draft-ietf-idmr-pim-sm-spec-02.txt   draft-ietf-idmr-pim-sm-spec-03.txt 
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[Page 1]
1 Introduction 1 Introduction
This document describes a protocol for efficiently routing to This document describes a protocol for efficiently routing to
multicast groups that may span wide-area (and inter-domain) multicast groups that may span wide-area (and inter-domain)
internets. We refer to the approach as Protocol Independent internets. We refer to the approach as Protocol Independent
Multicast--Sparse Mode (PIM-SM) because it is not dependent on any Multicast--Sparse Mode (PIM-SM) because it is not dependent on any
particular unicast routing protocol, and because it is designed to particular unicast routing protocol, and because it is designed to
support sparse groups as defined in [1][2]. This document describes support sparse groups as defined in [1][2]. This document describes
the protocol details. For the motivation behind the design and a the protocol details. For the motivation behind the design and a
description of the architecture, see [1][2]. Section 2 summarizes description of the architecture, see [1][2]. Section 2 summarizes
PIM-SM operation. It describes the protocol from a network PIM-SM operation. It describes the protocol from a network
perspective, in particular, how the participating routers interact to perspective, in particular, how the participating routers interact to
create and maintain the multicast distribution tree. Section 3 create and maintain the multicast distribution tree. Section 3
describes PIM-SM operations from the perspective of a single router describes PIM-SM operations from the perspective of a single router
implementing the protocol; this section constitutes the main body of implementing the protocol; this section constitutes the main body of
the protocol specification. It is organized according to PIM-SM the protocol specification. It is organized according to PIM-SM
message type; for each message type we describe its contents, its message type; for each message type we describe its contents, its
generation, and its processing. Interoperability with other protocols generation, and its processing.
will be further discussed in an appendix to this document.
Section 4 provides packet format details. Section 4 provides packet format details. Sections 3.8 and 3.9
summarize the timers and flags referred to throughout this document.
The most significant functional changes since the January '95 The most significant functional changes since the January '95 version
version, are the Rendezvous Point-related mechanisms and the removal involve the Rendezvous Point-related mechanisms, several resulting
of the PIM-DM protocol details to a separate [3] (for clarity). simplifications to the protocol, and removal of the PIM-DM protocol
details to a separate [3] (for clarity).
2 PIM-SM Protocol Overview 2 PIM-SM Protocol Overview
In this section we provide an overview of the architectural In this section we provide an overview of the architectural
components of PIM-SM. components of PIM-SM.
A router [*] A router [*]
receives explicit Join/Prune messages from those neighboring routers receives explicit Join/Prune messages from those neighboring routers
that have downstream group members. The router then forwards data that have downstream group members. The router then forwards data
packets addressed to a multicast group, G, only onto those interfaces packets addressed to a multicast group, G, only onto those interfaces
on which explicit joins have been received. on which explicit joins have been received.
A Designated Router (DR) sends periodic Join/Prune messages toward a A Designated Router (DR) sends periodic Join/Prune messages toward a
group-specific Rendezvous Point (RP) for each group for which it has group-specific Rendezvous Point (RP) for each group for which it has
active members. Each router along the path toward the RP builds active members. Each router along the path toward the RP builds a
wildcard (any-source) forwarding state for the group and sends wildcard (any-source) forwarding state. for the group and sends
messages on toward the RP. The wildcard forwarding entry's incoming
_________________________ _________________________
[*] All routers mentioned in this document are assumed [*] All routers mentioned in this document are assumed
to be PIM-SM capable, unless otherwise specified. to be PIM-SM capable, unless otherwise specified.
[Page 2] messages on toward the RP. We use the term entry to refer to the
interface points toward the RP; the outgoing interfaces point to the forwarding state maintained in a router to represent the distribution
neighboring downstream routers that have sent Join/Prune messages tree. Each entry includes such things as the incoming interface from
toward the RP. This forwarding state creates a shared, RP-centered, which packets are accepted, the list of outgoing interfaces to which
distribution tree that reaches all group members. When a data source packets are sent, timers, flag bits, etc. The wildcard forwarding
first sends to a group, its DR unicasts Register messages to the RP entry's incoming interface points toward the RP; the outgoing
with the source's data packets encapsulated within. If the data rate interfaces point to the neighboring downstream routers that have sent
is high, the RP can send source-specific Join/Prune messages back Join/Prune messages toward the RP. This forwarding state creates a
towards the source and the source's data packets will follow the shared, RP-centered, distribution tree that reaches all group
resulting forwarding state and travel unencapsulated to the RP. members. When a data source first sends to a group, its DR unicasts
Whether they arrive encapsulated or natively, the RP forwards the Register messages to the RP with the source's data packets
source's decapsulated data packets down the RP-centered distribution encapsulated within. If the data rate is high, the RP can send
tree toward group members. If the data rate warrants it, routers with source-specific Join/Prune messages back towards the source and the
local receivers can join a source-specific, shortest path, source's data packets will follow the resulting forwarding state and
distribution tree, and prune these source's packets off of the shared travel unencapsulated to the RP. Whether they arrive encapsulated or
RP-centered tree. Even if all receivers switch to the shortest path natively, the RP forwards the source's decapsulated data packets down
tree, state for that source will be kept at the RP, so that new the RP-centered distribution tree toward group members. If the data
members that join the RP-centered tree will receive data packets from rate warrants it, routers with local receivers can join a source-
the source. For low data rate sources, neither the RP, nor last hop specific, shortest path, distribution tree, and prune these source's
routers need join a source-specific shortest path tree and data packets off of the shared RP-centered tree. Even if all receivers
packets can be delivered via the shared, RP-tree. switch to the shortest path tree, state for that source will be kept
at the RP, so that new members that join the RP-centered tree will
receive data packets from the source. For low data rate sources,
neither the RP, nor last-hop routers need join a source-specific
shortest path tree and data packets can be delivered via the shared,
RP-tree.
The following subsections describe SM operation in more detail, in The following subsections describe SM operation in more detail, in
particular, the control messages, and the actions they trigger. particular, the control messages, and the actions they trigger.
Section 3 describes protocol operation from an implementors Section 3 describes protocol operation from an implementors
perspective, i.e., the actions performed by a single router. perspective, i.e., the actions performed by a single router.
2.1 Local hosts joining a group 2.1 Local hosts joining a group
In order to join a multicast group, G, a host sends an IGMP Host- In order to join a multicast group, G, a host sends an IGMP Host-
Membership-Report message identifying the particular group. As Membership-Report message identifying the particular group. As
specified in [4], IGMP Host-Membership-Report messages are sent in specified in [4], IGMP Host-Membership-Report messages are sent in
response to a directly-connected router's IGMP Host-Membership-Query response to a directly-connected router's IGMP Host-Membership-Query
message (see figure 1). [*] message (see figure 1) [*] From this point on we refer to such a
host as a receiver, R, (or member) of the group G.
From this point on we refer to such a host as a receiver, R, (or
member) of the group G.
_________________________ _________________________
[*] All figures used in this section are for illustra- [*] All figures used in this section are for illustra-
tion and are not intended to be complete. For complete tion and are not intended to be complete. For complete
and detailed protocol action see Section 3. and detailed protocol action see Section 3.
[Page 3]
Fig. 1 Example: how a receiver joins, and sets up shared tree Fig. 1 Example: how a receiver joins, and sets up shared tree
When a DR receives an IGMP Host-Membership-Report for a new group, G, When a DR receives an IGMP Host-Membership-Report for a new group, G,
the DR looks up the associated RP. The DR (e.g., router A in figure the DR looks up the associated RP. The DR (e.g., router A in figure
1) creates a wildcard multicast forwarding entry for the group, 1) creates a wildcard multicast forwarding entry for the group,
referred to here as a (*,G) entry; if there is no more specific match referred to here as a (*,G) entry; if there is no more specific match
for a particular source, the packet will be forwarded according to for a particular source, the packet will be forwarded according to
this entry. this entry.
The RP address is included in a special field in the forwarding entry The RP address is included in a special field in the forwarding entry
and is included in periodic upstream Join/Prune messages. The and is included in periodic upstream Join/Prune messages. The
outgoing interface is set to that over which the IGMP Host- outgoing interface is set to that over which the IGMP Host-
Membership-Report was received from the new member. The incoming Membership-Report was received from the new member. The incoming
interface is set to the interface used to send unicast packets to the interface is set to the interface used to send unicast packets to the
RP. An RP-bit associated with this entry is also set, indicating that RP. The RPT-bit flag associated with this entry is also set to 1,
this entry, (*,G), represents state on the shared RP-tree. Each DR on indicating that this entry, (*,G), represents state on the shared
the RP-tree with directly connected members sets a timer for this RP-tree. Each DR on the RP-tree with directly connected members sets
entry. If the timer expires and the DR has neither local members nor a timer for this entry. If the timer expires and the DR has neither
downstream receivers, the (*,G) state is deleted. If the DR does have local members nor downstream receivers, the (*,G) state is deleted.
local members, it refreshes the (*,G) entry timer each time it gets If the DR does have local members, it refreshes the (*,G) entry timer
an IGMP Host-Membership-Report. each time it gets an IGMP Host-Membership-Report.
2.2 Establishing the RP-rooted shared tree 2.2 Establishing the RP-rooted shared tree
Triggered by the (*,G) state, the DR creates a Join/Prune message Triggered by the (*,G) state, the DR creates a Join/Prune message
with the RP address in its join list and the WC-bit and RP-bit set; with the RP address in its join list and the the WC-bit and RPT-bit
nothing is listed in its prune list. The RP-bit flags the join as set to 1. The prune list is left empty. When the RPT-bit is set to 1
being associated with the shared tree and therefore the Join/Prune it indicates that the join is associated with the shared RP-tree and
message is propagated along the RP-tree. The WC-bit indicates that therefore the Join/Prune message is propagated along the RP-tree.
the address is an RP and the receiver expects to receive packets from When the WC-bit is set to 1 it indicates that the address is an RP
all sources via this (shared tree) path. and the downstream receivers expect to receive packets from all
sources via this (shared tree) path; WC stands for wildcard
[*]
Each upstream router creates or updates its multicast forwarding Each upstream router creates or updates its multicast forwarding
entry for (*,G) when it receives a Join/Prune with the RP-bit and _________________________
[*] Note that the term RPT-bit is used to refer to both
the RPT-bit flags associated with forwarding entries,
and the RPT-bit included in each encoded address in a
Join/Prune message.
entry for (*,G) when it receives a Join/Prune with the RPT-bit and
WC-bit set. The interface on which the Join/Prune message arrived is WC-bit set. The interface on which the Join/Prune message arrived is
added to the list of outgoing interfaces (oifs) for (*,G). Based on added to the list of outgoing interfaces (oifs) for (*,G). Based on
this entry each upstream router between the receiver and the RP sends this entry each upstream router between the receiver and the RP sends
a Join/Prune message in which the join list includes the RP. The a Join/Prune message in which the join list includes the RP. The
packet payload contains Multicast-Address=G, Join=RP,WCbit,RPbit, packet payload contains Multicast-Address=G, Join=RP,WC-bit,RPT-bit,
Prune=NULL. Prune=NULL.
[Page 4]
2.3 Hosts sending to a group 2.3 Hosts sending to a group
When a host first sends a multicast data packet to a group, its DR When a host starts sending multicast data packets to a group,
must deliver the packet to the RP for distribution down the RP-tree initially its DR must deliver each packet to the RP for distribution
(see figure 2). This is done by the sender's DR unicasting a Register down the RP-tree (see figure 2). The sender's DR initially
packet to the RP for the group. The data packet is encapsulated in encapsulates each data packet in a Register message and unicasts it
the Register packet so that the RP can decapsulate it and deliver it to the RP for that group. The RP decapsulates each Register message
to downstream members. and forwards the enclosed data packet natively to downstream members
on the shared RP-tree.
Fig. 2 Example: a host sending to a group Fig. 2 Example: a host sending to a group
If the data rate of the source warrants [*] If the data rate of the source warrants [*]
the use of a source-specific shortest path tree (SPT), the RP may the use of a source-specific shortest path tree (SPT), the RP may
construct a new multicast forwarding entry that is specific to the construct a new multicast forwarding entry that is specific to the
source, hereafter referred to as (S,G) state, and send periodic source, hereafter referred to as (S,G) state, and send periodic
Join/Prune messages toward the source. The routers between the source Join/Prune messages toward the source. The routers between the source
and the RP build and maintain (S,G) state in response to these and the RP build and maintain (S,G) state in response to these
messages and send (S,G) messages upstream toward the source. messages and send (S,G) messages upstream toward the source.
The source's DR must stop encapsulating data packets in Registers The source's DR must stop encapsulating data packets in Registers
when (and so long as) it receives Register-Stop messages from the RP. when (and so long as) it receives Register-Stop messages from the RP.
