draft-ietf-pim-bidir-05.txt   draft-ietf-pim-bidir-06.txt 
Internet Engineering Task Force PIM WG Internet Engineering Task Force PIM WG
INTERNET-DRAFT Mark Handley/UCL INTERNET-DRAFT Mark Handley/UCL
draft-ietf-pim-bidir-05.txt Isidor Kouvelas/Cisco draft-ietf-pim-bidir-06.txt Isidor Kouvelas/Cisco
Tony Speakman/Cisco Tony Speakman/Cisco
Lorenzo Vicisano/Cisco Lorenzo Vicisano/Cisco
19 June 2003 12 April 2004
Expires: December 2004 Expires: October 2004
Bi-directional Protocol Independent Multicast (BIDIR-PIM) Bi-directional Protocol Independent Multicast (BIDIR-PIM)
Status of this Document Status of this Document
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups Force (IETF), its areas, and its working groups. Note that other groups
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hence along the shared tree to receivers without requiring hence along the shared tree to receivers without requiring
source-specific state. The DF election takes place at RP source-specific state. The DF election takes place at RP
discovery time and provides the route to the RP thus discovery time and provides the route to the RP thus
eliminating the requirement for data-driven protocol events. eliminating the requirement for data-driven protocol events.
Table of Contents Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction. . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Definitions. . . . . . . . . . . . . . . . . . . . . 6 2.1. Definitions. . . . . . . . . . . . . . . . . . . . . 6
2.2. Pseudocode Notation. . . . . . . . . . . . . . . . . 7 2.2. Pseudocode Notation. . . . . . . . . . . . . . . . . 8
3. Protocol Specification. . . . . . . . . . . . . . . . . 8 3. Protocol Specification. . . . . . . . . . . . . . . . . 8
3.1. BIDIR-PIM Protocol State . . . . . . . . . . . . . . 8 3.1. BIDIR-PIM Protocol State . . . . . . . . . . . . . . 9
3.1.1. General Purpose State . . . . . . . . . . . . . . 9 3.1.1. General Purpose State . . . . . . . . . . . . . . 9
3.1.2. RPA State . . . . . . . . . . . . . . . . . . . . 10 3.1.2. RPA State . . . . . . . . . . . . . . . . . . . . 10
3.1.3. Group State . . . . . . . . . . . . . . . . . . . 10 3.1.3. Group State . . . . . . . . . . . . . . . . . . . 10
3.1.4. State Summarization Macros. . . . . . . . . . . . 11 3.1.4. State Summarization Macros. . . . . . . . . . . . 11
3.2. PIM Neighbor Discovery . . . . . . . . . . . . . . . 12 3.2. PIM Neighbor Discovery . . . . . . . . . . . . . . . 12
3.3. Data Packet Forwarding Rules . . . . . . . . . . . . 13 3.3. Data Packet Forwarding Rules . . . . . . . . . . . . 13
3.3.1. Upstream Forwarding at RP . . . . . . . . . . . . 14 3.3.1. Upstream Forwarding at RP . . . . . . . . . . . . 14
3.3.2. Source-Only Branches. . . . . . . . . . . . . . . 14 3.3.2. Source-Only Branches. . . . . . . . . . . . . . . 14
3.3.3. Directly Connected Sources. . . . . . . . . . . . 14 3.3.3. Directly Connected Sources. . . . . . . . . . . . 15
3.4. PIM Join/Prune Messages. . . . . . . . . . . . . . . 14 3.4. PIM Join/Prune Messages. . . . . . . . . . . . . . . 15
3.4.1. Receiving (*,G) Join/Prune Messages . . . . . . . 15 3.4.1. Receiving (*,G) Join/Prune Messages . . . . . . . 15
3.4.2. Sending Join/Prune Messages . . . . . . . . . . . 17 3.4.2. Sending Join/Prune Messages . . . . . . . . . . . 18
3.5. Designated Forwarder (DF) Election . . . . . . . . . 20 3.5. Designated Forwarder (DF) Election . . . . . . . . . 21
3.5.1. DF Requirements . . . . . . . . . . . . . . . . . 20 3.5.1. DF Requirements . . . . . . . . . . . . . . . . . 21
3.5.2. DF Election description . . . . . . . . . . . . . 21 3.5.2. DF Election description . . . . . . . . . . . . . 22
3.5.2.1. Bootstrap Election . . . . . . . . . . . . . . 21 3.5.2.1. Bootstrap Election . . . . . . . . . . . . . . 22
3.5.2.2. Loser Metric Changes . . . . . . . . . . . . . 22 3.5.2.2. Loser Metric Changes . . . . . . . . . . . . . 23
3.5.2.3. Winner Metric Changes. . . . . . . . . . . . . 23 3.5.2.3. Winner Metric Changes. . . . . . . . . . . . . 24
3.5.2.4. Winner Loses Path. . . . . . . . . . . . . . . 23 3.5.2.4. Winner Loses Path. . . . . . . . . . . . . . . 24
3.5.2.5. Late Router Starting Up. . . . . . . . . . . . 24 3.5.2.5. Late Router Starting Up. . . . . . . . . . . . 25
3.5.2.6. Winner Dies. . . . . . . . . . . . . . . . . . 24 3.5.2.6. Winner Dies. . . . . . . . . . . . . . . . . . 25
3.5.3. Election Protocol Specification . . . . . . . . . 24 3.5.3. Election Protocol Specification . . . . . . . . . 25
3.5.3.1. Election State . . . . . . . . . . . . . . . . 24 3.5.3.1. Election State . . . . . . . . . . . . . . . . 25
3.5.3.2. Election Messages. . . . . . . . . . . . . . . 25 3.5.3.2. Election Messages. . . . . . . . . . . . . . . 26
3.5.3.3. Election Events. . . . . . . . . . . . . . . . 26 3.5.3.3. Election Events. . . . . . . . . . . . . . . . 27
3.5.3.4. Election Actions . . . . . . . . . . . . . . . 27 3.5.3.4. Election Actions . . . . . . . . . . . . . . . 28
3.5.3.5. Election State Transitions . . . . . . . . . . 27 3.5.3.5. Election State Transitions . . . . . . . . . . 28
3.5.4. Election Reliability Enhancements . . . . . . . . 31 3.5.4. Election Reliability Enhancements . . . . . . . . 32
3.5.5. Missing Pass. . . . . . . . . . . . . . . . . . . 31 3.5.5. Missing Pass. . . . . . . . . . . . . . . . . . . 32
3.5.6. Periodic Winner Announcement. . . . . . . . . . . 31 3.5.6. Periodic Winner Announcement. . . . . . . . . . . 32
3.6. Timers Counters and Constants. . . . . . . . . . . . 31 3.6. Timers Counters and Constants. . . . . . . . . . . . 32
3.7. BIDIR PIM Packet Formats . . . . . . . . . . . . . . 35 3.7. BIDIR PIM Packet Formats . . . . . . . . . . . . . . 36
3.7.1. DF Election Packet Formats. . . . . . . . . . . . 35 3.7.1. DF Election Packet Formats. . . . . . . . . . . . 36
3.7.2. Backoff Message . . . . . . . . . . . . . . . . . 36 3.7.2. Backoff Message . . . . . . . . . . . . . . . . . 37
3.7.3. Pass Message. . . . . . . . . . . . . . . . . . . 37 3.7.3. Pass Message. . . . . . . . . . . . . . . . . . . 38
3.7.4. Bidir Capable PIM-Hello Option. . . . . . . . . . 38 3.7.4. Bidir Capable PIM-Hello Option. . . . . . . . . . 39
4. RP Discovery. . . . . . . . . . . . . . . . . . . . . . 38 4. RP Discovery. . . . . . . . . . . . . . . . . . . . . . 39
5. Security Considerations . . . . . . . . . . . . . . . . 39 5. Security Considerations . . . . . . . . . . . . . . . . 39
5.1. Attacks Based on Forged Messages . . . . . . . . . . 39 5.1. Attacks Based on Forged Messages . . . . . . . . . . 39
5.1.1. Election of an Incorrect DF . . . . . . . . . . . 39 5.1.1. Election of an Incorrect DF . . . . . . . . . . . 40
5.1.2. Preventing Election Convergence . . . . . . . . . 40 5.1.2. Preventing Election Convergence . . . . . . . . . 41
5.2. Non-cryptographic Authentication Mechanisms. . . . . 40 5.2. Non-cryptographic Authentication Mechanisms. . . . . 41
5.2.1. Basic Access Control. . . . . . . . . . . . . . . 40 5.2.1. Basic Access Control. . . . . . . . . . . . . . . 41
5.3. Authentication Using IPsec . . . . . . . . . . . . . 41 5.3. Authentication Using IPsec . . . . . . . . . . . . . 41
5.4. Denial of Service Attacks. . . . . . . . . . . . . . 41 5.4. Denial of Service Attacks. . . . . . . . . . . . . . 41
6. Change history. . . . . . . . . . . . . . . . . . . . . 41 6. Change history. . . . . . . . . . . . . . . . . . . . . 42
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . 41 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . 42
8. Authors' Addresses. . . . . . . . . . . . . . . . . . . 42 8. Authors' Addresses. . . . . . . . . . . . . . . . . . . 42
9. Normative . . . . . . . . . . . . . . . . . . . . . . . 42 9. Normative References. . . . . . . . . . . . . . . . . . 43
10. Informative. . . . . . . . . . . . . . . . . . . . . . 43 10. Informative References . . . . . . . . . . . . . . . . 43
11. Index. . . . . . . . . . . . . . . . . . . . . . . . . 44 11. Index. . . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction 1. Introduction
This document specifies Bi-directional PIM (BIDIR-PIM), a variant of PIM This document specifies Bi-directional PIM (BIDIR-PIM), a variant of PIM
Sparse-Mode (PIM-SM) [4] that builds bi-directional shared trees Sparse-Mode (PIM-SM) [4] that builds bi-directional shared trees
connecting multicast sources and receivers. connecting multicast sources and receivers.
