draft-ietf-pim-bidir-09.txt   rfc5015.txt 
Internet Engineering Task Force PIM WG
INTERNET-DRAFT Mark Handley/UCL
draft-ietf-pim-bidir-09.txt Isidor Kouvelas/Cisco
Intended Status: Proposed Standard Tony Speakman/Cisco
Lorenzo Vicisano/Digital Fountain
22 February 2007
Expires: August 2007
Bi-directional Protocol Independent Multicast (BIDIR-PIM) Network Working Group M. Handley
Request for Comments: 5015 UCL
Status of this Document Category: Standards Track I. Kouvelas
T. Speakman
By submitting this Internet-Draft, each author represents that any Cisco
applicable patent or other IPR claims of which he or she is aware L. Vicisano
have been or will be disclosed, and any of which he or she becomes Digital Fountain
aware will be disclosed, in accordance with Section 6 of BCP 79. October 2007
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This document is a product of the IETF PIM WG. Comments should be Bidirectional Protocol Independent Multicast (BIDIR-PIM)
addressed to the authors, or the mailing list at pim@ietf.org.
Abstract Status of This Memo
This document discusses Bi-directional PIM, a variant of PIM This document specifies an Internet standards track protocol for the
Sparse-Mode that builds bi-directional shared trees connecting Internet community, and requests discussion and suggestions for
multicast sources and receivers. Bi-directional trees are built improvements. Please refer to the current edition of the "Internet
using a fail-safe Designated Forwarder (DF) election mechanism Official Protocol Standards" (STD 1) for the standardization state
operating on each link of a multicast topology. With the and status of this protocol. Distribution of this memo is unlimited.
assistance of the DF, multicast data is natively forwarded from
sources to the Rendezvous-Point 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.
Table of Contents Abstract
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 5 This document discusses Bidirectional PIM (BIDIR-PIM), a variant of
2. Terminology. . . . . . . . . . . . . . . . . . . . . . . . 6 PIM Sparse-Mode that builds bidirectional shared trees connecting
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . 6 multicast sources and receivers. Bidirectional trees are built using
2.2. Pseudocode Notation . . . . . . . . . . . . . . . . . . 8 a fail-safe Designated Forwarder (DF) election mechanism operating on
3. Protocol Specification . . . . . . . . . . . . . . . . . . 8 each link of a multicast topology. With the assistance of the DF,
3.1. BIDIR-PIM Protocol State. . . . . . . . . . . . . . . . 9 multicast data is natively forwarded from sources to the Rendezvous-
3.1.1. General Purpose State. . . . . . . . . . . . . . . . 9 Point (RP) and hence along the shared tree to receivers without
3.1.2. RPA State. . . . . . . . . . . . . . . . . . . . . . 10 requiring source-specific state. The DF election takes place at RP
3.1.3. Group State. . . . . . . . . . . . . . . . . . . . . 10 discovery time and provides the route to the RP, thus eliminating the
3.1.4. State Summarization Macros . . . . . . . . . . . . . 11 requirement for data-driven protocol events.
3.2. PIM Neighbor Discovery. . . . . . . . . . . . . . . . . 12
3.3. Data Packet Forwarding Rules. . . . . . . . . . . . . . 13
3.3.1. Upstream Forwarding at RP. . . . . . . . . . . . . . 14
3.3.2. Source-Only Branches . . . . . . . . . . . . . . . . 14
3.3.3. Directly Connected Sources . . . . . . . . . . . . . 15
3.4. PIM Join/Prune Messages . . . . . . . . . . . . . . . . 15
3.4.1. Receiving (*,G) Join/Prune Messages. . . . . . . . . 15
3.4.2. Sending Join/Prune Messages. . . . . . . . . . . . . 18
3.5. Designated Forwarder (DF) Election. . . . . . . . . . . 21
3.5.1. DF Requirements. . . . . . . . . . . . . . . . . . . 21
3.5.2. DF Election description. . . . . . . . . . . . . . . 22
3.5.2.1. Bootstrap Election. . . . . . . . . . . . . . . . 22
3.5.2.2. Loser Metric Changes. . . . . . . . . . . . . . . 23
3.5.2.3. Winner Metric Changes . . . . . . . . . . . . . . 24
3.5.2.4. Winner Loses Path . . . . . . . . . . . . . . . . 24
3.5.2.5. Late Router Starting Up . . . . . . . . . . . . . 25
3.5.2.6. Winner Dies . . . . . . . . . . . . . . . . . . . 25
3.5.3. Election Protocol Specification. . . . . . . . . . . 25
3.5.3.1. Election State. . . . . . . . . . . . . . . . . . 25
3.5.3.2. Election Messages . . . . . . . . . . . . . . . . 26
3.5.3.3. Election Events . . . . . . . . . . . . . . . . . 27
3.5.3.4. Election Actions. . . . . . . . . . . . . . . . . 28
3.5.3.5. Election State Transitions. . . . . . . . . . . . 29
3.5.4. Election Reliability Enhancements. . . . . . . . . . 32
3.5.5. Missing Pass . . . . . . . . . . . . . . . . . . . . 32
3.5.6. Periodic Winner Announcement . . . . . . . . . . . . 32
3.6. Timers, Counters and Constants. . . . . . . . . . . . . 32
3.7. BIDIR-PIM Packet Formats. . . . . . . . . . . . . . . . 36
3.7.1. DF Election Packet Formats . . . . . . . . . . . . . 36
3.7.2. Backoff Message. . . . . . . . . . . . . . . . . . . 37
3.7.3. Pass Message . . . . . . . . . . . . . . . . . . . . 38
3.7.4. Bidir Capable PIM-Hello Option . . . . . . . . . . . 39
4. RP Discovery . . . . . . . . . . . . . . . . . . . . . . . 39
5. Security Considerations. . . . . . . . . . . . . . . . . . 39
5.1. Attacks Based on Forged Messages. . . . . . . . . . . . 39
5.1.1. Election of an Incorrect DF. . . . . . . . . . . . . 40
5.1.2. Preventing Election Convergence. . . . . . . . . . . 41
5.2. Non-cryptographic Authentication Mechanisms . . . . . . 41
5.2.1. Basic Access Control . . . . . . . . . . . . . . . . 41
5.3. Authentication Using IPsec. . . . . . . . . . . . . . . 41
5.4. Denial of Service Attacks . . . . . . . . . . . . . . . 41
6. IANA Considerations. . . . . . . . . . . . . . . . . . . . 42
7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . 42
8. Authors' Addresses . . . . . . . . . . . . . . . . . . . . 42
9. Normative References . . . . . . . . . . . . . . . . . . . 42
10. Informative References. . . . . . . . . . . . . . . . . . 43
11. Index . . . . . . . . . . . . . . . . . . . . . . . . . . 44
List of Figures Table of Contents
Figure 1. Downstream group per-interface state- 1. Introduction ....................................................3
machine . . . . . . . . . . . . . . . . . . . . . . 16 2. Terminology .....................................................4
Figure 2. Upstream group state-machine. . . . . . . . . . . . 19 2.1. Definitions ................................................4
Figure 3. Designated Forwarder election state- 2.2. Pseudocode Notation ........................................6
machine . . . . . . . . . . . . . . . . . . . . . . 29 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
3.7.4. Bidirectional Capable PIM-Hello Option .............37
4. RP Discovery ...................................................37
5. Security Considerations ........................................38
5.1. Attacks Based on Forged Messages ..........................38
5.1.1. Election of an Incorrect DF ........................38
5.1.2. Preventing Election Convergence ....................39
5.2. Non-Cryptographic Authentication Mechanisms ...............39
5.2.1. Basic Access Control ...............................39
5.3. Authentication Using IPsec ................................40
5.4. Denial-of-Service Attacks .................................40
6. IANA Considerations ............................................40
7. Acknowledgments ................................................40
8. Normative References ...........................................40
9. Informative References .........................................41
List of Figures
Figure 1. Downstream group per-interface state machine ............15
Figure 2. Upstream group state machine ............................17
Figure 3. Designated Forwarder election state machine .............27
1. Introduction 1. Introduction
This document specifies Bi-directional PIM (BIDIR-PIM), a variant of This document specifies Bidirectional PIM (BIDIR-PIM), a variant of
PIM Sparse-Mode (PIM-SM) [4] that builds bi-directional shared trees PIM Sparse-Mode (PIM-SM) [4] that builds bidirectional shared trees
connecting multicast sources and receivers. connecting multicast sources and receivers.
PIM-SM constructs uni-directional shared trees that are used to PIM-SM constructs unidirectional shared trees that are used to
forward data from senders to receivers of a multicast group. PIM-SM forward data from senders to receivers of a multicast group. PIM-SM
also allows the construction of source specific trees, but this also allows the construction of source-specific trees, but this
capability is not related to the protocol described in this document. capability is not related to the protocol described in this document.
The shared tree for each multicast group is rooted at a multicast The shared tree for each multicast group is rooted at a multicast
router called the Rendezvous Point (RP). Different multicast groups router called the Rendezvous Point (RP). Different multicast groups
can use separate RPs within a PIM domain. can use 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
packets are forwarded from a source to the RP: way 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 that 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.
o A transition from the above distribution mode can be made at a o A transition from the above distribution mode can be made at a
later stage. This is achieved by building source specific state on later stage. This is achieved by building source-specific state on
all routers along the path between the source and the RP. This all routers along the path between the source and the RP. This
state is then used to natively forward packets from that source. state is then used to natively forward packets from that source.
Both these mechanisms suffer from problems. Encapsulation results in Both of these mechanisms suffer from problems. Encapsulation results
significant processing, bandwidth and delay overheads. Forwarding in significant processing, bandwidth, and delay overheads.
using source specific state has additional protocol and memory Forwarding using source-specific state has additional protocol and
requirements. memory requirements.
Bi-directional PIM dispenses with both encapsulation and source state Bidirectional PIM dispenses with both encapsulation and source state
by allowing packets to be natively forwarded from a source to the RP by allowing packets to be natively forwarded from a source to the RP
using shared tree state. In contrast to PIM-SM this mode of using shared tree state. In contrast to PIM-SM, this mode of
forwarding does not require any data-driven events. forwarding does not require any data-driven events.
The protocol specification in this document assumes familiarity with The protocol specification in this document assumes familiarity with
the PIM-SM specification in [4]. Portions of the BIDIR-PIM protocol the 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", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant BIDIR-PIM implementations. indicate 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 Multicast Routing Information Base (MRIB)
topology table, which is typically derived from the unicast The multicast topology table, which is typically derived from the
routing table, or routing protocols such as MBGP that carry unicast routing table, or routing protocols such as Multiprotocol
multicast-specific topology information. It is used by PIM for BGP (MBGP) [8] that carry multicast-specific topology information.
establishing the RPF interface (used in the forwarding rules). It is used by PIM for establishing the RPF interface (used in the
In PIM-SM the MRIB is also used to make decisions regarding forwarding rules). In PIM-SM, the MRIB is also used to make
where to forward Join/Prune messages whereas in BIDIR-PIM it is decisions regarding where to forward Join/Prune messages, whereas
used as a source for routing metrics for the DF election in BIDIR-PIM, it is used as a source for routing metrics for the
process. DF election process.
Rendezvous Point Address (RPA): Rendezvous Point Address (RPA)
An RPA is an address that is used as the root of the An RPA is an address that is used as the root of the distribution
distribution tree for a range of multicast groups. The RPA must tree for a range of multicast groups. The RPA must be routable
be routable from all routers in the PIM domain. The RPA does from all routers in the PIM domain. The RPA does not need to
not need to correspond to an address for an interface of a real correspond to an address for an interface of a real router. In
router. In this respect BIDIR-PIM differs from PIM-SM which this respect, BIDIR-PIM differs from PIM-SM, which requires an
requires an actual router to be configured as the Rendezvous actual router to be configured as the Rendezvous Point (RP). Join
Point (RP). Join messages from receivers for a BIDIR-PIM group messages from receivers for a BIDIR-PIM group propagate hop-by-hop
propagate hop-by-hop towards the RPA. towards the RPA.
Rendezvous Point Link (RPL): Rendezvous Point Link (RPL)
An RPL for a particular RPA is the physical link to which the An RPL for a particular RPA is the physical link to which the RPA
RPA belongs. In BIDIR-PIM all multicast traffic to groups belongs. In BIDIR-PIM, all multicast traffic to groups mapping to
mapping to a specific RPA is forwarded on the RPL of that RPA. a specific RPA is forwarded on the RPL of that RPA. The RPL is
The RPL is special within a BIDIR-PIM domain as it is the only special within a BIDIR-PIM domain as it is the only link on which
link on which a Designated Forwarder election does not take a Designated Forwarder election does not take place (see DF
place (see DF definition below). definition below).
Upstream Upstream
Towards the root (RPA) of the tree. The direction used by Towards the root (RPA) of the tree. The direction used by packets
packets traveling from sources to the RPL. traveling from sources to the RPL.
Downstream Downstream
Away from the root of the tree. The direction on which packets Away from the root of the tree. The direction on which packets
travel from the RPL to receivers. travel from the RPL to receivers.
