Network Working Group M. Handley
Request for Comments: 5015 UCL
Category: Standards Track I. Kouvelas
T. Speakman
Cisco
L. Vicisano
Digital Fountain
October 2007
Bidirectional Protocol Independent Multicast (BIDIR-PIM)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document discusses Bidirectional PIM (BIDIR-PIM), a variant of
PIM Sparse-Mode that builds bidirectional shared trees connecting
multicast sources and receivers. Bidirectional trees are built using
a fail-safe Designated Forwarder (DF) election mechanism operating on
each link of a multicast topology. With the assistance of the DF,
multicast data is natively forwarded from sources to the Rendezvous-
Point (RP) and hence along the shared tree to receivers without
requiring source-specific state. The DF election takes place at RP
discovery time and provides the route to the RP, thus eliminating the
requirement for data-driven protocol events.
Handley, et al. Standards Track [Page 1]RFC 5015 Bidirectional PIM October 2007Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................4
2.1. Definitions ................................................4
2.2. Pseudocode Notation ........................................6
3. Protocol Specification ..........................................6
3.1. BIDIR-PIM Protocol State ...................................7
3.1.1. General Purpose State ...............................8
3.1.2. RPA State ...........................................8
3.1.3. Group State .........................................9
3.1.4. State Summarization Macros .........................10
3.2. PIM Neighbor Discovery ....................................11
3.3. Data Packet Forwarding Rules ..............................11
3.3.1. Upstream Forwarding at RP ..........................12
3.3.2. Source-Only Branches ...............................12
3.3.3. Directly Connected Sources .........................13
3.4. PIM Join/Prune Messages ...................................13
3.4.1. Receiving (*,G) Join/Prune Messages ................13
3.4.2. Sending Join/Prune Messages ........................16
3.5. Designated Forwarder (DF) Election ........................18
3.5.1. DF Requirements ....................................18
3.5.2. DF Election Description ............................19
3.5.2.1. Bootstrap Election ........................20
3.5.2.2. Loser Metric Changes ......................20
3.5.2.3. Winner Metric Changes .....................21
3.5.2.4. Winner Loses Path .........................22
3.5.2.5. Late Router Starting Up ...................22
3.5.2.6. Winner Dies ...............................22
3.5.3. Election Protocol Specification ....................22
3.5.3.1. Election State ............................22
3.5.3.2. Election Messages .........................23
3.5.3.3. Election Events ...........................24
3.5.3.4. Election Actions ..........................25
3.5.3.5. Election State Transitions ................26
3.5.4. Election Reliability Enhancements ..................30
3.5.5. Missing Pass .......................................30
3.5.6. Periodic Winner Announcement .......................30
3.6. Timers, Counters, and Constants ...........................31
3.7. BIDIR-PIM Packet Formats ..................................34
3.7.1. DF Election Packet Formats .........................34
3.7.2. Backoff Message ....................................36
3.7.3. Pass Message .......................................36
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