PIM-SM constructs uni-directional shared trees that are used to forward PIM-SM constructs uni-directional shared trees that are used to forward
data from senders to receivers of a multicast group. PIM-SM also allows data from senders to receivers of a multicast group. PIM-SM also allows
the construction of source specific trees, but this capability is not the construction of source specific trees, but this capability is not
related to the protocol described in this document. related to the protocol described in this document.
The shared tree for each multicast group is rooted at a multicast router The shared tree for each multicast group is rooted at a multicast router
called the Rendezvous Point (RP). Different multicast group ranges can called the Rendezvous Point (RP). Different multicast groups can use
use separate RPs within a PIM domain. separate RPs within a PIM domain.
In unidirectional PIM-SM, there are two possible methods for In unidirectional PIM-SM, there are two possible methods for
distributing data packets on the shared tree. These differ in the way distributing data packets on the shared tree. These differ in the way
packets are forwarded from a source to the RP: packets are forwarded from a source to the RP:
o Initially when a source starts transmitting, its first hop router o Initially when a source starts transmitting, its first hop router
encapsulates data packets in special control messages (Registers) encapsulates data packets in special control messages (Registers)
which are unicast to the RP. After reaching the RP the packets are which are unicast to the RP. After reaching the RP the packets are
decapsulated and distributed on the shared tree. decapsulated and distributed on the shared tree.
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stage. This is achieved by building source specific state on all stage. This is achieved by building source specific state on all
routers along the path between the source and the RP. This state is routers along the path between the source and the RP. This state is
then used to natively forward packets from that source. then used to natively forward packets from that source.
Both these mechanisms suffer from problems. Encapsulation results in Both these mechanisms suffer from problems. Encapsulation results in
significant processing, bandwidth and delay overheads. Forwarding using significant processing, bandwidth and delay overheads. Forwarding using
source specific state has additional protocol and memory requirements. source specific state has additional protocol and memory requirements.
Bi-directional PIM dispenses with both encapsulation and source state by Bi-directional PIM dispenses with both encapsulation and source state by
allowing packets to be natively forwarded from a source to the RP using allowing packets to be natively forwarded from a source to the RP using
shared tree state. shared tree state. In contrast to PIM-SM this mode of forwarding does
not require any data-driven events.
The protocol specification in this document assumes familiarity with the The protocol specification in this document assumes familiarity with the
PIM-SM specification in [4]. Portions of the BIDIR-PIM protocol PIM-SM specification in [4]. Portions of the BIDIR-PIM protocol
operation that are identical to that of PIM-SM are only defined by operation that are identical to that of PIM-SM are only defined by
reference. reference.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" are to be interpreted as described in RFC 2119 and indicate
"OPTIONAL" are to be interpreted as described in RFC 2119 and indicate
requirement levels for compliant BIDIR-PIM implementations. requirement levels for compliant BIDIR-PIM implementations.
2.1. Definitions 2.1. Definitions
This specification uses a number of terms to refer to the roles of This specification uses a number of terms to refer to the roles of
routers participating in BIDIR-PIM. The following terms have special routers participating in BIDIR-PIM. The following terms have special
significance for BIDIR-PIM: significance for BIDIR-PIM:
MRIB Multicast Routing Information Base. This is the multicast MRIB Multicast Routing Information Base. This is the multicast
topology table, which is typically derived from the unicast topology table, which is typically derived from the unicast
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The protocol presented in this document is largely based on the The protocol presented in this document is largely based on the
concept of a Designated Forwarder (DF). A single DF exists for concept of a Designated Forwarder (DF). A single DF exists for
each RPA on every link within a BIDIR-PIM domain (this includes each RPA on every link within a BIDIR-PIM domain (this includes
both multi-access and point-to-point links). The only exception is both multi-access and point-to-point links). The only exception is
the RPL on which no DF exists. The DF is the router on the link the RPL on which no DF exists. The DF is the router on the link
with the best route to the RPA (determined by comparing MRIB with the best route to the RPA (determined by comparing MRIB
provided metrics). A DF for a given RPA is in charge of forwarding provided metrics). A DF for a given RPA is in charge of forwarding
downstream traffic onto its link, and forwarding upstream traffic downstream traffic onto its link, and forwarding upstream traffic
from its link towards the RPL. It does this for all the bi- from its link towards the RPL. It does this for all the bi-
directional groups that map to the RPA. The DF on a link is also directional groups that map to the RPA. The DF on a link is also
responsible processing Join messages from downstream routers on responsible for processing Join messages from downstream routers
the link as well as ensuring that packets are forwarded to local on the link as well as ensuring that packets are forwarded to
receivers (discovered through a local membership mechanism such as local receivers (discovered through a local membership mechanism
MLD or IGMP [2]). such as MLD [3] or IGMP [2]).
RPF Interface RPF Interface
RPF stands for "Reverse Path Forwarding". The RPF Interface of a RPF stands for "Reverse Path Forwarding". The RPF Interface of a
router with respect to an address is the interface that the MRIB router with respect to an address is the interface that the MRIB
indicates should be used to forward packets to that address. In indicates should be used to reach that address. In the case of a
the case of a BIDIR-PIM multicast group, the RPF interface is BIDIR-PIM multicast group, the RPF interface is determined by
determined by looking up the RPA in the MRIB. The RPF information looking up the RPA in the MRIB. The RPF information determines the
determines the interface of the router that would be used to send interface of the router that would be used to send packets towards
packets towards the RPL for the group. the RPL for the group.
RPF Neighbor RPF Neighbor
The RPF Neighbor of a router with respect to an address is the The RPF Neighbor of a router with respect to an address is the
neighbor that the MRIB indicates should be used to forward packets neighbor that the MRIB indicates should be used to reach that
to that address. Note that in BIDIR-PIM, the RPF neighbor for a address. Note that in BIDIR-PIM, the RPF neighbor for a group is
group is not necessarily the router on the RPF interface that Join not necessarily the router on the RPF interface that Join messages
messages for that group would be directed to (Join messages are for that group would be directed to (Join messages are only
only directed to the DF on the RPF interface for the group). directed to the DF on the RPF interface for the group).
