIM-SM component receives a (*,*) Prune alert, then it sets
  DownstreamJPState(*,*,RP,I) to NoInfo state on the discard interface
  for all RPs in the PIM-SM domain.

We refer above to the discard interface because the macros and state-
machines are interface-specific, but we need to have PIM state that is
not associated with any actual PIM-SM interface. Implementors are free
to implement this in any reasonable manner.

Note that these state changes will then cause additional PIM-SM state
machine transitions in the normal way.


4.8.  PIM Bootstrap and RP Discovery

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

A notable exception to this is where a PIM domain is broken up into
multiple administrative scope regions - these are regions where a border
has been configured so that a range of multicast groups will not be
forwarded across that border.  For more information on Administratively



Fenner/Handley/Holbrook/Kouvelas                 Section 4.8.  [Page 98]

INTERNET-DRAFT             Expires: June 2003              December 2002


Scoped IP Multicast, see RFC 2365.  The modified criteria for admin-
scoped regions are that the region is convex with respect to forwarding
based on the MRIB, and that all PIM routers within the scope region map
scoped groups to the same RP within that region.

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

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

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

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

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

Any RP address configured or learned MUST be a domain-wide reachable
address.


4.8.1.  Group-to-RP Mapping

Using one of the mechanisms described above, a PIM router receives one
or more possible group-range-to-RP mappings.  Each mapping specifies a
range of multicast groups (expressed as a group and mask) and the RP to
which such groups should be mapped.  Each mapping may also have an



Fenner/Handley/Holbrook/Kouvelas               Section 4.8.1.  [Page 99]

INTERNET-DRAFT             Expires: June 2003              December 2002


associated priority.  It is possible to receive multiple mappings all of
which might match the same multicast group - this is the common case
with BSR.  The algorithm for performing the group-to-RP mapping is as
follows:

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

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

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

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

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

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

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

     Implementation note: the bootstrap mechanism described in RFC
     2362 omitted step (1) above.  However of the implementations
     we are are of, approximately half performed step (1) anyway.
     It should be noted that implementations of BSR that omit step
     1 will not correctly interoperate with implementations of this
     specification when used with the BSR mechanism described in
     [7].


4.8.2.  Hash Function

The hash function is used by all routers within a domain, to map a group
to one of the RPs from the matching set of group-range-to-RP mappings



Fenner/Handley/Holbrook/Kouvelas              Section 4.8.2.  [Page 100]

INTERNET-DRAFT             Expires: June 2003              December 2002


(this set all have the same longest mask length and same highest
priority). The algorithm takes as input the group address, and the
addresses of the candidate RPs from the mappings, and gives as output
one RP address to be used.

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

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

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


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

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

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


4.9.  Source-Specific Multicast

The Source-Specific Multicast (SSM) service model [10] 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



Fenner/Handley/Holbrook/Kouvelas                Section 4.9.  [Page 101]

INTERNET-DRAFT             Expires: June 2003              December 2002


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.

4.9.1.  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.

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 RegisterStop 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.

4.9.2.  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:





Fenner/Handley/Holbrook/Kouvelas              Section 4.9.2.  [Page 102]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

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

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

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

o     Packet forwarding rules (Section 4.2)

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


o     Register state machine (Section 4.4)

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

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

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

o     Bootstrap RP Election (Section 4.8)

o     Keepalive Timer

o     SptBit (Section 4.2.2)

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.




Fenner/Handley/Holbrook/Kouvelas              Section 4.9.2.  [Page 103]

INTERNET-DRAFT             Expires: June 2003              December 2002


4.10.  PIM Packet Formats

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

All PIM control messages have IP protocol number 103.

PIM messages are either unicast (e.g.  Registers and RegisterStop), or
multicast with TTL 1 to the `ALL-PIM-ROUTERS' group (e.g. Join/Prune,
Asserts, etc.).  The source address used for unicast messages is a
domain-wide reachable address; the source address used for multicast
messages is the link-local address of the interface on which the message
is being sent.

The IPv4 `ALL-PIM-ROUTERS' group is `224.0.0.13'.  The IPv6 `ALL-PIM-
ROUTERS' group is `ff02::d'.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Ver
     PIM Version number is 2.

Type Types for specific PIM messages.  PIM Types are:


Message Type                          Destination
---------------------------------------------------------------------------
0 = Hello                             Multicast to ALL-PIM-ROUTERS
1 = Register                          Unicast to RP
2 = RegisterStop                      Unicast to source of Register packet
3 = Join/Prune                        Multicast to ALL-PIM-ROUTERS
4 = Bootstrap                         Multicast to ALL-PIM-ROUTERS
5 = Assert                            Multicast to ALL-PIM-ROUTERS
6 = Graft (used in PIM-DM only)       Multicast to ALL-PIM-ROUTERS
7 = Graft-Ack (used in PIM-DM only)   Unicast to source of Graft packet
8 = Candidate-RP-Advertisement        Unicast to Domain's BSR


Reserved
     Set to zero on transmission.  Ignored upon receipt.






Fenner/Handley/Holbrook/Kouvelas               Section 4.10.  [Page 104]

INTERNET-DRAFT             Expires: June 2003              December 2002


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

     For IPv6, the checksum also includes the IPv6 "pseudo-header", as
     specified in RFC 2460, section 8.1 [5]. This "pseudo-header" is
     prepended to the PIM header for the purposes of calculating the
     checksum.  The "Upper-Layer Packet Length" in the pseudo-header is
     set to the length of the PIM message.  The Next Header value used
     in the pseudo-header is 103.  If the packet's length is not an
     integral number of 16-bit words, the packet is padded with a byte
     of zero before performing the checksum.


4.10.1.  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 [8]. Values 128-250 are reserved to be assigned by the
     IANA for PIM-specific Address Families.  Values 251 though 255 are
     designated for private use.  As there is no assignment authority
     for this space, collisions should be expected.

Encoding Type
     The type of encoding used within a specific Address Family.  The
     value `0' is reserved for this field, and represents the native
     encoding of the Address Family.


Unicast Address
     The unicast address as represented by the given Address Family and



Fenner/Handley/Holbrook/Kouvelas             Section 4.10.1.  [Page 105]

INTERNET-DRAFT             Expires: June 2003              December 2002


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


Addr Family
     described above.


Encoding Type
     described above.


[B]idirectional PIM
     indicates the group range should use Bidirectional PIM [9]. For
     PIM-SM defined in this specification, this bit MUST be zero.


Reserved
     Transmitted as zero. Ignored upon receipt.


Admin Scope [Z]one
     indicates the group range is an admin scope zone.  This is used in
     the Bootstrap Router Mechanism [7] only.  For all other purposes,
     this bit is set to zero and ignored on receipt.


Mask Len
     The Mask length field is 8 bits. The value is the number of
     contiguous one bits left justified used as a mask which, combined
     with the group address, describes a range of groups. It is less
     than or equal to the address length in bits for the given Address
     Family and Encoding Type. If the message is sent for a single group
     then the Mask length must equal the address length in bits for the
     given Address Family and Encoding Type.  (e.g. 32 for IPv4 native
     encoding, 128 for IPv6 native encoding).



