< draft-ietf-pim-bidir-08.txt   draft-ietf-pim-bidir-09.txt >
Internet Engineering Task Force PIM WG Internet Engineering Task Force PIM WG
INTERNET-DRAFT Mark Handley/UCL INTERNET-DRAFT Mark Handley/UCL
draft-ietf-pim-bidir-08.txt Isidor Kouvelas/Cisco draft-ietf-pim-bidir-09.txt Isidor Kouvelas/Cisco
Tony Speakman/Cisco Intended Status: Proposed Standard Tony Speakman/Cisco
Lorenzo Vicisano/Cisco Lorenzo Vicisano/Digital Fountain
22 October 2005 22 February 2007
Expires: April 2006 Expires: August 2007
Bi-directional Protocol Independent Multicast (BIDIR-PIM) Bi-directional Protocol Independent Multicast (BIDIR-PIM)
Status of this Document Status of this Document
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Abstract Abstract
This document discusses Bi-directional PIM, a variant of PIM This document discusses Bi-directional PIM, a variant of PIM
Sparse-Mode that builds bi-directional shared trees connecting Sparse-Mode that builds bi-directional shared trees connecting
multicast sources and receivers. Bi-directional trees are multicast sources and receivers. Bi-directional trees are built
built using a fail-safe Designated Forwarder (DF) election using a fail-safe Designated Forwarder (DF) election mechanism
mechanism operating on each link of a multicast topology. operating on each link of a multicast topology. With the
With the assistance of the DF, multicast data is natively assistance of the DF, multicast data is natively forwarded from
forwarded from sources to the Rendezvous-Point and hence along sources to the Rendezvous-Point and hence along the shared tree
the shared tree to receivers without requiring source-specific to receivers without requiring source-specific state. The DF
state. The DF election takes place at RP discovery time and election takes place at RP discovery time and provides the route
provides the route to the RP thus eliminating the requirement to the RP thus eliminating the requirement for data-driven
for data-driven protocol events. protocol events.
Table of Contents Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology. . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions. . . . . . . . . . . . . . . . . . . . . 6 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Pseudocode Notation. . . . . . . . . . . . . . . . . 8 2.2. Pseudocode Notation . . . . . . . . . . . . . . . . . . 8
3. Protocol Specification. . . . . . . . . . . . . . . . . 8 3. Protocol Specification . . . . . . . . . . . . . . . . . . 8
3.1. BIDIR-PIM Protocol State . . . . . . . . . . . . . . 9 3.1. BIDIR-PIM Protocol State. . . . . . . . . . . . . . . . 9
3.1.1. General Purpose State . . . . . . . . . . . . . . 9 3.1.1. General Purpose State. . . . . . . . . . . . . . . . 9
3.1.2. RPA State . . . . . . . . . . . . . . . . . . . . 10 3.1.2. RPA State. . . . . . . . . . . . . . . . . . . . . . 10
3.1.3. Group State . . . . . . . . . . . . . . . . . . . 10 3.1.3. Group State. . . . . . . . . . . . . . . . . . . . . 10
3.1.4. State Summarization Macros. . . . . . . . . . . . 11 3.1.4. State Summarization Macros . . . . . . . . . . . . . 11
3.2. PIM Neighbor Discovery . . . . . . . . . . . . . . . 12 3.2. PIM Neighbor Discovery. . . . . . . . . . . . . . . . . 12
3.3. Data Packet Forwarding Rules . . . . . . . . . . . . 13 3.3. Data Packet Forwarding Rules. . . . . . . . . . . . . . 13
3.3.1. Upstream Forwarding at RP . . . . . . . . . . . . 14 3.3.1. Upstream Forwarding at RP. . . . . . . . . . . . . . 14
3.3.2. Source-Only Branches. . . . . . . . . . . . . . . 14 3.3.2. Source-Only Branches . . . . . . . . . . . . . . . . 14
3.3.3. Directly Connected Sources. . . . . . . . . . . . 15 3.3.3. Directly Connected Sources . . . . . . . . . . . . . 15
3.4. PIM Join/Prune Messages. . . . . . . . . . . . . . . 15 3.4. PIM Join/Prune Messages . . . . . . . . . . . . . . . . 15
3.4.1. Receiving (*,G) Join/Prune Messages . . . . . . . 15 3.4.1. Receiving (*,G) Join/Prune Messages. . . . . . . . . 15
3.4.2. Sending Join/Prune Messages . . . . . . . . . . . 18 3.4.2. Sending Join/Prune Messages. . . . . . . . . . . . . 18
3.5. Designated Forwarder (DF) Election . . . . . . . . . 21 3.5. Designated Forwarder (DF) Election. . . . . . . . . . . 21
3.5.1. DF Requirements . . . . . . . . . . . . . . . . . 21 3.5.1. DF Requirements. . . . . . . . . . . . . . . . . . . 21
3.5.2. DF Election description . . . . . . . . . . . . . 22 3.5.2. DF Election description. . . . . . . . . . . . . . . 22
3.5.2.1. Bootstrap Election . . . . . . . . . . . . . . 22 3.5.2.1. Bootstrap Election. . . . . . . . . . . . . . . . 22
3.5.2.2. Loser Metric Changes . . . . . . . . . . . . . 23 3.5.2.2. Loser Metric Changes. . . . . . . . . . . . . . . 23
3.5.2.3. Winner Metric Changes. . . . . . . . . . . . . 24 3.5.2.3. Winner Metric Changes . . . . . . . . . . . . . . 24
3.5.2.4. Winner Loses Path. . . . . . . . . . . . . . . 24 3.5.2.4. Winner Loses Path . . . . . . . . . . . . . . . . 24
3.5.2.5. Late Router Starting Up. . . . . . . . . . . . 24 3.5.2.5. Late Router Starting Up . . . . . . . . . . . . . 25
3.5.2.6. Winner Dies. . . . . . . . . . . . . . . . . . 25 3.5.2.6. Winner Dies . . . . . . . . . . . . . . . . . . . 25
3.5.3. Election Protocol Specification . . . . . . . . . 25 3.5.3. Election Protocol Specification. . . . . . . . . . . 25
3.5.3.1. Election State . . . . . . . . . . . . . . . . 25 3.5.3.1. Election State. . . . . . . . . . . . . . . . . . 25
3.5.3.2. Election Messages. . . . . . . . . . . . . . . 26 3.5.3.2. Election Messages . . . . . . . . . . . . . . . . 26
3.5.3.3. Election Events. . . . . . . . . . . . . . . . 27 3.5.3.3. Election Events . . . . . . . . . . . . . . . . . 27
3.5.3.4. Election Actions . . . . . . . . . . . . . . . 28 3.5.3.4. Election Actions. . . . . . . . . . . . . . . . . 28
3.5.3.5. Election State Transitions . . . . . . . . . . 29 3.5.3.5. Election State Transitions. . . . . . . . . . . . 29
3.5.4. Election Reliability Enhancements . . . . . . . . 32 3.5.4. Election Reliability Enhancements. . . . . . . . . . 32
3.5.5. Missing Pass. . . . . . . . . . . . . . . . . . . 32 3.5.5. Missing Pass . . . . . . . . . . . . . . . . . . . . 32
3.5.6. Periodic Winner Announcement. . . . . . . . . . . 32 3.5.6. Periodic Winner Announcement . . . . . . . . . . . . 32
3.6. Timers, Counters and Constants . . . . . . . . . . . 32 3.6. Timers, Counters and Constants. . . . . . . . . . . . . 32
3.7. BIDIR-PIM Packet Formats . . . . . . . . . . . . . . 36 3.7. BIDIR-PIM Packet Formats. . . . . . . . . . . . . . . . 36
3.7.1. DF Election Packet Formats. . . . . . . . . . . . 36 3.7.1. DF Election Packet Formats . . . . . . . . . . . . . 36
3.7.2. Backoff Message . . . . . . . . . . . . . . . . . 37 3.7.2. Backoff Message. . . . . . . . . . . . . . . . . . . 37
3.7.3. Pass Message. . . . . . . . . . . . . . . . . . . 38 3.7.3. Pass Message . . . . . . . . . . . . . . . . . . . . 38
3.7.4. Bidir Capable PIM-Hello Option. . . . . . . . . . 39 3.7.4. Bidir Capable PIM-Hello Option . . . . . . . . . . . 39
4. RP Discovery. . . . . . . . . . . . . . . . . . . . . . 39 4. RP Discovery . . . . . . . . . . . . . . . . . . . . . . . 39
5. Security Considerations . . . . . . . . . . . . . . . . 39 5. Security Considerations. . . . . . . . . . . . . . . . . . 39
5.1. Attacks Based on Forged Messages . . . . . . . . . . 39 5.1. Attacks Based on Forged Messages. . . . . . . . . . . . 39
5.1.1. Election of an Incorrect DF . . . . . . . . . . . 40 5.1.1. Election of an Incorrect DF. . . . . . . . . . . . . 40
5.1.2. Preventing Election Convergence . . . . . . . . . 41 5.1.2. Preventing Election Convergence. . . . . . . . . . . 41
5.2. Non-cryptographic Authentication Mechanisms. . . . . 41 5.2. Non-cryptographic Authentication Mechanisms . . . . . . 41
5.2.1. Basic Access Control. . . . . . . . . . . . . . . 41 5.2.1. Basic Access Control . . . . . . . . . . . . . . . . 41
5.3. Authentication Using IPsec . . . . . . . . . . . . . 41 5.3. Authentication Using IPsec. . . . . . . . . . . . . . . 41
5.4. Denial of Service Attacks. . . . . . . . . . . . . . 41 5.4. Denial of Service Attacks . . . . . . . . . . . . . . . 41
6. Change history. . . . . . . . . . . . . . . . . . . . . 42 6. IANA Considerations. . . . . . . . . . . . . . . . . . . . 42
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . 42 7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . 42
8. Authors' Addresses. . . . . . . . . . . . . . . . . . . 42 8. Authors' Addresses . . . . . . . . . . . . . . . . . . . . 42
9. Normative References. . . . . . . . . . . . . . . . . . 43 9. Normative References . . . . . . . . . . . . . . . . . . . 42
10. Informative References . . . . . . . . . . . . . . . . 43 10. Informative References. . . . . . . . . . . . . . . . . . 43
11. Index. . . . . . . . . . . . . . . . . . . . . . . . . 45 11. Index . . . . . . . . . . . . . . . . . . . . . . . . . . 44
12. Full Copyright Statement . . . . . . . . . . . . . . . 46
List of Figures List of Figures
Figure 1. Downstream group per-interface state- Figure 1. Downstream group per-interface state-
machine. . . . . . . . . . . . . . . . . . . . . 16 machine . . . . . . . . . . . . . . . . . . . . . . 16
Figure 2. Upstream group state-machine. . . . . . . . . . . . 19
Figure 3. Designated Forwarder election state- Figure 3. Designated Forwarder election state-
machine. . . . . . . . . . . . . . . . . . . . . 29 machine . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction 1. Introduction
This document specifies Bi-directional PIM (BIDIR-PIM), a variant of PIM This document specifies Bi-directional PIM (BIDIR-PIM), a variant of
Sparse-Mode (PIM-SM) [4] that builds bi-directional shared trees PIM Sparse-Mode (PIM-SM) [4] that builds bi-directional shared trees
connecting multicast sources and receivers. connecting multicast sources and receivers.