TIB Tree Information Base. This is the collection of state at a PIM TIB Tree Information Base. This is the collection of state at a PIM
router that has been created by receiving PIM Join/Prune messages, router that has been created by receiving PIM Join/Prune messages,
PIM DF election messages and IGMP information from local hosts. PIM DF election messages and IGMP or MLD information from local
It essentially stores the state of all multicast distribution hosts. It essentially stores the state of all multicast
trees at that router. distribution trees at that router.
MFIB Multicast Forwarding Information Base. The TIB holds all the MFIB Multicast Forwarding Information Base. The TIB holds all the
state that is necessary to forward multicast packets at a router. state that is necessary to forward multicast packets at a router.
However, although this specification defines forwarding in terms However, although this specification defines forwarding in terms
of the TIB, to actually forward packets using the TIB is very of the TIB, to actually forward packets using the TIB is very
inefficient. Instead a real router implementation will normally inefficient. Instead a real router implementation will normally
build an efficient MFIB from the TIB state to perform forwarding. build an efficient MFIB from the TIB state to perform forwarding.
How this is done is implementation-specific, and is not discussed How this is done is implementation-specific, and is not discussed
in this document. in this document.
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3.1.1. General Purpose State 3.1.1. General Purpose State
A router holds the following state that is not specific to a RPA or A router holds the following state that is not specific to a RPA or
group: group:
Neighbor State: Neighbor State:
For each neighbor: For each neighbor:
o Information from neighbor's Hello
o Neighbor's Gen ID. o Neighbor's Gen ID.
o Neighbor liveness timer (NLT) o Neighbor liveness timer (NLT)
o Other information from neighbor's Hello
For more information on Hello information look at section 3.2 as well as
the PIM-SM specification in [4].
3.1.2. RPA State 3.1.2. RPA State
A router maintains a multicast-group to RPA mapping which is built A router maintains a multicast-group to RPA mapping which is built
through static configuration or by using an automatic RP discovery through static configuration or by using an automatic RP discovery
mechanism like BSR or AUTO-RP (see section 4 ). For each BIDIR-PIM RPA a mechanism like BSR or AUTO-RP (see section 4 ). For each BIDIR-PIM RPA a
router holds the following state: router holds the following state:
o RPA (actual address) o RPA (actual address)
Designated Forwarder (DF) State: Designated Forwarder (DF) State:
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messages on this interface, and is specified in section 3.4.1. The state messages on this interface, and is specified in section 3.4.1. The state
is used by the macros that calculate the outgoing interface list in is used by the macros that calculate the outgoing interface list in
section 3.1.4, and in the JoinDesired(G) macro (defined in section section 3.1.4, and in the JoinDesired(G) macro (defined in section
3.4.2) that is used in deciding whether a Join(*,G) should be sent 3.4.2) that is used in deciding whether a Join(*,G) should be sent
upstream. upstream.
The upstream Join/Prune timer is used to send out periodic Join(*,G) The upstream Join/Prune timer is used to send out periodic Join(*,G)
messages, and to override Prune(*,G) messages from peers on an upstream messages, and to override Prune(*,G) messages from peers on an upstream
LAN interface. LAN interface.
The last RPA used must be stored because if the RP Set changes (see [4]) The last RPA used must be stored because if the group to RPA mapping
then state must be torn down and rebuilt for groups whose RPA changes. changes (see RP Set changes in [4]) then state must be torn down and
rebuilt for groups whose RPA changes.
3.1.4. State Summarization Macros 3.1.4. State Summarization Macros
Using this state, we define the following "macro" definitions which we Using this state, we define the following "macro" definitions which we
will use in the descriptions of the state machines and pseudocode in the will use in the descriptions of the state machines and pseudocode in the
following sections. following sections.
olist(G) = olist(G) =
RPF_interface(RPA(G)) (+) joins(G) (+) pim_include(G) RPF_interface(RPA(G)) (+) joins(G) (+) pim_include(G)
RPF_interface(RPA) is the interface the MRIB indicates would be used to RPF_interface(RPA) is the interface the MRIB indicates would be used to
route packets to RPA. The olist(G) is the list of interfaces on which route packets to RPA. The olist(G) is the list of interfaces on which
packets to group G must be forwarded. packets to group G must be forwarded.
The macro pim_include(G) indicates the interfaces to which traffic might The macro pim_include(G) indicates the interfaces to which traffic might
be forwarded because of hosts that are local members on that interface. be forwarded because of hosts that are local members on that interface.
pim_include(G) = pim_include(G) =
{ all interfaces I such that: { all interfaces I such that:
I_am_DF(RPA(G),I) AND local_receiver_include(G,I) } I_am_DF(RPA(G),I) AND local_receiver_include(G,I) }
The clause "I_am_DF(RPA,I)" is TRUE if the router is in the Win or The clause "I_am_DF(RPA,I)" is TRUE if the router is in the Win or
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be forwarded because of hosts that are local members on that interface. be forwarded because of hosts that are local members on that interface.
pim_include(G) = pim_include(G) =
{ all interfaces I such that: { all interfaces I such that:
I_am_DF(RPA(G),I) AND local_receiver_include(G,I) } I_am_DF(RPA(G),I) AND local_receiver_include(G,I) }
The clause "I_am_DF(RPA,I)" is TRUE if the router is in the Win or The clause "I_am_DF(RPA,I)" is TRUE if the router is in the Win or
Backoff states in the DF election state machine (described in section Backoff states in the DF election state machine (described in section
3.5) for the given RPA on interface I. Otherwise it is FALSE. 3.5) for the given RPA on interface I. Otherwise it is FALSE.
The clause "local_receiver_include(G,I)" is true if the IGMP module or The clause "local_receiver_include(G,I)" is true if the IGMP module, MLD
other local membership mechanism has determined that there are local module or other local membership mechanism has determined that there are
members on interface I that desire to receive traffic sent to group G. local members on interface I that desire to receive traffic sent to
group G.
The set "joins(G)" is the set of all interfaces on which the router has The set "joins(G)" is the set of all interfaces on which the router has
received (*,G) Joins: received (*,G) Joins:
joins(G) = joins(G) =
{ all interfaces I such that { all interfaces I such that
I_am_DF(RPA(G),I) AND I_am_DF(RPA(G),I) AND
DownstreamJPState(G,I) is either Joined or PrunePending } DownstreamJPState(G,I) is either Joined or PrunePending }
DownstreamJPState(G,I) is the state of the finite state machine in DownstreamJPState(G,I) is the state of the finite state machine in
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in section 3.1. The procedures for generating and processing Hello in section 3.1. The procedures for generating and processing Hello
messages as well as maintaining Neighbor State are specified in the PIM- messages as well as maintaining Neighbor State are specified in the PIM-
SM [4] documentation. SM [4] documentation.
Bidir PIM introduces the Bidir_Capable PIM-Hello option that MUST be Bidir PIM introduces the Bidir_Capable PIM-Hello option that MUST be
included in all Hello messages from a Bidir-PIM capable router. The included in all Hello messages from a Bidir-PIM capable router. The
Bidir_Capable option advertises the router's ability to participate in Bidir_Capable option advertises the router's ability to participate in
the Bidir-PIM protocol. The format of the Bidir_Capable option is the Bidir-PIM protocol. The format of the Bidir_Capable option is
described in section 3.7. described in section 3.7.
If a Bidir PIM router receives a PIM-Hello message that does not contain
the Bidir_Capable option from one of its neighbours, the error must be
logged to the router administrator in a rate-limited manner.
3.3. Data Packet Forwarding Rules 3.3. Data Packet Forwarding Rules
For groups mapping to a given RPA, the following responsibilities are For groups mapping to a given RPA, the following responsibilities are
uniquely assigned to the DF for that RPA on each link: uniquely assigned to the DF for that RPA on each link:
o The DF is the only router that forwards packets traveling downstream o The DF is the only router that forwards packets traveling downstream
onto the link. onto the link.
o The DF is the only router that picks-up upstream traveling packets off o The DF is the only router that picks-up upstream traveling packets off
the link to forward towards the RPL. the link to forward towards the RPL.