Fenner/Handley/Holbrook/Kouvelas             Section 4.10.1.  [Page 106]

INTERNET-DRAFT             Expires: June 2003              December 2002


Group multicast Address
     Contains the group address.


Encoded-Source address

Encoded-Source address takes the following format:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Family   | Encoding Type | Rsrvd   |S|W|R|  Mask Len     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Source Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...


Addr Family
     described above.


Encoding Type
     described above.


Reserved
     Transmitted as zero, ignored on receipt.


S    The Sparse bit is a 1 bit value, set to 1 for PIM-SM.  It is used
     for PIM version 1 compatibility.


W    The WC (or WildCard) bit is a 1 bit value for use with PIM
     Join/Prune messages (see section 4.10.5.1 ).


R    The RPT (or Rendezvous Point Tree) bit is a 1 bit value for use
     with PIM Join/Prune messages (see section 4.10.5.1 ). If the WC bit
     is 1, the RPT bit MUST be 1.


Mask Len
     The mask length field is 8 bits. The value is the number of
     contiguous one bits left justified used as a mask which, combined
     with the Source Address, describes a source subnet. The mask length
     MUST be equal to the mask length in bits for the given Address
     Family and Encoding Type (32 for IPv4 native and 128 for IPv6



Fenner/Handley/Holbrook/Kouvelas             Section 4.10.1.  [Page 107]

INTERNET-DRAFT             Expires: June 2003              December 2002


     native).  A router SHOULD ignore any messages received with any
     other mask length.


Source Address
     The source address.


4.10.2.  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.




Fenner/Handley/Holbrook/Kouvelas             Section 4.10.2.  [Page 108]

INTERNET-DRAFT             Expires: June 2003              December 2002


     The Option fields may contain the following values:

     o OptionType 1: Holdtime

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 1             |         Length = 2            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Holdtime             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Holdtime is the amount of time a receiver must keep the neighbor
       reachable, in seconds. If the Holdtime is set to `0xffff', the
       receiver of this message never times out the neighbor. This may
       be used with dial-on-demand links, to avoid keeping the link up
       with periodic Hello messages.

       Hello messages with a Holdtime value set to `0' are also sent by
       a router on an interface about to go down or changing IP address
       (see section 4.3.1). These are effectively goodbye messages and
       the receiving routers should immediately time out the neighbor
       information for the sender.

     o OptionType 2: LAN Prune Delay

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 2             |         Length = 4            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |T|        LAN Delay            |      Override_Interval        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       The LAN_Prune_Delay option is used to tune the prune propagation
       delay on multi-access LANs.

     The T bit specifies the ability of the sending router to disable
     joins suppression.

     LAN Delay and Override_Interval are time intervals in units of
     milliseconds are are used to tune the value of the
     Override_Interval(I) and its derived timer values. Section 4.3.3
     describes how these values affect the behavior of a router.

     o OptionType 3 to 16: reserved to be defined in future versions of
       this document.




Fenner/Handley/Holbrook/Kouvelas             Section 4.10.2.  [Page 109]

INTERNET-DRAFT             Expires: June 2003              December 2002


     o OptionType 18: deprecated and should not be used.

     o OptionType 19: DR Priority

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 19            |         Length = 4            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         DR Priority                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       DR Priority is a 32-bit unsigned number and should be considered
       in the DR election as described in section 4.3.2.

     o OptionType 20: Generation ID

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type = 20            |         Length = 4            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Generation ID                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Generation ID is a random 32-bit value for the interface on which
       the Hello message is sent.  The Generation ID is regenerated
       whenever PIM forwarding is started or restarted on the interface.

     OptionTypes 17 thru 65000 are assigned by the IANA.  OptionTypes
     65001 through 65535 are reserved for Private Use, as defined in
     [12].
     Unknown options may be ignored.  The "Holdtime" option MUST be
     implemented; the "DR Priority" and "Generation ID" options SHOULD
     be implemented.


4.10.3.  Register Message Format

A Register message is sent by the DR or a PMBR to the RP when a
multicast packet needs to be transmitted on the RP-tree.  The IP source
address is set to the address of the DR, the destination address to the
RP's address.  The IP TTL of the PIM packet is the system's normal
unicast TTL.







Fenner/Handley/Holbrook/Kouvelas             Section 4.10.3.  [Page 110]

INTERNET-DRAFT             Expires: June 2003              December 2002


 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B|N|                       Reserved2                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
.                     Multicast data packet                     .
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Type, Reserved, Checksum
     Described above. Note that the checksum for Registers is done only
     on first 8 bytes of the packet, including the PIM header and the
     next 4 bytes, excluding the data packet portion. For
     interoperability reasons, a message carrying a checksum calculated
     over the entire PIM Register message should also be accepted.


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.


Reserved2
     Transmitted as zero, ignored on receipt.


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
     IPv6 data packet must be encapsulated in an IPv6 PIM packet.  Note
     that the TTL of the original packet is decremented before
     encapsulation, just like any other packet that is forwarded.  In
     addition, the RP decrements the TTL after decapsulating, before
     forwarding the packet down the shared tree.

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



Fenner/Handley/Holbrook/Kouvelas             Section 4.10.3.  [Page 111]

INTERNET-DRAFT             Expires: June 2003              December 2002


4.10.4.  RegisterStop Message Format

A RegisterStop 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 4.10.1. Note that for RegisterStops the
     Mask Len field contains the full address length * 8 (e.g. 32 for
     IPv4 native encoding), if the message is sent for a single group.


Source Address
     The host address of the source from the multicast data packet in
     the register.  The format for this address is given in the Encoded-
     Unicast address in section 4.10.1. A special wild card value
     consisting of an address field of all zeroes can be used to
     indicate any source.


4.10.5.  Join/Prune Message Format

A Join/Prune message is sent by routers towards upstream sources and
RPs.  Joins are sent to build shared trees (RP trees) or source trees
(SPT). Prunes are sent to prune source trees when members leave groups
as well as sources that do not use the shared tree.








Fenner/Handley/Holbrook/Kouvelas             Section 4.10.5.  [Page 112]

INTERNET-DRAFT             Expires: June 2003              December 2002


 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)        |



Fenner/Handley/Holbrook/Kouvelas             Section 4.10.5.  [Page 113]

INTERNET-DRAFT             Expires: June 2003              December 2002


+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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 4.10.1.
     This address should be the link-local address of the upstream
     neighbor, as obtained from the RPF lookup.


Reserved
     Transmitted as zero, ignored on receipt.


Holdtime
     The amount of time a receiver must keep the Join/Prune state alive,
     in seconds.  If the Holdtime is set to `0xffff', the receiver of
     this message should hold the state until canceled by the
     appropriate canceling Join/Prune message, or timed out according to
     local policy.  This may be used with dial-on-demand links, to avoid
     keeping the link up with periodic Join/Prune messages.

     Note that the HoldTime must be larger than the
     J/P_Override_Interval(I).


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


Multicast group address
     For format description see Section 4.10.1.

Number of Joined Sources
     Number of join source addresses listed for a given group.


Join Source Address 1 .. n
     This list contains the sources that the sending router will forward
     multicast datagrams for if received on the interface this message
     is sent on.

     See Encoded-Source-Address format in section 4.10.1.