PIM-SM constructs uni-directional shared trees that are used to forward PIM-SM constructs uni-directional shared trees that are used to
data from senders to receivers of a multicast group. PIM-SM also allows forward data from senders to receivers of a multicast group. PIM-SM
the construction of source specific trees, but this capability is not also allows the construction of source specific trees, but this
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 router The shared tree for each multicast group is rooted at a multicast
called the Rendezvous Point (RP). Different multicast groups can use router called the Rendezvous Point (RP). Different multicast groups
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 way
packets are forwarded from a source to the RP: packets are forwarded from a source to the RP:
o Initially when a source starts transmitting, its first hop router o Initially when a source starts transmitting, its first hop router
encapsulates data packets in special control messages (Registers) encapsulates data packets in special control messages (Registers)
which are unicast to the RP. After reaching the RP the packets are which are unicast to the RP. After reaching the RP the packets are
decapsulated and distributed on the shared tree. decapsulated and distributed on the shared tree.
o A transition from the above distribution mode can be made at a later o A transition from the above distribution mode can be made at a
stage. This is achieved by building source specific state on all later stage. This is achieved by building source specific state on
routers along the path between the source and the RP. This state is all routers along the path between the source and the RP. This
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 these mechanisms suffer from problems. Encapsulation results in
significant processing, bandwidth and delay overheads. Forwarding using significant processing, bandwidth and delay overheads. Forwarding
source specific state has additional protocol and memory requirements. using source specific state has additional protocol and memory
requirements.
Bi-directional PIM dispenses with both encapsulation and source state by Bi-directional PIM dispenses with both encapsulation and source state
allowing packets to be natively forwarded from a source to the RP using by allowing packets to be natively forwarded from a source to the RP
shared tree state. In contrast to PIM-SM this mode of forwarding does using shared tree state. In contrast to PIM-SM this mode of
not require any data-driven events. forwarding does not require any data-driven events.
The protocol specification in this document assumes familiarity with the The protocol specification in this document assumes familiarity with
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", "SHALL", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
"OPTIONAL" are to be interpreted as described in RFC 2119 and indicate and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
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 MRIB Multicast Routing Information Base. This is the multicast
topology table, which is typically derived from the unicast topology table, which is typically derived from the unicast
routing table, or routing protocols such as MBGP that carry routing table, or routing protocols such as MBGP that carry
multicast-specific topology information. It is used by PIM for multicast-specific topology information. It is used by PIM for
establishing the RPF interface (used in the forwarding rules). In establishing the RPF interface (used in the forwarding rules).
PIM-SM the MRIB is also used to make decisions regarding where to In PIM-SM the MRIB is also used to make decisions regarding
forward Join/Prune messages whereas in BIDIR-PIM it is used as a where to forward Join/Prune messages whereas in BIDIR-PIM it is
source for routing metrics for the DF election process. used as a source for routing metrics for the DF election
process.
Rendezvous Point Address (RPA): Rendezvous Point Address (RPA):
An RPA is an address that is used as the root of the distribution An RPA is an address that is used as the root of the
tree for a range of multicast groups. The RPA must be routable distribution tree for a range of multicast groups. The RPA must
from all routers in the PIM domain. The RPA does not need to be routable from all routers in the PIM domain. The RPA does
correspond to an address for an interface of a real router. In not need to correspond to an address for an interface of a real
this respect BIDIR-PIM differs from PIM-SM which requires an router. In this respect BIDIR-PIM differs from PIM-SM which
actual router to be configured as the Rendezvous Point (RP). Join requires an actual router to be configured as the Rendezvous
messages from receivers for a BIDIR-PIM group propagate hop-by-hop Point (RP). Join messages from receivers for a BIDIR-PIM group
towards the RPA. propagate hop-by-hop towards the RPA.
Rendezvous Point Link (RPL): Rendezvous Point Link (RPL):
An RPL for a particular RPA is the physical link to which the RPA An RPL for a particular RPA is the physical link to which the
belongs. In BIDIR-PIM all multicast traffic to groups mapping to a RPA belongs. In BIDIR-PIM all multicast traffic to groups
specific RPA is forwarded on the RPL of that RPA. The RPL is mapping to a specific RPA is forwarded on the RPL of that RPA.
special within a BIDIR-PIM domain as it is the only link on which The RPL is special within a BIDIR-PIM domain as it is the only
a Designated Forwarder election does not take place (see DF link on which a Designated Forwarder election does not take
definition below). place (see DF definition below).
Upstream Upstream
Towards the root (RPA) of the tree. The direction used by packets Towards the root (RPA) of the tree. The direction used by
traveling from sources to the RPL. packets 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 is both multi-access and point-to-point links). The only exception
the RPL on which no DF exists. The DF is the router on the link is the RPL on which no DF exists. The DF is the router on the
with the best route to the RPA (determined by comparing MRIB link with the best route to the RPA (determined by comparing
provided metrics). A DF for a given RPA is in charge of forwarding MRIB provided metrics). A DF for a given RPA is in charge of
downstream traffic onto its link, and forwarding upstream traffic forwarding downstream traffic onto its link, and forwarding
from its link towards the RPL. It does this for all the bi- upstream traffic from its link towards the RPL. It does this
directional groups that map to the RPA. The DF on a link is also for all the bi-directional groups that map to the RPA. The DF
responsible for processing Join messages from downstream routers on a link is also responsible for processing Join messages from
on the link as well as ensuring that packets are forwarded to downstream routers on the link as well as ensuring that packets
local receivers (discovered through a local membership mechanism are forwarded to local receivers (discovered through a local
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 a RPF stands for "Reverse Path Forwarding". The RPF Interface of
router with respect to an address is the interface that the MRIB a router with respect to an address is the interface that the
indicates should be used to reach that address. In the case of a MRIB indicates should be used to reach that address. In the
BIDIR-PIM multicast group, the RPF interface is determined by case of a BIDIR-PIM multicast group, the RPF interface is
looking up the RPA in the MRIB. The RPF information determines the determined by looking up the RPA in the MRIB. The RPF
interface of the router that would be used to send packets towards information determines the interface of the router that would
the RPL for the group. be used to send packets 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 is address. Note that in BIDIR-PIM, the RPF neighbor for a group
not necessarily the router on the RPF interface that Join messages is not necessarily the router on the RPF interface that Join
for that group would be directed to (Join messages are only messages for that group would be directed to (Join messages are
directed to the DF on the RPF interface for the group). only directed to the DF on the RPF interface for the group).
TIB Tree Information Base. This is the collection of state at a PIM TIB Tree Information Base. This is the collection of state at a
router that has been created by receiving PIM Join/Prune messages, PIM router that has been created by receiving PIM Join/Prune
PIM DF election messages and IGMP or MLD information from local messages, PIM DF election messages and IGMP or MLD information
hosts. It essentially stores the state of all multicast from local hosts. It essentially stores the state of all
distribution trees at that router. multicast distribution trees at that router.
MFIB Multicast Forwarding Information Base. The TIB holds all the MFIB Multicast Forwarding Information Base. The TIB holds all the
state that is necessary to forward multicast packets at a router. state that is necessary to forward multicast packets at a
However, although this specification defines forwarding in terms router. However, although this specification defines
of the TIB, to actually forward packets using the TIB is very forwarding in terms of the TIB, to actually forward packets
inefficient. Instead a real router implementation will normally using the TIB is very inefficient. Instead a real router
build an efficient MFIB from the TIB state to perform forwarding. implementation will normally build an efficient MFIB from the
How this is done is implementation-specific, and is not discussed TIB state to perform forwarding. How this is done is
in this document. implementation-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. neighbour 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 Designated Forwarder (DF) election is specified in Section 3.5.
o PIM packet formats are specified in Section 3.7. o PIM packet formats are specified in Section 3.7.
o A summary of BIDIR-PIM timers and their default values is given in o A summary of BIDIR-PIM timers and their default values is given in
Section 3.6. Section 3.6.
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 term implementation should maintain in order to function correctly. We
this state the Tree Information Base or TIB, as it holds the state of term this state the Tree Information Base or TIB, as it holds the
all the multicast distribution trees at this router. In this state of all the multicast distribution trees at this router. In
specification we define PIM mechanisms in terms of the TIB. However, this specification we define PIM mechanisms in terms of the TIB.
only a very simple implementation would actually implement packet However, only a very simple implementation would actually implement
forwarding operations in terms of this state. Most implementations will packet forwarding operations in terms of this state. Most
use this state to build a multicast forwarding table, which would then implementations will use this state to build a multicast forwarding
be updated when the relevant state in the TIB changes. table, which would then be updated when the relevant state in the TIB
changes.
Although we specify precisely the state to be kept, this does not mean Although we specify precisely the state to be kept, this does not
that an implementation of BIDIR-PIM needs to hold the state in this mean that an implementation of BIDIR-PIM needs to hold the state in
form. This is actually an abstract state definition, which is needed in this form. This is actually an abstract state definition, which is
order to specify the router's behavior. A BIDIR-PIM implementation is needed in order to specify the router's behavior. A BIDIR-PIM
free to hold whatever internal state it requires, and will still be implementation is free to hold whatever internal state it requires,
conformant with this specification so long as it results in the same and will still be conformant with this specification so long as it
externally visible protocol behavior as an abstract router that holds results in the same externally visible protocol behavior as an
the following state. abstract router that holds the following state.
We divide TIB state into two sections: We divide TIB state into two sections:
RPA state RPA state
State that maintains the DF election information for each RPA. State that maintains the DF election information for each RPA.
Group state Group state
State that maintains a group-specific tree for groups that map to a State that maintains a group-specific tree for groups that map to
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 assumed forwarding operations - for example, the "NoInfo" state might be
from the lack of other state information, rather than being held assumed from the lack of other state information, rather than being
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 a 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 as For more information on Hello information look at section 3.2 as well
the PIM-SM specification in [4]. as the PIM-SM specification in [4].