The RP triggers Register-Stop messages in response to Registers, if The RP triggers Register-Stop messages in response to Registers, if
the RP has no downstream receivers for the group (or for that the RP has no downstream receivers for the group (or for that
particular source), or if the RP has already joined the (S,G) tree particular source), or if the RP has already joined the (S,G) tree
and is receiving the data packets natively. _________________________
[*] This decision is a local policy established at the
RP. For example, when the Register rate exceeds a con-
figured threshold at the RP, this may warrant the use
of the SPT.
and is receiving the data packets natively. Each source's DR
maintains, per (S,G), a Register-bit and a Register-bit timer. The
Register-bit timer is started by the Register-Stop message; upon
expiration, the Register-bit is set to 1 and the source's DR resumes
sending data packets encapsulated in Register messages.
2.4 Switching from shared tree (RP-tree) to shortest path tree (SP- 2.4 Switching from shared tree (RP-tree) to shortest path tree (SP-
tree)} tree)
When a router has directly-connected members, it first joins the When a router has directly-connected members, it first joins the
shared RP-tree. The router can switch to a source's shortest path shared RP-tree. The router can switch to a source's shortest path
tree (SP-tree) after receiving packets from that source over the tree (SP-tree) after receiving packets from that source over the
shared RP-tree. The recommended policy is to initiate the switch to shared RP-tree. The recommended policy is to initiate the switch to
the SP-tree after receiving a significant number of data packets the SP-tree after receiving a significant number of data packets
_________________________
[*] This decision is a local policy established at the
RP. For example, when the Register rate exceeds a con-
figured threshold at the RP, this may warrant the use
of the SPT.
[Page 5]
during a specified time interval from a particular source. To realize during a specified time interval from a particular source. To realize
this policy the router can monitor data packets from sources for this policy the router can monitor data packets from sources for
which it has no source-specific multicast forwarding entry and which it has no source-specific multicast forwarding entry and
initiate such an entry when the data rate exceeds the configured initiate such an entry when the data rate exceeds the configured
threshold. As shown in figure 3, router `A' initiates a (S,G) state. threshold. As shown in figure 3, router `A' initiates a (S,G) state.
Fig. 3 Example: Switching from shared tree to shortest path tree Fig. 3 Example: Switching from shared tree to shortest path tree
When a (S,G) entry is activated (and periodically so long as the When a (S,G) entry is activated (and periodically so long as the
state exists), a Join/Prune message is sent upstream towards the state exists), a Join/Prune message is sent upstream towards the
source, S, with S in the join list. The payload contains Multicast- source, S, with S in the join list. The payload contains Multicast-
Address=G, Join=S, Prune=NULL. When the (S,G) entry is created, the Address=G, Join=S, Prune=NULL. When the (S,G) entry is created, the
outgoing interface list is copied from (*,G), i.e., all local shared outgoing interface list is copied from (*,G), i.e., all local shared
tree branches are replicated in the new shortest path tree [*] In tree branches are replicated in the new shortest path tree [*] In
this way when a data packet from S arrives and matches on this entry, this way when a data packet from S arrives and matches on this entry,
all receivers will continue to receive the source's packets along all receivers will continue to receive the source's packets along
this path. Note that (S,G) state must be maintained in all last-hop this path. Note that (S,G) state must be maintained in each last-hop
routers where an SP-tree is maintained. Even when (*,G) and (S,G) router that is responsible for initiating and maintaining an SP-tree.
overlap, both states are needed to trigger the source-specific [*]
Join/Prune messages. (S,G) state is kept alive by data packets _________________________
arriving from that source. A timer, S-timer, is set for the (S,G) [*] In more complicated scenarios, other entries in the
entry and this timer is restarted whenever a data packet for (S,G) is router have to be considered. For details see Section 3.
forwarded out at least one oif. When the S-timer expires the state is [*] By last-hop router we mean the router that delivers
deleted. the packets to their ultimate end-system destination.
This is the router that monitors if there is group
membership and joins or prunes the appropriate distri-
Even when (*,G) and (S,G) overlap, both states are needed to trigger
the source-specific Join/Prune messages. (S,G) state is kept alive by
data packets arriving from that source. A timer, S-timer, is set for
the (S,G) entry and this timer is restarted whenever a data packet
for (S,G) is forwarded out at least one oif. When the S-timer expires
the state is deleted.
Only the RP and routers with local members can initiate switching to Only the RP and routers with local members can initiate switching to
the SP-tree; intermediate routers do not. Consequently, last hop the SP-tree; intermediate routers do not. Consequently, last-hop
routers create (S,G) state in response to data packets from the routers create (S,G) state in response to data packets from the
source, S; whereas intermediate routers only create (S,G) state in source, S; whereas intermediate routers only create (S,G) state in
response to Join/Prune messages from downstream that have S in the response to Join/Prune messages from downstream that have S in the
Join list [*] Join list [*]
_________________________
[*] In more complicated scenarios, other entries in the
router have to be considered. For details see Section 3.
[*] For example, to implement the policy that source-
specific trees are only setup for high-data rate
source, a last-hop router might not create a (S,G) en-
try until it has received m data packets from the
source within some interval of n seconds.
[Page 6]
The (S,G) entry is initialized with the SPT-bit cleared, indicating The (S,G) entry is initialized with the SPT-bit cleared, indicating
that the shortest path tree branch from S has not yet been setup that the shortest path tree branch from S has not yet been setup
completely, and the router can still accept packets from S that completely, and the router can still accept packets from S that
arrive on the (*,G) entry's iif. arrive on the (*,G) entry's indicated incoming interface (iif). [*]
When a router with a (S,G) entry and a cleared SPT-bit starts to When a router with a (S,G) entry and a cleared SPT-bit starts to
receive packets from the new source S on the iif for the (S,G) entry, receive packets from the new source S on the iif for the (S,G) entry,
and that iif differs from the (*,G) entry's iif, the router sets the and that iif differs from the (*,G) entry's iif, the router sets the
SPT-bit, and sends a Join/Prune message towards the RP, indicating SPT-bit, and sends a Join/Prune message towards the RP, indicating
that the router no longer wants to receive packets from S via the that the router no longer wants to receive packets from S via the
shared RP-tree. The Join/Prune message sent towards the RP includes S shared RP-tree. The Join/Prune message sent towards the RP includes S
in the prune list, with the RP-bit set indicating that S's packets in the prune list, with the RPT-bit set indicating that S's packets
should not be forwarded down this branch of the shared tree. If the should not be forwarded down this branch of the shared tree. If the
router receiving the Join/Prune message has (S,G) state (with or router receiving the Join/Prune message has (S,G) state (with or
without the RPbit set), it deletes the arriving interface from the without the forwarding entry's RPT-bit flag set), it deletes the
(S,G) oif list. If the router has only (*,G) state, it creates an arriving interface from the (S,G) oif list. If the router has only
(S,G)RP-bit entry. The Join/Prune message payload contains (*,G) state, it creates an entry with the RPT-bit flag set to 1. For
Multicast-Address=G, Join=NULL, Prune=S,RPbit. brevity we refer to an (S,G) entry that has the RPT-bit flag set to 1
_________________________
If at a later time a new receiver joins the RP-tree, the negative bution trees in response. In general the last-hop
cache state on the RP-tree must be eradicated to bring all sources' router is the Desgnated Router (DR) for the LAN. Howev-
data packets down to the new receiver. Therefore, when a (*,G) Join er, under various conditions described later, a paral-
arrives with a null prune list at a router that has any (S,G)RP-bit lel router connected to the same LAN may take over as
entries (which is causing it to send source-specific prunes toward the last-hop router in place of the DR.
the RP), all RP-bit state for that group has to be updated upstream [*] For example, to implement the policy that source-
of the router; so as to bring all sources' packets down to the new specific trees are only setup for high-data rate
member. To accomplish this the router updates all existing (S,G)RP- source, a last-hop router might not create a (S,G) en-
bit entries; it adds to each (S,G)RP-bit entry's oif list the try until it has received m data packets from the
interface on which the (*,G) join arrived. The router also triggers a source within some interval of n seconds.
(*,G) join upstream to cause the same updating of RP-bit settings [*] As in DVMRP, each PIM multicast forwarding entry
upstream and pull down all active sources' packets. If the arriving has an associated incoming interface on which packets
(*,G) join has some sources included in its prune list, then the are expected to arrive.
corresponding (S,G)RP-bit entries are left unchanged (i.e., the RPbit
remains set and no oif is added).
2.5 Steady state maintenance of distribution tree (i.e., router state)} as an (S,G)RPT-bit entry. This notational distinction is useful to
point out the different actions taken for (S,G) entries depending on
the setting of the RPT-bit flag. Note that a router can have no more
than one (S,G) entry for any particular S and G, at any particular
time; whether the RPT-bit flag is set or not. In other words, a
router never has both an (S,G) and an (S,G)RPT-bit entry for the same
S and G at the same time. The Join/Prune message payload contains
Multicast-Address=G, Join=NULL, Prune=S,RPT-bit.
In the steady state each router sends periodic Join/Prune messages A new receiver may join an existing RP-tree on which source-specific
for each active (S,G), (*,G) or (*,*,RP) [*] prune state has been established (e.g., because downstream receivers
have switched to SP-trees). In this case the prune state must be
eradicated upstream of the new receiver to bring all sources' data
packets down to the new receiver. Therefore, when a (*,G) Join
arrives at a router that has any (Si,G)RPT-bit entries (i.e., entries
that cause the router to send source-specific prunes toward the RP),
these entries must be updated upstream of the router so as to bring
all sources' packets down to the new member. To accomplish this, each
router that receives a (*,G) Join/Prune message updates any existing
(S,G)RPT-bit entries. The router may also trigger a (*,G) join
upstream to cause the same updating of RPT-bit settings upstream and
pull down all active sources' packets. If the arriving (*,G) join has
some sources included in its prune list, then the corresponding
(S,G)RPT-bit entries are left unchanged (i.e., the RPT-bit remains
set and no oif is added).
entry; the Join/Prune messages are sent to the RPF neighbor on the 2.5 Steady state maintenance of distribution tree (i.e., router state)
iif of the corresponding entry. These messages are sent periodically
to capture state, topology, and membership changes. A Join/Prune
_________________________
[*] (*,*,RP) entry is introduced for interoperability,
see Sections 2.10 and 6.
[Page 7] In the steady state each router sends periodic Join/Prune messages
message is also sent on an event-triggered basis each time a new for each active PIM forwarding entry; the Join/Prune messages are
forwarding entry is established for some new source (note that some sent to the neighbor indicated in the iif field of the corresponding
damping function may be applied, e.g., a merge time). Join/Prune entry. These messages are sent periodically to capture state,
messages do not elicit any form of explicit acknowledgment; routers topology, and membership changes. A Join/Prune message is also sent
recover from lost packets using the periodic refresh mechanism. on an event-triggered basis each time a new forwarding entry is
established for some new source (note that some damping function may
be applied, e.g., a merge time). Join/Prune messages do not elicit
any form of explicit acknowledgment; routers recover from lost
packets using the periodic refresh mechanism.
2.6 Obtaining RP information 2.6 Obtaining RP information
To obtain the RP information, all routers collect RP-Set messages. To obtain the RP information, all routers within a PIM domain collect
RP-Set messages are sent hop-by-hop within the domain; originating at RP-Set messages. RP-Set messages are sent hop-by-hop within the
the domain's bootstrap router (BSR). The BSR is elected dynamically domain; the domain's bootstrap router (BSR) is responsible for
originating the RP-set messages. The BSR is elected dynamically
within each domain. within each domain.
[*] [*]
Routers then use the set of RPs to get the proper Group to RP Routers then use the set of RPs to get the proper Group to RP
mapping. Details are as follows: mapping. Details are as follows:
2.6.1 Bootstrap Router
A (small) set of routers, within a domain, are configured as A (small) set of routers, within a domain, are configured as
candidate bootstrap routers. Initially, each of these candidates candidate bootstrap routers. Initially, each of these candidates
includes its address in `RP-set' messages. Through a simple election includes its address in `RP-set' messages. Through a simple election
mechanism, a single bootstrap router (BSR) is elected for that domain mechanism, a single bootstrap router (BSR) is elected for that domain
(see Section 3.6). (see Section 3.6).
2.6.2 Candidate RPs
A set of routers within a domain are configured as candidate RPs (C- A set of routers within a domain are configured as candidate RPs (C-
RPs); typically these will be the same routers that are configured as RPs); typically these will be the same routers that are configured as
C-BSRs. Candidate RPs periodically unicast Candidate-RP-Advertisement C-BSRs. Candidate RPs periodically unicast Candidate-RP-Advertisement
messages (C-RP-Advs) to the BSR of that domain. C-RP-Advs include the messages (C-RP-Advs) to the BSR of that domain. C-RP-Advs include the
address of the advertising C-RP, as well as an optional group address address of the advertising C-RP, as well as an optional group address
and a mask length field, indicating the group prefix(es) for which and a mask length field, indicating the group prefix(es) for which
the candidacy is advertised. The BSR then includes a set of these the candidacy is advertised. The BSR then includes a set of these
Candidate-RPs in the RP-Set messages, along with the corresponding Candidate-RPs in the RP-Set messages, along with the corresponding
group prefixes (see Section group prefixes (see Section
3.6.2). RP-Set messages are periodically sent hop-by-hop throughout 3.6.2). RP-Set messages are periodically sent hop-by-hop throughout
the domain. the domain.