Fenner/Handley/Holbrook/Kouvelas             Section 4.10.5.  [Page 114]

INTERNET-DRAFT             Expires: June 2003              December 2002


Number of Pruned Sources
     Number of prune source addresses listed for a group.


Prune Source Address 1 .. n
     This list contains the sources that the sending router does not
     want to forward multicast datagrams for when received on the
     interface this message is sent on.


Within one PIM Join/Prune message, all the Multicast Group Addresses,
Joined Source addresses and Pruned Source addresses MUST be of the same
address family.  It is NOT PERMITTED to mix IPv4 and IPv6 addresses
within the same message.  In addition, the address family of the fields
in the message SHOULD be the same as the IP source and destination
addresses of the packet.  This permits maximum implementation
flexibility for dual-stack IPv4/IPv6 routers.


4.10.5.1.  Group Set Source List Rules

As described above, Join / Prune messages are composed of one or more
group sets. Each set contains two source lists, the Join Sources and the
Prune Sources. This section describes the different types of group sets
and source list entries that can exist in a Join / Prune message.

There are two valid group set types:


Wildcard Group Set
     The wildcard group set is represented by the entire multicast range
     - the beginning of the multicast address range in the group address
     field and the prefix length of the multicast address range in the
     mask length field of the Multicast Group Address, e.g. 224.0.0.0/4
     for IPv4 or ff00::/8 for IPv6.  Each wildcard group set may contain
     one or more (*,*,RP) source list entries in either the Join or
     Prune lists.

     A (*,*,RP) source list entry may only exist in a wildcard group
     set.  When added to a Join source list, this type of source entry
     expresses the routers interest in receiving traffic for all groups
     mapping to the specified RP. When added to a Prune source list a
     (*,*,RP) entry expresses the routers interest to stop receiving
     such traffic.  Note that as indicated by the Join/Prune state
     machines, such a Join or Prune will NOT override Join/Prune state
     created using a Group-Specific Set (see below).

     (*,*,RP) source list entries have the Source-Address set to the



Fenner/Handley/Holbrook/Kouvelas           Section 4.10.5.1.  [Page 115]

INTERNET-DRAFT             Expires: June 2003              December 2002


     address of the RP, the Source-Address Mask-Len set to the full
     length of the IP address and both the WC and RPT bits of the
     Source-Address set to 1.


Group Specific Set
     A Group Specific Set is represented by a valid IP multicast address
     in the group address field and the full length of the IP address in
     the mask length field of the Multicast Group Address. Each group
     specific set may contain (*,G), (S,G,rpt) and (S,G) source list
     entries in the Join or Prune lists.

     (*,G)
          The (*,G) source list entry is used in Join / Prune messages
          sent towards the RP for the specified group. It expresses
          interest (or lack of) in receiving traffic sent to the group
          through the Rendezvous-Point shared tree. There may only be
          one such entry in both the Join and Prune lists of a group
          specific set.

          (*,G) source list entries have the Source-Address set to the
          address of the RP for group G, the Source-Address Mask-Len set
          to the full length of the IP address and have both the WC and
          RPT bits of the Encoded-Source-Address set.


     (S,G,rpt)
          The (S,G,rpt) source list entry is used in Join / Prune
          messages sent towards the RP for the specified group. It
          expresses interest (or lack of) in receiving traffic through
          the shared tree sent by the specified source to this group.
          For each source address the entry may exist in only one of the
          Join and Prune source lists of a group specific set but not
          both.

          (S,G,rpt) source list entries have the Source-Address set to
          the address of the source S, the Source-Address Mask-Len set
          to the full length of the IP address and have the WC bit clear
          and the RPT bit set in the Encoded-Source-Address.


     (S,G)
          The (S,G) source list entry is used in Join / Prune messages
          sent towards the specified source. It expresses interest (or
          lack of) in receiving traffic through the shortest path tree
          sent by the source to the specified group. For each source
          address the entry may exist in only one of the Join and Prune
          source lists of a group specific set but not both.



Fenner/Handley/Holbrook/Kouvelas           Section 4.10.5.1.  [Page 116]

INTERNET-DRAFT             Expires: June 2003              December 2002


          (S,G) source list entries have the Source-Address set to the
          address of the source S, the Source-Address Mask-Len set to
          the full length of the IP address and have both the WC and RPT
          bits of the Encoded-Source-Address cleared.

The rules described above are sufficient to prevent invalid combinations
of source list entries in group-specific sets.  There are however a
number of combinations that have a valid interpretation but which are
not generated by the protocol as described in this specification:

o Combining a (*,G) Join and a (S,G,rpt) Join entry in the same message
  is redundant as the (*,G) entry covers the information provided by the
  (S,G,rpt) entry.

o The same applies for a (*,G) Prunes and (S,G,rpt) Prunes.

o The combination of a (*,G) Prune and a (S,G,rpt) Join is also not
  generated. (S,G,rpt) Joins are only sent when the router is receiving
  all traffic for a group on the shared tree and it wishes to indicate a
  change for the particular source. As a (*,G) prune indicates that the
  router no longer wishes to receive shared tree traffic, the (S,G,rpt)
  Join would be meaningless.

o As Join / Prune messages are targeted to a single PIM neighbor,
  including both a (S,G) Join and a (S,G,rpt) prune in the same message
  is redundant. The (S,G) Join informs the neighbor that the sender
  wishes to receive the particular source on the shortest path tree. It
  is therefore unnecessary for the router to say that it no longer
  wishes to receive it on the shared tree.

o The combination of a (S,G) Prune and a (S,G,rpt) Join could possibly
  be used by a router to switch from receiving a particular source on
  the shortest-path tree back to receiving it on the shared tree
  (provided that the RPF neighbor for the shortest-path and shared trees
  is common). However Sparse-Mode PIM does not provide a mechanism for
  switching back to the shared tree.















Fenner/Handley/Holbrook/Kouvelas           Section 4.10.5.1.  [Page 117]

INTERNET-DRAFT             Expires: June 2003              December 2002


The rules are summarized in the tables below.

+----------++------+-------+-----------+-----------+-------+-------+
|          ||Join  | Prune | Join      | Prune     | Join  | Prune |
|          ||(*,G) | (*,G) | (S,G,rpt) | (S,G,rpt) | (S,G) | (S,G) |
+----------++------+-------+-----------+-----------+-------+-------+
|Join      ||-     | no    | ?         | yes       | yes   | yes   |
|(*,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Prune     ||no    | -     | ?         | ?         | yes   | yes   |
|(*,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Join      ||?     | ?     | -         | no        | yes   | yes   |
|(S,G,rpt) ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Prune     ||yes   | ?     | no        | -         | ?     | ?     |
|(S,G,rpt) ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Join      ||yes   | yes   | yes       | ?         | -     | no    |
|(S,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+
|Prune     ||yes   | yes   | yes       | ?         | no    | -     |
|(S,G)     ||      |       |           |           |       |       |
+----------++------+-------+-----------+-----------+-------+-------+


+---------------++--------------+----------------+------------+
|               ||Join (*,*,RP) | Prune (*,*,RP) | all others |
+---------------++--------------+----------------+------------+
|Join (*,*,RP)  ||-             | no             | yes        |
+---------------++--------------+----------------+------------+
|Prune (*,*,RP) ||no            | -              | yes        |
+---------------++--------------+----------------+------------+
|all others     ||yes           | yes            | see above  |
+---------------++--------------+----------------+------------+


yes  Allowed and expected.


no   Combination is not allowed by the protocol and MUST NOT be
     generated by a router.