3.1.2. RPA State 3.1.2. RPA State
A router maintains a multicast-group to RPA mapping which is built A router maintains a multicast-group to RPA mapping which is built
through static configuration or by using an automatic RP discovery through static configuration or by using an automatic RP discovery
mechanism like BSR or AUTO-RP (see section 4). For each BIDIR-PIM RPA a mechanism like BSR or AUTO-RP (see section 4). For each BIDIR-PIM
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
o DF metric o DF metric
Election information: Election information:
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 Prune Pending Timer (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 (such Local membership is the result of the local membership mechanism
as IGMP [2]) running on that interface. This information is used by the (such as IGMP [2]) running on that interface. This information is
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 state messages on this interface, and is specified in section 3.4.1. The
is used by the macros that calculate the outgoing interface list in state is used by the macros that calculate the outgoing interface
section 3.1.4, and in the JoinDesired(G) macro (defined in section list in section 3.1.4, and in the JoinDesired(G) macro (defined in
3.4.2) that is used in deciding whether a Join(*,G) should be sent section 3.4.2) that is used in deciding whether a Join(*,G) should be
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 upstream messages, and to override Prune(*,G) messages from peers on an
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 we Using this state, we define the following "macro" definitions which
will use in the descriptions of the state machines and pseudocode in the we will use in the descriptions of the state machines and pseudocode
following sections. in 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 to RPF_interface(RPA) is the interface the MRIB indicates would be used
route packets to RPA. The olist(G) is the list of interfaces on which to route packets to RPA. The olist(G) is the list of interfaces on
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 might The macro pim_include(G) indicates the interfaces to which traffic
be forwarded because of hosts that are local members on that interface. might be forwarded because of hosts that are local members on that
interface.
pim_include(G) = pim_include(G) =
{ all interfaces I such that: { all interfaces I such that:
I_am_DF(RPA(G),I) AND local_receiver_include(G,I) } I_am_DF(RPA(G),I) AND local_receiver_include(G,I) }
The clause "I_am_DF(RPA,I)" is TRUE if the router is in the Win or The clause "I_am_DF(RPA,I)" is TRUE if the router is in the Win or
Backoff states in the DF election state machine (described in section Backoff states in the DF election state machine (described in section
3.5) for the given RPA on interface I. Otherwise it is FALSE. 3.5) for the given RPA on interface I. Otherwise it is FALSE.
The clause "local_receiver_include(G,I)" is true if the IGMP module, MLD The clause "local_receiver_include(G,I)" is true if the IGMP module,
module or other local membership mechanism has determined that there are MLD module or other local membership mechanism has determined that
local members on interface I that desire to receive traffic sent to there are local members on interface I that desire to receive traffic
group G. sent to group G.
The set "joins(G)" is the set of all interfaces on which the router has The set "joins(G)" is the set of all interfaces on which the router
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 order RPF_DF(RPA) is the neighbor that Join messages must be sent to in
to build the group shared tree rooted at the RPL for the given RPA. This order to build the group shared tree rooted at the RPL for the given
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 described routers. These messages are used to update the Neighbor State
in section 3.1. The procedures for generating and processing Hello described in section 3.1. The procedures for generating and
messages as well as maintaining Neighbor State are specified in the PIM- processing Hello messages as well as maintaining Neighbor State are
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 Bidir_Capable PIM-Hello option that MUST be
included in all Hello messages from a Bidir-PIM capable router. The included in all Hello messages from a Bidir-PIM capable router. The
Bidir_Capable option advertises the router's ability to participate in Bidir_Capable option advertises the router's ability to participate
the Bidir-PIM protocol. The format of the Bidir_Capable option is in the Bidir-PIM protocol. The format of the Bidir_Capable option is
described in section 3.7. described in section 3.7.
If a Bidir PIM router receives a PIM-Hello message that does not contain If a Bidir PIM router receives a PIM-Hello message that does not
the Bidir_Capable option from one of its neighbours, the error must be contain the Bidir_Capable option from one of its neighbours, the
logged to the router administrator in a rate-limited manner. error must be logged to the router administrator in a rate-limited
manner.
3.3. Data Packet Forwarding Rules 3.3. Data Packet Forwarding Rules
For groups mapping to a given RPA, the following responsibilities are For groups mapping to a given RPA, the following responsibilities are
uniquely assigned to the DF for that RPA on each link: uniquely assigned to the DF for that RPA on each link:
o The DF is the only router that forwards packets traveling downstream
onto the link.
o The DF is the only router that picks-up upstream traveling packets off o The DF is the only router that forwards packets traveling
the link to forward towards the RPL. downstream onto the link.
Non-DF routers on a link, that use that link as their RPF interface to o The DF is the only router that picks-up upstream traveling packets
reach the RPA, may perform the following forwarding actions for off the link to forward towards the RPL.
bidirectional groups:
o Forward packets from the link towards downstream receivers. Non-DF routers on a link, that use that link as their RPF interface
to reach the RPA, may perform the following forwarding actions for
bidirectional groups:
o Forward packets from downstream sources onto the link (provided they o Forward packets from the link towards downstream receivers.
are the DF for the downstream link from which the packet was picked-
up).
The BIDIR-PIM packet forwarding rules are defined below in pseudocode. o Forward packets from downstream sources onto the link (provided
they are the DF for the downstream link from which the packet was
picked-up).
iif is the incoming interface of the packet. The BIDIR-PIM packet forwarding rules are defined below in
G is the destination address of the packet (group address). pseudocode.
RPA is the Rendezvous Point Address for this group.
First we check to see whether the packet should be accepted based on TIB iif is the incoming interface of the packet.
state and the interface that the packet arrived on. A packet is accepted G is the destination address of the packet (group address).
if it arrives on the RPF_interface to reach the RPA (downstream RPA is the Rendezvous Point Address for this group.
traveling packet) or if the router is the DF on the interface the packet
arrives (upstream traveling packet).
If the packet should be forwarded we build an outgoing interface list First we check to see whether the packet should be accepted based on
for the packet. 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
(downstream traveling packet) or if the router is the DF on the
interface the packet arrives (upstream traveling packet).
Finally we remove the incoming interface from the outgoing interface If the packet should be forwarded we build an outgoing interface list
list we've created, and if the resulting outgoing interface list is not for the packet.
empty, we forward the packet out of those interfaces.
On receipt of data to G on interface iif: Finally we remove the incoming interface from the outgoing interface
list we've created, and if the resulting outgoing interface list is
not empty, we forward the packet out of those interfaces.
if( iif == RPF_interface(RPA) || I_am_DF(RPA,iif) ) { On receipt of data to G on interface iif:
oiflist = olist(G) (-) iif if( iif == RPF_interface(RPA) || I_am_DF(RPA,iif) ) {
forward packet on all interfaces in oiflist oiflist = olist(G) (-) iif
} forward packet on all interfaces in oiflist
}
3.3.1. Upstream Forwarding at RP 3.3.1. Upstream Forwarding at RP
When configuring a BIDIR-PIM domain it is possible to assign the When configuring a BIDIR-PIM domain it is possible to assign the
Rendezvous Point Address (RPA) such that it does not belong to a Rendezvous Point Address (RPA) such that it does not belong to a
physical box but instead is simply a routable address. Routers that have physical box but instead is simply a routable address. Routers that
interfaces on the RPL that the RPA belongs to will upstream forward have interfaces on the RPL that the RPA belongs to will upstream
traffic onto the link. Joins from receivers in the domain will propagate forward traffic onto the link. Joins from receivers in the domain
hop-by-hop till they reach one of the routers connected to the RPL where will propagate hop-by-hop till they reach one of the routers
they will terminate (as there will be no DF elected on the RPL). connected to the RPL where they will terminate (as there will be no
DF elected on the RPL).
If instead the administrator chooses to configure the RPA to be the If instead the administrator chooses to configure the RPA to be the
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 RPL changes. That router must still upstream forward traffic on to the
and behave no differently than any other router with an interface on the RPL and behave no differently than any other router with an interface
RPL. on the RPL.
To configure a BIDIR-PIM network to operate in a mode similar to that of To configure a BIDIR-PIM network to operate in a mode similar to that
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 branches Source-only branches of the distribution tree for a group G are
which do not lead to any receivers, but which are used to forward branches which do not lead to any receivers, but which are used to
packets traveling upstream from sources towards the RPL. Routers along forward packets traveling upstream from sources towards the RPL.
source-only branches only have the RPF_interface to the RPA in their Routers along source-only branches only have the RPF_interface to the
olist for G and hence do not need to maintain any group specific state. RPA in their olist for G and hence do not need to maintain any group
Upstream forwarding can be performed using only RPA specific state. An specific state. Upstream forwarding can be performed using only RPA
implementation may decide to maintain group state for source-only specific state. An implementation may decide to maintain group state
branches for accounting or performance reasons. However, doing so for source-only branches for accounting or performance reasons.
requires data-driven events (to discover the groups with active sources) However, doing so requires data-driven events (to discover the groups
thus sacrificing one of the main benefits of Bidir PIM. with active sources) thus sacrificing one of the main benefits of
Bidir PIM.
3.3.3. Directly Connected Sources 3.3.3. Directly Connected Sources
A major advantage of using a Designated Forwarder in BIDIR-PIM compared A major advantage of using a Designated Forwarder in BIDIR-PIM
to PIM-SM is that special treatment is no longer required for sources compared to PIM-SM is that special treatment is no longer required
that are directly connected to a router. Data from such sources does not for sources that are directly connected to a router. Data from such
need to be differentiated from other multicast traffic and will sources does not need to be differentiated from other multicast
automatically be picked up by the DF and forwarded upstream. This traffic and will automatically be picked up by the DF and forwarded
removes the need for performing a directly-connected-source check for upstream. This removes the need for performing a directly-connected-
data to groups that do not have existing state. 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 originated distribution trees between receivers and the RPL. Joins are
by last-hop routers that are elected as the DF on an interface with originated by last-hop routers that are elected as the DF on an
directly connected receivers. The Joins propagate hop-by-hop towards the interface with directly connected receivers. The Joins propagate hop-
RPA till they reach a router connected to the RPL. by-hop towards the RPA till they reach a router connected to the RPL.