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if( iif == RPF_interface(RPA) || I_am_DF(RPA,I) ) { if( iif == RPF_interface(RPA) || I_am_DF(RPA,I) ) {
oiflist = olist(G) (-) iif oiflist = olist(G) (-) iif
forward packet on all interfaces in oiflist forward packet on all interfaces in oiflist
} }
3.3.1. Upstream Forwarding at RP 3.3.1. Upstream Forwarding at RP
When configuring a BIDIR-PIM domain it is possible to assign the When configuring a BIDIR-PIM domain it is possible to assign the
Rendezvous Point Address (RPA) such that it does not belong to a Rendezvous Point Address (RPA) such that it does not belong to a
physical box but instead is simply a routable address. Routers that have physical box but instead is simply a routable address. Routers that have
interfaces on the RPL that the RPA belongs to will upstrem forward interfaces on the RPL that the RPA belongs to will upstream forward
traffic onto the link. Joins from receivers in the domain will propagate traffic onto the link. Joins from receivers in the domain will propagate
hop-by-hop till they reach one of the routers connected to the RPL where hop-by-hop till they reach one of the routers connected to the RPL where
they will terminate (as there will be no DF elected on the RPL). they will terminate (as there will be no DF elected on the RPL).
If instead the administrator chooses to configure the RPA to be the If instead the administrator chooses to configure the RPA to be the
addres of an interface of a specific router then nothing changes. That address of an interface of a specific router then nothing changes. That
router must still upstream forward traffic on to the RPL and behave no router must still upstream forward traffic on to the RPL and behave no
differently than any other router with an interface on the RPL. differently than any other router with an interface on the RPL.
To configure a BIDIR-PIM network to operate in a mode similar to that of To configure a BIDIR-PIM network to operate in a mode similar to that of
PIM-SM where a single router (the RP) is acting as the root of the PIM-SM where a single router (the RP) is acting as the root of the
distribution tree, the RPA address can be configured to be the loopback distribution tree, the RPA address can be configured to be the loopback
interface of a router. interface of a router.
3.3.2. Source-Only Branches 3.3.2. Source-Only Branches
Source-only branches of the distribution tree for a group G are branches Source-only branches of the distribution tree for a group G are branches
which do not lead to any receivers, but which are used to forward which do not lead to any receivers, but which are used to forward
packets traveling upstream from sources towards the RPL. Routers along packets traveling upstream from sources towards the RPL. Routers along
source-only branches only have the RPF_interface to the RPA in their source-only branches only have the RPF_interface to the RPA in their
olist for G and hence do not need to maintain any group specific state. olist for G and hence do not need to maintain any group specific state.
Upstream forwarding can be performed using only RPA specific state. An Upstream forwarding can be performed using only RPA specific state. An
implementation may decide to maintain group state for source-only implementation may decide to maintain group state for source-only
branches for accounting or performance reasons. branches for accounting or performance reasons. However, doing so
requires data-driven events thus sacrificing one of tha main benefits of
Bidir PIM.
3.3.3. Directly Connected Sources 3.3.3. Directly Connected Sources
A major advantage of using a Designated Forwarder in BIDIR-PIM compared A major advantage of using a Designated Forwarder in BIDIR-PIM compared
to PIM-SM is that special treatment is no longer required for sources to PIM-SM is that special treatment is no longer required for sources
that are directly connected to a router. Data from such sources does not that are directly connected to a router. Data from such sources does not
need to be differentiated from other multicast traffic and will need to be differentiated from other multicast traffic and will
automatically be picked up by the DF and forwarded upstream. This automatically be picked up by the DF and forwarded upstream. This
removes the need for performing a directly-connected-source check for removes the need for performing a directly-connected-source check for
data to groups that do not have existing state. data to groups that do not have existing state.
skipping to change at page 17, line 8 skipping to change at page 17, line 43
The transition events "Receive Join(*,G)" and "Receive Prune(*,G)" imply The transition events "Receive Join(*,G)" and "Receive Prune(*,G)" imply
receiving a Join or Prune targeted to this router's address on the receiving a Join or Prune targeted to this router's address on the
received interface. If the destination address is not correct, these received interface. If the destination address is not correct, these
state transitions in this state machine must not occur, although seeing state transitions in this state machine must not occur, although seeing
such a packet may cause state transitions in other state machines. such a packet may cause state transitions in other state machines.
On unnumbered interfaces on point-to-point links, the router's address On unnumbered interfaces on point-to-point links, the router's address
should be the same as the source address it chose for the hello packet should be the same as the source address it chose for the hello packet
it sent over that interface. However on point-to-point links we also it sent over that interface. However on point-to-point links we also
recommend that PIM messages with a 0.0.0.0 destination address are also recommend that PIM messages with a destination address of all zeros are
accepted. also accepted.
The transition event "Stop being DF" implies a DF re-election taking The transition event "Stop being DF" implies a DF re-election taking
place on this router interface for RPA(G) and the router changing status place on this router interface for RPA(G) and the router changing status
from being the active DF to being a non-DF router (the value of the from being the active DF to being a non-DF router (the value of the
I_am_DF macro changing to FALSE). I_am_DF macro changing to FALSE).
When ExpiryTimer is started or restarted, it is set to the HoldTime from When ExpiryTimer is started or restarted, it is set to the HoldTime from
the triggering received Join/Prune message. the triggering received Join/Prune message.
When PrunePendingTimer is started, it is set to the When PrunePendingTimer is started, it is set to the
skipping to change at page 20, line 26 skipping to change at page 21, line 26
This section presents a fail-safe mechanism for electing a per-RPA This section presents a fail-safe mechanism for electing a per-RPA
designated router on each link in a BIDIR-PIM domain. We call this designated router on each link in a BIDIR-PIM domain. We call this
router the Designated Forwarder (DF). The DF election does not take router the Designated Forwarder (DF). The DF election does not take
place on the RPL for a RPA. place on the RPL for a RPA.
3.5.1. DF Requirements 3.5.1. DF Requirements
The DF election chooses the best router on a link to assume the The DF election chooses the best router on a link to assume the
responsibility of forwarding traffic between the RPL and the link for responsibility of forwarding traffic between the RPL and the link for
the range of multicast groups served by the RPA. Different multicast the range of multicast groups served by the RPA. Different multicast
groups that share a common RPA must use the same bi-directional tree for groups that share a common RPA share the same upstream direction.
data forwarding. Hence, the election of an upstream forwarder on each Hence, the election of an upstream forwarder on each link does not have
link does not have to be a group specific decision but instead can be to be a group specific decision but instead can be RPA-specific. As the
RPA-specific. As the number of RPAs is typically small, the number of number of RPAs is typically small, the number of elections that have to
elections that have to be performed is significantly reduced by this be performed is significantly reduced by this observation.
observation.
To optimise tree creation, it is desirable that the winner of the To optimise tree creation, it is desirable that the winner of the
election process should be the router on the link with the "best" election process should be the router on the link with the "best"
unicast routing metric to reach the RPA (as reported by the MRIB). When unicast routing metric (as reported by the MRIB) to reach the RPA. When
comparing metrics from different unicast routing protocols, we use the comparing metrics from different unicast routing protocols, we use the
same comparison rules used by the PIM-SM assert process [4]. same comparison rules used by the PIM-SM assert process [4].