?    Combination not expected by the protocol, but well-defined. A
     router MAY accept it but SHOULD NOT generate it.





Fenner/Handley/Holbrook/Kouvelas           Section 4.10.5.1.  [Page 118]

INTERNET-DRAFT             Expires: June 2003              December 2002


The order of source list entries in a group set source list is not
important, except where limited by the packet format itself.


4.10.5.2.  Group Set Fragmentation

When building a Join / Prune for a particular neighbor, a router should
try and include in the message as much of the information it needs to
convey to the neighbor as possible.  This implies adding one group set
for each multicast group that has information pending transmission and
within each set including all relevant source list entries.

On a router with a large amount of multicast state the number of entries
that must be included may result in packets that are larger in the
maximum IP packet size. In most such cases the information may be split
into multiple messages.

There is an exception with group sets that contain a (*,G) Join source
list entry. The group set expresses the routers interest in receiving
all traffic for the specified group on the shared tree and it MUST
include an (S,G,rpt) Prune source list entry for every source that the
router does not wish to receive. This list of (S,G,rpt) Prune source-
list entries MUST not be split in multiple messages.

If only N (S,G,rpt) Prune entries fit into a maximum-sized Join / Prune
message, but the router has more than N (S,G,rpt) Prunes to add, then
the router MUST choose to include the first N (numerically smallest in
network byte order) IP addresses.


4.10.6.  Assert Message Format

The Assert message is used to resolve forwarder conflicts between
routers on a link. It is sent when a multicast data packet is received
on an interface that the router would normally forward that packet.
Assert messages may also be sent in response to an Assert message from
another router.














Fenner/Handley/Holbrook/Kouvelas             Section 4.10.6.  [Page 119]

INTERNET-DRAFT             Expires: June 2003              December 2002


 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 for which the router wishes to resolve the
     forwarding conflict.  This is an Encoded-Group address, as
     specified in 4.10.1.

Source Address
     Source address for which the router wishes to resolve the
     forwarding conflict. The source address MAY be set to INADDR_ANY
     for (*,G) asserts (see below).  The format for this address is
     given in Encoded-Unicast-Address in section 4.10.1.

R    RPT-bit is a 1 bit value. The RPT-bit is set to 1 for Assert(*,G)
     messages and 0 for Assert(S,G) messages.


Metric Preference
     Preference value assigned to the unicast routing protocol that
     provided the route to the multicast source or Rendezvous-Point.


Metric
     The unicast routing table metric associated with the route used to
     reach the multicast source or Rendezvous-Point. The metric is in
     units applicable to the unicast routing protocol used.


Assert messages can be sent to resolve a forwarding conflict for all
traffic to given group or for a specific source and group.




Fenner/Handley/Holbrook/Kouvelas             Section 4.10.6.  [Page 120]

INTERNET-DRAFT             Expires: June 2003              December 2002


Assert(S,G)
     Source specific asserts are sent by routers forwarding a specific
     source on the shortest-path tree (SPT bit is TRUE). (S,G) Asserts
     have the Group-Address field set to the group G and the Source-
     Address field set to the source S. The RPT-bit is set to 0, the
     Metric-Preference is set to MRIB.pref(S) and the Metric is set to
     MRIB.metric(S).

Assert(*,G)
     Group specific asserts are sent by routers forwarding data for the
     group and source(s) under contention on the shared tree. (*,G)
     asserts have the Group-Address field set to the group G. For data
     triggered Asserts the Source-Address field MAY be set to the IP
     source address of the data packet that triggered the Assert and is
     set to INADDR_ANY otherwise.  The RPT-bit is set to 1, the Metric-
     Preference is set to MRIB.pref(RP(G)) and the Metric is set to
     MRIB.metric(RP(G)).

4.11.  PIM Timers

PIM-SM maintains the following timers, as discussed in section 4.1. All
timers are countdown timers - they are set to a value and count down to
zero, at which point they typically trigger an action.  Of course they
can just as easily be implemented as count-up timers, where the absolute
expiry time is stored and compared against a real-time clock, but the
language in this specification assumes that they count downwards to
zero.


Global Timers

Per interface (I):

     Hello Timer: HT(I)

     Per neighbor (N):

          Neighbor liveness Timer: NLT(N,I)

     Per active RP (RP):

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

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

     Per Group (G):





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

INTERNET-DRAFT             Expires: June 2003              December 2002


          (*,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)

     Per Source (S):

          (S,G) Upstream Join Timer: JT(S,G)

          (S,G) Keepalive Timer: KAT(S,G)

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

At the DRs or relevant Assert Winners only:

     Per Source,Group pair (S,G):

          Register Stop Timer: RST(S,G)

4.12.  Timer Values

When timers are started or restarted, they are set to default values.
This section summarizes those default values.

Note that protocol events or configuration may change the default value
of a timer on a specific interface. When timers are initialized in this
document the value specific to the interface in context must be used.



Fenner/Handley/Holbrook/Kouvelas               Section 4.12.  [Page 122]

INTERNET-DRAFT             Expires: June 2003              December 2002


Some of the timers listed below (Prune Pending, Upstream Join, Upstream
Override) can be set to values which depend on the settings of the
Propagation Delay and Override_Interval of the corresponding interface.
The default values for these are given below.  Note that the value of
both the Propagation Delay and Override Interval of an interface can
change as a result of receiving Hello messages on that interface
(section 4.3.3).

Variable Name: Propagation_Delay(I)


+--------------------------+-----------------+--------------------------+
|   Value Name             |    Value        |     Explanation          |
+--------------------------+-----------------+--------------------------+
|   LAN_delay_default      |    0.5 sec      |     Expected             |
|                          |                 |     propagation delay    |
|                          |                 |     over the local       |
|                          |                 |     link.                |
+--------------------------+-----------------+--------------------------+

The default value of the LAN_delay_default is chosen to be relatively
large to provide compatibility with older PIM implementations.

Variable Name: Override_Interval(I)


+--------------------------+-----------------+--------------------------+
|   Value Name             |    Value        |    Explanation           |
+--------------------------+-----------------+--------------------------+
|   t_override_default     |    2.5 sec      |    Default delay         |
|                          |                 |    interval over         |
|                          |                 |    which to randomize    |
|                          |                 |    when scheduling a     |
|                          |                 |    delayed Join          |
|                          |                 |    message.              |
+--------------------------+-----------------+--------------------------+















Fenner/Handley/Holbrook/Kouvelas               Section 4.12.  [Page 123]

INTERNET-DRAFT             Expires: June 2003              December 2002


Timer Name: Hello Timer (HT(I))


+----------------------+--------+---------------------------------------+
|Value Name            | Value  | Explanation                           |
+----------------------+--------+---------------------------------------+
|Hello_Period          | 30 sec | Periodic interval for Hello messages. |
+----------------------+--------+---------------------------------------+
|Triggered_Hello_Delay | 5 sec  | Randomized interval for initial Hello |
|                      |        | message on bootup or triggered Hello  |
|                      |        | message to a rebooting neighbor.      |
+----------------------+--------+---------------------------------------+

At system power-up, the timer is initialized to
rand(0,Triggered_Hello_Delay) to prevent synchronization.  When a new or
rebooting neighbor is detected, a responding Hello is sent within
rand(0,Triggered_Hello_Delay).