A BIDIR-PIM Join/Prune message consists of a list of Joined and Pruned A BIDIR-PIM Join/Prune message consists of a list of Joined and
Groups. When processing a received Join/Prune message, each Joined or Pruned Groups. When processing a received Join/Prune message, each
Pruned Group is effectively considered individually by applying the Joined or Pruned Group is effectively considered individually by
following state machines. When considering a Join/Prune message whose applying the following state machines. When considering a Join/Prune
PIM Destination field addresses this router, (*,G) Joins and Prunes can message whose PIM Destination field addresses this router, (*,G)
affect the downstream state machine. When considering a Join/Prune Joins and Prunes can affect the downstream state machine. When
message whose PIM Destination field addresses another router, most Join considering a Join/Prune message whose PIM Destination field
or Prune entries could affect the upstream state machine. addresses another router, most Join or Prune entries could affect the
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 to When a router receives a Join(*,G) or Prune(*,G) it MUST first check
see whether the RP address in the message matches RPA(G) (the router's to see whether the RP address in the message matches RPA(G) (the
idea of what the Rendezvous Point Address is). If the RP address in the router's idea of what the Rendezvous Point Address is). If the RP
message does not match RPA(G) the Join or Prune MUST be silently address in the message does not match RPA(G) the Join or Prune MUST
dropped. be silently dropped.
If a router has no RPA information for the group (e.g. has not recently If a router has no RPA information for the group (e.g. has not
received a BSR message) then it MAY choose to accept Join(*,G) or recently received a BSR message) then it MAY choose to accept
Prune(*,G) and treat the RP address in the message as RPA(G). If the Join(*,G) or Prune(*,G) and treat the RP address in the message as
newly discovered RPA did not previously exist for any other group, a DF RPA(G). If the newly discovered RPA did not previously exist for any
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 if Note that a router will process a Join(*,G) targeted to itself even
it is not the DF for RP(G) on the interface on which the message was if it is not the DF for RP(G) on the interface on which the message
received. This is an optimisation to eliminate the Join delay of one was received. This is an optimisation to eliminate the Join delay of
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 such forwarding logic will ensure that data packets are not forwarded on
an interface while the router is no the DF (unless it is the such an interface while the router is no 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 Messages The per-interface state-machine for receiving (*,G) Join/Prune
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 this interface (I_am_DF(RPA(G),I) is TRUE), the Join state will
will cause us to forward packets destined for G on this cause us to forward packets destined for G on this interface.
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) | Prune Pending |
| | | | (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 | | || | | Prune Pending |
| | | | Timer | | || | | Timer |
+----------------+----------------+------------------+------------------+ +---------------++---------------+-----------------+-----------------+
| Receive | - | -> PP state | -> PP state | |Receive || - | -> PP state | -> PP state |
| Prune(*,G) | | start Prune | | |Prune(*,G) || | start Prune | |
| | | Pending Timer | | | || | Pending Timer | |
+----------------+----------------+------------------+------------------+ +---------------++---------------+-----------------+-----------------+
| Prune Pending | - | - | -> NI state | |Prune Pending || - | - | -> 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)" imply The transition events "Receive Join(*,G)" and "Receive Prune(*,G)"
receiving a Join or Prune targeted to this router's address on the imply receiving a Join or Prune targeted to this router's address on
received interface. If the destination address is not correct, these the received interface. If the destination address is not correct,
state transitions in this state machine must not occur, although seeing these state transitions in this state machine must not occur,
such a packet may cause state transitions in other state machines. although seeing such a packet may cause state transitions in other
state machines.
On unnumbered interfaces on point-to-point links, the router's address On unnumbered interfaces on point-to-point links, the router's
should be the same as the source address it chose for the Hello packet address should be the same as the source address it chose for the
it sent over that interface. However, on point-to-point links we also Hello packet it sent over that interface. However, on point-to-point
RECOMMEND that PIM messages with a destination address of all zeros are links we also RECOMMEND that PIM messages with a destination address
also accepted. of all zeros are also accepted.
The transition event "Stop being DF" implies a DF re-election taking The transition event "Stop being DF" implies a DF re-election taking
place on this router interface for RPA(G) and the router changing status place on this router interface for RPA(G) and the router changing
from being the active DF to being a non-DF router (the value of the status from being the active DF to being a non-DF router (the value
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 from When ExpiryTimer is started or restarted, it is set to the HoldTime
the triggering received Join/Prune message. from the triggering received Join/Prune message.
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 that J/P_Override_Interval if the router has more than one neighbor on
interface; otherwise it is set to zero causing it to expire immediately. that interface; otherwise it is set to zero causing it to expire
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) is forwarding on an interface as a result of a prune. A PruneEcho(*,G)
simply a Prune(*,G) message sent by the upstream router to itself on a is simply a Prune(*,G) message sent by the upstream router to itself
LAN. Its purpose is to add additional reliability so that if a Prune on a LAN. Its purpose is to add additional reliability so that if a
that should have been overridden by another router is lost locally on Prune that should have been overridden by another router is lost
the LAN, then the PruneEcho may be received and cause the override to locally on the LAN, then the PruneEcho may be received and cause the
happen. A PruneEcho(*,G) need not be sent when the router has only one override to happen. A PruneEcho(*,G) need not be sent when the
neighbour on the link. router has only one neighbour 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 a state from downstream PIM routers. This state then determines whether
router needs to propagate a Join(*,G) upstream towards the RPA. Such a router needs to propagate a Join(*,G) upstream towards the RPA.
Join(*,G) messages are sent on the RPF_interface towards the RPA and are Such Join(*,G) messages are sent on the RPF_interface towards the RPA
targeted at the DF on that interface. and are targeted at the DF on that interface.
If a router wishes to propagate a Join(*,G) upstream, it must also watch
for messages on its upstream interface from other routers on that
subnet, and these may modify its behavior. If it sees a Join(*,G) to
the correct upstream neighbor, it should suppress its own Join(*,G). If
it sees a Prune(*,G) to the correct upstream neighbor, it should be
prepared to override that prune by sending a Join(*,G) almost
immediately. Finally, if it sees the Generation ID (see PIM-SM
specification [4]) of the correct upstream neighbor change, it knows
that the upstream neighbor has lost state, and it should be prepared to
refresh the state by sending a Join(*,G) almost immediately.
In addition 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 change
can be caused by the following two events:
o The MRIB indicates that the RPF Interface towards the RPA has If a router wishes to propagate a Join(*,G) upstream, it must also
changed. In this case the DF on the new RPF_interface becomes watch for messages on its upstream interface from other routers on
the new RPF Neighbour. that subnet, and these may modify its behavior. If it sees a
Join(*,G) to the correct upstream neighbor, it should suppress its
own Join(*,G). If it sees a Prune(*,G) to the correct upstream
neighbor, it should be prepared to override that prune by sending a
Join(*,G) almost immediately. Finally, if it sees the Generation ID
(see PIM-SM specification [4]) of the correct upstream neighbor
change, it knows that the upstream neighbor has lost state, and it
should be prepared to refresh the state by sending a Join(*,G) almost
immediately.
o There is a DF re-election on the RPF_interface and a new router In addition changes in the next hop towards the RPA trigger a prune
emerges as the DF. off from the old next hop, and join towards the new next hop. Such a
change can be caused by the following two events:
The upstream (*,G) state-machine only contains two states: o The MRIB indicates that the RPF Interface towards the RPA has
changed. In this case the DF on the new RPF_interface becomes
the new RPF Neighbour.
Not Joined o There is a DF re-election on the RPF_interface and a new router
The downstream state-machines indicate that the router does not emerges as the DF.
need to join the RPA tree for this group.
Joined The upstream (*,G) state-machine only contains two states:
The downstream state-machines indicate that the router would like
to join the RPA tree for this group.
In addition, one timer JT(G) is kept which is used to trigger the Not Joined
sending of a Join(*,G) to the upstream next hop towards the RPA (the DF The downstream state-machines indicate that the router does not
on the RPF_interface for RPA(G)). need to join the RPA tree for this group.
+-----------------------------------+ Joined
| Figures omitted from text version | The downstream state-machines indicate that the router would like
+-----------------------------------+ to join the RPA tree for this group.
Figure 2: Upstream group state-machine 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
DF on the RPF_interface for RPA(G)).
In tabular form, the state machine is: 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 which 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 | | In Joined (J) State |
+-------------------------------------+---------------------------------+ +-----------------------------------+--------------------------------+
| Change of RPF_DF(RPA(G)) | RPF_DF(RPA(G)) GenID | | Change of RPF_DF(RPA(G)) | RPF_DF(RPA(G)) GenID |
| | changes | | | changes |
+-------------------------------------+---------------------------------+ +-----------------------------------+--------------------------------+
| Send Join(*,G) to new | Decrease Timer to | | Send Join(*,G) to new | Decrease Timer to |
| DF; Send Prune(*,G) to | t_override | | DF; Send Prune(*,G) to | t_override |
| old DF; set Timer to | | | old DF; set Timer to | |
| t_periodic | | | t_periodic | |
+-------------------------------------+---------------------------------+ +-----------------------------------+--------------------------------+
This state machine uses the following macro: 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 a RPA.
3.5.1. DF Requirements 3.5.1. DF Requirements
The DF election chooses the best router on a link to assume the The DF election chooses the best router on a link to assume the
responsibility of forwarding traffic between the RPL and the link for responsibility of forwarding traffic between the RPL and the link for
the range of multicast groups served by the RPA. Different multicast the range of multicast groups served by the RPA. Different multicast
groups that share a common RPA share the same upstream direction. groups that share a common RPA share the same upstream direction.
Hence, the election of an upstream forwarder on each link does not have Hence, the election of an upstream forwarder on each link does not
to be a group specific decision but instead can be RPA-specific. As the have to be a group specific decision but instead can be RPA-specific.
number of RPAs is typically small, the number of elections that have to As the number of RPAs is typically small, the number of elections
be performed is significantly reduced by this observation. that have to be performed is significantly reduced by 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. When unicast routing metric (as reported by the MRIB) to reach the RPA.
comparing metrics from different unicast routing protocols, we use the When comparing metrics from different unicast routing protocols, we
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 RPA The election process needs to take place when information on a new
initially becomes available. The result can be re-used as new bidir RPA initially becomes available. The result can be re-used as new
groups that map to the same RPA are encountered. There are however some bidir groups that map to the same RPA are encountered. There are
conditions under which an update to the election is required: however some conditions under which an update to the election is
required:
o There is a change in unicast metric to reach the RPA for any of o There is a change in unicast metric to reach the RPA for any of
the routers on the link. the routers on the link.
o The interface on which the RPA is reachable (RPF Interface) o The interface on which the RPA is reachable (RPF Interface)
changes to an interface for which the router was previously the changes to an interface for which the router was previously the
DF. DF.
o A new PIM neighbor starts up on a link that must participate in o A new PIM neighbor starts up on a link that must participate in
the elections and be informed of current outcome. the elections and be informed of current outcome.
o The elected DF 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 the probability that all routers on the link have a consistent view of
DF. This is because with the forwarding rules described in section 3.3 the DF. This is because with the forwarding rules described in
if multiple routers end-up thinking that they should be responsible for section 3.3 if multiple routers end-up thinking that they should be
forwarding, loops may result. To reduce the possibility of this responsible for forwarding, loops may result. To reduce the
occurrence to a minimum, the election algorithm has been biased towards possibility of this occurrence to a minimum, the election algorithm
discarding DF information and suspending forwarding during periods of has been biased towards discarding DF information and suspending
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 not
provide the definitive specification for the DF election. If any provide the definitive specification for the DF election. If any
discrepancy exists between section 3.5.3 and this section, the discrepancy exists between section 3.5.3 and this section, the
specification in section 3.5.3 is to be assumed correct. specification in section 3.5.3 is to be assumed correct.