Designated Forwarder (DF): Designated Forwarder (DF)
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 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 is 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 link with the best route to the RPA (determined by comparing MRIB
MRIB provided metrics). A DF for a given RPA is in charge of provided metrics). A DF for a given RPA is in charge of
forwarding downstream traffic onto its link, and forwarding forwarding downstream traffic onto its link, and forwarding
upstream traffic from its link towards the RPL. It does this upstream traffic from its link towards the RPL. It does this for
for all the bi-directional groups that map to the RPA. The DF all the bidirectional groups that map to the RPA. The DF on a
on a link is also responsible for processing Join messages from link is also responsible for processing Join messages from
downstream routers on the link as well as ensuring that packets downstream routers on the link as well as ensuring that packets
are forwarded to local receivers (discovered through a local are forwarded to local receivers (discovered through a local
membership mechanism such as MLD [3] or IGMP [2]). membership mechanism such as MLD [3] or IGMP [2]).
RPF Interface RPF Interface
RPF stands for "Reverse Path Forwarding". The RPF Interface of RPF stands for "Reverse Path Forwarding". The RPF Interface of a
a router with respect to an address is the interface that the router with respect to an address is the interface that the MRIB
MRIB indicates should be used to reach that address. In the indicates should be used to reach that address. In the case of a
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 looking up the RPA in the MRIB. The RPF information determines
information determines the interface of the router that would the interface of the router that would be used to send packets
be used to send packets towards the RPL for the group. towards 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 reach that neighbor that the MRIB indicates should be used to reach that
address. Note that in BIDIR-PIM, the RPF neighbor for a group address. Note that in BIDIR-PIM, the RPF neighbor for a group is
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 Tree Information Base (TIB)
PIM router that has been created by receiving PIM Join/Prune This is the collection of state at a PIM router that has been
messages, PIM DF election messages and IGMP or MLD information created by receiving PIM Join/Prune messages, PIM DF election
from local hosts. It essentially stores the state of all messages, and IGMP or MLD information from local hosts. It
multicast distribution trees at that router. essentially stores the state of all multicast distribution trees
at that router.
MFIB Multicast Forwarding Information Base. The TIB holds all the Multicast Forwarding Information Base (MFIB)
state that is necessary to forward multicast packets at a The TIB holds all the state that is necessary to forward multicast
router. However, although this specification defines packets at a router. However, although this specification defines
forwarding in terms of the TIB, to actually forward packets forwarding in terms of the TIB, to actually forward packets using
using the TIB is very inefficient. Instead a real router the TIB is very inefficient. Instead, a real router
implementation will normally build an efficient MFIB from the implementation will normally build an efficient MFIB from the TIB
TIB state to perform forwarding. How this is done is state to perform forwarding. How this is done is implementation-
implementation-specific, and is not discussed in this document. specific, and is not discussed in this document.
2.2. Pseudocode Notation 2.2. Pseudocode Notation
We use set notation in several places in this specification. We use set notation in several places in this specification.
A (+) B A (+) B
is the union of two sets A and B. is the union of two sets, A and B.
A (-) B A (-) B is the elements of set A that are not in set B.
is the elements of set A that are not in set B.
NULL NULL
is the empty set or list. is the empty set or list.
In addition we use C-like syntax: In addition, we use C-like syntax:
= denotes assignment of a variable. = denotes assignment of a variable.
== denotes a comparison for equality. == denotes a comparison for equality.
!= denotes a comparison for inequality. != denotes a comparison for inequality.
Braces { and } are used for grouping. Braces { and } are used for grouping.
3. Protocol Specification 3. Protocol Specification
The specification of BIDIR-PIM is broken into several parts: The specification of BIDIR-PIM is broken into several parts:
o Section 3.1 details the protocol state stored. o Section 3.1 details the protocol state stored.
o Section 3.2 defines the BIDIR-PIM extensions to the PIM-SM [4] o Section 3.2 defines the BIDIR-PIM extensions to the PIM-SM [4]
neighbour discovery mechanism. neighbor discovery mechanism.
o Section 3.3 specifies the data packet forwarding rules. o Section 3.3 specifies the data packet forwarding rules.
o Section 3.4 specifies the BIDIR-PIM Join/Prune generation and o Section 3.4 specifies the BIDIR-PIM Join/Prune generation and
processing rules. processing rules.
o Designated Forwarder (DF) election is specified in Section 3.5. o Section 3.5 specifies the Designated Forwarder (DF) election.
o PIM packet formats are specified in Section 3.7. o Section 3.7 specifies the PIM packet formats.
o A summary of BIDIR-PIM timers and their default values is given in o Section 3.6 summarizes BIDIR-PIM timers and gives their default
Section 3.6. values.
3.1. BIDIR-PIM Protocol State 3.1. BIDIR-PIM Protocol State
This section specifies all the protocol state that a BIDIR-PIM This section specifies all the protocol state that a BIDIR-PIM
implementation should maintain in order to function correctly. We implementation should maintain in order to function correctly. We
term this state the Tree Information Base or TIB, as it holds the term this state the Tree Information Base or TIB, as it holds the
state of all the multicast distribution trees at this router. In state of all the multicast distribution trees at this router. In
this specification we define PIM mechanisms in terms of the TIB. this specification, we define PIM mechanisms in terms of the TIB.
However, only a very simple implementation would actually implement However, only a very simple implementation would actually implement
packet forwarding operations in terms of this state. Most packet forwarding operations in terms of this state. Most
implementations will use this state to build a multicast forwarding implementations will use this state to build a multicast forwarding
table, which would then be updated when the relevant state in the TIB table, which would then be updated when the relevant state in the TIB
changes. changes.
Although we specify precisely the state to be kept, this does not Although we specify precisely the state to be kept, this does not
mean that an implementation of BIDIR-PIM needs to hold the state in mean that an implementation of BIDIR-PIM needs to hold the state in
this form. This is actually an abstract state definition, which is this form. This is actually an abstract state definition, which is
needed in order to specify the router's behavior. A BIDIR-PIM needed in order to specify the router's behavior. A BIDIR-PIM
skipping to change at page 9, line 44 skipping to change at page 8, line 7
a given RPA. a given RPA.
The state that should be kept is described below. Of course, The state that should be kept is described below. Of course,
implementations will only maintain state when it is relevant to implementations will only maintain state when it is relevant to
forwarding operations - for example, the "NoInfo" state might be forwarding operations - for example, the "NoInfo" state might be
assumed from the lack of other state information, rather than being assumed from the lack of other state information, rather than being
held explicitly. held explicitly.
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 an RPA or
group: group:
Neighbor State: Neighbor State:
For each neighbor: For each neighbor:
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 o Other information from neighbor's Hello
For more information on Hello information look at section 3.2 as well For more information on Hello information, look at Section 3.2 as
as the PIM-SM specification in [4]. 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 mechanism like BSR or AUTO-RP (see Section 4). For each BIDIR-PIM
RPA a router holds the following state: RPA, a router holds the following state:
o RPA (actual address) o RPA (actual address)
Designated Forwarder (DF) State: Designated Forwarder (DF) State:
For each router interface: For each router interface:
Acting DF information: Acting DF information:
o DF IP Address o DF IP Address
skipping to change at page 10, line 42 skipping to change at page 9, line 4
o Election State o Election State
o DF election-Timer (DFT) o DF election-Timer (DFT)
o Message-Count (MC) o Message-Count (MC)
Current best offer: Current best offer:
o IP address of best offering router o IP address of best offering router
o Best offering router metric o Best offering router metric
Designated Forwarder state is described in section 3.5. Designated Forwarder state is described in Section 3.5.
3.1.3. Group State 3.1.3. Group State
For every group G a router keeps the following state: For every group G, a router keeps the following state:
Group state: Group state:
For each interface: For each interface:
Local Membership: Local Membership:
o State: One of {"NoInfo", "Include"} o State: One of {"NoInfo", "Include"}
PIM Join/Prune State: PIM Join/Prune State:
o State: One of {"NoInfo" (NI), "Join" (J), o State: One of {"NoInfo" (NI), "Join" (J),
"PrunePending" (PP)} "PrunePending" (PP)}
o Prune Pending Timer (PPT) o PrunePendingTimer (PPT)
o Join/Prune Expiry Timer (ET) o Join/Prune Expiry Timer (ET)
Not interface specific: Not interface specific:
o Upstream Join/Prune Timer (JT) o Upstream Join/Prune Timer (JT)
o Last RPA Used o Last RPA Used
Local membership is the result of the local membership mechanism Local membership is the result of the local membership mechanism
(such as IGMP [2]) running on that interface. This information is (such as IGMP [2]) running on that interface. This information is
used by the pim_include(*,G) macro described in section 3.1.4. used by the pim_include(*,G) macro described in Section 3.1.4.
PIM Join/Prune state is the result of receiving PIM (*,G) Join/Prune PIM Join/Prune state is the result of receiving PIM (*,G) Join/Prune
messages on this interface, and is specified in section 3.4.1. The messages on this interface, and is specified in Section 3.4.1. The
state is used by the macros that calculate the outgoing interface state is used by the macros that calculate the outgoing interface
list in section 3.1.4, and in the JoinDesired(G) macro (defined in list in 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 Section 3.4.2) that is used in deciding whether a Join(*,G) should be
sent upstream. sent 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 messages, and to override Prune(*,G) messages from peers on an
upstream LAN interface. upstream LAN interface.
The last RPA used must be stored because if the group to RPA mapping The last RPA used must be stored because if the group to RPA mapping
changes (see RP Set changes in [4]) then state must be torn down and changes (see RP Set changes in [4]), then state must be torn down and
rebuilt for groups whose RPA changes. 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 Using this state, we define the following "macro" definitions that we
we will use in the descriptions of the state machines and pseudocode will use in the descriptions of the state machines and pseudocode in
in the following sections. the 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 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 to route packets to RPA. The olist(G) is the list of interfaces on
which packets to group G must be forwarded. which packets to group G must be forwarded.
The macro pim_include(G) indicates the interfaces to which traffic The macro pim_include(G) indicates the interfaces to which traffic
might be forwarded because of hosts that are local members on that might be forwarded because of hosts that are local members on that
interface. 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, The clause "local_receiver_include(G,I)" is true if the IGMP module,
MLD module or other local membership mechanism has determined that MLD module, or other local membership mechanism has determined that
there are local members on interface I that desire to receive traffic there are local members on interface I that desire to receive traffic
sent to group G. sent to group G.
The set "joins(G)" is the set of all interfaces on which the router The set "joins(G)" is the set of all interfaces on which the router
has received (*,G) Joins: has 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
section 3.4.1. Section 3.4.1.
RPF_DF(RPA) is the neighbor that Join messages must be sent to in RPF_DF(RPA) is the neighbor that Join messages must be sent to in
order to build the group shared tree rooted at the RPL for the given order to build the group shared tree rooted at the RPL for the given
RPA. This is the Designated-Forwarder on the RPF_interface(RPA). RPA. This is the Designated-Forwarder on the RPF_interface(RPA).
3.2. PIM Neighbor Discovery 3.2. PIM Neighbor Discovery
PIM routers exchange PIM-Hello messages with their neighboring PIM PIM routers exchange PIM-Hello messages with their neighboring PIM
routers. These messages are used to update the Neighbor State routers. These messages are used to update the Neighbor State
described in section 3.1. The procedures for generating and described in Section 3.1. The procedures for generating and
processing Hello messages as well as maintaining Neighbor State are processing Hello messages as well as maintaining Neighbor State are
specified in the PIM-SM [4] documentation. specified in the PIM-SM [4] documentation.
Bidir PIM introduces the Bidir_Capable PIM-Hello option that MUST be BIDIR-PIM introduces the Bidirectional Capable PIM-Hello option that
included in all Hello messages from a Bidir-PIM capable router. The MUST be included in all Hello messages from a BIDIR-PIM capable
Bidir_Capable option advertises the router's ability to participate router. The Bidirectional Capable option advertises the router's
in the Bidir-PIM protocol. The format of the Bidir_Capable option is ability to participate in the BIDIR-PIM protocol. The format of the
described in section 3.7. Bidirectional Capable option is described in Section 3.7.
If a Bidir PIM router receives a PIM-Hello message that does not If a BIDIR-PIM router receives a PIM-Hello message that does not
contain the Bidir_Capable option from one of its neighbours, the contain the Bidirectional Capable option from one of its neighbors,
error must be logged to the router administrator in a rate-limited the error must be logged to the router administrator in a rate-
manner. 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 o The DF is the only router that forwards packets traveling
downstream onto the link. downstream onto the link.
o The DF is the only router that picks-up upstream traveling packets o The DF is the only router that picks-up upstream traveling packets
off the link to forward towards the RPL. off the link to forward towards the RPL.
Non-DF routers on a link, that use that link as their RPF interface Non-DF routers on a link, which use that link as their RPF interface
to reach the RPA, may perform the following forwarding actions for to reach the RPA, may perform the following forwarding actions for
bidirectional groups: bidirectional groups:
o Forward packets from the link towards downstream receivers. o Forward packets from the link towards downstream receivers.
o Forward packets from downstream sources onto the link (provided o Forward packets from downstream sources onto the link (provided
they are the DF for the downstream link from which the packet was they are the DF for the downstream link from which the packet was
picked-up). picked-up).