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


+--------------------------+-----------------------+--------------------+
| Value Name               |  Value                |  Explanation       |
+--------------------------+-----------------------+--------------------+
| Default_Hello_Holdtime   |  3.5 * Hello_Period   |  Default holdtime  |
|                          |                       |  to keep neighbor  |
|                          |                       |  state alive       |
+--------------------------+-----------------------+--------------------+
| Hello_Holdtime           |  from message         |  Holdtime from     |
|                          |                       |  Hello Message     |
|                          |                       |  Holdtime option.  |
+--------------------------+-----------------------+--------------------+

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

Timer Names: Expiry Timer (ET(*,*,RP,I), ET(*,G,I), ET(S,G,I),
ET(S,G,rpt,I))


+----------------+-----------------+------------------------------------+
| Value Name     |  Value          |  Explanation                       |
+----------------+-----------------+------------------------------------+
| J/P_HoldTime   |  from message   |  Holdtime from Join/Prune Message  |
+----------------+-----------------+------------------------------------+

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



Fenner/Handley/Holbrook/Kouvelas               Section 4.12.  [Page 124]

INTERNET-DRAFT             Expires: June 2003              December 2002


Timer Names: Prune Pending Timer (PPT(*,*,RP,I), PPT(*,G,I), PPT(S,G,I),
PPT(S,G,rpt,I))


+--------------------------+-----------------------+--------------------+
|Value Name                | Value                 | Explanation        |
+--------------------------+-----------------------+--------------------+
|J/P_Override_Interval(I)  | Default:              | Short period after |
|                          | Propagation_Delay(I)  | a join or prune to |
|                          | +                     | allow other        |
|                          | Override_Interval(I)  | routers on the LAN |
|                          |                       | to override the    |
|                          |                       | join or prune      |
+--------------------------+-----------------------+--------------------+

Note that both the Propagation_Delay(I) and the Override_Interval(I) are
interface specific values that may change when Hello messages are
received.

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


+---------------------------+----------------------+--------------------+
| Value Name                |  Value               | Explanation        |
+---------------------------+----------------------+--------------------+
| Assert_Override_Interval  |  Default: 3 secs     | Short interval     |
|                           |                      | before an assert   |
|                           |                      | times out where    |
|                           |                      | the assert winner  |
|                           |                      | resends an Assert  |
|                           |                      | message            |
+---------------------------+----------------------+--------------------+
| Assert_Time               |  Default: 180 secs   | Period after last  |
|                           |                      | assert before      |
|                           |                      | assert state is    |
|                           |                      | timed out          |
+---------------------------+----------------------+--------------------+

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










Fenner/Handley/Holbrook/Kouvelas               Section 4.12.  [Page 125]

INTERNET-DRAFT             Expires: June 2003              December 2002


Timer Names: Upstream Join Timer (JT(*,*,RP), JT(*,G), JT(S,G))


+-------------+------------------------+-------------------------------------+
|Value Name   | Value                  | Explanation                         |
+-------------+------------------------+-------------------------------------+
|t_periodic   | Default: 60 secs       | Period between Join/Prune Messages  |
+-------------+------------------------+-------------------------------------+
|t_suppressed | rand(1.1 *             | Suppression period when someone     |
|             | t_periodic, 1.4 *      | else sends a J/P message so we      |
|             | t_periodic) when       | don't need to do so.                |
|             | Suppression_Enabled(I) |                                     |
|             | is true, 0             |                                     |
|             | otherwise              |                                     |
+-------------+------------------------+-------------------------------------+
|t_override   | rand(0,                | Randomized delay to prevent         |
|             | Override_Interval(I))  | 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.

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

t_override depends on the Override Interval of the upstream interface
which may change when Hello messages are received.

t_suppressed depends on the Suppression State of the upstream interface
( 4.3.3) and becomes zero when suppression is disabled.












Fenner/Handley/Holbrook/Kouvelas               Section 4.12.  [Page 126]

INTERNET-DRAFT             Expires: June 2003              December 2002


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


+---------------+---------------------------+---------------------------+
| Value Name    | Value                     |  Explanation              |
+---------------+---------------------------+---------------------------+
| t_override    | see Upstream Join Timer   |  see Upstream Join Timer  |
+---------------+---------------------------+---------------------------+

The upstream Override Timer is only ever set to t_override; this value
is defined in the section on Upstream Join Timers.

Timer Name: KeepAlive Timer (KAT(S,G))


+-----------------------+------------------------+----------------------+
| Value Name            |  Value                 |  Explanation         |
+-----------------------+------------------------+----------------------+
| Keepalive_Period      |  Default: 210 secs     |  Period after last   |
|                       |                        |  (S,G) data packet   |
|                       |                        |  during which (S,G)  |
|                       |                        |  Join state will be  |
|                       |                        |  maintained even in  |
|                       |                        |  the absence of      |
|                       |                        |  (S,G) Join          |
|                       |                        |  messages.           |
+-----------------------+------------------------+----------------------+
| RP_Keepalive_Period   |  ( 3 * Register_       |  As                  |
|                       |  Suppression_Time )    |  Keepalive_Period,   |
|                       |  + Register_           |  but at the RP when  |
|                       |  Probe_Time            |  a 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).













Fenner/Handley/Holbrook/Kouvelas               Section 4.12.  [Page 127]

INTERNET-DRAFT             Expires: June 2003              December 2002


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 [8].

     Values 128 through 250 are designated to be assigned by the IANA
     based upon IESG Approval, as defined in [12].

     Values 251 through 255 are designated for Private Use, as defined
     in [12].






Fenner/Handley/Holbrook/Kouvelas                Section 5.1.  [Page 128]

INTERNET-DRAFT             Expires: June 2003              December 2002


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
[12]. Such assignments are valid for one year, and may be renewed.
Permanent assignments require a specification (see "Specification
Required" in [12].)

6.  Security Considerations

The IPsec authentication header [11] MAY be used to provide data
integrity protection and groupwise data origin authentication of PIM
protocol messages.  Authentication of PIM messages can protect against
unwanted behaviors caused by unauthorized or altered PIM messages.

6.1.  Attacks based on forged messages

The extent of possible damage depends on the type of counterfeit
messages accepted.  We next consider the impact of possible forgeries,
including forged link-local (Join/Prune, Hello, and Assert) and forged
unicast (Register and RegisterStop) messages.

6.1.1.  Forged link-local messages

Join/Prune, Hello, and Assert messages are all sent to the link-local
ALL_PIM_ROUTERS multicast addresses, and thus are not forwarded by a
compliant router.  A forged message of this type can only reach a LAN if
it was sent by a local host or if it was allowed onto the LAN by a
compromised or non-compliant router.