_________________________
[*] A domain in this context is a multicast region in
which routers implement PIM-SM. PIM-SM border routers
are assumed to connect a domain to the rest of the in-
ternet.
[Page 8]
2.6.3 Group to RP mapping
Routers receive and store RP-Set messages originated by the BSR. When Routers receive and store RP-Set messages originated by the BSR. When
a DR receives IGMP Host-Membership-Report (or a data packet) from a a DR receives IGMP Host-Membership-Report (or a data packet) from a
directly connected host, for a group for which it has no entry, the directly connected host, for a group for which it has no entry, the
DR uses a hash function to map the pertinent group to one of the C- DR uses a hash function to map the pertinent group to one of the C-
RPs whose Group-prefix includes the group (see Section 3.7). The DR RPs whose Group-prefix includes the group (see Section 3.7). The DR
then sends a Join/Prune message towards (or unicasts Registers to) then sends a Join/Prune message towards (or unicasts Registers to)
that RP. that RP.
[*]
2.6.4 Providing RP liveness
The RP-Set message indicates liveness of the RPs included therein; if The RP-Set message indicates liveness of the RPs included therein; if
an RP is included in the message, then it is tagged as `up' at the an RP is included in the message, then it is tagged as `up' at the
routers, while RPs not included in the message are tagged as `down' routers, while RPs not included in the message are tagged as `down'
and removed from the list of RPs over which the hash algorithm acts. and removed from the list of RPs over which the hash algorithm acts.
Each router continues to use the contents of the most recently Each router continues to use the contents of the most recently
received RP-set message until it receives a new RP-set message. received RP-set message until it receives a new RP-set message.
_________________________
[*] A domain in this context is a contiguous set of
routers that all implement PIM and are configured to
operate within a common boundary defined by PIM Multi-
cast Border Routers (PMBRs). PMBRs connect each PIM
domain to the rest of the internet.
2.7 Multicast data packet processing 2.7 Interoperation with dense mode protocols such as DVMRP
In order to interoperate with networks that run dense-mode,
broadcast and prune, protocols, such as DVMRP, all packets generated
within a PIM-SM region must be pulled down to that region's PIM
Multicast Border Routers (PMBRs) and injected (i.e., broadcast) into
the DVMRP network. [*]
To achieve this capability, a special entry type, referred to as
(*,*,RP), must be supported by all PIM routers. For this reason we
include details about (*,*,RP) entry handling in this general PIM
specification.
A data packet will match on a (*,*,RP) entry if there is no more
specific entry (such as (S,G) or (*,G)) and the destination group
address in the packet maps to the RP listed in the (*,*,RP) entry. In
this sense, a (*,*,RP) entry represents an aggregation of all the
groups supported by that RP. PMBRs initialize (*,*,RP) state for each
RP in the domain's RPset. The (*,*,RP) state causes the PMBRs to send
Join/Prune messages toward each of the active RPs in the domain. As a
result distribution trees are built that carry all data packets
originated within the PIM domain (and sent to the RPs) down to the
PMBRs.
All PIM routers must be capable of supporting (*,*,RP) state and
interpreting associated Join/Prune messages. We describe the handling
of (*,*,RP) entries and messages throughout this document. However,
detailed PIM Multicast Border Router functions will be specified in a
separate interoperability document.
2.8 Multicast data packet processing
Data packets are processed in a manner similar to existing multicast Data packets are processed in a manner similar to existing multicast
schemes. A router first performs a longest match on the source and schemes. A router first performs a longest match on the source and
group address in the data packet. A (S,G) entry is matched first if group address in the data packet. A (S,G) entry is matched first if
one exists; a (*,G) entry is matched otherwise. If neither state one exists; a (*,G) entry is matched otherwise. If neither state
exists, then a (*,*,RP) entry match is attempted as follows: the exists, then a (*,*,RP) entry match is attempted as follows: the
router hashes on G to identify the RP for group G, and looks for a router hashes on G to identify the RP for group G, and looks for a
_________________________
[*] A PMBR is a router that sits at the boundary of a
PIM-SM domain and interoperates with other types of
multicast routers such as those that run DVMRP. Gen-
erally a PMBR would speak both protocols and implement
interoperability functions not required by regular PIM
routers.
(*,*,RP) entry that has this RP address associated with it. If none (*,*,RP) entry that has this RP address associated with it. If none
of the above exists, then the packet is dropped. If a state is of the above exists, then the packet is dropped. If a state is
matched, an incoming interface check (RPF check) is performed on the matched, the router compares the interface on which the packet
matching state and if it fails the packet is dropped, otherwise the arrived to the incoming interface field in the matched forwarding
entry. If the iif check fails the packet is dropped, otherwise the
packet is forwarded to all interfaces listed in the outgoing packet is forwarded to all interfaces listed in the outgoing
interface list. interface list.
Some special actions are needed to deliver packets continuously while Some special actions are needed to deliver packets continuously while
switching from the shared to shortest-path tree. In particular, when switching from the shared to shortest-path tree. In particular, when
a (S,G) entry is matched, incoming packets are forwarded as follows: a (S,G) entry is matched, incoming packets are forwarded as follows:
1 If the SPT-bit is set, then: 1 If the SPT-bit is set, then:
_________________________
[*] Each intermediate router also uses this same hash
function to determine the (*,*,RP) match for incoming
data packets.
[Page 9]
1 if the incoming interface is the same as a matching 1 if the incoming interface is the same as a matching
(S,G) iif, the packet is forwarded to the oif-list of (S,G) iif, the packet is forwarded to the oif-list of
(S,G). (S,G).
2 if the incoming interface is different than a matching 2 if the incoming interface is different than a matching
(S,G) iif , the packet is discarded. (S,G) iif , the packet is discarded.
2 If the SPT-bit is cleared, then: 2 If the SPT-bit is cleared, then:
1 if the incoming interface is the same as a matching 1 if the incoming interface is the same as a matching
skipping to change at line 422 skipping to change at page 12, line 9
the packet is discarded. the packet is discarded.
Data packets never trigger prunes. However, data packets may Data packets never trigger prunes. However, data packets may
trigger actions that in turn trigger prunes. For example, when trigger actions that in turn trigger prunes. For example, when
router B in figure 3 decides to switch to SP-tree at step 3, it router B in figure 3 decides to switch to SP-tree at step 3, it
creates a (S,G) entry with SPT-bit set to 0. When data packets creates a (S,G) entry with SPT-bit set to 0. When data packets
from S arrive at interface 2 of B, B sets the SPT-bit to 1 from S arrive at interface 2 of B, B sets the SPT-bit to 1
since the iif for (*,G) is different than that for (S,G). This since the iif for (*,G) is different than that for (S,G). This
triggers the sending of prunes towards the RP. triggers the sending of prunes towards the RP.
2.8 Operation over Multi-access Networks 2.9 Operation over Multi-access Networks
This section describes a few additional protocol mechanisms This section describes a few additional protocol mechanisms
needed to operate PIM over multi-access networks: Designated needed to operate PIM over multi-access networks: Designated
Router election, Assert messages to resolve parallel paths, and Router election, Assert messages to resolve parallel paths, and
the Joiner bit to suppress redundant Joins on multi-access the Joiner bit to suppress redundant Joins on multi-access
networks. networks.
[Page 10] 2.9.1 Designated router election
2.8.1 Designated router election
When there are multiple routers connected to a multi-access When there are multiple routers connected to a multi-access
network, one of them should be chosen to operate as the network, one of them should be chosen to operate as the
designated router (DR) at any point in time. The DR is designated router (DR) at any point in time. The DR is
responsible for sending triggered Join/Prune and Register responsible for sending triggered Join/Prune and Register
messages toward the RP [*] messages toward the RP [*]
A simple designated router (DR) election mechanism is used for A simple designated router (DR) election mechanism is used for
both SM and traditional IP multicast routing. both SM and traditional IP multicast routing.
Neighboring routers send Query messages to each other. The Neighboring routers send Query messages to each other. The
sender with the largest IP address assumes the role of DR. Each sender with the largest IP address assumes the role of DR. Each
router connected to the multi-access LAN sends the Queries router connected to the multi-access LAN sends the Queries
periodically in order to adapt to changes in router status. periodically in order to adapt to changes in router status.
2.8.2 Parallel paths to a source or the RP 2.9.2 Parallel paths to a source or the RP--Assert process
If a router receives a multicast datagram on a multi-access LAN If a router receives a multicast datagram on a multi-access LAN
from a source whose corresponding (S,G) outgoing interface list from a source whose corresponding (S,G) outgoing interface list
includes the interface to that LAN, the packet must be a includes the interface to that LAN, the packet must be a
duplicate. In this case a single forwarder must be elected. duplicate. In this case a single forwarder must be elected.
Using Assert messages addressed to `224.0.0.13' (ALL-PIM-ROUTERS Using Assert messages addressed to `224.0.0.13' (ALL-PIM-ROUTERS
group) on the LAN, upstream routers can resolve which one will group) on the LAN, upstream routers can resolve which one will
act as the forwarder. Downstream routers listen to the Asserts act as the forwarder. Downstream routers listen to the Asserts
so they know which one was elected, and therefore where to send so they know which one was elected, and therefore where to send
_________________________
[*] IGMP Queries are sent by a PIMv2 DR if it supports
IGMPv1. If a PIMv2 router is using IGMPv2 then Host
queries are not sent by the PIMv2 DR but by the IGMP
querier.
subsequent Joins. Typically this is the same as the downstream subsequent Joins. Typically this is the same as the downstream
router's RPF neighbor but there are circumstances where this router's RPF (Reverse Path Forwarding) neighbor; but there are
might not be the case, e.g., when using different unicast circumstances where this might not be the case, e.g., when using
protocols. different unicast protocols. [*]
The upstream router elected is the one that has the shortest The upstream router elected is the one that has the shortest
distance to the source. Therefore, when a packet is received on distance to the source. Therefore, when a packet is received on
an outgoing interface a router sends an Assert message on the an outgoing interface a router sends an Assert message on the
multi-access LAN indicating what metric it uses to reach the multi-access LAN indicating what metric it uses to reach the
source of the data packet. The router with the smallest source of the data packet. The router with the smallest
numerical metric (with ties broken by highest address) will numerical metric (with ties broken by highest address) will
become the forwarder. All other upstream routers will delete the become the forwarder. All other upstream routers will delete the
interface from their outgoing interface list. The downstream interface from their outgoing interface list. The downstream
routers also do the comparison in case the forwarder is routers also do the comparison in case the forwarder is
different than the RPF neighbor. different than the RPF neighbor.
_________________________
[*] IGMP Queries are sent by a PIMv2 DR if it supports
IGMPv1. If a PIMv2 router is using IGMPv2 then Host
queries are not sent by the PIMv2 DR but by the IGMP
querier.
[Page 11]
Associated with the metric is a metric preference value. This is Associated with the metric is a metric preference value. This is
provided to deal with the case where the upstream routers may provided to deal with the case where the upstream routers may
run different unicast routing protocols. The numerically smaller run different unicast routing protocols. The numerically smaller
metric preference is always preferred. The metric preference metric preference is always preferred. The metric preference
should be treated as the high-order part of an assert metric should be treated as the high-order part of an assert metric
comparison. Therefore, a metric value can be compared with comparison. Therefore, a metric value can be compared with
another metric value provided both metric preferences are the another metric value provided both metric preferences are the
same. A metric preference can be assigned per unicast routing same. A metric preference can be assigned per unicast routing
protocol and needs to be consistent for all routers on the protocol and needs to be consistent for all routers on the
multi-access network. multi-access network.
Asserts are also needed for (*,G) entries since there may be Asserts are also needed for (*,G) entries since there may be
parallel paths from the RP and sources to a multi-access parallel paths from the RP and sources to a multi-access
network. When an assert is sent for a (*,G) entry, the first bit network. When an assert is sent for a (*,G) entry, the first bit
in the metric preference (RP-bit) is always set to 1 to indicate in the metric preference (RPT-bit) is always set to 1 to
that this path corresponds to the RP tree, and that the match indicate that this path corresponds to the RP tree, and that the
should be done on (*,G) if exits. Furthermore, the RP-bit is match should be done on (*,G) if it exists. Furthermore, the
always cleared for SP-tree entries' metric preference; this RPT-bit is always cleared for metric preferences that refer to
causes an SP-tree path to always look better than an RP-tree SP-tree entries; this causes an SP-tree path to always look
path. When the SP-tree and RPtree cross the same LAN, this better than an RP-tree path. When the SP-tree and RPtree cross
mechanism eliminates the duplicates that would otherwise be the same LAN, this mechanism eliminates the duplicates that
carried over the LAN. would otherwise be carried over the LAN.
In case the packet, or the Assert message, matches on oif for In case the packet, or the Assert message, matches on oif for
_________________________
[*] The RPF neighbor for a particular source (or RP) is
the next-hop router to which packets are forwarded en
route to that source (or RP); and therefore is con-
sidered a good path via which to accept packets from
that source.
(*,*,RP) entry, a (*,G) entry is created, and asserts take place (*,*,RP) entry, a (*,G) entry is created, and asserts take place
as if the matching state were (*,G). as if the matching state were (*,G).