The BIDIR-PIM packet forwarding rules are defined below in The BIDIR-PIM packet forwarding rules are defined below in
pseudocode. pseudocode.
iif is the incoming interface of the packet. iif is the incoming interface of the packet.
G is the destination address of the packet (group address). G is the destination address of the packet (group address).
RPA is the Rendezvous Point Address for this group. RPA is the Rendezvous Point Address for this group.
First we check to see whether the packet should be accepted based on First we check to see whether the packet should be accepted based on
TIB state and the interface that the packet arrived on. A packet is TIB state and the interface that the packet arrived on. A packet is
accepted if it arrives on the RPF_interface to reach the RPA accepted if it arrives on the RPF interface to reach the RPA
(downstream traveling packet) or if the router is the DF on the (downstream traveling packet) or if the router is the DF on the
interface the packet arrives (upstream traveling packet). interface the packet arrives (upstream traveling packet).
If the packet should be forwarded we build an outgoing interface list If the packet should be forwarded, we build an outgoing interface
for the packet. list for the packet.
Finally we remove the incoming interface from the outgoing interface Finally, we remove the incoming interface from the outgoing interface
list we've created, and if the resulting outgoing interface list is list we've created, and if the resulting outgoing interface list is
not empty, we forward the packet out of those interfaces. not empty, we forward the packet out of those interfaces.
On receipt of data to G on interface iif: On receipt of data to G on interface iif:
if( iif == RPF_interface(RPA) || I_am_DF(RPA,iif) ) { if( iif == RPF_interface(RPA) || I_am_DF(RPA,iif) ) {
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 physical box but instead is simply a routable address. Routers that
have interfaces on the RPL that the RPA belongs to will upstream have interfaces on the RPL that the RPA belongs to will upstream
forward traffic onto the link. Joins from receivers in the domain forward traffic onto the link. Joins from receivers in the domain
will propagate hop-by-hop till they reach one of the routers will propagate hop-by-hop till they reach one of the routers
connected to the RPL where they will terminate (as there will be no connected to the RPL where they will terminate (as there will be no
DF elected on the RPL). 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
address of a physical interface of a specific router then nothing address of a physical interface of a specific router, then nothing
changes. That router must still upstream forward traffic on to the changes. That router must still upstream forward traffic on to the
RPL and behave no differently than any other router with an interface RPL and behave no differently than any other router with an interface
on the RPL. on the RPL.
To configure a BIDIR-PIM network to operate in a mode similar to that 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 of PIM-SM where a single router (the RP) is acting as the root of the
distribution tree, the RPA can be configured to be the loopback distribution tree, the RPA 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 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 branches that do not lead to any receivers, but that are used to
forward packets traveling upstream from sources towards the RPL. forward packets traveling upstream from sources towards the RPL.
Routers along source-only branches only have the RPF_interface to the Routers along 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 RPA in their olist for G, and hence do not need to maintain any group
specific state. Upstream forwarding can be performed using only RPA specific state. Upstream forwarding can be performed using only RPA
specific state. An implementation may decide to maintain group state specific state. An implementation may decide to maintain group state
for source-only branches for accounting or performance reasons. for source-only branches for accounting or performance reasons.
However, doing so requires data-driven events (to discover the groups However, doing so requires data-driven events (to discover the groups
with active sources) thus sacrificing one of the main benefits of with active sources), thus sacrificing one of the main benefits of
Bidir PIM. 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 A major advantage of using a Designated Forwarder in BIDIR-PIM
compared to PIM-SM is that special treatment is no longer required compared to PIM-SM is that special treatment is no longer required
for sources that are directly connected to a router. Data from such for sources that are directly connected to a router. Data from such
sources does not need to be differentiated from other multicast sources does not need to be differentiated from other multicast
traffic and will automatically be picked up by the DF and forwarded traffic and will automatically be picked up by the DF and forwarded
upstream. This removes the need for performing a directly-connected- upstream. This removes the need for performing a directly-
source check for data to groups that do not have existing state. connected-source check for data to groups that do not have existing
state.
3.4. PIM Join/Prune Messages 3.4. PIM Join/Prune Messages
BIDIR-PIM Join/Prune messages are used to construct group specific BIDIR-PIM Join/Prune messages are used to construct group-specific
distribution trees between receivers and the RPL. Joins are distribution trees between receivers and the RPL. Joins are
originated by last-hop routers that are elected as the DF on an originated by last-hop routers that are elected as the DF on an
interface with directly connected receivers. The Joins propagate hop- interface with directly connected receivers. The Joins propagate
by-hop towards the RPA till they reach a router connected to the RPL. hop-by-hop towards the RPA until they reach a router connected to the
RPL.
A BIDIR-PIM Join/Prune message consists of a list of Joined and A BIDIR-PIM Join/Prune message consists of a list of Joined and
Pruned Groups. When processing a received Join/Prune message, each Pruned Groups. When processing a received Join/Prune message, each
Joined or Pruned Group is effectively considered individually by Joined or Pruned Group is effectively considered individually by
applying the following state machines. When considering a Join/Prune applying the following state machines. When considering a Join/Prune
message whose PIM Destination field addresses this router, (*,G) message whose PIM Destination field addresses this router, (*,G)
Joins and Prunes can affect the downstream state machine. When Joins and Prunes can affect the downstream state machine. When
considering a Join/Prune message whose PIM Destination field considering a Join/Prune message whose PIM Destination field
addresses another router, most Join or Prune entries could affect the addresses another router, most Join or Prune entries could affect the
upstream state machine. upstream state machine.
3.4.1. Receiving (*,G) Join/Prune Messages 3.4.1. Receiving (*,G) Join/Prune Messages
When a router receives a Join(*,G) or Prune(*,G) it MUST first check When a router receives a Join(*,G) or Prune(*,G), it MUST first check
to see whether the RP address in the message matches RPA(G) (the to see whether the RP address in the message matches RPA(G) (the
router's idea of what the Rendezvous Point Address is). If the RP router's idea of what the Rendezvous Point Address is). If the RP
address in the message does not match RPA(G) the Join or Prune MUST address in the message does not match RPA(G), the Join or Prune MUST
be silently dropped. be silently dropped.
If a router has no RPA information for the group (e.g. has not If a router has no RPA information for the group (e.g., has not
recently received a BSR message) then it MAY choose to accept recently received a BSR message), then it MAY choose to accept
Join(*,G) or Prune(*,G) and treat the RP address in the message as Join(*,G) or Prune(*,G) and treat the RP address in the message as
RPA(G). If the newly discovered RPA did not previously exist for any RPA(G). If the newly discovered RPA did not previously exist for any
other group, a DF election has to be initiated. other group, a DF election has to be initiated.
Note that a router will process a Join(*,G) targeted to itself even Note that a router will process a Join(*,G) targeted to itself even
if it is not the DF for RP(G) on the interface on which the message if it is not the DF for RP(G) on the interface on which the message
was received. This is an optimisation to eliminate the Join delay of was received. This is an optimisation to eliminate the Join delay of
one Join period (t_periodic) in the case where a new DF processes the one Join period (t_periodic) in the case where a new DF processes the
received Pass and Join messages in reverse order. The BIDIR-PIM received Pass and Join messages in reverse order. The BIDIR-PIM
forwarding logic will ensure that data packets are not forwarded on forwarding logic will ensure that data packets are not forwarded on
such an interface while the router is no the DF (unless it is the such an interface while the router is not the DF (unless it is the
RPF_interface towards the RPA). RPF interface towards the RPA).
The per-interface state-machine for receiving (*,G) Join/Prune The per-interface state machine for receiving (*,G) Join/Prune
Messages is given below. There are three states: Messages is given below. There are three states:
NoInfo (NI) NoInfo (NI)
The interface has no (*,G) Join state and no timers running. The interface has no (*,G) Join state and no timers running.
Join (J) Join (J)
The interface has (*,G) Join state. If the router is the DF on The interface has (*,G) Join state. If the router is the DF on
this interface (I_am_DF(RPA(G),I) is TRUE), the Join state will this interface (I_am_DF(RPA(G),I) is TRUE), the Join state will
cause us to forward packets destined for G on this interface. cause us to forward packets destined for G on this interface.
PrunePending (PP) PrunePending (PP)
The router has received a Prune(*,G) on this interface from a The router has received a Prune(*,G) on this interface from a
downstream neighbor and is waiting to see whether the prune downstream neighbor and is waiting to see whether the Prune
will be overridden by another downstream router. For will be overridden by another downstream router. For
forwarding purposes, the PrunePending state functions exactly forwarding purposes, the PrunePending state functions exactly
like the Join state. like the Join state.
In addition the state-machine uses two timers: In addition, the state machine uses two timers:
ExpiryTimer (ET) ExpiryTimer (ET)
This timer is restarted when a valid Join(*,G) is received. This timer is restarted when a valid Join(*,G) is received.
Expiry of the ExpiryTimer causes the interface state to revert Expiry of the ExpiryTimer causes the interface state to revert
to NoInfo for this group. to NoInfo for this group.
PrunePendingTimer (PPT) PrunePendingTimer (PPT)
This timer is set when a valid Prune(*,G) is received. Expiry This timer is set when a valid Prune(*,G) is received. Expiry
of the PrunePendingTimer causes the interface state to revert of the PrunePendingTimer causes the interface state to revert
to NoInfo for this group. to NoInfo for this group.
Figure 1: Downstream group per-interface state-machine in tabular form Figure 1: Downstream group per-interface state machine in tabular
form
+---------------++---------------------------------------------------+ +---------------++---------------------------------------------------+
| || Prev State | | || Prev State |
|Event ++---------------+-----------------+-----------------+ |Event ++---------------+-----------------+-----------------+
| || NoInfo (NI) | Join (J) | Prune Pending | | || NoInfo (NI) | Join (J) | PrunePending |
| || | | (PP) | | || | | (PP) |
+---------------++---------------+-----------------+-----------------+ +---------------++---------------+-----------------+-----------------+
| || -> J state | -> J state | -> J state | | || -> J state | -> J state | -> J state |
|Receive || start Expiry | restart Expiry | restart Expiry | |Receive || start Expiry | restart Expiry | restart Expiry |
|Join(*,G) || Timer | Timer | Timer; stop | |Join(*,G) || Timer | Timer | Timer; stop |
| || | | Prune Pending | | || | | PrunePending- |
| || | | Timer | | || | | Timer |
+---------------++---------------+-----------------+-----------------+ +---------------++---------------+-----------------+-----------------+
|Receive || - | -> PP state | -> PP state | |Receive || - | -> PP state | -> PP state |
|Prune(*,G) || | start Prune | | |Prune(*,G) || | start Prune- | |
| || | Pending Timer | | | || | PendingTimer | |
+---------------++---------------+-----------------+-----------------+ +---------------++---------------+-----------------+-----------------+
|Prune Pending || - | - | -> NI state | |PrunePending- || - | - | -> NI state |
|Timer Expires || | | Send Prune- | |Timer Expires || | | Send Prune- |
| || | | Echo(*,G) | | || | | Echo(*,G) |
+---------------++---------------+-----------------+-----------------+ +---------------++---------------+-----------------+-----------------+
|Expiry Timer || - | -> NI state | -> NI state | |Expiry Timer || - | -> NI state | -> NI state |
|Expires || | | | |Expires || | | |
+---------------++---------------+-----------------+-----------------+ +---------------++---------------+-----------------+-----------------+
|Stop Being DF || - | -> NI state | -> NI state | |Stop Being DF || - | -> NI state | -> NI state |
|on I || | | | |on I || | | |
+---------------++---------------+-----------------+-----------------+ +---------------++---------------+-----------------+-----------------+
The transition events "Receive Join(*,G)" and "Receive Prune(*,G)" The transition events "Receive Join(*,G)" and "Receive Prune(*,G)"
imply receiving a Join or Prune targeted to this router's address on imply receiving a Join or Prune targeted to this router's address on
the received interface. If the destination address is not correct, the received interface. If the destination address is not correct,
these state transitions in this state machine must not occur, these state transitions in this state machine must not occur,
although seeing such a packet may cause state transitions in other although seeing such a packet may cause state transitions in other
state machines. state machines.
On unnumbered interfaces on point-to-point links, the router's On unnumbered interfaces on point-to-point links, the router's
address should be the same as the source address it chose for the address should be the same as the source address it chose for the
Hello packet it sent over that interface. However, on point-to-point Hello packet it sent over that interface. However, on point-to-point
links we also RECOMMEND that PIM messages with a destination address links, we also RECOMMEND that PIM messages with a destination address
of all zeros are also accepted. of all zeros also be 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 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 status from being the active DF to being a non-DF router (the value
of the I_am_DF macro changing to FALSE). of the I_am_DF macro changing to FALSE).