1.   A forged Join/Prune message can cause multicast traffic to be
     delivered to links where there are no legitimate requesters,
     potentially wasting bandwidth on that link.  A forged leave message
     on a multi-access LAN is generally not a significant attack in PIM,
     because any legitimately joined router on the LAN would override
     the leave with a join before the upstream router stops forwarding
     data to the LAN.

2.    By forging a Hello message, an unauthorized router can cause
     itself to be elected as the designated router on a LAN.  The
     designated router on a LAN is (in the absence of asserts)
     responsible for forwarding traffic to that LAN on behalf of any
     local members.  The designated router is also responsible for
     register-encapsulating to the RP any packets that are originated by
     hosts on the LAN.  Thus, the ability of local hosts to send and
     receive multicast traffic may be compromised by a forged Hello
     message.




Fenner/Handley/Holbrook/Kouvelas              Section 6.1.1.  [Page 129]

INTERNET-DRAFT             Expires: June 2003              December 2002


3.   By forging an Assert message on a multi-access LAN, an attacker
     could cause the legitimate designated forwarder to stop forwarding
     traffic to the LAN.  Such a forgery would prevent any hosts
     downstream of that LAN from receiving traffic.

6.1.2.  Forged unicast messages

Register messages and RegisterStop messages are sent by a source and
forwarded by intermediate routers to their destination using normal IP
forwarding.  Therefore, without data origin authentication, an attacker
who is located anywhere in the network may be able to forge a Register
or RegisterStop message.  The following attacks do not apply to a PIM-
SSM-only implementation, as these messages are not required for PIM-SSM.
We consider the effect of a forgery of each of these messages next.

1    By forging a Register message, an attacker can cause the RP to
     inject forged traffic onto the shared multicast tree.

2    By forging a Register-stop message, an attacker can prevent a
     legitimate DR from Registering packets to the RP.  This can prevent
     local hosts on that LAN from sending multicast packets.

The above two PIM messages are not changed by intermediate routers and
need only be examined by the intended receiver.  Thus these messages can
be authenticated end-to-end, using AH.

6.2.  Non-cryptographic Authentication Mechanisms

A PIM router SHOULD provide an option to limit the set of neighbors from
which it will accept Join/Prune, Assert, and Hello messages.  Either
static configuration of IP addresses or an IPsec security association
may be used.  Furthermore, a PIM router SHOULD NOT accept protocol
messages from a router from which it has not yet received a valid Hello
message.

A Designated Router MUST NOT register-encapsulate a packet and send it
to the RP unless the source address of the packet is a legal address for
the subnet on which the packet was received.  Similarly, a Designated
Router SHOULD NOT accept a RegisterStop packet whose IP source address
is not a valid RP address for the local domain.

An implementation SHOULD provide a mechanism to allow an RP to restrict
the range of source addresses from which it accepts Register-
encapsulated packets.

All options that restrict the range of addresses from which packets are
accepted MUST default to allowing all packets.




Fenner/Handley/Holbrook/Kouvelas                Section 6.2.  [Page 130]

INTERNET-DRAFT             Expires: June 2003              December 2002


6.3.  Authentication using IPsec

The IPsec [11] transport mode using the Authentication Header (AH) is
the recommended method to prevent the above attacks PIM.  The anti-
replay option provided by IPsec SHOULD also be enabled.  The specific AH
authentication algorithm and parameters, including the choice of
authentication algorithm and the choice of key, are configured by the
network administrator.  The Encapsulating Security Payload (ESP) MAY
also be used to provide both encryption and authentication of PIM
protocol messages.  When IPsec authentication is used, a PIM router
should reject (drop without processing) any unauthorized PIM protocol
messages.

To use IPsec, the administrator of a PIM network configures each PIM
router with one or more Security Associations and associated SPI(s) that
are used by senders to sign PIM protocol messages and are used by
receivers to authenticate received PIM protocol messages.  This document
does not describe protocols for establishing Security Associations.  It
assumes that manual configuration of Security Associations is performed,
but it does not preclude the use of some future negotiation protocol to
establish Security Associations.

The following sections describe the Security Associations required to
protect PIM protocol messages.

6.3.1.  Protecting link-local multicast messages

The network administrator defines a Security Association (SA) and
Security Parameters Index (SPI) that is to be used to authenticate all
link-local PIM protocol messages (Hello, Join/Prune, and Assert) on each
link in a PIM domain.  All link-local PIM protocol messages use SPI 0.

The Security Policy Database at a PIM router should be configured to
ensure that all incoming and outgoing Join/Prune, Assert, and Hello
packets use the SA associated with the interface to which the packet is
sent.

Note that, according to [11] there is nominally a different Security
Association Database (SAD) for each router interface.  Thus, the
selected Security Association for an inbound PIM packet can vary
depending on the interface on which the packet arrived.  This fact
allows the network administrator to use different authentication methods
for each link, even though the destination address is the same for all
link-local PIM packets, regardless of interface.







Fenner/Handley/Holbrook/Kouvelas              Section 6.3.1.  [Page 131]

INTERNET-DRAFT             Expires: June 2003              December 2002


6.3.2.  Protecting unicast messages

IPSec can also be used to provide data origin authentication and data
integrity protection for the Register and RegisterStop unicast messages.

6.3.2.1.  Register messages

The Security Policy Database at every PIM router is configured to select
a Security Association to use when sending PIM Register packets to each
rendezvous point.

In the most general mode of operation, the Security Policy Database at
each DR is configured to select a unique SA and SPI for traffic sent to
each RP.  This allows each DR to have a different authentication
algorithm and key to talk to the RP.  However, this creates a daunting
key management and distribution problem for the network administrator.
Therefore, it may be preferable in PIM domains where all Designated
Routers are under a single administrative control, to use the same
authentication algorithm parameters (including the key) for all
Registered packets in a domain, regardless of who is the RP and
regardless of who is the DR.

In this "single shared key" mode of operation, the network administrator
must choose an SPI for each DR that will be used to send it PIM protocol
packets.  The Security Policy Database at every DR is configured to
select a Security Association (including the authentication algorithm,
authentication parameters, and this SPI) when sending Register messages
to this RP.

By using a single authentication algorithm and associated parameters,
the key distribution problem is simplified.  Note however, that this
method has the property that, in order to change the authentication
method or authentication key used, all routers in the domain must be
updated.

6.3.2.2.  Register Stop messages

Similarly, the Security Policy Database at each Rendezvous Point should
be configured to choose a Security Association to use when sending
Register Stop messages.  Because Register Stop messages are unicast to
the destination DR, a different Security Association and a potentially
unique SPI is required for each DR.

[XXX Can we reserve a single SPI at all routers in the domain to
simplify the configuration problem?]

In order to simplify the management problem, it may be acceptable to use
the same authentication algorithm and authentication parameters,



Fenner/Handley/Holbrook/Kouvelas            Section 6.3.2.2.  [Page 132]

INTERNET-DRAFT             Expires: June 2003              December 2002


regardless of the sending RP and regardless of the destination DR.
Although a unique Security Association is needed for each DR, the same
authentication algorithm and authentication algorithm parameters (secret
key) can be shared by all DRs and by all RPs.