The election process needs to take place when information on a new RPA The election process needs to take place when information on a new RPA
initially becomes available. The result can be re-used as new bidir initially becomes available. The result can be re-used as new bidir
groups that map to the same RPA are encountered. There are however some groups that map to the same RPA are encountered. There are however some
conditions under which an update to the election is required: conditions under which an update to the election is required:
o There is a change in unicast metric to reach the RPA for any of o There is a change in unicast metric to reach the RPA for any of
the routers on the link. the routers on the link.
o The interface on which the RPA is reachable (RPF Interface) o The interface on which the RPA is reachable (RPF Interface)
changes to an interface for which the router was previously the changes to an interface for which the router was previously the
DF. DF.
o A new PIM neighbor starts up on a link that must participate in o A new PIM neighbor starts up on a link that must participate in
the elections and be informed of current outcome. the elections and be informed of current outcome.
o The elected DF dies (detected through neighbor information o The elected DF fails (detected through neighbor information
timeout or MRIB RPF change at downstream router). timeout or MRIB RPF change at downstream router).
The election process has to be robust enough to ensure with very high The election process has to be robust enough to ensure with very high
probability that all routers on the link have a consistent view of the probability that all routers on the link have a consistent view of the
DF. This is because with the forwarding rules described in section 3.3 DF. This is because with the forwarding rules described in section 3.3
if multiple routers end-up thinking that they should be responsible for if multiple routers end-up thinking that they should be responsible for
forwarding, loops may result. To reduce the possibility of this forwarding, loops may result. To reduce the possibility of this
occurrence to a minimum, the election algorithm has been biased towards occurrence to a minimum, the election algorithm has been biased towards
discarding DF information and suspending forwarding during periods of discarding DF information and suspending forwarding during periods of
ambiguity. ambiguity.
skipping to change at page 21, line 32 skipping to change at page 22, line 32
This section gives an outline of the DF election process. It does not This section gives an outline of the DF election process. It does not
provide the definitive specification for the DF election. If any provide the definitive specification for the DF election. If any
discrepancy exists between section 3.5.3 and this section, the discrepancy exists between section 3.5.3 and this section, the
specification in section 3.5.3 is to be assumed correct. specification in section 3.5.3 is to be assumed correct.
To perform the election of the DF for a particular RPA, routers on a To perform the election of the DF for a particular RPA, routers on a
link need to exchange their unicast routing metric information for link need to exchange their unicast routing metric information for
reaching the RPA. Routers advertise their own metrics in Offer, Winner, reaching the RPA. Routers advertise their own metrics in Offer, Winner,
Backoff and Pass messages. The advertised metric is calculated using the Backoff and Pass messages. The advertised metric is calculated using the
RPF Interface and metric to reach the RPA available through the MRIB. RPF Interface and metric to reach the RPA available through the MRIB.
When a router is paricipating in a DF election for an RPA on the When a router is participating in a DF election for an RPA on the
interface that its MRIB indicates as the RPF Interface then that router interface that its MRIB indicates as the RPF Interface then that router
MUST always advertise an infinite metric in its election messages. When MUST always advertise an infinite metric in its election messages. When
a router is participating in a DF election on an interface other than a router is participating in a DF election on an interface other than
the MRIB indicated RPF Interface then it MUST advertise the MRIB the MRIB indicated RPF Interface then it MUST advertise the MRIB
provided metrics in its election messages. provided metrics in its election messages.
In the election protocol described below, many message exchanges are In the election protocol described below, many message exchanges are
repeated Election_Robustness times for reliability. In all those cases repeated Election_Robustness times for reliability. In all those cases
the message retransmissions are spaced in time by a small random the message retransmissions are spaced in time by a small random
interval. All of the following description is specific to the election interval. All of the following description is specific to the election
skipping to change at page 22, line 22 skipping to change at page 23, line 22
The result should be that all routers except the best candidate stop The result should be that all routers except the best candidate stop
advertising their offers. advertising their offers.
A router assumes the role of the DF after having advertised its metrics A router assumes the role of the DF after having advertised its metrics
Election_Robustness times without receiving any offer from any other Election_Robustness times without receiving any offer from any other
neighbor. At that point it transmits a Winner message which declares to neighbor. At that point it transmits a Winner message which declares to
every other router on the link the identity of the winner and the every other router on the link the identity of the winner and the
metrics it is using. metrics it is using.
Routers hearing a winner message stop participating in the election and Routers receiving a winner message stop participating in the election
record the identity and metrics of the winner. If the local metrics are and record the identity and metrics of the winner. If the local metrics
better than those of the winner then the router records the identity of are better than those of the winner then the router records the identity
the winner (accepting it as the acting DF) but reinitiates the election of the winner (accepting it as the acting DF) but re-initiates the
to try and take over. election to try and take over.
3.5.2.2. Loser Metric Changes 3.5.2.2. Loser Metric Changes
Whenever the unicast metric to a RPA changes at a non-DF router to a Whenever the unicast metric to a RPA changes at a non-DF router to a
value that is better than that previously advertised by the acting DF, value that is better than that previously advertised by the acting DF,
the router with the new better metric should take action to eventually the router with the new better metric should take action to eventually
assume forwarding responsibility. When the metric change is detected, assume forwarding responsibility. When the metric change is detected,
the non-DF router with the now better metric restarts the DF election the non-DF router with the now better metric restarts the DF election
process by sending Offer messages with this new metric. Note that at process by sending Offer messages with this new metric. Note that at
any point during an election if no response is received after any point during an election if no response is received after
skipping to change at page 22, line 51 skipping to change at page 23, line 51
will respond with a Winner message declaring its status and advertising will respond with a Winner message declaring its status and advertising
its better metric. Upon receiving the Winner message, the originator of its better metric. Upon receiving the Winner message, the originator of
the Offer records the identity of the DF and aborts the election. the Offer records the identity of the DF and aborts the election.
Upon receipt of an offer that is better than its current metric, the DF Upon receipt of an offer that is better than its current metric, the DF
records the identity and metrics of the offering router and responds records the identity and metrics of the offering router and responds
with a Backoff message. This instructs the offering router to hold off with a Backoff message. This instructs the offering router to hold off
for a short period of time while the unicast routing stabilises and for a short period of time while the unicast routing stabilises and
other routers get a chance to put in their offers. The Backoff message other routers get a chance to put in their offers. The Backoff message
includes the offering router's new metric and address. All routers on includes the offering router's new metric and address. All routers on
the link who have pending offers with metrics worse than those in the the link that have pending offers with metrics worse than those in the
backoff message (including the original offering router) will hold backoff message (including the original offering router) will hold
further offers for a period of time defined in the Backoff message. further offers for a period of time defined in the Backoff message.
If during the Backoff_Period, a third router sends a new better offer, If during the Backoff_Period, a third router sends a new better offer,
the Backoff message is repeated for the new offer and the Backoff_Period the Backoff message is repeated for the new offer and the Backoff_Period
restarted. restarted.
Before the Backoff_Period expires, the acting DF nominates the router Before the Backoff_Period expires, the acting DF nominates the router
having made the best offer as the new DF using a Pass message. This having made the best offer as the new DF using a Pass message. This
message includes the IDs and metrics of both the old and new DFs. The message includes the IDs and metrics of both the old and new DFs. The
old DF stops performing its tasks at the time the Pass message old DF stops performing its tasks at the time the Pass message
transmission is made. The new DF assumes the role of the DF as soon as transmission is made. The new DF assumes the role of the DF as soon as
it receives the Pass message. All other routers on the link take note of it receives the Pass message. All other routers on the link take note of
the new DF and its metric. Note that this event constitutes an RPF the new DF and its metric. Note that this event constitutes an RPF
Neighbour change which may trigger Join messags to the new DF (see Neighbour change which may trigger Join messages to the new DF (see
section 3.4). section 3.4).
3.5.2.3. Winner Metric Changes 3.5.2.3. Winner Metric Changes
If the DF's routing metric to reach the RPA changes to a worse value, it If the DF's routing metric to reach the RPA changes to a worse value, it
sends a set of Election_Robustness randomly spaced Winner messages on sends a set of Election_Robustness randomly spaced Winner messages on
the link, advertising the new metric. Routers who receive this the link, advertising the new metric. Routers that receive this
announcement but have a better metric may respond with an Offer message announcement but have a better metric may respond with an Offer message
which results in the same handoff procedure described above. All which results in the same handoff procedure described above. All
routers assume the DF has not changed until they see a Pass or Winner routers assume the DF has not changed until they see a Pass or Winner
message indicating the change. message indicating the change.