When ExpiryTimer is started or restarted, it is set to the HoldTime When ExpiryTimer is started or restarted, it is set to the HoldTime
from the triggering received Join/Prune message. from the Join/Prune message that triggered the timer.
When PrunePendingTimer is started, it is set to the When PrunePendingTimer is started, it is set to the
J/P_Override_Interval if the router has more than one neighbor on J/P_Override_Interval if the router has more than one neighbor on
that interface; otherwise it is set to zero causing it to expire that interface; otherwise, it is set to zero causing it to expire
immediately. immediately.
The action "Send PruneEcho(*,G)" is triggered when the router stops The action "Send PruneEcho(*,G)" is triggered when the router stops
forwarding on an interface as a result of a prune. A PruneEcho(*,G) forwarding on an interface as a result of a Prune. A PruneEcho(*,G)
is simply a Prune(*,G) message sent by the upstream router to itself is simply a Prune(*,G) message sent by the upstream router to itself
on a LAN. Its purpose is to add additional reliability so that if a on a LAN. Its purpose is to add additional reliability so that if a
Prune that should have been overridden by another router is lost Prune that should have been overridden by another router is lost
locally on the LAN, then the PruneEcho may be received and cause the locally on the LAN, then the PruneEcho may be received and cause the
override to happen. A PruneEcho(*,G) need not be sent when the override to happen. A PruneEcho(*,G) need not be sent when the
router has only one neighbour on the link. router has only one neighbor on the link.
3.4.2. Sending Join/Prune Messages 3.4.2. Sending Join/Prune Messages
The downstream per-interface state-machines described above hold join The downstream per-interface state machines described above hold Join
state from downstream PIM routers. This state then determines whether state from downstream PIM routers. This state then determines
a router needs to propagate a Join(*,G) upstream towards the RPA. whether a router needs to propagate a Join(*,G) upstream towards the
Such Join(*,G) messages are sent on the RPF_interface towards the RPA RPA. Such Join(*,G) messages are sent on the RPF interface towards
and are targeted at the DF on that interface. the RPA and are targeted at the DF on that interface.
If a router wishes to propagate a Join(*,G) upstream, it must also If a router wishes to propagate a Join(*,G) upstream, it must also
watch for messages on its upstream interface from other routers on watch for messages on its upstream interface from other routers on
that subnet, and these may modify its behavior. If it sees a that subnet, and these may modify its behavior. If it sees a
Join(*,G) to the correct upstream neighbor, it should suppress its Join(*,G) to the correct upstream neighbor, it should suppress its
own Join(*,G). If it sees a Prune(*,G) to the correct upstream own Join(*,G). If it sees a Prune(*,G) to the correct upstream
neighbor, it should be prepared to override that prune by sending a neighbor, it should be prepared to override that Prune by sending a
Join(*,G) almost immediately. Finally, if it sees the Generation ID Join(*,G) almost immediately. Finally, if it sees the Generation ID
(see PIM-SM specification [4]) of the correct upstream neighbor (see PIM-SM specification [4]) of the correct upstream neighbor
change, it knows that the upstream neighbor has lost state, and it change, it knows that the upstream neighbor has lost state, and it
should be prepared to refresh the state by sending a Join(*,G) almost should be prepared to refresh the state by sending a Join(*,G) almost
immediately. immediately.
In addition changes in the next hop towards the RPA trigger a prune In addition, changes in the next hop towards the RPA trigger a Prune
off from the old next hop, and join towards the new next hop. Such a off from the old next hop and join towards the new next hop. Such a
change can be caused by the following two events: change can be caused by the following two events:
o The MRIB indicates that the RPF Interface towards the RPA has o The MRIB indicates that the RPF Interface towards the RPA has
changed. In this case the DF on the new RPF_interface becomes changed. In this case the DF on the new RPF interface becomes
the new RPF Neighbour. the new RPF Neighbor.
o There is a DF re-election on the RPF_interface and a new router o There is a DF re-election on the RPF interface and a new router
emerges as the DF. emerges as the DF.
The upstream (*,G) state-machine only contains two states: The upstream (*,G) state machine only contains two states:
Not Joined Not Joined
The downstream state-machines indicate that the router does not The downstream state machines indicate that the router does not
need to join the RPA tree for this group. need to join the RPA tree for this group.
Joined Joined
The downstream state-machines indicate that the router would like The downstream state machines indicate that the router would
to join the RPA tree for this group. like to join the RPA tree for this group.
In addition, one timer JT(G) is kept which is used to trigger the In addition, one timer JT(G) is kept, which is used to trigger the
sending of a Join(*,G) to the upstream next hop towards the RPA (the sending of a Join(*,G) to the upstream next hop towards the RPA (the
DF on the RPF_interface for RPA(G)). DF on the RPF interface for RPA(G)).
Figure 2: Upstream group state-machine in tabular form Figure 2: Upstream group state machine in tabular form
+---------------------+----------------------------------------------+ +---------------------+----------------------------------------------+
| | Event | | | Event |
| Prev State +-----------------------+----------------------+ | Prev State +-----------------------+----------------------+
| | JoinDesired(G) | JoinDesired(G) | | | JoinDesired(G) | JoinDesired(G) |
| | ->True | ->False | | | ->True | ->False |
+---------------------+-----------------------+----------------------+ +---------------------+-----------------------+----------------------+
| | -> J state | - | | | -> J state | - |
| NotJoined (NJ) | Send Join(*,G); | | | NotJoined (NJ) | Send Join(*,G); | |
| | Set Timer to | | | | Set Timer to | |
| | t_periodic | | | | t_periodic | |
+---------------------+-----------------------+----------------------+ +---------------------+-----------------------+----------------------+
| Joined (J) | - | -> NJ state | | Joined (J) | - | -> NJ state |
| | | Send Prune(*,G) | | | | Send Prune(*,G) |
+---------------------+-----------------------+----------------------+ +---------------------+-----------------------+----------------------+
In addition, we have the following transitions which occur within the In addition, we have the following transitions that occur within the
Joined state: Joined state:
+--------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Joined (J) State | | In Joined (J) State |
+----------------+----------------+-----------------+----------------+ +----------------+----------------+-----------------+----------------+
|Timer Expires | See Join(*,G) | See Prune(*,G) | RPF_DF(RPA(G)) | |Timer Expires | See Join(*,G) | See Prune(*,G) | RPF_DF(RPA(G)) |
| | to | to | GenID changes | | | to | to | GenID changes |
| | RPF_DF(RPA(G)) | RPF_DF(RPA(G)) | | | | RPF_DF(RPA(G)) | RPF_DF(RPA(G)) | |
+----------------+----------------+-----------------+----------------+ +----------------+----------------+-----------------+----------------+
|Send | Increase Timer | Decrease Timer | Decrease Timer | |Send | Increase Timer | Decrease Timer | Decrease Timer |
|Join(*,G); Set | to | to t_override | to t_override | |Join(*,G); Set | to | to t_override | to t_override |
|Timer to | t_suppressed | | | |Timer to | t_suppressed | | |
|t_periodic | | | | |t_periodic | | | |
+----------------+----------------+-----------------+----------------+ +----------------+----------------+-----------------+----------------+
+--------------------------------------------------------------------+
| In Joined (J) State |
+-----------------------------------+--------------------------------+
| Change of RPF_DF(RPA(G)) | RPF_DF(RPA(G)) GenID |
| | changes |
+-----------------------------------+--------------------------------+
| Send Join(*,G) to new | Decrease Timer to |
| DF; Send Prune(*,G) to | t_override |
| old DF; set Timer to | |
| t_periodic | |
+-----------------------------------+--------------------------------+
+--------------------------------------------------------------------+ This state machine uses the following macro:
| In Joined (J) State |
+-----------------------------------+--------------------------------+
| Change of RPF_DF(RPA(G)) | RPF_DF(RPA(G)) GenID |
| | changes |
+-----------------------------------+--------------------------------+
| Send Join(*,G) to new | Decrease Timer to |
| DF; Send Prune(*,G) to | t_override |
| old DF; set Timer to | |
| t_periodic | |
+-----------------------------------+--------------------------------+
This state machine uses the following macro:
bool JoinDesired(G) { bool JoinDesired(G) {
if (olist(G) (-) RPF_interface(RPA(G))) != NULL if (olist(G) (-) RPF_interface(RPA(G))) != NULL
return TRUE return TRUE
else else
return FALSE return FALSE
} }
3.5. Designated Forwarder (DF) Election 3.5. Designated Forwarder (DF) Election
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 an 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
responsibility of forwarding traffic between the RPL and the link for responsibility for forwarding traffic between the RPL and the link
the range of multicast groups served by the RPA. Different multicast for the range of multicast groups served by the RPA. Different
groups that share a common RPA share the same upstream direction. multicast groups that share a common RPA share the same upstream
Hence, the election of an upstream forwarder on each link does not direction. Hence, the election of an upstream forwarder on each link
have to be a group specific decision but instead can be RPA-specific. does not have to be a group-specific decision but instead can be
As the number of RPAs is typically small, the number of elections RPA-specific. As the number of RPAs is typically small, the number
that have to be performed is significantly reduced by this of elections that have to be performed is significantly reduced by
observation. this 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 (as reported by the MRIB) to reach the RPA. unicast routing metric (as reported by the MRIB) to reach the RPA.
When comparing metrics from different unicast routing protocols, we When comparing metrics from different unicast routing protocols, we
use the same comparison rules used by the PIM-SM assert process [4]. use the same comparison rules used by the PIM-SM assert process [4].
The election process needs to take place when information on a new The election process needs to take place when information on a new
RPA initially becomes available. The result can be re-used as new RPA initially becomes available. The result can be re-used as new
bidir groups that map to the same RPA are encountered. There are bidir groups that map to the same RPA are encountered. However,
however some conditions under which an update to the election is there are some conditions under which an update to the election is
required: 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 the current outcome.
o The elected DF fails (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 probability that all routers on the link have a consistent view of
the DF. This is because with the forwarding rules described in the DF. Given the forwarding rules described in Section 3.3, loops
section 3.3 if multiple routers end-up thinking that they should be may result if multiple routers end-up thinking that they should be
responsible for forwarding, loops may result. To reduce the responsible for forwarding. To minimize the possibility of this
possibility of this occurrence to a minimum, the election algorithm occurrence, the election algorithm has been biased towards discarding
has been biased towards discarding DF information and suspending DF information and suspending forwarding during periods of ambiguity.
forwarding during periods of ambiguity.
3.5.2. DF Election description 3.5.2. DF Election Description
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
provide the definitive specification for the DF election. If any not 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, reaching the RPA. Routers advertise their own metrics in Offer,
Winner, Backoff and Pass messages. The advertised metric is Winner, Backoff, and Pass messages. The advertised metric is
calculated using the RPF Interface and metric to reach the RPA calculated using the RPF Interface and metric to reach the RPA
available through the MRIB. When a router is participating in a DF available through the MRIB. When a router is participating in a DF
election for an RPA on the interface that its MRIB indicates as the election for an RPA on the interface that its MRIB indicates as the
RPF Interface then that router MUST always advertise an infinite RPF Interface, then that router MUST always advertise an infinite
metric in its election messages. When a router is participating in a metric in its election messages. When a router is participating in a
DF election on an interface other than the MRIB indicated RPF DF election on an interface other than the MRIB-indicated RPF
Interface then it MUST advertise the MRIB provided metrics in its Interface then it MUST advertise the MRIB-provided metrics in its
election messages. 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 repeated Election_Robustness times for reliability. In all those
cases the message retransmissions are spaced in time by a small cases, the message retransmissions are spaced in time by a small
random interval. All of the following description is specific to the random interval. All of the following description is specific to the
election on a single link for a single RPA. election on a single link for a single RPA.
3.5.2.1. Bootstrap Election 3.5.2.1. Bootstrap Election
Initially when no DF has been elected, routers finding out about a Initially, when no DF has been elected, routers finding out about a
new RPA start participating in the election by sending Offer new RPA start participating in the election by sending Offer
messages. Offer messages include the router's metric to reach the messages. Offer messages include the router's metric to reach the
RPA. Offers are periodically retransmitted with a period of RPA. Offers are periodically retransmitted with a period of
Offer_Interval. Offer_Interval.
If a router hears a better offer than its own from a neighbor, it If a router hears a better offer than its own from a neighbor, it
stops participating in the election for a period of stops participating in the election for a period of
Election_Robustness * Offer_Interval thus giving a chance to the Election_Robustness * Offer_Interval, thus giving a chance to the
neighbour with the better metric to be elected DF. If during this neighbor with the better metric to be elected DF. If during this
period no winner is elected, the router restarts the election from period no winner is elected, the router restarts the election from
the beginning. If at any point during the initial election a router the beginning. If at any point during the initial election a router
receives an out of order offer with worse metrics than its own, then receives an out of order offer with worse metrics than its own, then
it restarts the election from the beginning. it restarts the election from the beginning.
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 A router assumes the role of the DF after having advertised its
metrics Election_Robustness times without receiving any offer from metrics Election_Robustness times without receiving any offer from
any other neighbor. At that point it transmits a Winner message which any other neighbor. At that point, it transmits a Winner message
declares to every other router on the link the identity of the winner that declares to every other router on the link the identity of the
and the metrics it is using. winner and the metrics it is using.