The DR may lose to another router on the LAN by the Assert The DR may lose the (*,G) Assert process to another router on
process if there are multiple paths to the RP through the LAN. the LAN if there are multiple paths to the RP through the LAN.
From then on, the DR is no longer the last-hop router for local From then on, the DR is no longer the last-hop router for local
receivers. The winning router becomes the last-hop router and is receivers and removes the LAN from its (*,G) oif list. The
responsible for sending (*,G) join messages to the RP. Asserts winning router becomes the last-hop router and is responsible
are rate limited. for sending (*,G) join messages to the RP. Asserts are rate
limited.
2.8.3 Join/Prune suppression 2.9.3 Join/Prune suppression
If a Join/Prune message arrives on the incoming interface for an If a Join/Prune message arrives and matches on the incoming
existing (S,G) entry, and the sender of the Join/Prune has a interface for an existing (S,G), (*,G), or (*,*,RP) entry, and
higher IP address than the recipient of the message, a Joiner- the sender of the Join/Prune has a higher IP address than the
bit in the multicast routing table entry is cleared to suppress recipient of the message, the Joiner-bit in the recipient's
further Join/Prune messages. A timer is set for the Joiner-bit; multicast routing table entry is cleared to suppress further
after it expires the Joiner-bit is set indicating further Join/Prune messages. A timer is set for the Joiner-bit; after it
periodic Join/Prunes should be sent for this entry. The Joiner- expires the recipient sets the Joiner-bit to resume further
bit timer is restarted each time a Join/Prune message is periodic Join/Prunes for this entry. The Joiner-bit timer is
received from a higher-IP-addressed PIM neighbor. restarted each time a Join/Prune message is received from a
higher-IP-addressed PIM neighbor.
[Page 12] 2.10 Unicast Routing Changes
2.9 Unicast Routing Changes
When unicast routing changes, an RPF check is done on all active When unicast routing changes, an RPF check is done on all active
(S,G), (*,G) and (*,*,RP) entries, and all affected expected (S,G), (*,G) and (*,*,RP) entries, and all affected expected
incoming interfaces are updated. In particular, if the new incoming interfaces are updated. In particular, if the new
incoming interface appears in the outgoing interface list, it is incoming interface appears in the outgoing interface list, it is
deleted from the outgoing interface list. The previous incoming deleted from the outgoing interface list. The previous incoming
interface may be added to the outgoing interface list by a interface may be added to the outgoing interface list by a
subsequent Join/Prune from downstream. Join/Prune messages subsequent Join/Prune from downstream. Join/Prune messages
received on the current incoming interface are ignored. received on the current incoming interface are ignored.
Join/Prune messages received on new interfaces or existing Join/Prune messages received on new interfaces or existing
skipping to change at line 552 skipping to change at page 15, line 7
iif(*,*,RP), then the router resets the SPT-bit. iif(*,*,RP), then the router resets the SPT-bit.
The router must send a Join/Prune message with S in the Join The router must send a Join/Prune message with S in the Join
list out its new incoming interface to inform upstream routers list out its new incoming interface to inform upstream routers
that it expects multicast datagrams over the interface. It may that it expects multicast datagrams over the interface. It may
also send a Join/Prune message with S in the Prune list out the also send a Join/Prune message with S in the Prune list out the
old incoming interface, if the link is operational, to inform old incoming interface, if the link is operational, to inform
upstream routers that this part of the distribution tree is upstream routers that this part of the distribution tree is
going away. going away.
2.10 Interaction with dense mode protocols such as DVMRP
The essential problem in connecting to dense mode protocols is
to pull all packets generated within the PIM-SM region down to
the dense mode routers. To do this, a special entry type,
referred to as (*,*,RP), is introduced. Every (*,*,RP) entry is
associated with a particular RP in the domain; that RP is used
to conduct RPF checks. Border routers initiate the building of
(*,*,RP) towards all internal Candidate RPs. (*,*,RP) entries
represent an aggregation of all the groups supported by the RP.
Most of the mechanisms needed to support interoperability with
dense mode protocols such as DVMRP are implemented in BRs, i.e.,
special routers that sit at the boundary between a PIM-SM
regions and the DVMRP regions and which speak both protocols.
However, all PIM-SM routers must be capable of supporting
(*,*,RP) state and interpreting associated Join messages.
Interaction with non-PIM-SM networks will be discussed in a
separate interoperability appendix.
[Page 13]
2.11 PIM-SM for Inter-Domain Multicast 2.11 PIM-SM for Inter-Domain Multicast
Future documents will address the use of PIM-SM as a backbone Future documents will address the use of PIM-SM as a backbone
inter-domain multicast routing protocol. Design choices center inter-domain multicast routing protocol. Design choices center
primarily around the distribution and usage of RP information primarily around the distribution and usage of RP information
for wide area, inter-domain groups. for wide area, inter-domain groups.
2.12 Security 2.12 Security
{ Editors Note: This section requires further work.}
All PIM control messages may use [5] to address security All PIM control messages may use [5] to address security
concerns. concerns. Security mechanisms are likely to be enhanced in the
near future.
[Page 14]
3 Detailed Protocol Description 3 Detailed Protocol Description
This section describes the protocol operations from the This section describes the protocol operations from the
perspective of an individual router implementation. In perspective of an individual router implementation. In
particular, for each message type we describe how it is particular, for each message type we describe how it is
generated and processed. generated and processed.
3.1 Query 3.1 Query
Query messages are sent so neighboring routers can discover each Query messages are sent so neighboring routers can discover each
skipping to change at line 633 skipping to change at page 17, line 5
3.1.3 Timing out neighbor entries 3.1.3 Timing out neighbor entries
A periodic process is run to time out PIM neighbors that have A periodic process is run to time out PIM neighbors that have
not sent queries. If the DR has gone down, a new DR is chosen by not sent queries. If the DR has gone down, a new DR is chosen by
scanning all neighbors on the interface and selecting the new DR scanning all neighbors on the interface and selecting the new DR
to be the one with the highest IP address. If an interface has to be the one with the highest IP address. If an interface has
gone down, the router may optionally time out all PIM neighbors gone down, the router may optionally time out all PIM neighbors
associated with the interface. associated with the interface.
[Page 15]
3.2 Join/Prune 3.2 Join/Prune
Join/Prune messages are sent to join or prune a branch off of Join/Prune messages are sent to join or prune a branch off of
the multicast distribution tree. A single message contains both the multicast distribution tree. A single message contains both
a join and prune list, either one of which may be null. Each a join and prune list, either one of which may be null. Each
list contains a set of source addresses, indicating the source- list contains a set of source addresses, indicating the source-
specific trees or shared tree that the router wants to join or specific trees or shared tree that the router wants to join or
prune. prune.
3.2.1 Sending Join/Prune Messages 3.2.1 Sending Join/Prune Messages
Join/Prune messages are merged such that a message sent to a Join/Prune messages are merged such that a message sent to a
particular upstream neighbor, N, includes all of the current particular upstream neighbor, N, includes all of the current
joined and pruned sources that are reached via N; according to joined and pruned sources that are reached via N; according to
unicast routing Join/Prune messages are multicast to all routers unicast routing Join/Prune messages are multicast to all routers
on multi-access networks with the target address set to the next on multi-access networks with the target address set to the next
hop router towards S or RP. Join/Prune messages are sent hop router towards S or RP. Join/Prune messages are sent
periodically. Currently the period is set to 60 seconds. [*] periodically. Currently the period is set to 60 seconds. [*]
A router sends a periodic Join/Prune message to each In addition, certain events cause triggered Join/Prune messages
distinct RPF neighbor associated with each (S,G), (*,G) and to be sent.
(*,*,RP) entry. Join/Prune messages are only sent if the RPF
neighbor is a PIM neighbor. A periodic Join/Prune message sent 3.2.1.1 Periodic Join/Prune Messages
towards a particular RPF neighbor is constructed as follows:
A router sends a periodic Join/Prune message to each distinct
RPF neighbor associated with each (S,G), (*,G) and (*,*,RP)
entry. Join/Prune messages are only sent if the RPF neighbor is
a PIM neighbor. A periodic Join/Prune message sent to a
particular RPF neighbor is constructed as follows:
1 Each router determines the RP for a (*,G) entry by using 1 Each router determines the RP for a (*,G) entry by using
the hash function described. The RP address (with RP and WC the hash function described. The RP address (with RP and WC
bits set) is included in the join list of a periodic bits set) is included in the join list of a periodic
Join/Prune message under the following conditions: Join/Prune message under the following conditions:
1 The Join/Prune message is being sent to the RPF 1 The Join/Prune message is being sent to the RPF
neighbor to the RP for an active (*,G) or (*,*,RP) neighbor toward the RP for an active (*,G) or (*,*,RP)
entry, and entry, and
2 The outgoing interface list in the (*,G) or (*,*,RP)
entry is non-NULL, or the router is the DR on the same
interface as the RPF neighbor.
_________________________ _________________________
[*] In the future we will introduce mechanisms to [*] In the future we will introduce mechanisms to
rate-limit this control traffic on a hop by hop basis, rate-limit this control traffic on a hop by hop basis,
in order to avoid excessive overhead on small links. in order to avoid excessive overhead on small links.
[Page 16] 2 The outgoing interface list in the (*,G) or (*,*,RP)
entry is non-NULL, or the router is the DR on the same
interface as the RPF neighbor.
2 A particular source address, S, is included in the join 2 A particular source address, S, is included in the join
list with the RP and WC bits cleared under the following list with the RP and WC bits cleared under the following
conditions: conditions:
1 The Join/Prune message is being sent to the RPF 1 The Join/Prune message is being sent to the RPF
neighbor to S, and neighbor toward S, and
2 There exists an active (S,G) entry with the RPbit 2 There exists an active (S,G) entry with the RPT-bit
cleared, and flag cleared, and
3 The oif list in the (S,G) entry is not null. 3 The oif list in the (S,G) entry is not null.
3 A particular source address, S, is included in the prune 3 A particular source address, S, is included in the prune
list with the RP and WC bits cleared under the following list with the RP and WC bits cleared under the following
conditions: conditions:
1 The Join/Prune message is being sent to the RPF 1 The Join/Prune message is being sent to the RPF
neighbor to S, and neighbor toward S, and
2 There exists an active (S,G) entry with the RPbit 2 There exists an active (S,G) entry with the RPT-bit
cleared, and flag cleared, and
3 The oif list in the (S,G) entry is null. 3 The oif list in the (S,G) entry is null.
4 A particular source address, S, is included in the prune 4 A particular source address, S, is included in the prune
list with the RP bit set and the WC bit cleared under the list with the RPT-bit set and the WC bit cleared under the
following conditions: following conditions:
1 The Join/Prune message is being sent to the RPF 1 The Join/Prune message is being sent to the RPF
neighbor toward the RP and there exists a (S,G) entry neighbor toward the RP and there exists a (S,G) entry
with the RPbit set and null oif list, or with the RPT-bit flag set and null oif list, or
2 The Join/Prune message is being sent to the RPF 2 The Join/Prune message is being sent to the RPF
neighbor toward the RP, there exists a (S,G) entry neighbor toward the RP, there exists a (S,G) entry
with the RPbit cleared and SPT-bit set, and the with the RPT-bit flag cleared and SPT-bit set, and the
incoming interface toward S is different than the incoming interface toward S is different than the
incoming interface toward the RP, or incoming interface toward the RP, or
3 The Join/Prune message is being sent to the RPF 3 The Join/Prune message is being sent to the RPF
neighbor toward the RP, and there exists a (*,G) entry neighbor toward the RP, and there exists a (*,G) entry
and (S,G) entry for a directly connected source. and (S,G) entry for a directly connected source.
[Page 17]
5 The RP address (with RP and WC bits set) is included in the 5 The RP address (with RP and WC bits set) is included in the
prune list if: prune list if:
1 The Join/Prune message is being sent to the RPF 1 The Join/Prune message is being sent to the RPF
neighbor toward the RP and there exists a (*,G) entry neighbor toward the RP and there exists a (*,G) entry
with a null oif list (see Section 3.5.2). with a null oif list (see Section 3.5.2).
In addition to these periodic messages, the following events 3.2.1.2 Triggered Join/Prune Messages
will trigger Join/Prune messages (the contents of triggered
messages are the same as the periodic, described above) In addition to periodic messages, the following events will
trigger Join/Prune messages (the contents of triggered messages
are the same as the periodic, described above):
1 Receipt of an IGMP Host-Membership-Report message for a 1 Receipt of an IGMP Host-Membership-Report message for a
group G will cause building or modifying corresponding group G will cause building or modifying corresponding
(*,G) state, and subsequent triggering of upstream (*,G) state, and subsequent triggering of upstream
Join/Prune messages as follows: Join/Prune messages as follows:
1 If the receiving router does not have a forwarding 1 If the receiving router does not have a forwarding
entry for G the router creates a (*,G) entry, with the entry for G the router creates a (*,G) entry, with the
interface upon which the IGMP Host-Membership-Report interface upon which the IGMP Host-Membership-Report
was received included in the oif list. The router was received included in the oif list. The router
sends a Join/Prune message towards the RP with the RP sends a Join/Prune message towards the RP with the RP
address and RP-bit and WC-bits set in the join list. A address and RPT-bit and WC-bits set in the join list.
timer is initiated for each interface in the oif list. A timer is initiated for each interface in the oif
Or, list. Or,
2 If the (*,G) already exists, the interface upon which 2 If the (*,G) already exists, the interface upon which
the IGMP Host-Membership-Report was received is added the IGMP Host-Membership-Report was received is added
to the oif list (if it was not included already) and to the oif list (if it was not included already) and
the timer for that interface is restarted. the timer for that interface is restarted.