There is no pressure to make this handoff quickly if the acting DF still There is no pressure to make this handoff quickly if the acting DF still
has a path to the RPL. The old path may now be suboptimal but it will has a path to the RPL. The old path may now be suboptimal but it will
still work while the re-election is in progress. still work while the re-election is in progress.
If the routing metric at the DF changes to a better value, a single If the routing metric at the DF changes to a better value, a single
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The router is the acting DF but another router has made a bid The router is the acting DF but another router has made a bid
to take over. to take over.
In the state machine a router is considered to be an acting DF if it is In the state machine a router is considered to be an acting DF if it is
in the Win or Backoff states. in the Win or Backoff states.
The operation of the election protocol makes use of the variables and The operation of the election protocol makes use of the variables and
timers described below: timers described below:
Acting DF information Acting DF information
Used to store the election winner who is the currently acting Used to store the identity and advertised metrics of the
DF. election winner that is the currently acting DF.
DF election-Timer (DFT) DF election-Timer (DFT)
Used to schedule transmission of Offer, Winner and Pass Used to schedule transmission of Offer, Winner and Pass
messages. messages.
Message-Count (MC) Message-Count (MC)
Used to maintain the number of times an Offer or Winner Used to maintain the number of times an Offer or Winner
message has been transmitted. message has been transmitted.
Best-Offer Best-Offer
Used by the DF to record who has made the last offer for Used by the DF to record the identity and advertised metrics
sending the Pass message. of the router has made the last offer for use when sending the
Pass message.
3.5.3.2. Election Messages 3.5.3.2. Election Messages
The election process uses the following PIM control messages the packet The election process uses the following PIM control messages the packet
format of which is described in section 3.7: format of which is described in section 3.7:
Offer (OfferingID, Metric) Offer (OfferingID, Metric)
Sent by routers that believe they have a better metric to the Sent by routers that believe they have a better metric to the
RPA than the metric that has been on offer so far. RPA than the metric that has been on offer so far.
skipping to change at page 26, line 16 skipping to change at page 27, line 16
BackoffInterval) BackoffInterval)
Used by the DF to acknowledge better offers. It instructs Used by the DF to acknowledge better offers. It instructs
other routers with equal or worse offers to wait till the DF other routers with equal or worse offers to wait till the DF
passes responsibility to the sender of the offer. passes responsibility to the sender of the offer.
Pass (Old-DF-ID, Old-DF-Metric, New-DF-ID, New-DF-Metric) Pass (Old-DF-ID, Old-DF-Metric, New-DF-ID, New-DF-Metric)
Used by the old DF to pass forwarding responsibility to a Used by the old DF to pass forwarding responsibility to a
router that has previously made an offer. The Old-DF-Metric router that has previously made an offer. The Old-DF-Metric
is the current metric of the DF at the time the pass is sent. is the current metric of the DF at the time the pass is sent.
Note that when a router is paricipating in a DF election for an RPA on Note that when a router is participating in a DF election for an RPA on
the interface that its MRIB indicates as the RPF Interface then that the interface that its MRIB indicates as the RPF Interface then that
router MUST always advertise an infinite metric in its election router MUST always advertise an infinite metric in its election
messages. When a router is participating in a DF election on an messages. When a router is participating in a DF election on an
interface other than the MRIB indicated RPF Interface then it MUST interface other than the MRIB indicated RPF Interface then it MUST
advertise the MRIB provided metrics in its election messages. advertise the MRIB provided metrics in its election messages.
3.5.3.3. Election Events 3.5.3.3. Election Events
During protocol operation the following events can take place: During protocol operation the following events can take place:
skipping to change at page 26, line 48 skipping to change at page 27, line 48
o On receipt of a Backoff or Pass message compare our current o On receipt of a Backoff or Pass message compare our current
metrics for the RPA with the metrics advertised for the metrics for the RPA with the metrics advertised for the
target of the message. target of the message.
Path to RPA lost Path to RPA lost
Losing the path to the RPA can happen in two ways. The first Losing the path to the RPA can happen in two ways. The first
happens when the route learned through the MRIB is withdrawn happens when the route learned through the MRIB is withdrawn
and the MRIB no longer reports an available route to reach the and the MRIB no longer reports an available route to reach the
RPA. The second case happens when the next-hop information RPA. The second case happens when the next-hop information
reported by the MRIB changes to indicate a next-hop that is reported by the MRIB changes to indicate a next-hop that is
reachable through the router interface for which the DF reachable through the router interface under consideration.
election is taking place. Clearly as the router is using the Clearly as the router is using the interface as its RPF
interface as its RPF Interface it cannot offer forwarding Interface it cannot offer forwarding services towards the RPL
services towards the RPL to other routers on that link. to other routers on that link.
Metric reported by the MRIB to reach the RPA changes Metric reported by the MRIB to reach the RPA changes
This event is triggered when the MRIB supplied information for This event is triggered when the MRIB supplied information for
the RPA changes and the new information provides a path to the the RPA changes and the new information provides a path to the
RPA. If the new MRIB information either reports no route or RPA. If the new MRIB information either reports no route or
reports a next-hop interface through the interface for which reports a next-hop interface through the interface for which
the DF election is taking place then the "Path to RPA lost" the DF election is taking place then the "Path to RPA lost"
event triggers instead. In specific states the event may be event triggers instead. In specific states the event may be
further filtered by specifying whether it is expected of the further filtered by specifying whether it is expected of the
metric to become better or worse and which stored metric the metric to become better or worse and which stored metric the
skipping to change at page 30, line 11 skipping to change at page 31, line 11
| Send Offer; DFT = | Send Winner | Set DF to None | | Send Offer; DFT = | Send Winner | Set DF to None |
| OPlow; MC = MC + 1 | | | | OPlow; MC = MC + 1 | | |
+-----------------------+-----------------------+-----------------------+ +-----------------------+-----------------------+-----------------------+
+-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+
| In Offer State | | In Offer State |
+-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+
| Metric changes and is now worse | | Metric changes and is now worse |
+-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+
| DFT ?= OPlow | | DFT ?= OPlow |
| OC = 0 | | MC = 0 |
+-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+
+-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+
| In Lose State | | In Lose State |
+--------------------------------+--------------------------------------+ +--------------------------------+--------------------------------------+
| Detect DF Failure | Metric changes and now | | Detect DF Failure | Metric changes and now |
| | is better than DF | | | is better than DF |
+--------------------------------+--------------------------------------+ +--------------------------------+--------------------------------------+
| -> Offer | -> Offer | | -> Offer | -> Offer |
| DF = None; DFT = | DFT = OPlow_int; MC = 0 | | DF = None; DFT = | DFT = OPlow_int; MC = 0 |
skipping to change at page 31, line 27 skipping to change at page 32, line 27
messages (like a CPU overload), the new candidate will transmit three messages (like a CPU overload), the new candidate will transmit three
offers and assume the role of the forwarder resulting in two DFs on the offers and assume the role of the forwarder resulting in two DFs on the
link. This situation is pathological and should be corrected by fixing link. This situation is pathological and should be corrected by fixing
the overloaded router. It is desirable that such an event can be the overloaded router. It is desirable that such an event can be
detected by a network administrator. detected by a network administrator.
When a router becomes the DF for a link without receiving a Pass message When a router becomes the DF for a link without receiving a Pass message
from the known old DF, the PIM neighbor information for the old DF can from the known old DF, the PIM neighbor information for the old DF can
be marked to this effect. Upon receiving the next PIM Hello message from be marked to this effect. Upon receiving the next PIM Hello message from
the old DF, the router can retransmit Winner messages for all the RPAs the old DF, the router can retransmit Winner messages for all the RPAs
for which it acting as the DF. The anomaly may also be logged by the for which it is acting as the DF. The anomaly may also be logged by the
router in a rate-limited manner to alert the operator. router in a rate-limited manner to alert the operator.