Routers receiving a winner message stop participating in the election Routers receiving a Winner message stop participating in the election
and record the identity and metrics of the winner. If the local and record the identity and metrics of the winner. If the local
metrics are better than those of the winner then the router records metrics are better than those of the winner, then the router records
the identity of the winner (accepting it as the acting DF) but re- the identity of the winner (accepting it as the acting DF) but re-
initiates the election to try and take over. initiates the 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 an RPA changes at a non-DF router to a
value that is better than that previously advertised by the acting value that is better than that previously advertised by the acting
DF, the router with the new better metric should take action to DF, the router with the new better metric should take action to
eventually assume forwarding responsibility. When the metric change eventually assume forwarding responsibility. When the metric change
is detected, the non-DF router with the now better metric restarts is detected, the non-DF router with the now better metric restarts
the DF election process by sending Offer messages with this new the DF election process by sending Offer messages with this new
metric. Note that at any point during an election if no response is metric. Note that at any point during an election if no response is
received after Election_Robustness retransmissions of an offer, a received after Election_Robustness retransmissions of an offer, a
router assumes the role of the DF following the usual Winner router assumes the role of the DF following the usual Winner
announcement procedure. announcement procedure.
Upon receipt of an offer that is worse than its current metric, the Upon receipt of an offer that is worse than its current metric, the
DF will respond with a Winner message declaring its status and DF will respond with a Winner message declaring its status and
advertising its better metric. Upon receiving the Winner message, the advertising its better metric. Upon receiving the Winner message,
originator of the Offer records the identity of the DF and aborts the the originator of the Offer records the identity of the DF and aborts
election. the election.
Upon receipt of an offer that is better than its current metric, the Upon receipt of an offer that is better than its current metric, the
DF records the identity and metrics of the offering router and DF records the identity and metrics of the offering router and
responds with a Backoff message. This instructs the offering router responds with a Backoff message. This instructs the offering router
to hold off for a short period of time while the unicast routing to hold off for a short period of time while the unicast routing
stabilises and other routers get a chance to put in their offers. The stabilizes and other routers get a chance to put in their offers.
Backoff message includes the offering router's new metric and The Backoff message includes the offering router's new metric and
address. All routers on the link that have pending offers with address. All routers on the link that have pending offers with
metrics worse than those in the backoff message (including the metrics worse than those in the Backoff message (including the
original offering router) will hold further offers for a period of original offering router) will hold further offers for a period of
time defined in the Backoff message. time defined in the Backoff message.
If during the Backoff_Period, a third router sends a new better If a third router sends a better offer during the Backoff_Period, the
offer, the Backoff message is repeated for the new offer and the Backoff message is repeated for the new offer and the Backoff_Period
Backoff_Period restarted. is 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. 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 The 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 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 as 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 note of the new DF and its metric. Note that this event constitutes
an RPF Neighbour change which may trigger Join messages to the new DF an RPF Neighbor change, which may trigger Join messages to the new DF
(see section 3.4). (see 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, 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 it sends a set of Election_Robustness randomly spaced Winner messages
on the link, advertising the new metric. Routers that receive this on the link, advertising the new metric. Routers that receive this
announcement but have a better metric may respond with an Offer announcement but have a better metric may respond with an Offer
message which results in the same handoff procedure described above. message that results in the same handoff procedure described above.
All routers assume the DF has not changed until they see a Pass or All routers assume the DF has not changed until they see a Pass or
Winner message indicating the change. Winner message indicating the change.
There is no pressure to make this handoff quickly if the acting DF 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 still 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. it will still work while the re-election is in progress.
3.5.2.4. Winner Loses Path 3.5.2.4. Winner Loses Path
If a router's RPF Interface to the RPA switches to be on a link for If a router's RPF Interface to the RPA switches to be on a link for
which it is acting as the DF, then it can no longer provide which it is acting as the DF, then it can no longer provide
forwarding services for that link. It therefore immediately stops forwarding services for that link. It therefore immediately stops
being the DF and restarts the election. As its path to the RPA is being the DF and restarts the election. As its path to the RPA is
through the link, an infinite metric is used in the Offer message it through the link, an infinite metric is used in the Offer message it
sends. sends.
3.5.2.5. Late Router Starting Up 3.5.2.5. Late Router Starting Up
A late router starting up after the DF election process has completed A late router starting up after the DF election process has completed
will have no immediate knowledge of the election outcome. As a will have no immediate knowledge of the election outcome. As a
result, it will start advertising its metric in Offer messages. As result, it will start advertising its metric in Offer messages. As
soon as this happens, the currently elected DF will respond with a soon as this happens, the currently elected DF will respond with a
Winner message if its metric is better than the metric in the Offer Winner message if its metric is better than the metric in the Offer
message, or with a Backoff message if its metric is worse than the message, or with a Backoff message if its metric is worse than the
metric in the Offer message. metric in the Offer message.
3.5.2.6. Winner Dies 3.5.2.6. Winner Dies
Whenever the DF dies, a new DF has to be elected. The speed at which Whenever the DF dies, a new DF has to be elected. The speed at which
this can be achieved depends on whether there are any downstream this can be achieved depends on whether there are any downstream
routers on the link. routers on the link.
If there are downstream routers, typically their MRIB reported next- If there are downstream routers, typically their MRIB reported next-
hop before the DF dies will be the DF itself. They will therefore hop before the DF dies will be the DF itself. They will therefore
notice either a change in the metric for the route to the RPA or a notice either a change in the metric for the route to the RPA or a
change in next-hop away from the DF and can restart the election by change in next-hop away from the DF and can restart the election by
transmitting Offer messages. If according to the MRIB the RPA is now transmitting Offer messages. If according to the MRIB the RPA is now
reachable through the same link via another upstream router, an reachable through the same link via another upstream router, an
infinite metric will be used in the Offer. infinite metric will be used in the Offer.
If no downstream routers are present, the only way for other upstream If no downstream routers are present, the only way for other upstream
routers to detect a DF failure is by the timeout of the PIM neighbor routers to detect a DF failure is by the timeout of the PIM neighbor
information, which will take significantly longer. information, which will take significantly longer.
3.5.3. Election Protocol Specification 3.5.3. Election Protocol Specification
This section provides the definitive specification for the DF This section provides the definitive specification for the DF
election process. If any discrepancy exists between section 3.5.2 and election process. If any discrepancy exists between Section 3.5.2
this section, the specification in this section is to be assumed and this section, the specification in this section is to be assumed
correct. correct.
3.5.3.1. Election State 3.5.3.1. Election State
The DF election state is maintained per RPA for each multicast The DF election state is maintained per RPA for each multicast
enabled interface I on the router as introduced in section 3.1. enabled interface I on the router as introduced in Section 3.1.
The state machine has the following four states: The state machine has the following four states:
Offer Offer
Initial election state. When in the Offer state a router thinks Initial election state. When in the Offer state, a router
it can eventually become the winner and periodically generates thinks it can eventually become the winner and periodically
Offer messages. generates Offer messages.
Lose Lose
In this state the router knows that there either is a different In this state, the router knows that there either is a
election winner or that no router on the link has a path to the different election winner or that no router on the link has a
RPA. path to the RPA.
Winner Win
The router is the acting DF without any contest. The router is the acting DF without any contest.
Backoff Backoff
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 In the state machine, a router is considered to be an acting DF if it
is in the Win or Backoff states. is 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 identity and advertised metrics of the Used to store the identity and advertised metrics of the
election winner that is the currently acting 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 message Used to maintain the number of times an Offer or Winner message
has been transmitted. has been transmitted.
Best-Offer Best-Offer
Used by the DF to record the identity and advertised metrics of Used by the DF to record the identity and advertised metrics of
the router that has made the last offer, for use when sending the router that has made the last offer, for use when sending
the Path message. the Path message.
3.5.3.2. Election Messages 3.5.3.2. Election Messages
The election process uses the following PIM control messages, the The election process uses the following PIM control messages. The
packet format of which is described in section 3.7: packet format 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.
Winner (DF-ID, DF-Metric) Winner (DF-ID, DF-Metric)
Sent by a router when assuming the role of the DF or when re- Sent by a router when assuming the role of the DF or when re-
asserting in response to worse offers. asserting in response to worse offers.
Backoff (DF-ID, DF-Metric, OfferingID, OfferMetric, Backoff (DF-ID, DF-Metric, OfferingID, OfferMetric,
BackoffInterval) BackoffInterval)
Used by the DF to acknowledge better offers. It instructs other Used by the DF to acknowledge better offers. It instructs
routers with equal or worse offers to wait till the DF passes other routers with equal or worse offers to wait until the DF
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 is 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. the current metric of the DF at the time the pass is sent.
Note that when a router is participating in a DF election for an RPA 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 on the interface that its MRIB indicates as the RPF Interface, then
that router MUST always advertise an infinite metric in its election that 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:
Control message reception Control message reception
Reception of one of the four control DF election messages Reception of one of the four control DF election messages
(Offer, Winner, Backoff and Pass). When a control message is (Offer, Winner, Backoff, and Pass). When a control message is
received and actions are specified on a condition that metrics received and actions are specified on a condition that metrics
are Better or Worse the comparison must be performed as are Better or Worse, the comparison must be performed as
follows: follows:
o On receipt of an Offer or Winner message compare our current o On receipt of an Offer or Winner message, compare the current
metrics for the RPA with the metrics advertised for the metrics for the RPA with the metrics advertised for the
sender of the message. sender of the message.
o On receipt of a Backoff or Pass message compare our current o On receipt of a Backoff or Pass message, compare the 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 under consideration. reachable through the router interface under consideration.
Clearly as the router is using the interface as its RPF Clearly, as the router is using the interface as its RPF
Interface it cannot offer forwarding services towards the RPL Interface, it cannot offer forwarding 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 of the stored
new MRIB information must be compared against. The new metrics the new MRIB information must be compared against. The
information must be compared with either the router's old new information must be compared with either the router's old
metric, the stored DF metric or the stored Best Offer metric. metric, the stored DF metric, or the stored Best Offer metric.
Election-Timer (DFT) Expiration Election-Timer (DFT) expiration
Expiration of the DFT election timer can cause message Expiration of the DFT election timer can cause message
transmission and state transitions. The event might be further transmission and state transitions. The event might be further
qualified by specifying the value of the Message Count (MC) as qualified by specifying the value of the Message Count (MC) as
well as the current existence of a path to the RPA (as defined well as the current existence of a path to the RPA (as defined
above). above).
Detection of DF failure Detection of DF failure
Detection of DF failure can occur through the timeout of PIM Detection of DF failure can occur through the timeout of PIM
neighbor state. neighbor state.
3.5.3.4. Election Actions 3.5.3.4. Election Actions
The DF election state machine action descriptions use the following The DF election state machine action descriptions use the following
notation in addition to the pseudocode notation described earlier in notation in addition to the pseudocode notation described earlier in
this spec. this specification:
?= denotes the operation of lowering a timer to a new value. If ?= denotes the operation of lowering a timer to a new value. If
the timer is not running then it is started using the new the timer is not running, then it is started using the new
value. If the timer is running with an expiration lower than value. If the timer is running with an expiration lower than
the new value, then the timer is not altered. the new value, then the timer is not altered.
When an action of "set DF to Sender or Target" is encountered during When an action of "set DF to Sender or Target" is encountered during
receipt of a Winner, Pass or Backoff message it means the following: receipt of a Winner, Pass, or Backoff message, it means the
following:
o On receipt of a Winner message set the DF to be the originator o On receipt of a Winner message, set the DF to be the originator
of the message and record its metrics. of the message and record its metrics.
o On receipt of a Pass message set the DF to be the target of the o On receipt of a Pass message, set the DF to be the target of the
message and record its metrics. message and record its metrics.
o On receipt of a Backoff message set the DF to be the originator o On receipt of a Backoff message, set the DF to be the originator
of the message and record its metrics. of the message and record its metrics.
3.5.3.5. Election State Transitions 3.5.3.5. Election State Transitions
When a Designated Forwarder election is initiated the starting state When a Designated Forwarder election is initiated, the starting state
is the Offer state, the message counter (MC) is set to zero and the is the Offer state, the message counter (MC) is set to zero, and the
DF election Timer (DFT) is set to OPlow (see section 3.6 for a DF election Timer (DFT) is set to OPlow (see Section 3.6 for a
definition of timer values). definition of timer values).