To perform the election of the DF for a particular RPA, routers on a To perform the election of the DF for a particular RPA, routers on a
link need to exchange their unicast routing metric information for link need to exchange their unicast routing metric information for
reaching the RPA. Routers advertise their own metrics in Offer, Winner, reaching the RPA. Routers advertise their own metrics in Offer,
Backoff and Pass messages. The advertised metric is calculated using the Winner, Backoff and Pass messages. The advertised metric is
RPF Interface and metric to reach the RPA available through the MRIB. calculated using the RPF Interface and metric to reach the RPA
When a router is participating in a DF election for an RPA on the available through the MRIB. When a router is participating in a DF
interface that its MRIB indicates as the RPF Interface then that router election for an RPA on the interface that its MRIB indicates as the
MUST always advertise an infinite metric in its election messages. When RPF Interface then that router MUST always advertise an infinite
a router is participating in a DF election on an interface other than metric in its election messages. When a router is participating in a
the MRIB indicated RPF Interface then it MUST advertise the MRIB DF election on an interface other than the MRIB indicated RPF
provided metrics in its election messages. Interface then it MUST advertise the MRIB provided metrics in its
election messages.
In the election protocol described below, many message exchanges are In the election protocol described below, many message exchanges are
repeated Election_Robustness times for reliability. In all those cases repeated Election_Robustness times for reliability. In all those
the message retransmissions are spaced in time by a small random cases the message retransmissions are spaced in time by a small
interval. All of the following description is specific to the election random interval. All of the following description is specific to the
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 new Initially when no DF has been elected, routers finding out about a
RPA start participating in the election by sending Offer messages. new RPA start participating in the election by sending Offer
Offer messages include the router's metric to reach the RPA. Offers are messages. Offer messages include the router's metric to reach the
periodically retransmitted with a period of Offer_Interval. RPA. Offers are periodically retransmitted with a period of
Offer_Interval.
If a router hears a better offer than its own from a neighbor, it stops If a router hears a better offer than its own from a neighbor, it
participating in the election for a period of Election_Robustness * stops participating in the election for a period of
Offer_Interval thus giving a chance to the neighbour with the better Election_Robustness * Offer_Interval thus giving a chance to the
metric to be elected DF. If during this period no winner is elected, the neighbour with the better metric to be elected DF. If during this
router restarts the election from the beginning. If at any point during period no winner is elected, the router restarts the election from
the initial election a router receives an out of order offer with worse the beginning. If at any point during the initial election a router
metrics than its own, then it restarts the election from the beginning. receives an out of order offer with worse metrics than its own, then
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 metrics A router assumes the role of the DF after having advertised its
Election_Robustness times without receiving any offer from any other metrics Election_Robustness times without receiving any offer from
neighbor. At that point it transmits a Winner message which declares to any other neighbor. At that point it transmits a Winner message which
every other router on the link the identity of the winner and the declares to every other router on the link the identity of the winner
metrics it is using. 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 metrics and record the identity and metrics of the winner. If the local
are better than those of the winner then the router records the identity metrics are better than those of the winner then the router records
of the winner (accepting it as the acting DF) but re-initiates the the identity of the winner (accepting it as the acting DF) but re-
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 a RPA changes at a non-DF router to a
value that is better than that previously advertised by the acting DF, value that is better than that previously advertised by the acting
the router with the new better metric should take action to eventually DF, the router with the new better metric should take action to
assume forwarding responsibility. When the metric change is detected, eventually assume forwarding responsibility. When the metric change
the non-DF router with the now better metric restarts the DF election is detected, the non-DF router with the now better metric restarts
process by sending Offer messages with this new metric. Note that at the DF election process by sending Offer messages with this new
any point during an election if no response is received after metric. Note that at any point during an election if no response is
Election_Robustness retransmissions of an offer, a router assumes the received after Election_Robustness retransmissions of an offer, a
role of the DF following the usual Winner announcement procedure. router assumes the role of the DF following the usual Winner
announcement procedure.
Upon receipt of an offer that is worse than its current metric, the DF Upon receipt of an offer that is worse than its current metric, the
will respond with a Winner message declaring its status and advertising DF will respond with a Winner message declaring its status and
its better metric. Upon receiving the Winner message, the originator of advertising its better metric. Upon receiving the Winner message, the
the Offer records the identity of the DF and aborts the election. originator of the Offer records the identity of the DF and aborts the
election.
Upon receipt of an offer that is better than its current metric, the DF Upon receipt of an offer that is better than its current metric, the
records the identity and metrics of the offering router and responds DF records the identity and metrics of the offering router and
with a Backoff message. This instructs the offering router to hold off responds with a Backoff message. This instructs the offering router
for a short period of time while the unicast routing stabilises and to hold off for a short period of time while the unicast routing
other routers get a chance to put in their offers. The Backoff message stabilises and other routers get a chance to put in their offers. The
includes the offering router's new metric and address. All routers on Backoff message includes the offering router's new metric and
the link that have pending offers with metrics worse than those in the address. All routers on the link that have pending offers with
backoff message (including the original offering router) will hold metrics worse than those in the backoff message (including the
further offers for a period of time defined in the Backoff message. original offering router) will hold further offers for a period of
time defined in the Backoff message.
If during the Backoff_Period, a third router sends a new better offer, If during the Backoff_Period, a third router sends a new better
the Backoff message is repeated for the new offer and the Backoff_Period offer, the Backoff message is repeated for the new offer and the
restarted. Backoff_Period restarted.
Before the Backoff_Period expires, the acting DF nominates the router Before the Backoff_Period expires, the acting DF nominates the router
having made the best offer as the new DF using a Pass message. This having made the best offer as the new DF using a Pass message. This
message includes the IDs and metrics of both the old and new DFs. The message includes the IDs and metrics of both the old and new DFs.
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 as transmission is made. The new DF assumes the role of the DF as soon
it receives the Pass message. All other routers on the link take note of as it receives the Pass message. All other routers on the link take
the new DF and its metric. Note that this event constitutes an RPF note of the new DF and its metric. Note that this event constitutes
Neighbour change which may trigger Join messages to the new DF (see an RPF Neighbour change which may trigger Join messages to the new DF
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, it If the DF's routing metric to reach the RPA changes to a worse value,
sends a set of Election_Robustness randomly spaced Winner messages on it sends a set of Election_Robustness randomly spaced Winner messages
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 message announcement but have a better metric may respond with an Offer
which results in the same handoff procedure described above. All message which results in the same handoff procedure described above.
routers assume the DF has not changed until they see a Pass or Winner All routers assume the DF has not changed until they see a Pass or
message indicating the change. Winner message indicating the change.
There is no pressure to make this handoff quickly if the acting DF still There is no pressure to make this handoff quickly if the acting DF
has a path to the RPL. The old path may now be suboptimal but it will still has a path to the RPL. The old path may now be suboptimal but
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 forwarding which it is acting as the DF, then it can no longer provide
services for that link. It therefore immediately stops being the DF and forwarding services for that link. It therefore immediately stops
restarts the election. As its path to the RPA is through the link, an being the DF and restarts the election. As its path to the RPA is
infinite metric is used in the Offer message it sends. through the link, an infinite metric is used in the Offer message it
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 result, will have no immediate knowledge of the election outcome. As a
it will start advertising its metric in Offer messages. As soon as this result, it will start advertising its metric in Offer messages. As
happens, the currently elected DF will respond with a Winner message if soon as this happens, the currently elected DF will respond with a
its metric is better than the metric in the Offer message, or with a Winner message if its metric is better than the metric in the Offer
Backoff message if its metric is worse than the metric in the Offer message, or with a Backoff message if its metric is worse than the
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 routers this can be achieved depends on whether there are any downstream
on the link. routers on the link.
If there are downstream routers, typically their MRIB reported next-hop If there are downstream routers, typically their MRIB reported next-
before the DF dies will be the DF itself. They will therefore notice hop before the DF dies will be the DF itself. They will therefore
either a change in the metric for the route to the RPA or a change in notice either a change in the metric for the route to the RPA or a
next-hop away from the DF and can restart the election by transmitting change in next-hop away from the DF and can restart the election by
Offer messages. If according to the MRIB the RPA is now reachable transmitting Offer messages. If according to the MRIB the RPA is now
through the same link via another upstream router, an infinite metric reachable through the same link via another upstream router, an
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 election This section provides the definitive specification for the DF
process. If any discrepancy exists between section 3.5.2 and this election process. If any discrepancy exists between section 3.5.2 and
section, the specification in this section is to be assumed correct. this section, the specification in this section is to be assumed
correct.
3.5.3.1. Election State 3.5.3.1. Election State
The DF election state is maintained per RPA for each multicast enabled The DF election state is maintained per RPA for each multicast
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 Initial election state. When in the Offer state a router thinks
thinks it can eventually become the winner and periodically it can eventually become the winner and periodically generates
generates Offer messages. Offer messages.
Lose In this state the router knows that there either is a Lose
different election winner or that no router on the link has a In this state the router knows that there either is a different
path to the RPA. election winner or that no router on the link has a path to the
RPA.
Winner Winner
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 is In the state machine a router is considered to be an acting DF if it
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 Used to maintain the number of times an Offer or Winner message
message has been transmitted. has been transmitted.