2 Receipt of a Join/Prune message for (S,G), (*,G) or 2 Receipt of a Join/Prune message for (S,G), (*,G) or
(*,*,RP) will cause building or modifying corresponding (*,*,RP) will cause building or modifying corresponding
state, and subsequent triggering of upstream Join/Prune state, and subsequent triggering of upstream Join/Prune
messages, in the following cases: messages, in the following cases:
1 When there is no current forwarding entry, the RP 1 When there is no current forwarding entry, the RP
address included in the Join/Prune message is checked address included in the Join/Prune message is checked
against the local RP-Set information. If it matches, against the local RP-Set information. If it matches,
an entry will be created. If the router has no RP-Set an entry will be created. If the router has no RP-Set
[Page 18]
information it may discard the message, or optionally information it may discard the message, or optionally
use the RP address included in the message. use the RP address included in the message.
The new entry will in turn trigger an upstream The new entry will in turn trigger an upstream
Join/Prune message. Join/Prune message.
2 When the outgoing interface list of (S,G) RPbit entry 2 When the outgoing interface list of (S,G)RPT-bit entry
is null, the triggered Join/Prune message will contain is null, the triggered Join/Prune message will contain
S in the prune list. S in the prune list.
3 Receipt of a packet on a (S,G) entry whose SPT-bit is 3 Receipt of a packet that matches on a (S,G) entry whose
cleared triggers the following if the packet arrived on the SPT-bit is cleared triggers the following if the packet
correct incoming interface and there is a (*,G) or (*,*,RP) arrived on the correct incoming interface and there is a
entry with a different incoming RPF neighbor: a) setting of (*,G) or (*,*,RP) entry with a different incoming RPF
the SPT-bit on (S,G) entry, and b) sending a Join/Prune neighbor: a) the router sets the SPT-bit on the (S,G)
message towards the RP with S,RP-bit in the prune list if entry, and b) if the iif of the (S,G) entry is different
the iif of (S,G) is different from the iif of (*,G) or from the iif of the local (*,G) or (*,*,RP) entries, the
(*,*,RP). router sends a Join/Prune message towards the RP with S and
a set RPT-bit in the prune list.
4 When a Join/Prune message is received for a group G, the 4 When a Join/Prune message is received for a group G, the
prune list is checked. If it contains a source for which prune list is checked. If it contains a source for which
the receiving router has a corresponding active (S,G), the receiving router has a corresponding active (S,G),
(*,G) or (*,*,RP) entry, and whose iif is that on which (*,G) or (*,*,RP) entry, and whose iif is that on which
the Join/Prune was received, then a join for (S,G), (*,G) the Join/Prune was received, then a join for (S,G), (*,G)
or (*,*,RP) is triggered to override the prune, or (*,*,RP) is triggered to override the prune,
respectively. (This is necessary in the case of parallel respectively. (This is necessary in the case of parallel
downstream routers connected to a multi-access network.) downstream routers connected to a multi-access network.)
5 When the RP fails, the RP will not be included in the RP- 5 When the RP fails, the RP will not be included in the RP-
Set messages sent to the receivers' last-hop routers. This Set messages sent to all routers in that domain. This
triggers the last-hop routers to send (*,G) joins towards triggers the DRs to send (*,G) Join/Prune messages towards
the new RP for the group, as determined by the RP-Set and the new RP for the group, as determined by the RP-Set and
the hash function [*] the hash function [*]
_________________________
[*] PIM Multicast Border Routers (PMBRs), handling in-
teroperability functionality, trigger (*,*,RP) joins
towards each RP in the RP-Set.
[Page 19]
We do not trigger prunes onto interfaces for SM groups based on We do not trigger prunes onto interfaces for SM groups based on
data packets. Data packets that arrive on the wrong incoming data packets. Data packets that arrive on the wrong incoming
interface for an SM group are silently dropped. interface for an SM group are silently dropped.
It is possible that a Join/Prune message constructed according 3.2.1.3 Fragmentation
to the preceeding rules could exceed the MTU of a network. In It is possible that a Join/Prune message
this case, the message can undergo semantic fragmentation constructed according to the preceeding rules could exceed the
whereby information corresponding to different groups can be MTU of a network. In this case, the message can undergo semantic
sent in different messages. However, if a Join/Prune message fragmentation whereby information corresponding to different
must be fragmented the following rule must be followed: groups can be sent in different messages. However, if a
Join/Prune message must be fragmented the complete prune list
1 The complete prune list corresponding to a group G must be corresponding to a group G must be included in the same
included in the same Join/Prune message as the associated Join/Prune message as the associated RP-tree Join for G.
RP-tree Join for G.
3.2.2 Receiving Join/Prune Messages When a router receives a 3.2.2 Receiving Join/Prune Messages When a router receives a
Join/Prune message, it processes it as follows: Join/Prune message, it processes it as follows.
1 The receiver of the Join/Prune notes the interface on which The receiver of the Join/Prune notes the interface on which the
the PIM message arrived, call it I. The router accepts this PIM message arrived, call it I. The receiver then checks to see
Join/Prune message if this Join/Prune message is addressed if the Join/Prune message was addressed to the receiving router
to the router itself. If the Join/Prune is for this router itself (i.e., the router's address appears in the Unicast
the following actions are taken: Upstream Neighbor Router field of the the Join/Prune message)
[*] If the Join/Prune is for this router the following actions
are taken.
1 If an address Sj in the join list has RP-bit and WC- For each Sj in the join list of the Join/Prune message:
bit set, then Sj is the RP address used by the
downstream router and the following actions are taken:
1 If Sj is not the same as the receiving router's 1 If an address, Sj, in the join list of the Join/Prune
RP mapping for G, the receiving router may ignore messagehas the RPT-bit and WC-bit set, then Sj is the RP
that group entry in the Join/Prune message. If address used by the downstream router(s) and the following
the router does not have any RP-Set information, actions are taken:
it may use the address Sj included in the
Join/Prune message as the RP for the group.
2 If Sj is the same as the receiving router's RP 1 If Sj is not the same as the receiving router's RP
mapping for G, it adds I to the outgoing mapping for G, the receiving router may ignore the
interface list of the (*,G) forwarding entry and _________________________
[*] As described earlier, PMBRs trigger (*,*,RP) joins
towards each RP in the RP-Set.
[*] If the router is connected to a multiaccess LAN,
the message could be intended for a different router.
[Page 20] Join/Prune message with respect to that group entry.
sets the timer for that interface (if there is no If the router does not have any RP-Set information, it
(*,G) entry, the router creates one first). If a may use the address Sj included in the Join/Prune
(*,*,RP) exists, for the RP associated with G, message as the RP for the group.
then the oif list of the newly created (*,G) is
copied from that (*,*,RP) state, excluding
iif(*,G),
3 For each (Si,G) entry associated with group G, if 2 If Sj is the same as the receiving router's RP mapping
Si is not included in the prune list, and if I is for G, the receiving router adds I to the outgoing
not the iif then interface I is added to the interface list of the (*,G) forwarding entry and sets
oif list and the timers are restarted for that the timer for that interface (if there is no (*,G)
interface in each affected entry. If the G in the entry, the router creates one first). If a (*,*,RP)
join message is `*' [*] , then every (*,G) and entry exists, for the RP associated with G, then the
(S,G) entry, whose group address hashes to the RP oif list of the newly created (*,G) entry is copied
indicated in the (*,*,RP) join message, is from that (*,*,RP) entry.
updated accordingly,
4 If the (Si,G) entry is an RP-bit entry and its 3 For each (Si,G) entry associated with group G, if Si
oif list is the same as (*,G) oif list, is not included in the prune list, and if I is not the
then the (Si,G,RPbit) entry is deleted, iif then interface I is added to the oif list and
the timers are restarted for that interface in each
affected entry. If the group address in the Join/Prune
message is `*' then every (*,G) and (S,G) entry, whose
group address hashes to the RP indicated in the
(*,*,RP) Join/Prune message, is updated accordingly
[*]
5 The incoming interface is set to the interface 4 If the (Si,G) entry has its RPT-bit flag set to 1, and
used to send unicast packets to the RP in the its oif list is the same as the (*,G) oif
(*,G) forwarding entry, i.e., RPF interface to list, then the (Si,G)RPT-bit entry is deleted,
the RP.
2 For each address Si in the join list whose RP-bit and 5 The incoming interface is set to the interface used to
WC-bit are not set, and for which there is no send unicast packets to the RP in the (*,G) forwarding
existing (Si,G) forwarding entry, the router initiates entry, i.e., RPF interface toward the RP.
one.
2 For each address, Sj, in the join list whose RPT-bit and
WC-bit are not set, and for which there is no existing
(Sj,G) forwarding entry, the router initiates one.
[*] [*]
_________________________ _________________________
[*] A `*' in the group field of the Join/Prune is [*] A `*' in the group field of the Join/Prune is
represented by a group address 224.0.0.0 and a group represented by a group address 224.0.0.0 and a group
mask length of 4, indicating a (*,*,RP) Join. mask length of 4, indicating a (*,*,RP) Join.
[*] The router creates a (S,G) entry and copies all [*] The router creates a (S,G) entry and copies all
outgoing interfaces, excluding iif(S,G), from the 1 The outgoing interface for (Sj,G) is set to I. The
(S,G)RP-bit, (*,G), or (*,*,RP), entry, if it exists. incoming interface for (Sj,G) is set to the interface
If a router does not copy all outgoing interfaces from used to send unicast packets to Sj (i.e., the RPF
the (*,G), or (*,*,RP) entry, all receivers on RP-tree, neighbor).
downstream from outgoing interfaces other than the one
[Page 21] 2 If the interface, I, used to reach Sj, is the same as
1 The outgoing interface for (Si,G) is set to I. the outgoing interface being initialized, this
The incoming interface for (Si,G) is set to the represents an error (or a unicast routing change) and
interface used to send unicast packets to Si the Join/Prune should not be processed.
(i.e., the RPF neighbor).
2 If the interface used to reach Si is the same as 3 For each address, Sj, in the join list of the Join/Prune
the outgoing interface being built, I, this message, for which there is an existing (Sj,G) forwarding
represents an error and the Join/Prune should not entry,
be processed.
3 For any Si included in the join list of the Join/Prune 1 If the RPT-bit is not set for Sj listed in the
message, for which there is an existing (Si,G) Join/Prune message, but the RPT-bit flag is set on the
forwarding entry, existing (Sj,G) entry, the router clears the RPT-bit
flag on the (Sj,G) entry, sets the incoming interface
to point towards Sj for that (Sj,G) entry, and sends a
Join/Prune message corresponding to that entry through
the new incoming interface; and
1 If the RP-bit is not set for Si listed in the 2 If I is not the same as the existing incoming
Join/Prune message, but the RP-bit is set on the interface, the router adds I to the list of outgoing
existing (Si,G) entry, the router clears the RP- interfaces.
bit on (Si,G) entry, sets the incoming interface
to point towards Si for that (Si,G) entry, and
sends a Join/Prune to the new incoming interface;
and
2 The router adds I to the list of outgoing 3 The timer for I is restarted.
interfaces if I is not the same as the existing
incoming interface; the timer for I is restarted.
3 The (Si,G) SPT bit is initialized to be cleared 4 The (Sj,G) entry's SPT bit is cleared until data comes
until data comes down the shortest path tree. down the shortest path tree.
4 For each address Si in the prune list, with the RP-bit
is either set or cleared, and the WC-bit cleared:
_________________________ _________________________
newly added to (S,G), will not receive packets from outgoing interfaces from the (S,G)RPT-bit entry, if it
source S. Data packets of S arriving from the RP will exists. If there is no (S,G) entry, the oif list is
match the (S,G) entry instead of (*,G), or (*,*,RP), copied from the (*,G) entry; and if there is no (*,G)
entry, and will be dropped because the incoming inter- entry, the oif list is copied from the (*,*,RP) entry,
face is incorrect. if it exists. In all cases, the iif of the (S,G) entry
is always excluded from the oif list.
[Page 22]
1 If there is an existing (Si,G) forwarding entry,
the router schedules a deletion of I from the
list of outgoing interfaces by lowering that oif
timer to 5 seconds (unless it is already lower).
The deletion is not executed until this timer
expires, allowing for other downstream routers on
a multi-access LAN to override the prune.
2 If the router has a current (*,G), or (*,*,RP), For each Sp in the prune list of the Join/Prune message:
forwarding entry, and if a (Si,G)RP-bit entry
also exists then the (Si,G)RP-bit entry is
maintained even if its outgoing interface list is
null.