Figure 3: Designated Forwarder election state-machine in tabular form Figure 3: Designated Forwarder election state machine in tabular form
+-------------+------------------------------------------------------+
| | Event |
| Prev State +-----------------+------------------+-----------------+
| | Recv better | Recv better | Recv better |
| | Pass / Win | Backoff | Offer |
+-------------+-----------------+------------------+-----------------+
| | -> Lose | - | - |
| Offer | DF = Sender or | DFT = BOperiod | DFT = OPhigh; |
| | Target; Stop | + OPlow; MC = | MC = 0 |
| | DFT | 0 | |
+-------------+-----------------+------------------+-----------------+
| | - | - | -> Offer |
| Lose | DF = Sender or | DF = Sender | DFT = OPhigh; |
| | Target | | MC = 0 |
+-------------+-----------------+------------------+-----------------+
| | -> Lose | -> Lose | -> Backoff |
| | DF = Sender or | DF = Sender; | Set Best to |
| Win | Target; Stop | Stop DFT | Sender; Send |
| | DFT | | Backoff; DFT = |
| | | | BOperiod |
+-------------+-----------------+------------------+-----------------+
| | -> Lose | -> Lose | - |
| | DF = Sender or | DF = Sender; | Set Best to |
| Backoff | Target; Stop | Stop DFT | Sender; Send |
| | DFT | | Backoff; DFT = |
| | | | BOperiod |
+-------------+-----------------+------------------+-----------------+
+-----------+-------------------------------------------------------+
| | Event |
| +-------------+-------------+--------------+------------+
|Prev State |Recv Backoff |Recv Pass |Recv Worse |Recv worse |
| |for us |for us |Pass / Win / |Offer |
| | | |Backoff | |
+-----------+-------------+-------------+--------------+------------+
| |- |-> Win |- |- |
| |DFT = |Stop DFT |Set DF to |DFT ?= |
|Offer |BOperiod + | |Sender or |OPlow; MC = |
| |OPlow; MC = | |Target; DFT |0 |
| |0 | |?= OPlow; MC | |
| | | |= 0 | |
+-----------+-------------+-------------+--------------+------------+
| |-> Offer |-> Offer |-> Offer |-> Offer |
| |DF = Sender; |DF = Sender; |DF = Sender |DFT = OPlow;|
|Lose |DFT = OPlow; |DFT = OPlow; |or Target; |MC = 0 |
| |MC = 0 |MC = 0 |DFT = OPlow; | |
| | | |MC = 0 | |
+-----------+-------------+-------------+--------------+------------+
| |-> Offer |-> Offer |-> Offer |- |
| |DF = Sender; |DF = Sender; |DF = Sender |Send Winner |
|Win |DFT = OPlow; |DFT = OPlow; |or Target; | |
| |MC = 0 |MC = 0 |DFT = OPlow; | |
| | | |MC = 0 | |
+-----------+-------------+-------------+--------------+------------+
| |-> Offer |-> Offer |-> Offer |-> Win |
| |DF = Sender; |DF = Sender; |DF = Sender |Send Winner;|
|Backoff |DFT = OPlow; |DFT = OPlow; |or Target; |Stop DFT |
| |MC = 0 |MC = 0 |DFT = OPlow; | |
| | | |MC = 0 | |
+-----------+-------------+-------------+--------------+------------+
+--------------------------------------------------------------------+
| In Offer State |
+----------------------+----------------------+----------------------+
| DFT Expires and MC | DFT Expires and MC | DFT Expires and MC |
| is less than | is equal to | is equal to |
| Robustness | Robustness and we | Robustness and |
| | have path to RPA | there is no path |
| | | to RPA |
+----------------------+----------------------+----------------------+
| - | -> Win | -> Lose |
| Send Offer; DFT = | Send Winner | Set DF to None |
| OPlow; MC = MC + 1 | | |
+----------------------+----------------------+----------------------+
+--------------------------------------------------------------------+
| In Offer State |
+--------------------------------------------------------------------+
| Metric changes and is now worse |
+--------------------------------------------------------------------+
| DFT ?= OPlow |
| MC = 0 |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+ +-------------+------------------------------------------------------+
| In Lose State | | | Event |
+------------------------------+-------------------------------------+ | Prev State +-----------------+------------------+-----------------+
| Detect DF Failure | Metric changes and now | | | Recv better | Recv better | Recv better |
| | is better than DF | | | Pass / Win | Backoff | Offer |
+------------------------------+-------------------------------------+ +-------------+-----------------+------------------+-----------------+
| -> Offer | -> Offer | | | -> Lose | - | - |
| DF = None; DFT = | DFT = OPlow_int; MC = 0 | | Offer | DF = Sender or | DFT = BOperiod | DFT = OPhigh; |
| OPlow_int; MC = 0 | | | | Target; Stop | + OPlow; MC = | MC = 0 |
+------------------------------+-------------------------------------+ | | DFT | 0 | |
+-------------+-----------------+------------------+-----------------+
| | - | - | -> Offer |
| Lose | DF = Sender or | DF = Sender | DFT = OPhigh; |
| | Target | | MC = 0 |
+-------------+-----------------+------------------+-----------------+
| | -> Lose | -> Lose | -> Backoff |
| | DF = Sender or | DF = Sender; | Set Best to |
| Win | Target; Stop | Stop DFT | Sender; Send |
| | DFT | | Backoff; DFT = |
| | | | BOperiod |
+-------------+-----------------+------------------+-----------------+
| | -> Lose | -> Lose | - |
| | DF = Sender or | DF = Sender; | Set Best to |
| Backoff | Target; Stop | Stop DFT | Sender; Send |
| | DFT | | Backoff; DFT = |
| | | | BOperiod |
+-------------+-----------------+------------------+-----------------+
+-----------+-------------------------------------------------------+
| | Event |
| +-------------+-------------+--------------+------------+
|Prev State |Recv Backoff |Recv Pass |Recv Worse |Recv worse |
| |for us |for us |Pass / Win / |Offer |
| | | |Backoff | |
+-----------+-------------+-------------+--------------+------------+
| |- |-> Win |- |- |
| |DFT = |Stop DFT |Set DF to |DFT ?= |
|Offer |BOperiod + | |Sender or |OPlow; MC = |
| |OPlow; MC = | |Target; DFT |0 |
| |0 | |?= OPlow; MC | |
| | | |= 0 | |
+-----------+-------------+-------------+--------------+------------+
| |-> Offer |-> Offer |-> Offer |-> Offer |
| |DF = Sender; |DF = Sender; |DF = Sender |DFT = OPlow;|
|Lose |DFT = OPlow; |DFT = OPlow; |or Target; |MC = 0 |
| |MC = 0 |MC = 0 |DFT = OPlow; | |
| | | |MC = 0 | |
+-----------+-------------+-------------+--------------+------------+
| |-> Offer |-> Offer |-> Offer |- |
| |DF = Sender; |DF = Sender; |DF = Sender |Send Winner |
|Win |DFT = OPlow; |DFT = OPlow; |or Target; | |
| |MC = 0 |MC = 0 |DFT = OPlow; | |
| | | |MC = 0 | |
+-----------+-------------+-------------+--------------+------------+
| |-> Offer |-> Offer |-> Offer |-> Win |
| |DF = Sender; |DF = Sender; |DF = Sender |Send Winner;|
|Backoff |DFT = OPlow; |DFT = OPlow; |or Target; |Stop DFT |
| |MC = 0 |MC = 0 |DFT = OPlow; | |
| | | |MC = 0 | |
+-----------+-------------+-------------+--------------+------------+
+--------------------------------------------------------------------+
| In Offer State |
+----------------------+----------------------+----------------------+
| DFT Expires and MC | DFT Expires and MC | DFT Expires and MC |
| is less than | is equal to | is equal to |
| Robustness | Robustness and we | Robustness and |
| | have path to RPA | there is no path |
| | | to RPA |
+----------------------+----------------------+----------------------+
| - | -> Win | -> Lose |
| Send Offer; DFT = | Send Winner | Set DF to None |
| OPlow; MC = MC + 1 | | |
+----------------------+----------------------+----------------------+
+--------------------------------------------------------------------+
| In Offer State |
+--------------------------------------------------------------------+
| Metric changes and is now worse |
+--------------------------------------------------------------------+
| DFT ?= OPlow |
| MC = 0 |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Win State | | In Lose State |
+----------------------+-----------------------+---------------------+ +------------------------------+-------------------------------------+
| Metric changes and | Timer Expires and | Path to RPA lost | | Detect DF Failure | Metric changes and now |
| is now worse | MC is less than | | | | is better than DF |
| | Robustness | | +------------------------------+-------------------------------------+
+----------------------+-----------------------+---------------------+ | -> Offer | -> Offer |
| - | - | -> Offer | | DF = None; DFT = | DFT = OPlow_int; MC = 0 |
| DFT = OPlow; MC = | Send Winner; DFT = | Set DF to None; | | OPlow_int; MC = 0 | |
| 0 | OPlow; MC = MC + 1 | DFT = OPlow; MC = | +------------------------------+-------------------------------------+
| | | 0 |
+----------------------+-----------------------+---------------------+
+--------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Backoff State | | In Win State |
+----------------------+-----------------------+---------------------+ +----------------------+-----------------------+---------------------+
| Metric changes and | Timer Expires | Path to RPA lost | | Metric changes and | Timer Expires and | Path to RPA lost |
| is now better than | | | | is now worse | MC is less than | |
| Best | | | | | Robustness | |
+----------------------+-----------------------+---------------------+ +----------------------+-----------------------+---------------------+
| -> Win | -> Lose | -> Offer | | - | - | -> Offer |
| Stop Timer | Send Pass; Set DF | Set DF to None; | | DFT = OPlow; MC = | Send Winner; DFT = | Set DF to None; |
| | to stored Best | DFT = OPlow; MC = | | 0 | OPlow; MC = MC + 1 | DFT = OPlow; MC = |
| | | 0 | | | | 0 |
+----------------------+-----------------------+---------------------+ +----------------------+-----------------------+---------------------+
+--------------------------------------------------------------------+
| In Backoff State |
+----------------------+-----------------------+---------------------+
| Metric changes and | Timer Expires | Path to RPA lost |
| is now better than | | |
| Best | | |
+----------------------+-----------------------+---------------------+
| -> Win | -> Lose | -> Offer |
| Stop Timer | Send Pass; Set DF | Set DF to None; |
| | to stored Best | DFT = OPlow; MC = |
| | | 0 |
+----------------------+-----------------------+---------------------+
3.5.4. Election Reliability Enhancements 3.5.4. Election Reliability Enhancements
For the correct operation of BIDIR-PIM it is very important to avoid For the correct operation of BIDIR-PIM, it is very important to avoid
situations where two routers consider themselves to be Designated situations where two routers consider themselves to be Designated
Forwarders for the same link. The two precautions below are not Forwarders for the same link. The two precautions below are not
required for correct operation but can help diagnose anomalies and required for correct operation but can help diagnose and correct
correct them. anomalies.
3.5.5. Missing Pass 3.5.5. Missing Pass
After a DF has been elected, a router whose metrics change to become After a DF has been elected, a router whose metrics change to become
better than the DF will attempt to take over. If during the re- better than the DF will attempt to take over. If during the re-
election the acting DF has a condition that causes it to lose all of election the acting DF has a condition that causes it to lose all of
the election messages (like a CPU overload), the new candidate will the election messages (like a CPU overload), the new candidate will
transmit three offers and assume the role of the forwarder resulting transmit three offers and assume the role of the forwarder resulting
in two DFs on the link. This situation is pathological and should be in two DFs on the link. This situation is pathological and should be
corrected by fixing the overloaded router. It is desirable that such corrected by fixing the overloaded router. It is desirable that such
an event can be detected by a network administrator. an event can be detected by a network administrator.
When a router becomes the DF for a link without receiving a Pass 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 message from the known old DF, the PIM neighbor information for the
old DF can be marked to this effect. Upon receiving the next PIM old DF can be marked to this effect. Upon receiving the next PIM
Hello message from the old DF, the router can retransmit Winner Hello message from the old DF, the router can retransmit Winner
messages for all the RPAs for which it is acting as the DF. The messages for all the RPAs for which it is acting as the DF. The
anomaly may also be logged by the router in a rate-limited manner to anomaly may also be logged by the router in a rate-limited manner to
alert the operator. 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 An additional degree of safety can be achieved by having the DF for
each RPA periodically announce its status in a Winner message. each RPA periodically announce its status in a Winner message.
Transmission of the periodic Winner message can be restricted to Transmission of the periodic Winner message can be restricted to
occur only for RPAs which have active groups, thus avoiding the occur only for RPAs that have active groups, thus avoiding the
periodic control traffic in areas of the network without senders or periodic control traffic in areas of the network without senders or
receivers for a particular RPA. receivers for a particular RPA.
3.6. Timers, Counters and Constants 3.6. Timers, Counters, and Constants
BIDIR-PIM maintains the following timers, as discussed in section BIDIR-PIM maintains the following timers, as discussed in Section
3.1. All timers are countdown timers - they are set to a value and 3.1. All timers are countdown timers - they are set to a value and
count down to zero, at which point they typically trigger an action. count down to zero, at which point they typically trigger an action.
Of course they can just as easily be implemented as count-up timers, Of course they can just as easily be implemented as count-up timers,
where the absolute expiry time is stored and compared against a real- where the absolute expiry time is stored and compared against a real-
time clock, but the language in this specification assumes that they time clock, but the language in this specification assumes that they
count downwards to zero. count downwards to zero.