Best-Offer Best-Offer
Used by the DF to record the identity and advertised metrics Used by the DF to record the identity and advertised metrics of
of the router that has made the last offer, for use when the router that has made the last offer, for use when sending
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 packet The election process uses the following PIM control messages, the
format of which is described in section 3.7: packet format of which is described in section 3.7:
Offer (OfferingID, Metric) Offer (OfferingID, Metric)
Sent by routers that believe they have a better metric to the Sent by routers that believe they have a better metric to the
RPA than the metric that has been on offer so far. RPA than the metric that has been on offer so far.
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 Used by the DF to acknowledge better offers. It instructs other
other routers with equal or worse offers to wait till the DF routers with equal or worse offers to wait till the DF passes
passes responsibility to the sender of the offer. responsibility to the sender of the offer.
Pass (Old-DF-ID, Old-DF-Metric, New-DF-ID, New-DF-Metric) Pass (Old-DF-ID, Old-DF-Metric, New-DF-ID, New-DF-Metric)
Used by the old DF to pass forwarding responsibility to a Used by the old DF to pass forwarding responsibility to a
router that has previously made an offer. The Old-DF-Metric router that has previously made an offer. The Old-DF-Metric is
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 on Note that when a router is participating in a DF election for an RPA
the interface that its MRIB indicates as the RPF Interface then that on the interface that its MRIB indicates as the RPF Interface then
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 our 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 our current
metrics for the RPA with the metrics advertised for the metrics for the RPA with the metrics advertised for the
target of the message. target of the message.
Path to RPA lost Path to RPA lost
Losing the path to the RPA can happen in two ways. The first Losing the path to the RPA can happen in two ways. The first
happens when the route learned through the MRIB is withdrawn happens when the route learned through the MRIB is withdrawn
and the MRIB no longer reports an available route to reach the and the MRIB no longer reports an available route to reach the
RPA. The second case happens when the next-hop information RPA. The second case happens when the next-hop information
reported by the MRIB changes to indicate a next-hop that is reported by the MRIB changes to indicate a next-hop that is
reachable through the router interface 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 stored metric the
new MRIB information must be compared against. The new new MRIB information must be compared against. The new
information must be compared with either the router's old 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 spec.
?= 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 of o On receipt of a Winner message set the DF to be the originator
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 is When a Designated Forwarder election is initiated the starting state
the Offer state, the message counter (MC) is set to zero and the DF is the Offer state, the message counter (MC) is set to zero and the
election Timer (DFT) is set to OPlow (see section 3.6 for a definition DF election Timer (DFT) is set to OPlow (see section 3.6 for a
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 | | | Event |
| Prev State ++------------------+------------------+------------------+ | Prev State +-----------------+------------------+-----------------+
| || Recv better | Recv better | Recv better | | | Recv better | Recv better | Recv better |
| || Pass / Win | Backoff | Offer | | | Pass / Win | Backoff | Offer |
+-------------++------------------+------------------+------------------+ +-------------+-----------------+------------------+-----------------+
| || -> Lose | - | - | | | -> Lose | - | - |
| Offer || DF = Sender or | DFT = BOperiod | DFT = OPhigh; | | Offer | DF = Sender or | DFT = BOperiod | DFT = OPhigh; |
| || Target; Stop | + OPlow; MC = | MC = 0 | | | Target; Stop | + OPlow; MC = | MC = 0 |
| || DFT | 0 | | | | DFT | 0 | |
+-------------++------------------+------------------+------------------+ +-------------+-----------------+------------------+-----------------+
| || - | - | -> Offer | | | - | - | -> Offer |
| Lose || DF = Sender or | DF = Sender | DFT = OPhigh; | | Lose | DF = Sender or | DF = Sender | DFT = OPhigh; |
| || Target | | MC = 0 | | | Target | | MC = 0 |
+-------------++------------------+------------------+------------------+ +-------------+-----------------+------------------+-----------------+
| || -> Lose | -> Lose | -> Backoff | | | -> Lose | -> Lose | -> Backoff |
| || DF = Sender or | DF = Sender; | Set Best to | | | DF = Sender or | DF = Sender; | Set Best to |
| Win || Target; Stop | Stop DFT | Sender; Send | | Win | Target; Stop | Stop DFT | Sender; Send |
| || DFT | | Backoff; DFT = | | | DFT | | Backoff; DFT = |
| || | | BOperiod | | | | | BOperiod |
+-------------++------------------+------------------+------------------+ +-------------+-----------------+------------------+-----------------+
| || -> Lose | -> Lose | - | | | -> Lose | -> Lose | - |
| || DF = Sender or | DF = Sender; | Set Best to | | | DF = Sender or | DF = Sender; | Set Best to |
| Backoff || Target; Stop | Stop DFT | Sender; Send | | Backoff | Target; Stop | Stop DFT | Sender; Send |
| || DFT | | Backoff; DFT = | | | DFT | | Backoff; DFT = |
| || | | BOperiod | | | | | BOperiod |
+-------------++------------------+------------------+------------------+ +-------------+-----------------+------------------+-----------------+
+-----------++----------------------------------------------------------+ +-----------+-------------------------------------------------------+
| || Event | | | Event |
| ++-------------+--------------+--------------+--------------+ | +-------------+-------------+--------------+------------+
|Prev State ||Recv Backoff | Recv Pass | Recv Worse | Recv worse | |Prev State |Recv Backoff |Recv Pass |Recv Worse |Recv worse |
| ||for us | for us | Pass / Win / | Offer | | |for us |for us |Pass / Win / |Offer |
| || | | Backoff | | | | | |Backoff | |
+-----------++-------------+--------------+--------------+--------------+ +-----------+-------------+-------------+--------------+------------+
| ||- | -> Win | - | - | | |- |-> Win |- |- |
| ||DFT = | Stop DFT | Set DF to | DFT ?= | | |DFT = |Stop DFT |Set DF to |DFT ?= |
|Offer ||BOperiod + | | Sender or | OPlow; MC = | |Offer |BOperiod + | |Sender or |OPlow; MC = |
| ||OPlow; MC = | | Target; DFT | 0 | | |OPlow; MC = | |Target; DFT |0 |
| ||0 | | ?= OPlow; MC | | | |0 | |?= OPlow; MC | |
| || | | = 0 | | | | | |= 0 | |
+-----------++-------------+--------------+--------------+--------------+ +-----------+-------------+-------------+--------------+------------+
| ||-> Offer | -> Offer | -> Offer | -> Offer | | |-> Offer |-> Offer |-> Offer |-> Offer |
| ||DF = Sender; | DF = Sender; | DF = Sender | DFT = OPlow; | | |DF = Sender; |DF = Sender; |DF = Sender |DFT = OPlow;|
|Lose ||DFT = OPlow; | DFT = OPlow; | or Target; | MC = 0 | |Lose |DFT = OPlow; |DFT = OPlow; |or Target; |MC = 0 |
| ||MC = 0 | MC = 0 | DFT = OPlow; | | | |MC = 0 |MC = 0 |DFT = OPlow; | |
| || | | MC = 0 | | | | | |MC = 0 | |
+-----------++-------------+--------------+--------------+--------------+ +-----------+-------------+-------------+--------------+------------+
| ||-> Offer | -> Offer | -> Offer | - | | |-> Offer |-> Offer |-> Offer |- |
| ||DF = Sender; | DF = Sender; | DF = Sender | Send Winner | | |DF = Sender; |DF = Sender; |DF = Sender |Send Winner |
|Win ||DFT = OPlow; | DFT = OPlow; | or Target; | | |Win |DFT = OPlow; |DFT = OPlow; |or Target; | |
| ||MC = 0 | MC = 0 | DFT = OPlow; | | | |MC = 0 |MC = 0 |DFT = OPlow; | |
| || | | MC = 0 | | | | | |MC = 0 | |
+-----------++-------------+--------------+--------------+--------------+ +-----------+-------------+-------------+--------------+------------+
| ||-> Offer | -> Offer | -> Offer | -> Win | | |-> Offer |-> Offer |-> Offer |-> Win |
| ||DF = Sender; | DF = Sender; | DF = Sender | Send Winner; | | |DF = Sender; |DF = Sender; |DF = Sender |Send Winner;|
|Backoff ||DFT = OPlow; | DFT = OPlow; | or Target; | Stop DFT | |Backoff |DFT = OPlow; |DFT = OPlow; |or Target; |Stop DFT |
| ||MC = 0 | MC = 0 | DFT = OPlow; | | | |MC = 0 |MC = 0 |DFT = OPlow; | |
| || | | MC = 0 | | | | | |MC = 0 | |
+-----------++-------------+--------------+--------------+--------------+ +-----------+-------------+-------------+--------------+------------+
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Offer State | | In Offer State |
+-----------------------+-----------------------+-----------------------+ +----------------------+----------------------+----------------------+
| DFT Expires and MC | DFT Expires and MC | DFT Expires and MC | | DFT Expires and MC | DFT Expires and MC | DFT Expires and MC |
| is less than | is equal to | is equal to | | is less than | is equal to | is equal to |
| Robustness | Robustness and we | Robustness and | | Robustness | Robustness and we | Robustness and |
| | have path to RPA | there is no path | | | have path to RPA | there is no path |
| | | to RPA | | | | to RPA |
+-----------------------+-----------------------+-----------------------+ +----------------------+----------------------+----------------------+
| - | -> Win | -> Lose | | - | -> Win | -> Lose |
| Send Offer; DFT = | Send Winner | Set DF to None | | Send Offer; DFT = | Send Winner | Set DF to None |
| OPlow; MC = MC + 1 | | | | OPlow; MC = MC + 1 | | |
+-----------------------+-----------------------+-----------------------+ +----------------------+----------------------+----------------------+
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Offer State | | In Offer State |
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
| Metric changes and is now worse | | Metric changes and is now worse |
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
| DFT ?= OPlow | | DFT ?= OPlow |
| MC = 0 | | MC = 0 |
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Lose State | | In Lose State |
+--------------------------------+--------------------------------------+ +------------------------------+-------------------------------------+
| Detect DF Failure | Metric changes and now | | Detect DF Failure | Metric changes and now |
| | is better than DF | | | is better than DF |
+--------------------------------+--------------------------------------+ +------------------------------+-------------------------------------+
| -> Offer | -> Offer | | -> Offer | -> Offer |
| DF = None; DFT = | DFT = OPlow_int; MC = 0 | | DF = None; DFT = | DFT = OPlow_int; MC = 0 |
| OPlow_int; MC = 0 | | | OPlow_int; MC = 0 | |
+--------------------------------+--------------------------------------+ +------------------------------+-------------------------------------+
+-----------------------------------------------------------------------+ +--------------------------------------------------------------------+
| In Win State | | In Win State |
+-----------------------+------------------------+----------------------+ +----------------------+-----------------------+---------------------+
| Metric changes and | Timer Expires and | Path to RPA lost | | Metric changes and | Timer Expires and | Path to RPA lost |
| is now worse | MC is less than | | | is now worse | MC is less than | |
| | Robustness | | | | Robustness | |
+-----------------------+------------------------+----------------------+ +----------------------+-----------------------+---------------------+
| - | - | -> Offer | | - | - | -> Offer |
| DFT = OPlow; MC = | Send Winner; DFT = | Set DF to None; | | DFT = OPlow; MC = | Send Winner; DFT = | Set DF to None; |
| 0 | OPlow; MC = MC + 1 | 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 |
+----------------------+-----------------------+---------------------+
+-----------------------------------------------------------------------+
| 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 required Forwarders for the same link. The two precautions below are not
for correct operation but can help diagnose anomalies and correct them. required for correct operation but can help diagnose anomalies and
correct them.