3.5.6. Periodic Winner Announcement 3.5.6. Periodic Winner Announcement
An additional degree of safety can be achieved by having the DF for each An additional degree of safety can be achieved by having the DF for each
RPA periodically announce its status in a Winner message. Transmission RPA periodically announce its status in a Winner message. Transmission
of the periodic Winner message can be restricted to occur only for RPAs of the periodic Winner message can be restricted to occur only for RPAs
which have active groups, thus avoiding the periodic control traffic in which have active groups, thus avoiding the periodic control traffic in
areas of the network without senders or receivers for a particular RPA. areas of the network without senders or receivers for a particular RPA.
skipping to change at page 35, line 21 skipping to change at page 36, line 21
| | | election messages | | | | election messages |
| | | that must be lost | | | | that must be lost |
| | | in order for | | | | in order for |
| | | election to fail. | | | | election to fail. |
+--------------------------+-------------------+------------------------+ +--------------------------+-------------------+------------------------+
3.7. BIDIR PIM Packet Formats 3.7. BIDIR PIM Packet Formats
This section describes the details of the packet formats for BIDIR-PIM This section describes the details of the packet formats for BIDIR-PIM
control messages. BIDIR-PIM shares a number of control messages in control messages. BIDIR-PIM shares a number of control messages in
common with PIM-SM [4] well as the format for the Encoded-Unicast common with PIM-SM [4]. These include the Hello and Join/Prune messages
address. For details on the format of these packets please refer to the as well as the format for the Encoded-Unicast address. For details on
PIM-SM documentation. Here we will only define the additional packets the format of these packets please refer to the PIM-SM documentation.
that are introduced by BIDIR-PIM. These are the packets used in the DF Here we will only define the additional packets that are introduced by
election process as well as the Bidir_Capable PIM-Hello option. BIDIR-PIM. These are the packets used in the DF election process as
well as the Bidir_Capable PIM-Hello option.
3.7.1. DF Election Packet Formats 3.7.1. DF Election Packet Formats
All PIM control messages have IP protocol number 103. All PIM control messages have IP protocol number 103.
BIDIR-PIM messages are multicast with TTL 1 to the `ALL-PIM-ROUTERS' BIDIR-PIM messages are multicast with TTL 1 to the `ALL-PIM-ROUTERS'
group `224.0.0.13'. group `224.0.0.13'.
All DF election BIDIR-PIM control messages share the common header All DF election BIDIR-PIM control messages share the common header
below: below:
skipping to change at page 38, line 33 skipping to change at page 39, line 33
0 1 2 3 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 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 = 22 | Length = 0 | | Type = 22 | Length = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4. RP Discovery 4. RP Discovery
Routers discover that a range of multicast group addresses operates in Routers discover that a range of multicast group addresses operates in
bi-directional mode and the address of the Rendezvous-Point serving the bi-directional mode and the address of the Rendezvous-Point address
group range either through static configuration or using an automatic RP (RPA) serving the group range either through static configuration or
discovery mechanism like the PIM Bootsrtap mechanism (BSR). [9]. using an automatic RP discovery mechanism like the PIM Bootsrtap
mechanism (BSR). [9] or Auto-RP.
By default the BSR protocol advertises RPs that operate the PIM-SM
protocol. In order to identify a RP as operating in BIDIR mode, the
Encoded-Group Address field in Bootstrap and Candidate-RP Advertisement
messages has been extended by adding the BIDIR bit (B-bit) as specified
below:
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 | Mask Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Multicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
B-bit
When the Bidir-bit is set, all BIDIR capable PIM routers will
operate the protocol described in this document for the specified
group range.
5. Security Considerations 5. Security Considerations
The IPsec [5] authentication header MAY be used to provide data The IPsec [5] authentication header MAY be used to provide data
integrity protection and group-wise data origin authentication of BIDIR- integrity protection and group-wise data origin authentication of BIDIR-
PIM protocol messages. Authentication of BIDIR-PIM messages can protect PIM protocol messages. Authentication of BIDIR-PIM messages can protect
against unwanted behaviour caused by unauthorized or altered BIDIR-PIM against unwanted behaviour caused by unauthorized or altered BIDIR-PIM
messages. messages.
5.1. Attacks Based on Forged Messages 5.1. Attacks Based on Forged Messages
skipping to change at page 40, line 26 skipping to change at page 41, line 9
attack, BIDIR-PIM routers SHOULD check the destination MAC address of attack, BIDIR-PIM routers SHOULD check the destination MAC address of
received DF-election messages. This however is ineffective on links received DF-election messages. This however is ineffective on links
that do not support layer-2 multicast delivery. that do not support layer-2 multicast delivery.
Source authentication is also sufficient to prevent this kind of attack. Source authentication is also sufficient to prevent this kind of attack.
5.1.2. Preventing Election Convergence 5.1.2. Preventing Election Convergence
By forging DF election messages, an attacker can prevent the election By forging DF election messages, an attacker can prevent the election
from converging thus disrupting the establishment of multicast from converging thus disrupting the establishment of multicast
forwarding trees. There are many way to achieve this. The simplest is by forwarding trees. There are many ways to achieve this. The simplest is
sending an infinite sequence of Offer messages (the metric used in the by sending an infinite sequence of Offer messages (the metric used in
messages is not important). the messages is not important).
5.2. Non-cryptographic Authentication Mechanisms 5.2. Non-cryptographic Authentication Mechanisms
A BIDIR-PIM router SHOULD provide an option to limit the set of A BIDIR-PIM router SHOULD provide an option to limit the set of
neighbors from which it will accept Join/Prune, Assert, and DF-election neighbors from which it will accept Join/Prune, Assert, and DF-election
messages. Either static configuration of IP addresses or an IPsec messages. Either static configuration of IP addresses or an IPsec
security association may be used. Furthermore, a PIM router SHOULD NOT security association may be used. Furthermore, a PIM router SHOULD NOT
accept protocol messages from a router from which it has not yet accept protocol messages from a router from which it has not yet
received a valid Hello message. received a valid Hello message.
5.2.1. Basic Access Control 5.2.1. Basic Access Control
In a PIM-SM domain, when all router are trusted, it is possible to In a PIM-SM domain, when all routers are trusted, it is possible to
implement a basic form of access control for both sources and receivers: implement a basic form of access control for both sources and receivers:
Receivers can be validated by the last-hop DR and sources can be Receivers can be validated by the last-hop DR and sources can be
validated by the first-hop DR and/or the RP. validated by the first-hop DR and/or the RP.
In BIDIR-PIM this is generally feasible only for receivers, as sources In BIDIR-PIM this is generally feasible only for receivers, as sources
can send to the multicast group without the need for routers to detect can send to the multicast group without the need for routers to detect
their activity and create source-specific state. However it is possible their activity and create source-specific state. However it is possible
to modify the standard BIDIR-PIM behaviour, in a backward compatible to modify the standard BIDIR-PIM behaviour, in a backward compatible
way, to allow per-source access control. The tradeoff would be protocol way, to allow per-source access control. The tradeoff would be protocol
simplicity, memory and processing requirements. simplicity, memory and processing requirements.
5.3. Authentication Using IPsec 5.3. Authentication Using IPsec
The IPsec [5] transport mode using the Authentication Header (AH) is the The IPsec [5] transport mode using the Authentication Header (AH) is the
RECOMMENDED method to prevent the above attacks against BIDIR-PIM. RECOMMENDED method to prevent the above attacks against BIDIR-PIM.
It is RECOMMENDED that IPsec authentication be applied to all BIDIR-PIM It is RECOMMENDED that IPsec authentication be applied to all BIDIR-PIM
protocol messages. The specification on how this is done is to be found protocol messages. The specification on how this is done is to be found
in [4]. pecifically the authentication of PIM-SM link-local messages, in [4]. specifically the authentication of PIM-SM link-local messages,
described in [4] applies to all BIDIR-PIM messages as well. described in [4] applies to all BIDIR-PIM messages as well.