Per Rendezvous-Point Address (RPA): Per Rendezvous-Point Address (RPA):
Per interface (I): Per interface (I):
skipping to change at page 33, line 19 skipping to change at page 31, line 29
DF Election Timer: DFT(RPA,I) DF Election Timer: DFT(RPA,I)
Per Group (G): Per Group (G):
Upstream Join Timer: JT(G) Upstream Join Timer: JT(G)
Per interface (I): Per interface (I):
Join Expiry Timer: ET(G,I) Join Expiry Timer: ET(G,I)
PrunePending Timer: PPT(G,I) PrunePendingTimer: PPT(G,I)
When timers are started or restarted, they are set to default values. When timers are started or restarted, they are set to default values.
This section summarizes those default values. This section summarizes those default values.
Timer Name: DF Election Timer (DFT) Timer Name: DF Election Timer (DFT)
+-------------------+------------------------+-----------------------+
| Value Name | Value | Explanation |
+-------------------+------------------------+-----------------------+
| Offer_Period | 100 ms | Interval to wait |
| | | between repeated |
| | | Offer and Winner |
| | | messages. |
+-------------------+------------------------+-----------------------+
| Backoff_Period | 1 sec | Period that acting |
| | | DF waits between |
| | | receiving a better |
| | | Offer and sending |
| | | the Pass message |
| | | to transfer DF |
| | | responsibility. |
+-------------------+------------------------+-----------------------+
| OPlow | rand(0.5, 1) * | Range of actual |
| | Offer_Period | randomised value |
| | | used between |
| | | repeated messages. |
+-------------------+------------------------+-----------------------+
| OPhigh | Election_Robustness | Interval to wait |
| | * Offer_Period | in order to give a |
| | | chance to a router |
| | | with a better |
| | | Offer to become |
| | | the DF. |
+-------------------+------------------------+-----------------------+
Timer Names: Join Expiry Timer (ET(G,I)) +-------------------+------------------------+-----------------------+
| Value Name | Value | Explanation |
+-------------------+------------------------+-----------------------+
| Offer_Period | 100 ms | Interval to wait |
| | | between repeated |
| | | Offer and Winner |
| | | messages. |
+-------------------+------------------------+-----------------------+
| Backoff_Period | 1 sec | Period that acting |
| | | DF waits between |
| | | receiving a better |
| | | Offer and sending |
| | | the Pass message |
| | | to transfer DF |
| | | responsibility. |
+-------------------+------------------------+-----------------------+
| OPlow | rand(0.5, 1) * | Range of actual |
| | Offer_Period | randomised value |
| | | used between |
| | | repeated messages. |
+-------------------+------------------------+-----------------------+
| OPhigh | Election_Robustness | Interval to wait |
| | * Offer_Period | in order to give a |
| | | chance to a router |
| | | with a better |
| | | Offer to become |
| | | the DF. |
+-------------------+------------------------+-----------------------+
Timer Names: Join Expiry Timer (ET(G,I))
+---------------+---------------+------------------------------------+ +---------------+---------------+------------------------------------+
|Value Name | Value | Explanation | |Value Name | Value | Explanation |
+---------------+---------------+------------------------------------+ +---------------+---------------+------------------------------------+
|J/P HoldTime | from message | Hold Time from Join/Prune Message | |J/P HoldTime | from message | Hold Time from Join/Prune Message |
+---------------+---------------+------------------------------------+ +---------------+---------------+------------------------------------+
Timer Names: Prune Pending Timer (PPT(G,I)) Timer Names: PrunePendingTimer (PPT(G,I))
+-------------------------+-------------------+----------------------+ +-------------------------+-------------------+----------------------+
| Value Name | Value | Explanation | | Value Name | Value | Explanation |
+-------------------------+-------------------+----------------------+ +-------------------------+-------------------+----------------------+
| J/P Override Interval | Default: 3 secs | Short period after | | J/P Override Interval | Default: 3 secs | Short period after |
| | | a join or prune to | | | | a Join or Prune to |
| | | allow other | | | | allow other |
| | | routers on the LAN | | | | routers on the LAN |
| | | to override the | | | | to override the |
| | | join or prune | | | | Join or Prune |
+-------------------------+-------------------+----------------------+ +-------------------------+-------------------+----------------------+
Note that the value of the J/P Override Interval is interface Note that the value of the J/P Override Interval is interface specific
specific and depends on both the Propagation_Delay and the and depends on both the Propagation_Delay and the Override_Interval
Override_Interval values that may change when Hello messages are values that may change when Hello messages are received [4].
received [4].
Timer Names: Upstream Join Timer (JT(G)) Timer Names: Upstream Join Timer (JT(G))
+------------+-------------------+-----------------------------------+ +------------+-------------------+-----------------------------------+
Value Name |Value Explanation | Value Name |Value Explanation |
+------------+-------------------+-----------------------------------+ +------------+-------------------+-----------------------------------+
t_periodic |Default: 60 secs Period between Join/Prune Messages | t_periodic |Default: 60 secs Period between Join/Prune Messages |
+------------+-------------------+-----------------------------------+ +------------+-------------------+-----------------------------------+
t_suppressed |rand(1.1 * Suppression period when someone | t_suppressed |rand(1.1 * Suppression period when someone |
| |t_periodic, 1.4 * else sends a J/P message so we | | |t_periodic, 1.4 * else sends a J/P message so we |
| |t_periodic) don't need to do so. | | |t_periodic) don't need to do so. |
+------------+-------------------+-----------------------------------+ +------------+-------------------+-----------------------------------+
t_override |rand(0, 0.9 * J/P Randomized delay to prevent | t_override |rand(0, 0.9 * J/P Randomized delay to prevent |
| |Override Interval) response implosion when sending a | | |Override Interval) response implosion when sending a |
| | join message to override someone | | | Join message to override someone |
| | else's prune message. | | | else's Prune message. |
+------------+-------------------+-----------------------------------+ +------------+-------------------+-----------------------------------+
For more information about these values refer to the PIM-SM [4] For more information about these values, refer to the PIM-SM [4]
documentation. documentation.
Constant Name: DF Election Robustness Constant Name: DF Election Robustness
+-------------------------+------------------+-----------------------+ +-------------------------+------------------+-----------------------+
| Constant Name | Value | Explanation | | Constant Name | Value | Explanation |
+-------------------------+------------------+-----------------------+ +-------------------------+------------------+-----------------------+
| Election_Robustness | Default: 3 | Minimum number of | | Election_Robustness | Default: 3 | Minimum number of |
| | | 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- This section describes the details of the packet formats for BIDIR-
PIM control messages. BIDIR-PIM shares a number of control messages PIM control messages. BIDIR-PIM shares a number of control messages
in common with PIM-SM [4]. These include the Hello and Join/Prune in common with PIM-SM [4]. These include the Hello and Join/Prune
messages as well as the format for the Encoded-Unicast address. For messages as well as the format for the Encoded-Unicast address. For
details on the format of these packets please refer to the PIM-SM details on the format of these packets, please refer to the PIM-SM
documentation. Here we will only define the additional packets that documentation. Here we will only define the additional packets that
are introduced by BIDIR-PIM. These are the packets used in the DF are introduced by BIDIR-PIM. These are the packets used in the DF
election process as well as the Bidir_Capable PIM-Hello option. election process as well as the Bidirectional 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 The IPv4 `ALL-PIM-ROUTERS' group is `224.0.0.13'. The IPv6 group. The IPv4 `ALL-PIM-ROUTERS' group is `224.0.0.13'. The IPv6
`ALL-PIM-ROUTERS' group is `ff02::d'. `ALL-PIM-ROUTERS' group is `ff02::d'.
All DF election BIDIR-PIM control messages share the common header All DF election BIDIR-PIM control messages share the common header
below: below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type |Subtype| Rsvd | Checksum | |PIM Ver| Type |Subtype| Rsvd | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 37, line 4 skipping to change at page 35, line 19
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type |Subtype| Rsvd | Checksum | |PIM Ver| Type |Subtype| Rsvd | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Address (Encoded-Unicast format) ... | RP Address (Encoded-Unicast format) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Metric Preference | | Sender Metric Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Metric | | Sender Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PIM Ver PIM Ver
PIM Version number is 2. PIM Version number is 2.
Type Type
All DF-Election PIM control messages share the PIM message Type of All DF-Election PIM control messages share the PIM message Type of
10. 10.
Subtype Subtype
Subtypes for DF election messages are: Subtypes for DF election messages are:
1 = Offer 1 = Offer
2 = Winner 2 = Winner
3 = Backoff 3 = Backoff
4 = Pass 4 = Pass
Rsvd Rsvd
Set to zero on transmission. Ignored upon receipt. Set to zero on transmission. Ignored on receipt.
Checksum Checksum
The checksum is standard IP checksum, i.e. the 16-bit one's A standard checksum IP checksum is used, i.e., the 16-bit one's
complement of the one's complement sum of the entire PIM message. complement of the one's complement sum of the entire PIM message.
For computing the checksum, the checksum field is zeroed. For computing the checksum, the checksum field is zeroed.
RP Address RP Address
The bidir RPA for which the election is taking place. Format The bidirectional RPA for which the election is taking place. The
described in [4] Section 4.9.1. format is described in [4], Section 4.9.1.
Sender Metric Preference Sender Metric Preference
Preference value assigned to the unicast routing protocol that the Preference value assigned to the unicast routing protocol that the
message sender used to obtain the route to the RPA. message sender used to obtain the route to the RPA.
Sender Metric Sender Metric
The unicast routing table metric used by the message sender to The unicast routing table metric used by the message sender to
reach the RPA. The metric is in units applicable to the unicast reach the RPA. The metric is in units applicable to the unicast
routing protocol used. routing protocol used.
In addition to the fields defined above the Backoff and Pass messages In addition to the fields defined above, the Backoff and Pass
have the extra fields described below. messages have the extra fields described below.
3.7.2. Backoff Message 3.7.2. Backoff Message
The Backoff message uses the following fields in addition to the The Backoff message uses the following fields in addition to the
common election message format described above. common election message format described above.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offering Address (Encoded-Unicast format) ... | Offering Address (Encoded-Unicast format) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offering Metric Preference | | Offering Metric Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offering Metric | | Offering Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval | | Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Offering Address Offering Address
The address of the router that made the last (best) Offer. Format The address of the router that made the last (best) Offer. The
described in [4] Section 4.9.1. format is described in [4], Section 4.9.1.
Offering Metric Preference Offering Metric Preference
Preference value assigned to the unicast routing protocol that the Preference value assigned to the unicast routing protocol that the
offering router used to obtain the route to the RPA. offering router used to obtain the route to the RPA.
Offering Metric Offering Metric
The unicast routing table metric used by the offering router to The unicast routing table metric used by the offering router to
reach the RPA. The metric is in units applicable to the unicast reach the RPA. The metric is in units applicable to the unicast
routing protocol used. routing protocol used.
Interval Interval
The backoff interval in milliseconds to be used by routers with The backoff interval in milliseconds to be used by routers with
worse metrics than the offering router. worse metrics than the offering router.
3.7.3. Pass Message 3.7.3. Pass Message
The Pass message uses the following fields in addition to the common The Pass message uses the following fields in addition to the common
election fields described above. election fields described above.
skipping to change at page 39, line 4 skipping to change at page 37, line 14
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New Winner Address (Encoded-Unicast format) ... | New Winner Address (Encoded-Unicast format) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New Winner Metric Preference | | New Winner Metric Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New Winner Metric | | New Winner Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
New Winner Address New Winner Address
The address of the router that made the last (best) Offer. Format The address of the router that made the last (best) Offer. The
described in [4] Section 4.9.1. format is described in [4], Section 4.9.1.
New Winner Metric Preference New Winner Metric Preference
Preference value assigned to the unicast routing protocol that the Preference value assigned to the unicast routing protocol that the
offering router used to obtain the route to the RPA. offering router used to obtain the route to the RPA.
New Winner Metric New Winner Metric
The unicast routing table metric used by the offering router to The unicast routing table metric used by the offering router to
reach the RPA. The metric is in units applicable to the unicast reach the RPA. The metric is in units applicable to the unicast
routing protocol used. routing protocol used.
3.7.4. Bidir Capable PIM-Hello Option 3.7.4. Bidirectional Capable PIM-Hello Option
BIDIR-PIM introduces one new PIM-Hello option. BIDIR-PIM introduces one new PIM-Hello option.
o OptionType 22: Bidir Capable o OptionType 22: Bidirectional Capable
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 Routers discover that a range of multicast group addresses operates
in bi-directional mode and the address of the Rendezvous-Point in bidirectional mode, and that the address of the Rendezvous-Point
address (RPA) serving the group range either through static address (RPA) is serving the group range either through static
configuration or using an automatic RP discovery mechanism like the configuration or using an automatic RP discovery mechanism like the
PIM Bootstrap mechanism (BSR) [7] or Auto-RP. PIM Bootstrap mechanism (BSR) [7] or Auto-RP.
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 integrity protection and group-wise data origin authentication of
BIDIR-PIM protocol messages. Authentication of BIDIR-PIM messages can BIDIR-PIM protocol messages. Authentication of BIDIR-PIM messages
protect against unwanted behaviour caused by unauthorized or altered can protect against unwanted behaviour caused by unauthorized or
BIDIR-PIM messages. altered BIDIR-PIM messages.