6.4.  Denial of Service Attacks

There are a number of possible denial of service attacks against PIM
that can be caused by generating false PIM protocol messages or even by
generating data false traffic.  Authenticating PIM protocol traffic
prevents some, but not all of these attacks.  The possible attacks
include:

-    Sending packets to many different group addresses quickly can be a
     denial of service attack in and of itself.  This will cause many
     register-encapsulated packets, loading the DR, the RP, and the
     routers between the DR and the RP.

-    Forging Join messages can cause a multicast tree to get set up.  A
     large number of forged joins can consume router resources and
     result in denial of service.

-    [XXX Many others]

7.  Authors' Addresses

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


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


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





Fenner/Handley/Holbrook/Kouvelas                  Section 7.  [Page 133]

INTERNET-DRAFT             Expires: June 2003              December 2002


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



8.  Acknowledgments

PIM-SM was designed over many years by a large group of people,
including ideas, comments, and corrections from Deborah Estrin, Dino
Farinacci, Ahmed Helmy, David Thaler, Steve Deering, Van Jacobson, C.
Liu, Puneet Sharma, Liming Wei, Tom Pusateri, Tony Ballardie, Scott
Brim, Jon Crowcroft, Paul Francis, Joel Halpern, Horst Hodel, Polly
Huang, Stephen Ostrowski, Lixia Zhang, Girish Chandranmenon, Brian
Haberman, Hal Sandick, Mike Mroz and Garry Kump.

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] D. Black, "Differentiated Services and Tunnels", RFC 2983.

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

[4] S. Deering, W. Fenner, B. Haberman, "Multicast Listener Discovery
     (MLD) for IPv6", RFC 2710.

[5] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6)
     Specification", RFC 2460.

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

[7] W. Fenner, M. Handley, H. Holbrook, I. Kouvelas, "Bootstrap Router
     (BSR) Mechanism for PIM Sparse Mode", draft-ietf-pim-sm-bsr-02.txt,
     work in progress.

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





Fenner/Handley/Holbrook/Kouvelas                  Section 9.  [Page 134]

INTERNET-DRAFT             Expires: June 2003              December 2002


[9] M. Handley, I. Kouvelas, T. Speakman, L. Vicisano, "Bi-directional
     Protocol Independent Multicast", draft-ietf-pim-bidir-02.txt, work
     in progress.

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

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

[12] T. Narten , H. Alvestrand, "Guidelines for Writing an IANA
     Considerations Section in RFCs", RFC 2434.  [13] D. Thaler,
     "Interoperability Rules for Multicast Routing Protocols", RFC 2715.






































Fenner/Handley/Holbrook/Kouvelas                  Section 9.  [Page 135]

INTERNET-DRAFT             Expires: June 2003              December 2002


10.  Index
Assert(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . .26,121
Assert(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . . .26,121
AssertCancel(*,G). . . . . . . . . . . . . . . . . . . . . . . . . 90,92
AssertCancel(S,G). . . . . . . . . . . . . . . . . . . . . . . .75,84,92
AssertTimer(*,G,I) . . . . . . . . . . . . . . . . . . . . .16,24,84,125
AssertTimer(S,G,I) . . . . . . . . . . . . . . . . . . . . .18,24,77,125
AssertTrackingDesired(*,G,I) . . . . . . . . . . . . . . . . . .87,88,90
AssertTrackingDesired(S,G,I) . . . . . . . . . . . . . . . . 79,79,81,83
AssertWinner(*,G,I). . . . . . . . . . . . . . . . . . . .21,24,87,90,94
AssertWinner(S,G,I). . . . . . . . . . . . . . . . . . 21,24,79,83,93,94
AssertWinnerMetric(*,G,I). . . . . . . . . . . . . . . . . . . . . 90,94
AssertWinnerMetric(S,G,I). . . . . . . . . . . . . . . . . . . . . 83,94
assert_metric. . . . . . . . . . . . . . . . . . . . . . . . . . . .  91
Assert_Override_Interval . . . . . . . . . . . . . . . . . . . 83,90,125
Assert_Time. . . . . . . . . . . . . . . . . . . . . . . . . . 83,90,125
AT(*,G,I). . . . . . . . . . . . . . . . . . . . . . . .16,24,84,122,125
AT(S,G,I). . . . . . . . . . . . . . . . . . . . . . . .18,24,77,122,125
CheckSwitchToSpt(S,G). . . . . . . . . . . . . . . . . . . . . . . 26,27
CouldAssert(*,G,I) . . . . . . . . . . . . . . . . . . . .85,87,88,89,91
CouldAssert(S,G,I) . . . . . . . . . . . . . . . . . . 78,79,81,82,83,91
CouldRegister(S,G) . . . . . . . . . . . . . . . . . . . . . . . . 36,38
Default_Hello_Holdtime . . . . . . . . . . . . . . . . . . . . . . .  31
DirectlyConnected(S) . . . . . . . . . . . . . . . . . . .26,26,28,38,97
DownstreamJPState(*,*,RP,I). . . . . . . . . . . . . . . . . . . . 22,98
DownstreamJPState(*,G,I) . . . . . . . . . . . . . . . . . . . . . .  22
DownstreamJPState(S,G,I) . . . . . . . . . . . . . . . . . . . . . 22,38
DownstreamJPState(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . .  23
DR(I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  31
dr_is_better(a,b,I). . . . . . . . . . . . . . . . . . . . . . . . 31,32
DR_priority. . . . . . . . . . . . . . . . . . . . . . . . . . . . 31,32
ET(*,*,RP,I) . . . . . . . . . . . . . . . . . . . . . . . 15,42,121,124
ET(*,G,I). . . . . . . . . . . . . . . . . . . . . . . . . 16,46,122,124
ET(S,G,I). . . . . . . . . . . . . . . . . . . . . . . . . 18,50,122,124
ET(S,G,rpt,I). . . . . . . . . . . . . . . . . . . . . .19,53,55,122,124
GenID. . . . . . . . . . . . . . . . . . . 16,17,19,30,59,63,66,68,78,85
Hash_Function. . . . . . . . . . . . . . . . . . . . . . . . . . .13,101
Hello_Holdtime . . . . . . . . . . . . . . . . . . . . . . . . . .31,124
Hello_Period . . . . . . . . . . . . . . . . . . . . . . . . . . .29,124
HT(I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29,124
IGMP . . . . . . . . . . . . . . . . . . . . . . . . . .7,9,17,22,95,100
immediate_olist(*,*,RP). . . . . . . . . . . . . . . . . . . . . . 21,60
immediate_olist(*,G) . . . . . . . . . . . . . . . . . . . . . . . 21,64
immediate_olist(S,G) . . . . . . . . . . . . . . . . . . . . . .21,38,68
infinite_assert_metric() . . . . . . . . . . . . . . . . . . . . . .  92
inherited_olist(S,G) . . . . . . . . . . . . . . . . .21,26,40,68,79,103
inherited_olist(S,G,rpt) . . . . . . . . . . . . . . . 21,26,28,72,74,76
I_Am_Assert_Loser(*,G,I) . . . . . . . . . . . . . . . . . . . . . .  24



Fenner/Handley/Holbrook/Kouvelas                 Section 10.  [Page 136]