5.4. Denial of Service Attacks 5.4. Denial of Service Attacks
The denial of service attack based on forged Join described in [4] also The denial of service attack based on forged Join described in [4] also
apply to BIDIR-PIM. apply to BIDIR-PIM.
6. Change history 6. Change history
>From 03 to 04: >From 05 to 06:
Minor editorial corrections.
>From 03 to 05:
RP concept replaced by RP Address (RPA) and RP Link (RPL). No DF RP concept replaced by RP Address (RPA) and RP Link (RPL). No DF
election on RPL. RP forwards upstream on RPL. Accept joins even if not election on RPL. RP forwards upstream on RPL. Accept joins even if not
DF but do not forward. Added event description for DF election state DF but do not forward. Added event description for DF election state
machine. Removed comparison with Dino's draft. machine. Security considerations by Lorenzo.Removed comparison with
Dino's draft.
>From 02 to 03: >From 02 to 03:
Consistency fixes in DF election tables to match state transition Consistency fixes in DF election tables to match state transition
diagram pointed out by Apoorva. diagram pointed out by Apoorva.
>From 00 to 01: >From 00 to 01:
The differences between this version (-01) of the BIDIR-PIM The differences between this version (-01) of the BIDIR-PIM
specification and draft-ietf-pim-bidir-new-00.txt are mostly in the specification and draft-ietf-pim-bidir-new-00.txt are mostly in the
skipping to change at page 42, line 5 skipping to change at page 42, line 42
documentation [4] where necessary. In addition the method in which the documentation [4] where necessary. In addition the method in which the
protocol specification is presented has been updated to follow the protocol specification is presented has been updated to follow the
format of [4]. format of [4].
7. Acknowledgments 7. Acknowledgments
The bidir proposal in this draft is heavily based on the ideas and text The bidir proposal in this draft is heavily based on the ideas and text
presented by Estrin and Farinacci in [7]. The main difference between presented by Estrin and Farinacci in [7]. The main difference between
the two proposals is in the method chosen for upstream forwarding. the two proposals is in the method chosen for upstream forwarding.
We would also like to thank John Zwiebel at procket, Deborah Estrin at We would also like to thank John Zwiebel at Procket, Deborah Estrin at
ISI/USC as well as Nidhi Bhaskar, Yiqun Cai, Toerless Eckert, Apoorva ISI/USC as well as Nidhi Bhaskar, Yiqun Cai, Toerless Eckert, Apoorva
Karan, Rajitha Sumanasekera and Beau Williamson at cisco for their Karan, Rajitha Sumanasekera and Beau Williamson at cisco for their
contributions and comments to this draft. contributions and comments to this draft.
8. Authors' Addresses 8. Authors' Addresses
Mark Handley Mark Handley
Computer Science Department Computer Science Department
University College London University College London
M.Handley@cs.ucl.ac.uk M.Handley@cs.ucl.ac.uk
skipping to change at page 42, line 29 skipping to change at page 43, line 24
kouvelas@cisco.com kouvelas@cisco.com
Tony Speakman Tony Speakman
Cisco Systems Cisco Systems
speakman@cisco.com speakman@cisco.com
Lorenzo Vicisano Lorenzo Vicisano
Cisco Systems Cisco Systems
lorenzo@cisco.com lorenzo@cisco.com
9. Normative 9. Normative References
[1] S.E. Deering, "Host extensions for IP multicasting", RFC 1112, Aug [1] S.E. Deering, "Host extensions for IP multicasting", RFC 1112, Aug
1989. 1989.
[2] B. Cain, S Deering, W. Fenner, I Kouvelas, A. Thyagarajan, "Internet [2] B. Cain, S Deering, W. Fenner, I Kouvelas, A. Thyagarajan, "Internet
Group Management Protocol, Version 3", RFC 3376. Group Management Protocol, Version 3", RFC 3376.
[3] S. Deering, W. Fenner, B. Haberman, "Multicast Listener Discovery [3] S. Deering, W. Fenner, B. Haberman, "Multicast Listener Discovery
(MLD) for IPv6", RFC 2710. (MLD) for IPv6", RFC 2710.
[4] B. Fenner, M. Handley, H. Holbrook, I. Kouvelas "Protocol [4] B. Fenner, M. Handley, H. Holbrook, I. Kouvelas "Protocol
Independent Multicast - Sparse Mode (PIM-SM): Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol
Specification (Revised)", Work In Progress, <draft-ietf-pim-sm- Specification (Revised)", Work In Progress, <draft-ietf-pim-sm-
v2-new-01.txt>, 2000. v2-new-09.txt>, 2004.
[5] S. Kent, R. Atkinson, "Security Architecture for the Internet [5] S. Kent, R. Atkinson, "Security Architecture for the Internet
Protocol.", RFC 2401. Protocol.", RFC 2401.
10. Informative 10. Informative References
[6] T. Bates , R. Chandra , D. Katz , Y. Rekhter, "Multiprotocol [6] T. Bates , R. Chandra , D. Katz , Y. Rekhter, "Multiprotocol
Extensions for BGP-4", RFC 2283 Extensions for BGP-4", RFC 2283
[7] D. Estrin, D. Farinacci, "Bi-directional Shared Trees in PIM-SM", [7] D. Estrin, D. Farinacci, "Bi-directional Shared Trees in PIM-SM",
Work In Progress, <draft-farinacci-bidir-pim-01.txt>, May 1999. <draft-farinacci-bidir-pim-01.txt>, May 1999.
[8] D. Estrin et al, "Protocol Independent Multicast-Sparse Mode (PIM- [8] D. Estrin et al, "Protocol Independent Multicast-Sparse Mode (PIM-
SM): Protocol Specification", RFC 2362, Nov 1999. SM): Protocol Specification", RFC 2362, Nov 1999.
[9] W. Fenner, M. Handley, R. Kermode and D. Thaler, "Bootstrap Router [9] W. Fenner, M. Handley, R. Kermode and D. Thaler, "Bootstrap Router
(BSR) Mechanism for PIM Sparse Mode", draft-ietf-pim-sm-bsr-00.txt, (BSR) Mechanism for PIM Sparse Mode", Work in progress <draft-ietf-
work in progress. pim-sm-bsr-03.txt>, 2003.
11. Index 11. Index
DF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,21
Downstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
DownstreamJPState(G,I) . . . . . . . . . . . . . . . . . . . . . . . 12 DownstreamJPState(G,I) . . . . . . . . . . . . . . . . . . . . . . . 12
ET(G,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,15,33 ET(G,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,34
ET(RPA,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ET(RPA,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
I_am_DF(RPA,I) . . . . . . . . . . . . . . . . . . . . . . . . .12,14,17 I_am_DF(RPA,I) . . . . . . . . . . . . . . . . . . . . . . . . .12,14,17
J/P_HoldTime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 J/P_HoldTime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
J/P_Override_Interval. . . . . . . . . . . . . . . . . . . . . . . 17,34 J/P_Override_Interval. . . . . . . . . . . . . . . . . . . . . . . 18,35
JoinDesired(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 JoinDesired(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
joins(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 joins(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
JT(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 JT(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
JT(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11,34 JT(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11,35
local_receiver_include(G,I). . . . . . . . . . . . . . . . . . . . . 12 local_receiver_include(G,I). . . . . . . . . . . . . . . . . . . . . 12
NLT(N,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 MFIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Offer_Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 NLT(N,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
olist(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,14,19 Offer_Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
OT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 olist(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . .12,14,20
OT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
pim_include(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 pim_include(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PPT(G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,34 PPT(G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,35
RPA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
RPF_interface(RPA) . . . . . . . . . . . . . . . . . . . . . . . . 12,14 RPF_interface(RPA) . . . . . . . . . . . . . . . . . . . . . . . . 12,14
t_override . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19,34 RPL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
t_periodic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19,34 TIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
t_suppressed . . . . . . . . . . . . . . . . . . . . . . . . . . . 19,34 t_override . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
t_periodic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
t_suppressed . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
Upstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
 End of changes. 

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