draft-ietf-pim-sm-v2-new-03.txt

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Internet Engineering Task Force                                   PIM WG
INTERNET-DRAFT                                          Bill Fenner/AT&T
draft-ietf-pim-sm-v2-new-03.txt                       Mark Handley/ACIRI
                                                     Hugh Holbrook/Cisco
                                                   Isidor Kouvelas/Cisco
                                                            20 July 2001
                                                   Expires: January 2002


         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
[e-mail].

                                Abstract


     This document specifies Protocol Independent Multicast -
     Sparse Mode (PIM-SM).  PIM-SM is a multicast routing protocol
     that can use the underlying unicast routing information base
     or a separate multicast-capable routing information base.  It



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

Note on PIM-SM status

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



































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                           Table of Contents


1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . .   5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
 2.1. Definitions. . . . . . . . . . . . . . . . . . . . . . . . . .   5
 2.2. Pseudocode Notation. . . . . . . . . . . . . . . . . . . . . .   6
3. PIM-SM Protocol Overview. . . . . . . . . . . . . . . . . . . . .   7
4. Protocol Specification. . . . . . . . . . . . . . . . . . . . . .  12
 4.1. PIM Protocol State . . . . . . . . . . . . . . . . . . . . . .  12
  4.1.1. General Purpose State . . . . . . . . . . . . . . . . . . .  13
  4.1.2. (*,*,RP) State. . . . . . . . . . . . . . . . . . . . . . .  14
  4.1.3. (*,G) State . . . . . . . . . . . . . . . . . . . . . . . .  15
  4.1.4. (S,G) State . . . . . . . . . . . . . . . . . . . . . . . .  16
  4.1.5. (S,G,rpt) State . . . . . . . . . . . . . . . . . . . . . .  18
  4.1.6. State Summarization Macros. . . . . . . . . . . . . . . . .  19
 4.2. Data Packet Forwarding Rules . . . . . . . . . . . . . . . . .  23
  4.2.1. Last hop switchover to the SPT. . . . . . . . . . . . . . .  26
  4.2.2. Setting and Clearing the (S,G) SPT bit. . . . . . . . . . .  26
 4.3. PIM Register Messages. . . . . . . . . . . . . . . . . . . . .  28
  4.3.1. Sending Register Messages from the DR . . . . . . . . . . .  28
  4.3.2. Receiving Register Messages at the RP . . . . . . . . . . .  31
 4.4. PIM Join/Prune Messages. . . . . . . . . . . . . . . . . . . .  33
  4.4.1. Receiving (*,*,RP) Join/Prune Messages. . . . . . . . . . .  33
  4.4.2. Receiving (*,G) Join/Prune Messages . . . . . . . . . . . .  37
  4.4.3. Receiving (S,G) Join/Prune Messages . . . . . . . . . . . .  41
  4.4.4. Receiving (S,G,rpt) Join/Prune Messages . . . . . . . . . .  44
  4.4.5. Sending (*,*,RP) Join/Prune Messages. . . . . . . . . . . .  50
  4.4.6. Sending (*,G) Join/Prune Messages . . . . . . . . . . . . .  55
  4.4.7. Sending (S,G) Join/Prune Messages . . . . . . . . . . . . .  59
  4.4.8. (S,G,rpt) Periodic Messages . . . . . . . . . . . . . . . .  64
  4.4.9. State Machine for (S,G,rpt) Triggered
  Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  65
 4.5. PIM Assert Messages. . . . . . . . . . . . . . . . . . . . . .  69
  4.5.1. (S,G) Assert Message State Machine. . . . . . . . . . . . .  69
  4.5.2. (*,G) Assert Message State Machine. . . . . . . . . . . . .  76
  4.5.3. Assert Metrics. . . . . . . . . . . . . . . . . . . . . . .  82
  4.5.4. AssertCancel Messages . . . . . . . . . . . . . . . . . . .  84
  4.5.5. Assert State Macros . . . . . . . . . . . . . . . . . . . .  84
 4.6. Designated Routers (DR) and Hello Messages . . . . . . . . . .  87
  4.6.1. Sending Hello Messages. . . . . . . . . . . . . . . . . . .  87
  4.6.2. DR Election . . . . . . . . . . . . . . . . . . . . . . . .  88
  4.6.3. Reducing Prune Propagation Delay on LANs. . . . . . . . . .  90
 4.7. PIM Bootstrap and RP Discovery . . . . . . . . . . . . . . . .  92
  4.7.1. Group-to-RP Mapping . . . . . . . . . . . . . . . . . . . .  94
  4.7.2. Hash Function . . . . . . . . . . . . . . . . . . . . . . .  94
 4.8. Source-Specific Multicast. . . . . . . . . . . . . . . . . . .  95
  4.8.1. Protocol Modifications for SSM destination



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  addresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . .  96
  4.8.2. PIM-SSM-only Routers. . . . . . . . . . . . . . . . . . . .  96
 4.9. PIM Packet Formats . . . . . . . . . . . . . . . . . . . . . .  98
  4.9.1. Encoded Source and Group Address Formats. . . . . . . . . .  99
  4.9.2. Hello Message Format. . . . . . . . . . . . . . . . . . . . 102
  4.9.3. Register Message Format . . . . . . . . . . . . . . . . . . 104
  4.9.4. Register-Stop Message Format. . . . . . . . . . . . . . . . 106
  4.9.5. Join/Prune Message Format . . . . . . . . . . . . . . . . . 106
   4.9.5.1. Group Set Source List Rules. . . . . . . . . . . . . . . 109
   4.9.5.2. Group Set Fragmentation. . . . . . . . . . . . . . . . . 112
  4.9.6. Assert Message Format . . . . . . . . . . . . . . . . . . . 113
 4.10. PIM Timers. . . . . . . . . . . . . . . . . . . . . . . . . . 114
 4.11. Timer Values. . . . . . . . . . . . . . . . . . . . . . . . . 116
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 122
 5.1. PIM Address Family . . . . . . . . . . . . . . . . . . . . . . 122
 5.2. PIM Hello Options. . . . . . . . . . . . . . . . . . . . . . . 123
6. Security Considerations . . . . . . . . . . . . . . . . . . . . . 123
 6.1. Attacks based on forged messages . . . . . . . . . . . . . . . 123
  6.1.1. Forged link-local messages. . . . . . . . . . . . . . . . . 123
  6.1.2. Forged unicast messages . . . . . . . . . . . . . . . . . . 124
 6.2. Non-cryptographic Authentication Mechanisms. . . . . . . . . . 124
  6.2.1. Register Nonces . . . . . . . . . . . . . . . . . . . . . . 125
 6.3. Authentication using IPsec . . . . . . . . . . . . . . . . . . 125
  6.3.1. Protecting link-local multicast messages. . . . . . . . . . 126
  6.3.2. Protecting unicast messages . . . . . . . . . . . . . . . . 126
   6.3.2.1. Register messages. . . . . . . . . . . . . . . . . . . . 126
   6.3.2.2. Register Stop messages . . . . . . . . . . . . . . . . . 127
 6.4. Denial of Service Attacks. . . . . . . . . . . . . . . . . . . 127
7. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 127
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 128
9. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
10. Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130



















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1.  Introduction

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

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

2.  Terminology

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

2.1.  Definitions

This specification uses a number of terms to refer to the roles of
routers participating in PIM-SM.  The following terms have special
significance for PIM-SM:

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

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





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

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

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

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

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

Downstream
      Away from the root of the tree.

2.2.  Pseudocode Notation

We use set notation in several places in this specification.

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

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

NULL
    is the empty set or list.



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