INTERNET-DRAFT             Expires: June 2003              December 2002


I_Am_Assert_Loser(S,G,I) . . . . . . . . . . . . . . . . . . . . . .  24
I_am_DR(I) . . . . . . . . . . . . . . . . . . . . . . . .21,32,38,79,87
I_am_RP(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40,40
J/P_Holdtime . . . . . . . . . . . . . .43,48,51,55,61,65,70,114,124,126
J/P_Override_Interval(I) . . . . . . . . . . . . . . 44,48,51,55,114,125
JoinDesired(*,*,RP). . . . . . . . . . . . . . . . . . . . . . . . 60,73
JoinDesired(*,G) . . . . . . . . . . . . . . . . . . . . .17,64,73,79,91
JoinDesired(S,G) . . . . . . . . . . . . . . . . . . . 18,28,68,79,82,84
joins(*,*,RP(G)) . . . . . . . . . . . . . . . . . . . . . . . . . .  21
joins(*,*,RP). . . . . . . . . . . . . . . . . . . . . . . . 21,22,79,87
joins(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . 21,22,79,87
joins(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . . .21,22,79
JT(*,*,RP) . . . . . . . . . . . . . . . . . . . . . . . . 15,58,122,126
JT(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . 16,62,122,126
JT(S,G). . . . . . . . . . . . . . . . . . . . . . . . . . 18,67,122,126
KAT(S,G) . . . . . . . . . . . . . . . .18,25,26,27,38,40,68,103,122,127
KeepaliveTimer(S,G). . . . . . . . . 18,25,26,26,27,38,40,68,103,122,127
Keepalive_Period . . . . . . . . . . . . . . . . . . . . . . . . .26,127
LAN_delay_default. . . . . . . . . . . . . . . . . . . . . . . . .34,123
lan_delay_enabled(I) . . . . . . . . . . . . . . . . . . . . . . . 33,35
LAN_Prune_Delay. . . . . . . . . . . . . . . . . . . . . . . . . . .  30
local_receiver_exclude(S,G,I). . . . . . . . . . . . . . . . . . . .  22
local_receiver_include(*,G,I). . . . . . . . . . . . . . . . . .22,87,98
local_receiver_include(S,G,I). . . . . . . . . . . . . . . . . .22,79,98
lost_assert(*,G) . . . . . . . . . . . . . . . . . . . . . . . .21,23,79
lost_assert(*,G,I) . . . . . . . . . . . . . . . . . . . . . . .21,23,94
lost_assert(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . 21,23
lost_assert(S,G,I) . . . . . . . . . . . . . . . . . . . . . . .21,23,93
lost_assert(S,G,rpt) . . . . . . . . . . . . . . . . . . . . . . . .  23
lost_assert(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . . . . 23,93
MBGP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,8
MFIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,13
MLD. . . . . . . . . . . . . . . . . . . . . . . . . . .7,9,17,22,95,100
MRIB . . . . . . . . . . . . . . . 7,8,12,16,19,24,58,61,62,71,92,99,121
MRIB.next_hop(host). . . . . . . . . . . . . . . . .24,24,58,59,63,68,96
my_assert_metric(S,G,I). . . . . . . . . . . . . . . . . .79,83,85,87,91
NLT(N,I) . . . . . . . . . . . . . . . . . . . . . . . . . 15,31,121,124
OT(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . 20,72,122,127
Override_Interval(I) . . . . . . . . . . . . . . 14,30,33,34,109,123,125
packet_arrives_on_rp_tunnel(pkt) . . . . . . . . . . . . . . . . . .  40
pim_exclude(S,G) . . . . . . . . . . . . . . . . . . . . . . 21,22,27,79
pim_include(*,G) . . . . . . . . . . . . . . . . . . . 17,21,21,27,79,87
pim_include(S,G) . . . . . . . . . . . . . . . . . . . . .18,21,21,27,79
PPT(*,*,RP,I). . . . . . . . . . . . . . . . . . . . . . . 15,42,121,125
PPT(*,G,I) . . . . . . . . . . . . . . . . . . . . . . . . 16,46,122,125
PPT(S,G,I) . . . . . . . . . . . . . . . . . . . . . . . . 18,50,122,125
PPT(S,G,rpt,I) . . . . . . . . . . . . . . . . . . . . .19,53,55,122,125
Propagation_Delay(I) . . . . . . . . . . . . . . . . . . . 30,34,123,125



Fenner/Handley/Holbrook/Kouvelas                 Section 10.  [Page 137]

INTERNET-DRAFT             Expires: June 2003              December 2002


PruneDesired(S,G,rpt). . . . . . . . . . . . . . . . . . . . 74,75,82,84
prunes(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . .21,23,79
RegisterStop(*,G). . . . . . . . . . . . . . . . . . . . . . . . . .  39
RegisterStop(S,G). . . . . . . . . . . . . . . . . . . . . . . . . .  40
RegisterStopTimer(S,G) . . . . . . . . . . . . . . . . . . 36,37,122,128
Register_Probe_Time. . . . . . . . . . . . . . . . . . . . . . 37,41,128
Register_Suppression_Time. . . . . . . . . . . . . . . . . . . 37,41,128
RP(G). . . . . . . . . . . . . . .6,21,24,38,40,46,64,72,79,87,92,95,121
RPF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
RPF'(*,G). . . . . . . . . . . . . . . . . . .24,28,62,63,66,72,73,91,94
RPF'(S,G). . . . . . . . . . . . . . . . . . . . . .24,28,67,72,73,84,94
RPF'(S,G,rpt). . . . . . . . . . . . . . . . . . . . . . . . 24,72,74,95
RPF_interface. . . . . . . . . . . . . . . . . . . . . . . . . . . .  87
RPF_interface(host). . . . . . . . .24,26,28,38,64,65,70,79,87,93,97,103
RPTJoinDesired(G). . . . . . . . . . . . . . . . . . . . . . . .73,76,87
rpt_assert_metric(G,I) . . . . . . . . . . . . . . . . . . . . . . 90,92
RST(S,G) . . . . . . . . . . . . . . . . . . . . . . . . . 36,37,122,128
SPTbit(S,G). . . . . . . . . .19,26,28,40,49,69,72,74,79,79,83,84,93,103
spt_assert_metric(S,I) . . . . . . . . . . . . . . . . . . . . .83,92,93
SSM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,101
Suppression_Enabled(I) . . . . . . . . . . . . . . . . . . . . . .35,126
SwitchToSptDesired(S,G). . . . . . . . . . . . . . . . . . . . . . 27,27
TIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,13,25
Triggered_Hello_Delay. . . . . . . . . . . . . . . . . . . . . 29,30,124
t_joinsuppress . . . . . . . . . . . . . . . . . . . . . .59,61,63,65,70
t_override . . . . . . . . . . . . . . . . . . . . . 59,63,68,73,126,127
t_override_default . . . . . . . . . . . . . . . . . . . . . . . .34,123
t_periodic . . . . . . . . . . . . . . . . . . . . . . . . .59,63,68,126
t_suppressed . . . . . . . . . . . . . . . . . . . . .35,61,65,68,70,126
Update_SPTbit(S,G,iif) . . . . . . . . . . . . . . . . . . . . . . 26,28
UpstreamJPState(S,G) . . . . . . . . . . . . . . . . . . . . . . .26,103




















Fenner/Handley/Holbrook/Kouvelas                 Section 10.  [Page 138]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/