5 For any Si in the prune list that has the RP-bit set, 1 For each address, Sp, in the prune list whose RPT-bit and
and the WC-bit cleared: WC-bit are cleared:
1 If (*,G), or corresponding (*,*,RP), state 1 If there is an existing (Sp,G) forwarding entry, the
exists, but there is no (Si,G) entry, an router schedules a deletion of I from the list of
(Si,G)RP-bit entry is created . The outgoing outgoing interfaces by lowering that oif timer to 5
interface list is copied from the (*,G), or seconds (unless it is already lower). The deletion is
(*,*,RP), entry, with the interface, I, on which not executed until this timer expires, allowing for
the prune was received deleted. Packets from the other downstream routers on a multi-access LAN to
pruned source, Si, match on this state and are override the prune.
not forwarded toward the pruned receivers.
2 If there exists a (Si,G) entry, with or without 2 If the router has a current (*,G), or (*,*,RP),
the RPbit set, the iif on which the prune was forwarding entry, and if the existing (Sp,G) entry has
received, I, is deleted from the oif list, its RPT-bit flag set to 1, then this (Sp,G)RPT-bit
and the entry timer is restarted. entry is maintained (not deleted) even if its outgoing
interface list is null.
6 For each address Si in the prune list, with the RP-bit 2 For each address, Sp, in the prune list whose RPT-bit is
and the WC-bit set: set and whose WC-bit cleared:
[Page 23] 1 If there is an existing (Sp,G) forwarding entry, the
1 If there is an existing (*,G) entry, with Si as router schedules a deletion of I from the list of
the RP for G, the router schedules a deletion of outgoing interfaces by lowering that oif timer to 5
I from the list of outgoing interfaces by seconds (unless it is already lower). The deletion is
lowering that oif timer to 5 seconds (unless it not executed until this timer expires, allowing for
is already lower). The deletion is not executed other downstream routers on a multi-access LAN to
until this timer expires, allowing for other
downstream routers on a multi-access LAN to
override the prune. override the prune.
2 If the corresponding (*,*,RP) state exists, but 2 If the router has a current (*,G), or (*,*,RP),
there is no (*,G) entry, a (*,G) entry is forwarding entry, and if the existing (Sp,G) entry has
created. The outgoing interface list is copied its RPT-bit flag set to 1, then this (Sp,G)RPT-bit
from (*,*,RP) entry, with the interface, I, on entry is maintained (not deleted) even if its outgoing
which the prune was received, deleted. interface list is null.
3 If there exists a (*,G) entry, the interface on 3 If (*,G), or corresponding (*,*,RP), state exists, but
which the prune was received, I, is deleted from there is no (Sp,G) entry, an (Sp,G)RPT-bit entry is
the oif list, and the entry timer is created . The outgoing interface list is copied from
restarted. the (*,G), or (*,*,RP), entry, with the interface, I,
on which the prune was received, is deleted. Packets
from the pruned source, Sp, match on this state and
are not forwarded toward the pruned receivers.
2 If the received Join/Prune does not indicate the router as 4 If there exists a (Sp,G) entry, with or without the
its target, then if the Join/Prune is for a (S,G) pair for RPT-bit set, the iif on which the prune was received,
which the router has an active (S,G) entry, and if the I, is deleted from the oif list, and the entry
Join/Prune arrived on the iif for that entry, then the timer is restarted.
router compares the IP address of the generator of the
Join/Prune, to its own IP address.
1 If its own IP address is higher, the Joiner-bit in the 3 For each address, Sp, in the prune list whose RPT-bit and
(S,G) entry is set. WC-bit are both set:
2 If its own IP address is lower, the Joiner-bit in the 1 If there is an existing (*,G) entry, with Sp as the RP
(S,G) entry is cleared, and the Joiner-bit timer is for G, the router schedules a deletion of I from the
activated. list of outgoing interfaces by lowering that oif timer
to 5 seconds (unless it is already lower). The
deletion is not executed until this timer expires,
allowing for other downstream routers on a multi-
access LAN to override the prune.
After the timer expires the Joiner-bit is set indicating 2 If the corresponding (*,*,RP) state exists, but there
further periodic Join/Prunes should be sent for this entry. is no (*,G) entry, a (*,G) entry is created. The
The Joiner-bit timer is restarted each time a Join/Prune outgoing interface list is copied from (*,*,RP) entry,
message is received from a higher-IP-addressed PIM with the interface, I, on which the prune was
received, deleted.
[Page 24] 3 If there exists a (*,G) entry, the interface on which
neighbor. the prune was received, I, is deleted from the oif
list, and the entry timer is restarted.
For any new (S,G), (*,G) or (*,*,RP) entry created by an For any new (S,G), (*,G) or (*,*,RP) entry created by an
incoming Join/Prune message, the Joiner-bit is set and the incoming Join/Prune message, the Joiner-bit is initialized
SPT-bit is cleared. to 1 and the SPT-bit is cleared.
If the received Join/Prune does not indicate the router as its
target, then if the Join/Prune matches an existing (S,G), (*,G),
or (*,*,RP) entry and the Join/Prune arrived on the iif for
that entry, then the router compares the IP address of the
generator of the Join/Prune, to its own IP address and sets the
Joiner-bit as follows.
1 If its own IP address is higher, the Joiner-bit in the
entry is set.
2 If its own IP address is lower, the Joiner-bit in the entry
is cleared, and the Joiner-bit timer is activated.
After the timer expires the Joiner-bit is set indicating further
periodic Join/Prunes should be sent for this entry. The Joiner-
bit timer is restarted each time a Join/Prune message is
received from a higher-IP-addressed PIM neighbor.
3.3 Register and Register-Stop 3.3 Register and Register-Stop
When a source first starts sending to a group its packets are When a source first starts sending to a group its packets are
encapsulated in Register messages and sent to the RP. If the encapsulated in Register messages and sent to the RP. If the
data rate warrants source-specific paths, the RP sets up source data rate warrants source-specific paths, the RP sets up source
specific state and starts sending (S,G) Join/Prune messages specific state and starts sending (S,G) Join/Prune messages
toward the source. toward the source, with S in the join list.
3.3.1 Sending Registers and Receiving Register-Stops 3.3.1 Sending Registers and Receiving Register-Stops
Register messages are sent as follows: Register messages are sent as follows:
1 When a DR receives a packet from a directly connected 1 When a DR receives a packet from a directly connected
source, S [*] : source, S [*] :
1 If there is no corresponding (S,G) entry, and the 1 If there is no corresponding (S,G) entry, and the
_________________________
[*] When a PMBR (e.g., a router that connects the PIM-
SM region to a dense mode region running DVMRP or PIM-
DM) receives a packet from a source in the dense mode
region, the router treats the packet as if it were from
a directly connected source. A separate document will
describe the details of interoperabiity.
router has RP-Set information, the DR creates one with router has RP-Set information, the DR creates one with
the Register-bit set to 1 and the RP address set the Register-bit set to 1 and the RP address set
according to the hash function mapping for the according to the hash function mapping for the
corresponding group. The Register-bit-timer is corresponding group. The Register-bit-timer is
initialized to zero; the Register-bit-timer is non- initialized to zero; the Register-bit-timer is non-
zero only when the Register-bit is set to 0. zero only when the Register-bit is set to 0.
2 If there is a (S,G) entry in existence, the DR simply 2 If there is a (S,G) entry in existence, the DR simply
restarts the corresponding S-timer (entry timer). restarts the corresponding S-timer (entry timer).
_________________________
[*] When a border router (e.g., a router that connects
the PIM-SM region to a dense mode region running DVMRP
or PIM-DM) receives a packet from a source in the dense
mode region, the router treats the packet as if it were
from a directly connected source. See the Appendix on
Interoperability for more details.
[Page 25]
2 If the new or previously-existing (S,G) entry has the 2 If the new or previously-existing (S,G) entry has the
Register-bit set, the data packet is encapsulated in a Register-bit set, the data packet is encapsulated in a
Register message and unicast to the RP for that group. The Register message and unicast to the RP for that group. The
data packet is also forwarded according to (S,G) state in data packet is also forwarded according to (S,G) state in
the DR if the oif list is not null; since a receiver may the DR if the oif list is not null; since a receiver may
join the SP-tree while the DR is still registering to the join the SP-tree while the DR is still registering to the
RP. RP.
3 If the (S,G) entry has the Register-bit cleared, the data 3 If the (S,G) entry has the Register-bit cleared, the data
packet is not sent in a Register message, it is just packet is not sent in a Register message, it is just
forwarded according to the (S,G) oif list. forwarded according to the (S,G) oif list.
The DR processes Register-Stop messages as follows: When the DR receives a Register-Stop message it clears the
Register-bit and restarts the Register-bit-timer in the
1 The DR clears the Register-bit and restarts the Register- corresponding (S,G) entry(ies).
bit-timer in the corresponding (S,G) entry(ies).
When a Register-bit-timer expires, the corresponding entry(ies) When a Register-bit-timer expires, the corresponding entry(ies)
Register-bit is set to 1 to reinstigate encapsulation of data Register-bit is set to 1 to reinstigate encapsulation of data
packets in Register messages. packets in Register messages.
3.3.2 Receiving Register Messages and Sending Register-Stops 3.3.2 Receiving Register Messages and Sending Register-Stops
When a router (i.e., the RP) receives a Register message, the When a router (i.e., the RP) receives a Register message, the
router does the following: router does the following:
1 Decapsulates the data packet, and checks for a 1 Decapsulates the data packet, and checks for a
corresponding (S,G) entry. corresponding (S,G) entry.
1 If a (S,G) entry exists, the packet is forwarded but 1 If a (S,G) entry exists, the packet is forwarded but
the SPT bit is left cleared (0). If the SPT bit is 1, the SPT bit is left cleared (0). If the SPT bit is 1,
the packet is dropped, and Register-Stop messages are the packet is dropped, and Register-Stop messages are
triggered. Register-Stops are rate limited. [*] triggered. Register-Stops are rate limited. [*]
_________________________
[*] Register-Stops should be rate limited so that no
more than a few are sent per round trip time. This
[Page 26]
2 If there is no (S,G) entry, but there is a (*,G) 2 If there is no (S,G) entry, but there is a (*,G)
entry, or a (*,*,RP) entry with the RP corresponding entry, or a (*,*,RP) entry with the RP corresponding
to G, the packet is forwarded according to that entry. to G, the packet is forwarded according to that entry.
3 If there is a (*,*,RP) entry but no (*,G) entry, a 3 If there is a (*,*,RP) entry but no (*,G) entry, a
(*,G) or (S,G) entry is created and the oif is copied (*,G) or (S,G) entry is created and the oif is copied
from the (*,*,RP) entry to the new entry. from the (*,*,RP) entry to the new entry.
4 If there is no G or (*,*,RP) entry corresponding to G, 4 If there is no G or (*,*,RP) entry corresponding to G,
the packet is dropped, and a Register-Stop is the packet is dropped, and a Register-Stop is
triggered. triggered.
5 A ``Border bit'' bit is added to the Register message, 5 A ``Border bit'' bit is added to the Register message,
to facilitate interoperability mechanisms. PIM MBRs to facilitate interoperability mechanisms. PMBRs set
set this bit when registering for external sources this bit when registering for external sources (see
(see Sections 2.10 and 6). If the ``Border bit'' is Section 2.7). If the ``Border bit'' is set in the
set in the Register, the RP does the following: Register, the RP does the following:
1 If there is no matching (S,G) state, the RP 1 If there is no matching (S,G) state, the RP
creates one, with a `PMBR' field. This field creates one, with a `PMBR' field. This field
holds the source of the Register (i.e. the outer holds the source of the Register (i.e. the outer
IP address of the register packet). The RP IP address of the register packet). The RP
triggers a (S,G) join towards the source of the triggers a (S,G) join towards the source of the
data packet, and clears the SPT bit for the (S,G) data packet, and clears the SPT bit for the (S,G)
entry, else entry, else
_________________________
[*] Register-Stops should be rate limited so that no
more than a few are sent per round trip time. This
prevents a high datarate stream of packets from
triggering a large number of Register-stop messages
between the time that the first packet is received and
the time when the source receives the first Register-
Stop.
2 If the `PMBR' field for the corresponding (S,G) 2 If the `PMBR' field for the corresponding (S,G)
entry matches the source of the Register packet, entry matches the source of the Register packet,
the decapsulated packet is forwarded to the oif the decapsulated packet is forwarded to the oif
list of that entry, else list of that entry, else
3 The packet is dropped, and a Register-stop is 3 The packet is dropped, and a Register-stop is
triggered towards the source of the Register. triggered towards the source of the Register.
_________________________
prevents a high datarate stream of packets from
triggering a large number of Register-stop messages
between the time that the first packet is received and
the time when the source receives the first Register-
Stop.
[Page 27]
The (S,G) state timer is restarted by Registers arriving The (S,G) state timer is restarted by Registers arriving
from that source to that group. from that source to that group.