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-election better than the DF will attempt to take over. If during the re-
the acting DF has a condition that causes it to lose all of the election election the acting DF has a condition that causes it to lose all of
messages (like a CPU overload), the new candidate will transmit three the election messages (like a CPU overload), the new candidate will
offers and assume the role of the forwarder resulting in two DFs on the transmit three offers and assume the role of the forwarder resulting
link. This situation is pathological and should be corrected by fixing in two DFs on the link. This situation is pathological and should be
the overloaded router. It is desirable that such an event can be corrected by fixing the overloaded router. It is desirable that such
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 message When a router becomes the DF for a link without receiving a Pass
from the known old DF, the PIM neighbor information for the old DF can message from the known old DF, the PIM neighbor information for the
be marked to this effect. Upon receiving the next PIM Hello message from old DF can be marked to this effect. Upon receiving the next PIM
the old DF, the router can retransmit Winner messages for all the RPAs Hello message from the old DF, the router can retransmit Winner
for which it is acting as the DF. The anomaly may also be logged by the messages for all the RPAs for which it is acting as the DF. The
router in a rate-limited manner to alert the operator. anomaly may also be logged by the router in a rate-limited manner to
alert the operator.
3.5.6. Periodic Winner Announcement 3.5.6. Periodic Winner Announcement
An additional degree of safety can be achieved by having the DF for each An additional degree of safety can be achieved by having the DF for
RPA periodically announce its status in a Winner message. Transmission each RPA periodically announce its status in a Winner message.
of the periodic Winner message can be restricted to occur only for RPAs Transmission of the periodic Winner message can be restricted to
which have active groups, thus avoiding the periodic control traffic in occur only for RPAs which have active groups, thus avoiding the
areas of the network without senders or receivers for a particular RPA. periodic control traffic in areas of the network without senders or
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 3.1. BIDIR-PIM maintains the following timers, as discussed in section
All timers are countdown timers - they are set to a value and count down 3.1. All timers are countdown timers - they are set to a value and
to zero, at which point they typically trigger an action. Of course count down to zero, at which point they typically trigger an action.
they can just as easily be implemented as count-up timers, where the Of course they can just as easily be implemented as count-up timers,
absolute expiry time is stored and compared against a real-time clock, where the absolute expiry time is stored and compared against a real-
but the language in this specification assumes that they count downwards time clock, but the language in this specification assumes that they
to zero. count downwards to zero.
Per Rendezvous-Point Address (RPA): Per Rendezvous-Point Address (RPA):
Per interface (I): Per interface (I):
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) PrunePending Timer: 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 | | Value Name | Value | Explanation |
+--------------------+-------------------------+------------------------+ +-------------------+------------------------+-----------------------+
| Offer_Period | 100 ms | Interval to wait | | Offer_Period | 100 ms | Interval to wait |
| | | between repeated | | | | between repeated |
| | | Offer and Winner | | | | Offer and Winner |
| | | messages. | | | | messages. |
+--------------------+-------------------------+------------------------+ +-------------------+------------------------+-----------------------+
| Backoff_Period | 1 sec | Period that acting | | Backoff_Period | 1 sec | Period that acting |
| | | DF waits between | | | | DF waits between |
| | | receiving a better | | | | receiving a better |
| | | Offer and sending | | | | Offer and sending |
| | | the Pass message | | | | the Pass message |
| | | to transfer DF | | | | to transfer DF |
| | | responsibility. | | | | responsibility. |
+--------------------+-------------------------+------------------------+ +-------------------+------------------------+-----------------------+
| OPlow | rand(0.5, 1) * | Range of actual | | OPlow | rand(0.5, 1) * | Range of actual |
| | Offer_Period | randomised value | | | Offer_Period | randomised value |
| | | used between | | | | used between |
| | | repeated messages. | | | | repeated messages. |
+--------------------+-------------------------+------------------------+ +-------------------+------------------------+-----------------------+
| OPhigh | Election_Robustness | Interval to wait | | OPhigh | Election_Robustness | Interval to wait |
| | * Offer_Period | in order to give a | | | * Offer_Period | in order to give a |
| | | chance to a router | | | | chance to a router |
| | | with a better | | | | with a better |
| | | Offer to become | | | | Offer to become |
| | | the DF. | | | | the DF. |
+--------------------+-------------------------+------------------------+ +-------------------+------------------------+-----------------------+
Timer Names: Join Expiry Timer (ET(G,I)) 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: Prune Pending Timer (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 specific Note that the value of the J/P Override Interval is interface
and depends on both the Propagation_Delay and the Override_Interval specific and depends on both the Propagation_Delay and the
values that may change when Hello messages are received [4]. Override_Interval values that may change when Hello messages are
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-PIM This section describes the details of the packet formats for BIDIR-
control messages. BIDIR-PIM shares a number of control messages in PIM control messages. BIDIR-PIM shares a number of control messages
common with PIM-SM [4]. These include the Hello and Join/Prune messages in common with PIM-SM [4]. These include the Hello and Join/Prune
as well as the format for the Encoded-Unicast address. For details on messages as well as the format for the Encoded-Unicast address. For
the format of these packets please refer to the PIM-SM documentation. details on the format of these packets please refer to the PIM-SM
Here we will only define the additional packets that are introduced by documentation. Here we will only define the additional packets that
BIDIR-PIM. These are the packets used in the DF election process as are introduced by BIDIR-PIM. These are the packets used in the DF
well as the Bidir_Capable PIM-Hello option. election process as well as the Bidir_Capable PIM-Hello option.
3.7.1. DF Election Packet Formats 3.7.1. DF Election Packet Formats
All PIM control messages have IP protocol number 103. All PIM control messages have IP protocol number 103.
BIDIR-PIM messages are multicast with TTL 1 to the `ALL-PIM-ROUTERS' BIDIR-PIM messages are multicast with TTL 1 to the `ALL-PIM-ROUTERS'
group The IPv4 `ALL-PIM-ROUTERS' group is `224.0.0.13'. The IPv6 `ALL- group The IPv4 `ALL-PIM-ROUTERS' group is `224.0.0.13'. The IPv6
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Unicast-RP-Address | 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 All DF-Election PIM control messages share the PIM message Type of Type
10. All DF-Election PIM control messages share the PIM message Type of
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 Set to zero on transmission. Ignored upon receipt. Rsvd
Set to zero on transmission. Ignored upon receipt.
Checksum Checksum
The checksum is standard IP checksum, i.e. the 16-bit one's The checksum is standard IP checksum, 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 (note that the The bidir RPA for which the election is taking place. Format
length of this field will be different than 32 bits depending on described in [4] Section 4.9.1.
the family and encoding of the address).
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 messages
have the extra fields described below. 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 common The Backoff message uses the following fields in addition to the
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Unicast-Offering-Address | 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 (note The address of the router that made the last (best) Offer. Format
that the length of this field will be different than 32 bits described in [4] Section 4.9.1.
depending on the family and encoding of the address).
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.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Unicast-New-Winner-Address | 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 (note The address of the router that made the last (best) Offer. Format
that the length of this field will be different than 32 bits described in [4] Section 4.9.1.
depending on the family and encoding of the address).
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. Bidir 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: Bidir 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 in Routers discover that a range of multicast group addresses operates
bi-directional mode and the address of the Rendezvous-Point address in bi-directional mode and the address of the Rendezvous-Point
(RPA) serving the group range either through static configuration or address (RPA) serving the group range either through static
using an automatic RP discovery mechanism like the PIM Bootstrap configuration or using an automatic RP discovery mechanism like the
mechanism (BSR) [9] 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 BIDIR- integrity protection and group-wise data origin authentication of
PIM protocol messages. Authentication of BIDIR-PIM messages can protect BIDIR-PIM protocol messages. Authentication of BIDIR-PIM messages can
against unwanted behaviour caused by unauthorized or altered BIDIR-PIM protect against unwanted behaviour caused by unauthorized or altered
messages. 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 type As in PIM Sparse-Mode, the extent of possible damage depends on the
of counterfeit messages accepted. BIDIR-PIM only uses link-local type of counterfeit messages accepted. BIDIR-PIM only uses link-local
multicast messages sent to the ALL_PIM_ROUTERS address, hence attacks multicast messages sent to the ALL_PIM_ROUTERS address, hence attacks
can only be carried out by directly connected nodes, or with the can only be carried out by directly connected nodes, or with the
complicity of directly connected routers. 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 messages identical, both in format and functionality, to the respective
used in PIM-SM. Security considerations for these messages are to be messages used in PIM-SM. Security considerations for these messages
found in [4]. Other messages (DF-election messages) are specific to are to be found in [4]. Other messages (DF-election messages) are
BIDIR-PIM and will be discussed in the following paragraphs. specific to BIDIR-PIM and will be discussed in the following
paragraphs.
By forging DF-election messages an attacker can disrupt the election of By forging DF-election messages an attacker can disrupt the election
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 regular An attacker can force its election as DF by participating in a
election and advertising the best metric to reach the RPA. An attacker regular election and advertising the best metric to reach the RPA.
can also try to force the election of another router as DF by sending an An attacker can also try to force the election of another router as
Offer, Winner or Pass message and impersonating another router. In some DF by sending an Offer, Winner or Pass message and impersonating
cases (e.g. the Offer) multiple messages might be needed to carry out an another router. In some cases (e.g. the Offer) multiple messages
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 of impersonate the node that it wants to have become the DF. In the case
the Pass it will have to impersonate the current DF. This type of attack of the Pass it will have to impersonate the current DF. This type of
causes the wrong DF to be recorded in all nodes apart from the one that attack causes the wrong DF to be recorded in all nodes apart from the
is being impersonated. This node typically will be able to detect the one that is being impersonated. This node typically will be able to
anomaly and, possibly, restart a new election. detect the anomaly and, possibly, restart a new election.