5.1. Attacks Based on Forged Messages 5.1. Attacks Based on Forged Messages
As in PIM Sparse-Mode, the extent of possible damage depends on the As in PIM Sparse-Mode, the extent of possible damage depends on the
type of counterfeit messages accepted. BIDIR-PIM only uses link-local type of counterfeit messages accepted. BIDIR-PIM only uses link-
multicast messages sent to the ALL_PIM_ROUTERS address, hence attacks local multicast messages sent to the ALL_PIM_ROUTERS address, hence
can only be carried out by directly connected nodes, or with the attacks can only be carried out by directly connected nodes, or with
complicity of directly connected routers. the complicity of directly connected routers.
Some of the BIDIR-PIM protocol messages (Join/Prune and Hello) are Some of the BIDIR-PIM protocol messages (Join/Prune and Hello) are
identical, both in format and functionality, to the respective identical, both in format and functionality, to the respective
messages used in PIM-SM. Security considerations for these messages messages used in PIM-SM. Security considerations for these messages
are to be found in [4]. Other messages (DF-election messages) are are to be found in [4]. Other messages (DF-election messages) are
specific to BIDIR-PIM and will be discussed in the following specific to BIDIR-PIM and will be discussed in the following
paragraphs. paragraphs.
By forging DF-election messages an attacker can disrupt the election By forging DF-election messages, an attacker can disrupt the election
of the Designated Forwarder on a link in two different ways: of the Designated Forwarder on a link in two different ways:
5.1.1. Election of an Incorrect DF 5.1.1. Election of an Incorrect DF
An attacker can force its election as DF by participating in a An attacker can force its election as DF by participating in a
regular election and advertising the best metric to reach the RPA. regular election and advertising the best metric to reach the RPA.
An attacker can also try to force the election of another router as An attacker can also try to force the election of another router as
DF by sending an Offer, Winner or Pass message and impersonating DF by sending an Offer, Winner, or Pass message and impersonating
another router. In some cases (e.g. the Offer) multiple messages another router. In some cases (e.g., the Offer), multiple messages
might be needed to carry out an attack. might be needed to carry out an attack.
In the case of Offer or Winner messages the attacker will have to In the case of Offer or Winner messages, the attacker will have to
impersonate the node that it wants to have become the DF. In the case impersonate the node that it wants to have become the DF. In the
of the Pass it will have to impersonate the current DF. This type of case of the Pass, it will have to impersonate the current DF. This
attack causes the wrong DF to be recorded in all nodes apart from the type of attack causes the wrong DF to be recorded in all nodes apart
one that is being impersonated. This node typically will be able to from the one that is being impersonated. This node typically will be
detect the anomaly and, possibly, restart a new election. able to detect the anomaly and, possibly, restart a new election.
A more sophisticated attacker might carry out a concurrent DoS attack A more sophisticated attacker might carry out a concurrent DoS attack
on the node being impersonated, so that it will not be able to detect on the node being impersonated, so that it will not be able to detect
the forged packets and/or take countermeasures. the forged packets and/or take countermeasures.
All attacks based on impersonation can be detected by all routers and All attacks based on impersonation can be detected by all routers and
avoided if the source of DF-election messages can be authenticated. avoided if the source of DF-election messages can be authenticated.
When authentication is available, spoofed messages MUST be discarded When authentication is available, spoofed messages MUST be discarded
and a rate-limited warning message SHOULD be logged. and a rate-limited warning message SHOULD be logged.
A more subtle attacker could use MAC-level addresses to partition the A more subtle attacker could use MAC-level addresses to partition the
set of recipients of DF-election messages and create an inconsistent set of recipients of DF-election messages and create an inconsistent
DF view on the link. For example the attacker could use unicast MAC DF view on the link. For example, the attacker could use unicast MAC
addresses for its forged DF-election messages. To prevent this type addresses for its forged DF-election messages. To prevent this type
of 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 of received DF-election messages. This however is ineffective on
links that do not support layer-2 multicast delivery. links that do not support layer-2 multicast delivery.
Source authentication is also sufficient to prevent this kind of Source authentication is also sufficient to prevent this kind of
attack. 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 ways to achieve this. The simplest forwarding trees. There are many ways to achieve this. The simplest
is by sending an infinite sequence of Offer messages (the metric used is by sending an infinite sequence of Offer messages (the metric used
in the messages is not important). in 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- neighbors from which it will accept Join/Prune, Assert, and DF-
election messages. Either static configuration of IP addresses or an election messages. Either static configuration of IP addresses or an
IPsec security association may be used. Furthermore, a PIM router IPsec security association may be used. Furthermore, a PIM router
SHOULD NOT accept protocol messages from a router from which it has SHOULD NOT accept protocol messages from a router from which it has
not yet received a valid Hello message. not yet received a valid Hello message.
5.2.1. Basic Access Control 5.2.1. Basic Access Control
In a PIM-SM domain, when all routers 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 implement a basic form of access control for both sources and
receivers: Receivers can be validated by the last-hop DR and sources receivers: Receivers can be validated by the last-hop DR and sources
can be validated by the first-hop DR and/or the RP. can be validated by the first-hop DR and/or the RP.
In BIDIR-PIM this is generally feasible only for receivers, as In BIDIR-PIM, this is generally feasible only for receivers, as
sources can send to the multicast group without the need for routers sources can send to the multicast group without the need for routers
to detect their activity and create source-specific state. However it to detect their activity and create source-specific state. However,
is possible to modify the standard BIDIR-PIM behaviour, in a backward it is possible to modify the standard BIDIR-PIM behaviour, in a
compatible way, to allow per-source access control. The tradeoff backward compatible way, to allow per-source access control. The
would be protocol simplicity, memory and processing requirements. tradeoff would be protocol simplicity, memory, and processing
requirements.
5.3. Authentication Using IPsec 5.3. Authentication Using IPsec
Just like for PIM-SM, the IPsec [5] transport mode using the Just as with PIM-SM, the IPsec [5] transport mode using the
Authentication Header (AH) is the recommended method to prevent the Authentication Header (AH) is the recommended method to prevent the
above attacks against BIDIR-PIM. above attacks against BIDIR-PIM.
It is recommended that IPsec authentication be applied to all BIDIR- It is recommended that IPsec authentication be applied to all BIDIR-
PIM protocol messages. The specification on how this is done is to be PIM protocol messages. The specification on how this is done is
found in [4]. specifically the authentication of PIM-SM link-local found in [4]. Specifically, the authentication of PIM-SM link-local
messages, described in [4] applies to all BIDIR-PIM messages as well. messages, 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] The denial-of-service attack based on forged Join messages, described
also apply to BIDIR-PIM. in [4], also applies to BIDIR-PIM.
6. IANA Considerations 6. IANA Considerations
IANA has assigned OptionType 22 to the "Bidir Capable" option. IANA has assigned OptionType 22 to the "Bidirectional Capable"
option.
7. Acknowledgments 7. Acknowledgments
The bidir proposal in this draft is heavily based on the ideas and The bidirectional proposal in this document is heavily based on the
text presented by Estrin and Farinacci in [6]. The main difference ideas and text presented by Estrin and Farinacci in [6]. The main
between the two proposals is in the method chosen for upstream difference between the two proposals is in the method chosen for
forwarding. upstream forwarding.
We would also like to thank John Zwiebel at Cisco, Deborah Estrin at We would also like to thank John Zwiebel at Cisco, Deborah Estrin at
ISI/USC, Bill Fenner at AT&T Research as well as Nidhi Bhaskar, Yiqun ISI/USC, Bill Fenner at AT&T Research, as well as Nidhi Bhaskar,
Cai, Toerless Eckert, Apoorva Karan, Rajitha Sumanasekera and Beau Yiqun Cai, Toerless Eckert, Apoorva Karan, Rajitha Sumanasekera, and
Williamson at cisco for their contributions and comments to this Beau Williamson at Cisco for their contributions and comments to this
draft. document.
8. Authors' Addresses
Mark Handley
Computer Science Department
University College London
M.Handley@cs.ucl.ac.uk
Isidor Kouvelas
Cisco Systems
kouvelas@cisco.com
Tony Speakman
Cisco Systems
speakman@cisco.com
Lorenzo Vicisano
Digital Fountain
lorenzo@digitalfountain.com
9. Normative References 8. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. [2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3", RFC Thyagarajan, "Internet Group Management Protocol, Version 3", RFC
3376, October 2002. 3376, October 2002.
[3] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener [3] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999. Discovery (MLD) for IPv6", RFC 2710, October 1999.
[4] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol [4] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol
Independent Multicast - Sparse Mode (PIM-SM): Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol
Specification (Revised)", RFC 4601, August 2006. Specification (Revised)", RFC 4601, August 2006.
[5] Kent, S. and R. Atkinson, "Security Architecture for the Internet [5] Kent, S. and R. Atkinson, "Security Architecture for the Internet
Protocol", RFC 2401, November 1998. [Note to RFC Editor: this is Protocol", RFC 2401, November 1998.
intended to be the obsolete document, just like RFC 4601's]
10. Informative References 9. Informative References
[6] Estrin, D. and D. Farinacci, "Bi-directional Shared Trees in PIM- [6] Estrin, D. and D. Farinacci, "Bi-directional Shared Trees in
SM", Work in progress <draft-farinacci-bidir-pim-01.txt>, May PIM-SM", Work in Progress, May 1999.
1999.
[7] Bhaskar, N., Gall, A., Lingard, J. and S. Venaas, "Bootstrap [7] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas, "Bootstrap
Router (BSR) Mechanism for PIM", Work in progress <draft-ietf-pim- Router (BSR) Mechanism for PIM", Work in Progress, February 2007.
sm-bsr-09.txt>, June 2006.
11. Index [8] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol
DF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,21 Extensions for BGP-4", RFC 4760, January 2007.
Downstream. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
DownstreamJPState(G,I). . . . . . . . . . . . . . . . . . . . . . 12 Index
ET(G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,34
DF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5,18
Downstream. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
DownstreamJPState(G,I). . . . . . . . . . . . . . . . . . . . . . 10
ET(G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . 9,14,33
ET(RPA,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ET(RPA,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
I_am_DF(RPA,I). . . . . . . . . . . . . . . . . . . . . . . .12,14,17 I_am_DF(RPA,I). . . . . . . . . . . . . . . . . . . . . . . .10,12,14
J/P_HoldTime. . . . . . . . . . . . . . . . . . . . . . . . . . . 34 J/P_HoldTime. . . . . . . . . . . . . . . . . . . . . . . . . . . 33
J/P_Override_Interval . . . . . . . . . . . . . . . . . . . . . 18,35 J/P_Override_Interval . . . . . . . . . . . . . . . . . . . . . 16,33
JoinDesired(G). . . . . . . . . . . . . . . . . . . . . . . . . . 21 JoinDesired(G). . . . . . . . . . . . . . . . . . . . . . . . . . 18
joins(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 joins(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
JT(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 JT(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
JT(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11,35 JT(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9,33
local_receiver_include(G,I) . . . . . . . . . . . . . . . . . . . 12 local_receiver_include(G,I) . . . . . . . . . . . . . . . . . . . 10
MFIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 MFIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
NLT(N,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 NLT(N,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Offer_Period. . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Offer_Period. . . . . . . . . . . . . . . . . . . . . . . . . . . 32
olist(G). . . . . . . . . . . . . . . . . . . . . . . . . . .12,14,21 olist(G). . . . . . . . . . . . . . . . . . . . . . . . . . .10,12,18
OT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Bidirectional Capable OptionType . . . . . . . . . . . . . . . . 37
pim_include(G). . . . . . . . . . . . . . . . . . . . . . . . . . 12 pim_include(G). . . . . . . . . . . . . . . . . . . . . . . . . . 10
PPT(G,I). . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,35 PPT(G,I). . . . . . . . . . . . . . . . . . . . . . . . . . . 9,14,33
RPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 RPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
RPF_interface(RPA). . . . . . . . . . . . . . . . . . . . . . . 12,14 RPF_interface(RPA). . . . . . . . . . . . . . . . . . . . . . . 10,12
RPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 RPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
TIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 TIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
t_override. . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35 t_override. . . . . . . . . . . . . . . . . . . . . . . . . . . 17,33
t_periodic. . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35 t_periodic. . . . . . . . . . . . . . . . . . . . . . . . . . . 17,33
t_suppressed. . . . . . . . . . . . . . . . . . . . . . . . . . 20,35 t_suppressed. . . . . . . . . . . . . . . . . . . . . . . . . . 17,33
Upstream. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Upstream. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses
Mark Handley
Computer Science Department
University College London
EMail: M.Handley@cs.ucl.ac.uk
Isidor Kouvelas
Cisco Systems
EMail: kouvelas@cisco.com
Tony Speakman
Cisco Systems
EMail: speakman@cisco.com
Lorenzo Vicisano
Digital Fountain
EMail: lorenzo@digitalfountain.com
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