2 If the matching (S,G) or (*,G) state contains a null oif 2 If the matching (S,G) or (*,G) state contains a null oif
list, the RP unicasts a Register-Stop message to the source list, the RP unicasts a Register-Stop message to the source
of the Register message; in the latter case, the source- of the Register message; in the latter case, the source-
address field, within the Register-Stop message, is set to address field, within the Register-Stop message, is set to
the wildcard value (all 0's). This message is not processed the wildcard value (all 0's). This message is not processed
by intermediate routers, hence no (S,G) state is by intermediate routers, hence no (S,G) state is
constructed between the RP and the source. constructed between the RP and the source.
skipping to change at line 1151 skipping to change at page 30, line 5
entry causes the RP to send a Join/Prune message for the entry causes the RP to send a Join/Prune message for the
indicated group towards the source of the register message. indicated group towards the source of the register message.
If the (S,G) oif list becomes null, Join/Prune messages If the (S,G) oif list becomes null, Join/Prune messages
will not be sent towards the source, S. will not be sent towards the source, S.
3.4 Multicast Data Packet Forwarding 3.4 Multicast Data Packet Forwarding
Processing a multicast data packet involves the following steps: Processing a multicast data packet involves the following steps:
1 Lookup forwarding state based on a longest match 1 Lookup forwarding state based on a longest match of the
[*] source address, and an exact match of the destination
address in the data packet. If neither S, nor G, find a
of the source address, and an exact match of the longest match entry, and the RP for the packet's
destination address in the data packet and compare the RPF destination group address has a corresponding (*,*,RP)
check on the source address in the packet header with the entry, then the longest match does not require an exact
_________________________ match on the destination group address. In summary, the
[*] The longest match is performed in the following longest match is performed in the following order: (1)
order: (1) (S,G), (2) (*,G). If neither is matched, (S,G), (2) (*,G). If neither is matched, then a lookup is
then a lookup is performed on (*,*,RP) entries. performed on (*,*,RP) entries.
[Page 28]
iif specified in the forwarding entry.
2 If the packet arrived on the interface found in the 2 If the packet arrived on the interface found in the
matching-entry's iif field, and the oif list is not matching-entry's iif field, and the oif list is not
null: null:
1 Forward the packet to the oif list for that entry 1 Forward the packet to the oif list for that entry
and restarted the entry's timer if the matching entry and restarted the entry's timer if the matching entry
is (S,G) [*] is (S,G) [*]
2 If the entry is a (S,G) entry with a cleared SPT-bit, 2 If the entry is a (S,G) entry with a cleared SPT-bit,
and a (*,G) or associated (*,*,RP) also exists whose and a (*,G) or associated (*,*,RP) also exists whose
incoming interface is different than that for (S,G), incoming interface is different than that for (S,G),
set the SPT-bit for the (S,G) entry and trigger an set the SPT-bit for the (S,G) entry and trigger an
(S,G) RP-bit prune towards the RP. (S,G) RPT-bit prune towards the RP.
3 If the source of the packet is a directly-connected 3 If the source of the packet is a directly-connected
host and the router is the DR on a multi-access host and the router is the DR on a multi-access
network, check the Register-bit associated with the network, check the Register-bit associated with the
(S,G) entry. If it is set, then the router (S,G) entry. If it is set, then the router
encapsulates the data packet in a register message and encapsulates the data packet in a register message and
sends it to the RP. sends it to the RP.
This covers the common case of a packet arriving on the RPF This covers the common case of a packet arriving on the RPF
interface to the source or RP and being forwarded to all interface to the source or RP and being forwarded to all
joined branches. It also detects when packets arrive on the joined branches. It also detects when packets arrive on the
SP-tree, and triggers their pruning from the RP-tree. If it SP-tree, and triggers their pruning from the RP-tree. If it
_________________________
[*] Optionally, the (S,G) timer may be restarted by
periodic checking of the matching packet count.
is the DR for the source, it sends data packets is the DR for the source, it sends data packets
encapsulated in Registers to the RPs. encapsulated in Registers to the RPs.
3 If the packet matches to an entry but did not arrive on the 3 If the packet matches to an entry but did not arrive on the
interface found in the entry's iif field, check the interface found in the entry's iif field, check the
SPT-bit of the entry. If the SPT-bit is set, drop the SPT-bit of the entry. If the SPT-bit is set, drop the
packet. If the SPT-bit is cleared, then lookup the (*,G), packet. If the SPT-bit is cleared, then lookup the (*,G),
or (*,*,RP), entry for G. If the packet arrived on the or (*,*,RP), entry for G. If the packet arrived on the
_________________________
[*] Optionally, the (S,G) timer may be restarted by
periodic checking of the matching packet count.
[Page 29]
iif found in (*,G), or the corresponding (*,*,RP), iif found in (*,G), or the corresponding (*,*,RP),
forward the packet to the oif list of the matching forward the packet to the oif list of the matching
entry. This covers the case when a data packet matches on a entry. This covers the case when a data packet matches on a
(S,G) entry for which the SP-tree has not yet been (S,G) entry for which the SP-tree has not yet been
completely established upstream. completely established upstream.
4 If the packet does not match to any entry, but the source 4 If the packet does not match to any entry, but the source
of the data packet is a local, directly-connected host, and of the data packet is a local, directly-connected host, and
the router is the DR on a multi-access LAN and has RP-Set the router is the DR on a multi-access LAN and has RP-Set
information, the DR uses the hash function to determine the information, the DR uses the hash function to determine the
skipping to change at line 1246 skipping to change at page 32, line 13
router initiates `source-specific' data rate counters for the router initiates `source-specific' data rate counters for the
following data packets. Then, each counter for a source, is following data packets. Then, each counter for a source, is
incremented when packets matching on (*,G), or (*,*,RP), are incremented when packets matching on (*,G), or (*,*,RP), are
received from that source. If the data rate from the particular received from that source. If the data rate from the particular
source exceeds a configured threshold (t2), a (S,G) entry is source exceeds a configured threshold (t2), a (S,G) entry is
created and a Join/Prune message is sent towards the source. If created and a Join/Prune message is sent towards the source. If
the RPF interface for (S,G) is the RPF interface for (S,G) is
not the same as that for (*,G) -or (*,*,RP), then the SPT-bit not the same as that for (*,G) -or (*,*,RP), then the SPT-bit
is cleared in the (S,G) entry. is cleared in the (S,G) entry.
[Page 30]
Other configured rules may be enforced to cause or prevent Other configured rules may be enforced to cause or prevent
establishment of (S,G) state. establishment of (S,G) state.
3.5 Assert 3.5 Assert
Asserts are used to resolve which of the parallel routers Asserts are used to resolve which of the parallel routers
connected to a multi-access LAN is responsible for forwarding connected to a multi-access LAN is responsible for forwarding
packets onto the LAN. packets onto the LAN.
3.5.1 Sending Asserts 3.5.1 Sending Asserts
skipping to change at line 1270 skipping to change at page 32, line 36
(S,G) entry: (S,G) entry:
1 Do unicast routing table lookup on source IP address from 1 Do unicast routing table lookup on source IP address from
data packet, and send assert on interface for source IP data packet, and send assert on interface for source IP
address in data packet; include metric preference of address in data packet; include metric preference of
routing protocol and metric from routing table lookup. routing protocol and metric from routing table lookup.
2 If route is not found, use metric preference of 0x7fffffff 2 If route is not found, use metric preference of 0x7fffffff
and metric 0xffffffff. and metric 0xffffffff.
3 When an assert is sent for a (*,G) entry, the first bit in When an assert is sent for a (*,G) entry, the first bit in the
the metric preference (the RP-bit) is set to 1, indicating metric preference (the RPT-bit) is set to 1, indicating the data
the data packet is routed down the RP-tree. packet is routed down the RP-tree.
Asserts are rate-limited by the router. Asserts are rate-limited by the router.
3.5.2 Receiving Asserts 3.5.2 Receiving Asserts
When an assert is received the router performs a longest match When an assert is received the router performs a longest match
on the source and group address in the assert message. The on the source and group address in the assert message. The
router checks the first bit of the metric preference (RP-bit). router checks the first bit of the metric preference (RPT-bit).
If the RP-bit is set, the router does a match on (*,G), or
(*,*,RP), entries, otherwise, the router matches (S,G) entries. 1 If the RPT-bit is set, the router first does a match on
If the matching entry is (*,*,RP), the router creates a (*,G) (*,G), or (*,*,RP), entries; if no matching entry is found,
entry. the router matches (S,G) entries.
2 If the RPT-bit is not set in the Assert, the router first
does a match on (S,G) entries; if no matching entry is
found, the router matches (*,G) or (*,*,RP) entries.
3.5.2.1 Receiving Asserts on an entry's outgoing interface
[Page 31]
If the interface that received the Assert message is in the If the interface that received the Assert message is in the
oif list of the matched entry, then this assert should be oif list of the matched entry, then this assert should be
processed by this router as follows: processed by this router as follows:
1 Compare the metric received in the Assert with the one the 1 If the Assert's RPT-bit is set and the matching entry is
(*,*,RP), the router creates a (*,G) entry. If the Assert's
RPT-bit is cleared and the matching entry is (*,G), or
(*,*,RP), the router creates a (S,G)RPT-bit entry.
2 Compare the metric received in the Assert with the one the
router would have advertised in an assert. The metric router would have advertised in an assert. The metric
preference should be treated as the high-order part of an preference should be treated as the high-order part of an
assert metric comparison. If the value in the assert is assert metric comparison. If the value in the assert is
less than the router's value, delete the interface from the less than the router's value, delete the interface from the
entry. If the value is the same, compare IP addresses, if entry. If the value is the same, compare IP addresses, if
the routers address is less than the assert sender, delete the routers address is less than the assert sender, delete
the interface. the interface.
2 If the router has won the election and there are directly 3 If the router has won the election and there are directly
connected members on the multi-access LAN, the router keeps connected members on the multi-access LAN, the router keeps
the interface in its outgoing interface list. It acts as the interface in its outgoing interface list. It acts as
the forwarder for the LAN. the forwarder for the LAN.
3 If the router won the election but there are no directly 4 If the router won the election but there are no directly
connected members on the multi-access LAN, the router connected members on the multi-access LAN, the router
schedules to delete the interface. The LAN might be a stub schedules to delete the interface. The LAN might be a stub
LAN with no members (and no downstream routers). If no LAN with no members (and no downstream routers). If no
subsequent Join/Prunes are received, the router deletes the subsequent Join/Prunes are received, the router deletes the
interface from the outgoing interface list; otherwise it interface from the outgoing interface list; otherwise it
keeps the interface in its outgoing interface and acts as keeps the interface in its outgoing interface and acts as
the forwarder for the LAN. the forwarder for the LAN.
The winning router should send out an assert message including The winning router should send out an assert message including
its own metric to that outgoing interface. This will cause other its own metric to that outgoing interface. This will cause other
routers on the LAN to prune that interface from their forwarding routers on the LAN to prune that interface from their forwarding
entries. entries.
Note that when an Assert is received, the router performs an 3.5.2.2 Receiving Asserts on an entry's incoming interface
exact match based on the source address, group address and the
RP-bit of the metric preference in the assert message. This is
not a longest match; only exact state will be matched. If there
is no such state, then the router drops the Assert message.
Otherwise, If the interface that received the Assert matches the
incoming interface of the exactly matched entry, then the Assert
message is processed as follows:
1 Downstream routers will select the upstream router with the If the Assert arrived on the incoming interface of an existing
(S,G), (*,G), or (*,*,RP) entry, the Assert is processed as
follows. If the Assert message does not match the entry,
exactly, it is ignored; i.e, longest-match is not used in this
case. If the Assert message does match exactly, then:
[Page 32] 1 Downstream routers will select the upstream router with the
smallest metric as their RPF neighbor. If two metrics are smallest metric as their RPF neighbor. If two metrics are
the same, the highest IP address is chosen to break the the same, the highest IP address is chosen to break the
tie. [*] tie. [*]
2 If the downstream routers have downstream members, they 2 If the downstream routers have downstream members, they
must schedule a join to inform the upstream router that must schedule a join to inform the upstream router that
packets should be forwarded on the multi-access network. packets should be forwarded on the multi-access network.
This will cause the upstream forwarder to cancel its This will cause the upstream forwarder to cancel its
scheduled deletion of the interface.
_________________________ _________________________
[*] This is important so that downstream routers send [*] This is important so that downstream routers send
subsequent Joins/Prunes (in SM) to the correct neigh- subsequent Joins/Prunes (in SM) to the correct neigh-
bor. An Assert timer is initiated when changing the RPF bor. An Assert timer is initiated when changing the RPF
neighbor to the Assert winner. When the timer expires neighbor to the Assert winner. When the timer expires
the router resets its RPF neighbor according to its un- the router resets its RPF neighbor according to its un-
icast routing tables to capture failures of the Assert icast routing tables to capture failures of the Assert
winner. winner.
[Page 33] scheduled deletion of the interface.
3.6 Candidate-RP-Advertisements and RP-Set messages 3.6 Candidate-RP-Advertisements and RP-Set messages
Candidate-RP-Advertisements (C-RP-Advs) are periodic PIM Candidate-RP-Advertisements (C-RP-Advs) are periodic PIM
messages unicast by those routers that are configured as messages unicast by those routers that are configured as
Candidate-RPs (C-RPs). Candidate-RPs (C-RPs).