A more sophisticated attacker might carry out a concurrent DoS attack on A more sophisticated attacker might carry out a concurrent DoS attack
the node being impersonated, so that it will not be able to detect the on the node being impersonated, so that it will not be able to detect
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 and When authentication is available, spoofed messages MUST be discarded
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 DF set of recipients of DF-election messages and create an inconsistent
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 of addresses for its forged DF-election messages. To prevent this type
attack, BIDIR-PIM routers SHOULD check the destination MAC address of of attack, BIDIR-PIM routers SHOULD check the destination MAC address
received DF-election messages. This however is ineffective on links of received DF-election messages. This however is ineffective on
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 attack. Source authentication is also sufficient to prevent this kind of
attack.
5.1.2. Preventing Election Convergence 5.1.2. Preventing Election Convergence
By forging DF election messages, an attacker can prevent the election By forging DF election messages, an attacker can prevent the election
from converging thus disrupting the establishment of multicast from converging thus disrupting the establishment of multicast
forwarding trees. There are many ways to achieve this. The simplest is forwarding trees. There are many ways to achieve this. The simplest
by sending an infinite sequence of Offer messages (the metric used in is by sending an infinite sequence of Offer messages (the metric used
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-election neighbors from which it will accept Join/Prune, Assert, and DF-
messages. Either static configuration of IP addresses or an IPsec election messages. Either static configuration of IP addresses or an
security association may be used. Furthermore, a PIM router SHOULD NOT IPsec security association may be used. Furthermore, a PIM router
accept protocol messages from a router from which it has not yet SHOULD NOT accept protocol messages from a router from which it has
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 receivers: implement a basic form of access control for both sources and
Receivers can be validated by the last-hop DR and sources can be receivers: Receivers can be validated by the last-hop DR and sources
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 sources In BIDIR-PIM this is generally feasible only for receivers, as
can send to the multicast group without the need for routers to detect sources can send to the multicast group without the need for routers
their activity and create source-specific state. However it is possible to detect their activity and create source-specific state. However it
to modify the standard BIDIR-PIM behaviour, in a backward compatible is possible to modify the standard BIDIR-PIM behaviour, in a backward
way, to allow per-source access control. The tradeoff would be protocol compatible way, to allow per-source access control. The tradeoff
simplicity, memory and processing requirements. 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 like for 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-PIM It is recommended that IPsec authentication be applied to all BIDIR-
protocol messages. The specification on how this is done is to be found PIM protocol messages. The specification on how this is done is to be
in [4]. specifically the authentication of PIM-SM link-local messages, found in [4]. specifically the authentication of PIM-SM link-local
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] also The denial of service attack based on forged Join described in [4]
apply to BIDIR-PIM. also apply to BIDIR-PIM.
6. Change history
>From 06 to 07: Minor corrections in response to WG last call comments.
>From 05 to 06:
Minor editorial corrections.
>From 03 to 05:
RP concept replaced by RP Address (RPA) and RP Link (RPL). No DF
election on RPL. RP forwards upstream on RPL. Accept joins even if not
DF but do not forward. Added event description for DF election state
machine. Security considerations by Lorenzo.Removed comparison with
Dino's draft.
>From 02 to 03:
Consistency fixes in DF election tables to match state transition
diagram pointed out by Apoorva.
>From 00 to 01: 6. IANA Considerations
The differences between this version (-01) of the BIDIR-PIM IANA has assigned OptionType 22 to the "Bidir Capable" option.
specification and draft-ietf-pim-bidir-new-00.txt are mostly in the
format of the information presented. As BIDIR-PIM has many similarities
in operation to Sparse-Mode PIM, the earlier version of this spec relied
heavily on the now obsolete PIM-SM [8] specification. This revision
removes this dependency and instead references the new Sparse-Mode
documentation [4] where necessary. In addition the method in which the
protocol specification is presented has been updated to follow the
format of [4].
7. Acknowledgments 7. Acknowledgments
The bidir proposal in this draft is heavily based on the ideas and text The bidir proposal in this draft is heavily based on the ideas and
presented by Estrin and Farinacci in [7]. The main difference between text presented by Estrin and Farinacci in [6]. The main difference
the two proposals is in the method chosen for upstream forwarding. between the two proposals is in the method chosen for upstream
forwarding.
We would also like to thank John Zwiebel at Procket, Deborah Estrin at We would also like to thank John Zwiebel at Cisco, Deborah Estrin at
ISI/USC as well as Nidhi Bhaskar, Yiqun Cai, Toerless Eckert, Apoorva ISI/USC, Bill Fenner at AT&T Research as well as Nidhi Bhaskar, Yiqun
Karan, Rajitha Sumanasekera and Beau Williamson at cisco for their Cai, Toerless Eckert, Apoorva Karan, Rajitha Sumanasekera and Beau
contributions and comments to this draft. Williamson at cisco for their contributions and comments to this
draft.
8. Authors' Addresses 8. Authors' Addresses
Mark Handley Mark Handley
Computer Science Department Computer Science Department
University College London University College London
M.Handley@cs.ucl.ac.uk M.Handley@cs.ucl.ac.uk
Isidor Kouvelas Isidor Kouvelas
Cisco Systems Cisco Systems
kouvelas@cisco.com kouvelas@cisco.com
Tony Speakman Tony Speakman
Cisco Systems Cisco Systems
speakman@cisco.com speakman@cisco.com
Lorenzo Vicisano Lorenzo Vicisano
Cisco Systems Digital Fountain
lorenzo@cisco.com lorenzo@digitalfountain.com
9. Normative References 9. Normative References
[1] S.E. Deering, "Host extensions for IP multicasting", RFC 1112, Aug [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
1989. Levels", BCP 14, RFC 2119, March 1997.
[2] B. Cain, S Deering, W. Fenner, I Kouvelas, A. Thyagarajan, "Internet [2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Group Management Protocol, Version 3", RFC 3376. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC
3376, October 2002.
[3] S. Deering, W. Fenner, B. Haberman, "Multicast Listener Discovery [3] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
(MLD) for IPv6", RFC 2710. Discovery (MLD) for IPv6", RFC 2710, October 1999.
[4] B. Fenner, M. Handley, H. Holbrook, 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)", Work In Progress, <draft-ietf-pim-sm- Specification (Revised)", RFC 4601, August 2006.
v2-new-09.txt>, 2004.
[5] S. Kent, R. Atkinson, "Security Architecture for the Internet [5] Kent, S. and R. Atkinson, "Security Architecture for the Internet
Protocol.", RFC 2401. Protocol", RFC 2401, November 1998. [Note to RFC Editor: this is
intended to be the obsolete document, just like RFC 4601's]
10. Informative References 10. Informative References
[6] T. Bates , R. Chandra , D. Katz , Y. Rekhter, "Multiprotocol [6] Estrin, D. and D. Farinacci, "Bi-directional Shared Trees in PIM-
Extensions for BGP-4", RFC 2283 SM", Work in progress <draft-farinacci-bidir-pim-01.txt>, May
1999.
[7] D. Estrin, D. Farinacci, "Bi-directional Shared Trees in PIM-SM", [7] Bhaskar, N., Gall, A., Lingard, J. and S. Venaas, "Bootstrap
<draft-farinacci-bidir-pim-01.txt>, May 1999. Router (BSR) Mechanism for PIM", Work in progress <draft-ietf-pim-
sm-bsr-09.txt>, June 2006.
[8] D. Estrin et al, "Protocol Independent Multicast-Sparse Mode (PIM- 11. Index
SM): Protocol Specification", RFC 2362, Nov 1999. DF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,21
Downstream. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
DownstreamJPState(G,I). . . . . . . . . . . . . . . . . . . . . . 12
ET(G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,34
ET(RPA,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
I_am_DF(RPA,I). . . . . . . . . . . . . . . . . . . . . . . .12,14,17
J/P_HoldTime. . . . . . . . . . . . . . . . . . . . . . . . . . . 34
J/P_Override_Interval . . . . . . . . . . . . . . . . . . . . . 18,35
JoinDesired(G). . . . . . . . . . . . . . . . . . . . . . . . . . 21
joins(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
JT(*,G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
JT(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11,35
local_receiver_include(G,I) . . . . . . . . . . . . . . . . . . . 12
MFIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
NLT(N,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Offer_Period. . . . . . . . . . . . . . . . . . . . . . . . . . . 34
olist(G). . . . . . . . . . . . . . . . . . . . . . . . . . .12,14,21
OT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
pim_include(G). . . . . . . . . . . . . . . . . . . . . . . . . . 12
PPT(G,I). . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,35
RPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
RPF_interface(RPA). . . . . . . . . . . . . . . . . . . . . . . 12,14
RPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
TIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
t_override. . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
t_periodic. . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
t_suppressed. . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
Upstream. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
[9] W. Fenner, M. Handley, R. Kermode and D. Thaler, "Bootstrap Router Intellectual Property
(BSR) Mechanism for PIM Sparse Mode", Work in progress <draft-ietf-
pim-sm-bsr-03.txt>, 2003.
11. Index The IETF takes no position regarding the validity or scope of any
DF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7,21 Intellectual Property Rights or other rights that might be claimed to
Downstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 pertain to the implementation or use of the technology described in
DownstreamJPState(G,I) . . . . . . . . . . . . . . . . . . . . . . . 12 this document or the extent to which any license under such rights
ET(G,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,34 might or might not be available; nor does it represent that it has
ET(RPA,I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 made any independent effort to identify any such rights. Information
I_am_DF(RPA,I) . . . . . . . . . . . . . . . . . . . . . . . . .12,14,17 on the procedures with respect to rights in RFC documents can be
J/P_HoldTime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 found in BCP 78 and BCP 79.
J/P_Override_Interval. . . . . . . . . . . . . . . . . . . . . . . 18,35
JoinDesired(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
joins(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
JT(*,G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
JT(G). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11,35
local_receiver_include(G,I). . . . . . . . . . . . . . . . . . . . . 12
MFIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
NLT(N,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Offer_Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
olist(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . .12,14,20
OT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
pim_include(G) . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PPT(G,I) . . . . . . . . . . . . . . . . . . . . . . . . . . . .11,16,35
RPA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
RPF_interface(RPA) . . . . . . . . . . . . . . . . . . . . . . . . 12,14
RPL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
TIB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
t_override . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
t_periodic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
t_suppressed . . . . . . . . . . . . . . . . . . . . . . . . . . . 20,35
Upstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
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