RP-Set messages are periodic PIM messages originated by the RP-Set messages are periodic PIM messages originated by the
Bootstrap router (BSR) within a domain, and forwarded hop-by-hop Bootstrap router (BSR) within a domain, and forwarded hop-by-hop
to distribute the current RP-set to all routers in that domain. to distribute the current RP-set to all routers in that domain.
The RP-Set messages also support a simple mechanism by which the The RP-Set messages also support a simple mechanism by which the
Candidate BSR (C-BSR) with the highest BSR-priority and IP Candidate BSR (C-BSR) with the highest BSR-priority and IP
address (referred to as the preferred BSR) is elected as the BSR address (referred to as the preferred BSR) is elected as the BSR
for the domain [*] for the domain [*] Sections 3.6.2 and 3.6.3 describe the
combined function of RP-Set messages as the vehicle for BSR
election and RP-Set distribution.
_________________________
[*] We recommend that each router configured as a C-RP
also be configured as a C-BSR.
3.6.1 Sending Candidate-RP-Advertisements 3.6.1 Sending Candidate-RP-Advertisements
C-RPs periodically unicast C-RP-Advs to the BSR for that domain. C-RPs periodically unicast C-RP-Advs to the BSR for that domain.
The interval for sending these messages is subject to local The interval for sending these messages is subject to local
configuration at the C-RP. A recommended default value is 60 configuration at the C-RP. A recommended default value is 60
seconds. seconds.
Candidate-RP-Advertisements carry group address and group mask Candidate-RP-Advertisements carry group address and group mask
fields. This enables the advertising router to limit the fields. This enables the advertising router to limit the
skipping to change at line 1390 skipping to change at page 36, line 30
Upon receiving a C-RP-Adv, a router does the following: Upon receiving a C-RP-Adv, a router does the following:
1 If the router is not the elected BSR, it ignores the 1 If the router is not the elected BSR, it ignores the
message, else message, else
2 The BSR adds the RP address to its local pool of candidate 2 The BSR adds the RP address to its local pool of candidate
RPs, according to the associated group prefix(es) in the RPs, according to the associated group prefix(es) in the
C-RP-Adv message [*] The BSR may override the prefix C-RP-Adv message [*] The BSR may override the prefix
indicated in a C-RP-Adv. indicated in a C-RP-Adv.
_________________________
[*] We recommend that each router configured as a C-RP
also be configured as a C-BSR.
[*] The BSR may apply a local policy to limit the
number of Candidate RPs included in the RP-Set message.
[Page 34]
The BSR keeps an RP-timer per RP in its local RP-set. The RP- The BSR keeps an RP-timer per RP in its local RP-set. The RP-
timer is initialized to three times the holdtime in the RP's C- timer is initialized to the holdtime in the RP's C-RP-Adv. When
RP-Adv. When the timer expires, the corresponding RP is removed the timer expires, the corresponding RP is removed from the RP-
from the RP-set. The RP-timer is restarted by the C-RP-Advs from set. The RP-timer is restarted by the C-RP-Advs from the
the corresponding RP. corresponding RP.
The BSR also keeps an RP-Set timer to send RP-Set messages The BSR also keeps an RP-Set timer to send RP-Set messages
periodically. In particular, when the RP-Set timer expires, the periodically. In particular, when the RP-Set timer expires, the
BSR originates an RP-Set message on each of its interfaces. The BSR originates an RP-Set message on each of its PIM interfaces.
message is sent with a TTL of 1 to the `ALL-PIM-ROUTERS' group. The message is sent with a TTL of 1 to the `ALL-PIM-ROUTERS'
In steady state, the BSR originates RP-Set messages every 60 group. In steady state, the BSR originates RP-Set messages every
seconds. At startup, the RP-Set timer is initialized to 180 60 seconds. At startup, the RP-Set timer is initialized to 180
seconds, causing the first RP-Set message to be originated after seconds, causing the first RP-Set message to be originated after
180 seconds, when/if the timer expires. For timer details see 180 seconds, when/if the timer expires. For timer details see
Section 3.6.3. A DR unicasts an RP-Set message to new PIM Section 3.6.3. A DR unicasts an RP-Set message to new PIM
neighbors starting up, after receiving their Query messages. neighbors starting up, after receiving their Query messages.
_________________________
[*] The BSR may apply a local policy to limit the
number of Candidate RPs included in the RP-Set message.
(since after DR election the new neighbor may become the new (since after DR election the new neighbor may become the new
DR.) DR.)
The RP-Set message is subdivided into sets of group-prefix,RP- The RP-Set message is subdivided into sets of group-prefix,RP-
Count,RP-addresses. The format of the RP-Set message allows Count,RP-addresses. The format of the RP-Set message allows
`semantic fragmentation', if the length of the original RP-Set `semantic fragmentation', if the length of the original RP-Set
message exceeds the packet maximum boundaries (see Section 4). message exceeds the packet maximum boundaries (see Section 4).
However, we recommend against configuring a large number of However, we recommend against configuring a large number of
routers as C-RPs, to reduce the semantic fragmentation required. routers as C-RPs, to reduce the semantic fragmentation required.
skipping to change at line 1441 skipping to change at page 37, line 33
1 If the message was not sent by the RPF neighbor towards the 1 If the message was not sent by the RPF neighbor towards the
BSR address included, the message is dropped. Else BSR address included, the message is dropped. Else
2 If the included BSR is not preferred over, and not equal 2 If the included BSR is not preferred over, and not equal
to, the currently active BSR: to, the currently active BSR:
1 If the RP-Set timer is not yet expired, or if the 1 If the RP-Set timer is not yet expired, or if the
receiving router is a C-BSR, then the RP-Set message receiving router is a C-BSR, then the RP-Set message
is dropped. Else is dropped. Else
2 The RP-Set timer is expired and the receiving router 2 The RP-Set timer has expired and the receiving router
is not a C-BSR, so the receiving router stores the
[Page 35] RP-Set and BSR address and priority found in the
is message, and restarts the timer with its maximum
value. The RP-Set message is then forwarded out all
not a C-BSR, so the receiving router stores the RP-Set PIM interfaces, excluding the one over which the
and BSR address found in the message. The RP-Set message arrived, to `ALL-PIM-ROUTERS' group, with a
message is then forwarded out all PIM interfaces, TTL of 1.
excluding the one over which the message arrived, to
`ALL-PIM-ROUTERS' group, with a TTL of 1.
3 If the RP-Set message includes a BSR address that is 3 If the RP-Set message includes a BSR address that is
preferred over, or equal to, the currently active BSR, the preferred over, or equal to, the currently active BSR, the
router resets its RP-Set timer to 180 seconds, and stores router resets its RP-Set timer to 180 seconds, and stores
the BSR address and RP-Set information. The RP-Set message the BSR address and RP-Set information. The RP-Set message
is then forwarded out all PIM interfaces, excluding the one is then forwarded out all PIM interfaces, excluding the one
over which the message arrived, to `ALL-PIM-ROUTERS' group, over which the message arrived, to `ALL-PIM-ROUTERS' group,
with a TTL of 1. with a TTL of 1.
If the receiving router has no current RP set information and 4 If the receiving router has no current RP set information
the RP-set was unicast to it from a directly connected neighbor, and the RP-set was unicast to it from a directly connected
the router stores the information as its new RP-set. This covers neighbor, the router stores the information as its new RP-
the startup condition when a newly booted router obtains the set. This covers the startup condition when a newly booted
RP-Set and BSR address from its DR. router obtains the RP-Set and BSR address from its DR.
When a router receives a new RP-Set it checks if each of the RPs When a router receives a new RP-Set it checks if each of the RPs
referred to by existing state (i.e., by (*,G), (*,*,RP), or referred to by existing state (i.e., by (*,G), (*,*,RP), or
(S,G)RPbit entries) is in the new RP-Set. If an RP is not in the (S,G)RPT-bit entries) is in the new RP-Set. If an RP is not in
new RP-set, that RP is considered unreachable and the hash the new RP-set, that RP is considered unreachable and the hash
algorithm (see below) is re-performed for each group with algorithm (see below) is re-performed for each group with
locally active state that previously hashed to that RP. This locally active state that previously hashed to that RP. This
will cause those groups to be distributed among the remaining will cause those groups to be distributed among the remaining
RPs. When the new RP-Set contains a new RP, the value of the new RPs. When the new RP-Set contains a new RP, the value of the new
RP is calculated for each group covered by that C-RP's Group- RP is calculated for each group covered by that C-RP's Group-
prefix. Any group for which the new RP's value is greater than prefix. Any group for which the new RP's value is greater than
the previously active RP's value is switched over to the new RP. the previously active RP's value is switched over to the new RP.
3.7 Hash Function 3.7 Hash Function
The hash function is used by all routers within a domain, to map The hash function is used by all routers within a domain, to map
a group to one of the C-RPs from the RP-Set. For a particular a group to one of the C-RPs from the RP-Set. For a particular
group, G, the hash function uses only those C-RPs whose Group- group, G, the hash function uses only those C-RPs whose Group-
prefix covers G. The algorithm takes as input the group address, prefix covers G. The algorithm takes as input the group address,
and the addresses of the Candidate RPs, and gives as output one and the addresses of the Candidate RPs, and gives as output one
RP address to be used. RP address to be used.
[Page 36]
The protocol requires that all routers hash to the same RP The protocol requires that all routers hash to the same RP
within a domain (except for transients). The following hash within a domain (except for transients). The following hash
function must be used in each router: function must be used in each router:
1 For each candidate RP address Ci in the Candidate-RP- 1 For each candidate RP address Ci in the Candidate-RP-
Set, whose Group-prefix covers G, compute a value: Set, whose Group-prefix covers G, compute a value:
Value(G,M,Ci) = Value(G,M,Ci) =
1103515245 ((1103515245 (G&M)+12345) XOR Ci)+ 12345 mod 2^31 1103515245 ((1103515245 (G&M)+12345) XOR Ci)+ 12345 mod 2^31
where M is a hash-mask included in RP-Set messages. where M is a hash-mask included in RP-Set messages.
This hash-mask allows a small number of This hash-mask allows a small number of
skipping to change at line 1526 skipping to change at page 39, line 28
The hash function algorithm is invoked by a DR, upon reception The hash function algorithm is invoked by a DR, upon reception
of a packet, or IGMP Host-Membership-Report, for a group, for of a packet, or IGMP Host-Membership-Report, for a group, for
which the DR has no entry. It is invoked by any router that has which the DR has no entry. It is invoked by any router that has
(*,*,RP) state when a packet is received for which there is no (*,*,RP) state when a packet is received for which there is no
corresponding (S,G) or (*,G) entry. Furthermore, the hash corresponding (S,G) or (*,G) entry. Furthermore, the hash
function is invoked by all routers upon receiving a Join/Prune function is invoked by all routers upon receiving a Join/Prune
message with WC-bit set. message with WC-bit set.
3.8 Processing Timer Events 3.8 Processing Timer Events
{ Editors Note: Timers are also discussed individually in the
sections that pertain to the protocol messages that they
[Page 37]
trigger/affect. Until we finalize this section, if discrepencies
exist, then assume that the individual sections are
authoritative over this table.}
In this subsection, we enumerate all timers that have been In this subsection, we enumerate all timers that have been
discussed or implied. Since some critical timer events are not discussed or implied. Since some critical timer events are not
associated with the receipt or sending of messages, they are not associated with the receipt or sending of messages, they are not
fully covered by earlier subsections. fully covered by earlier subsections.
Timers may either count up or count down. If they count up then
expiration means that the timer has reached its configured
maximum value. If they count down then expiration means that the
timer has reached zero.
In many cases, the values for timers come from Holdtime fields In many cases, the values for timers come from Holdtime fields
in PIM control messages, in which case the default values used in PIM control messages, in which case the default values used
in these Holdtime fields are shown in the tables below. in these Holdtime fields are shown in the tables below.
Otherwise, the default value used when setting the timer is Otherwise, the default value used when setting the timer is
shown. In general, the default timeout value for state shown. In general, the default timeout value for state
information is three times the refresh period. For example, information is three times the refresh period. For example,
Queries refresh Neighbor state and the default Query-timer Queries refresh Neighbor state and the default Query-timer
period is 30 seconds, so a default Neighbor-timer duration of 90 period is 30 seconds, so a default Neighbor-timer duration of 90
seconds is included in the Holdtime field of the Queries. seconds is included in the Holdtime field of the Queries.
In this version of the spec we suggest particular numerical In this version of the spec we suggest particular numerical
timer settings. A future version of the specification will timer settings. A future version of the specification will
specify a mechanism for timers to be set as a function of the specify a mechanism for timers to be set as a function of the
outgoing link bandwidth. outgoing link bandwidth.
bsubsection*Timers related to tree maintenance 3.8.1 Timers related to tree maintenance
Each (S,G), (*,G), and (*,*,RP) entry has multiple timers Each (S,G), (*,G), and (*,*,RP) entry has multiple timers
associated with it: one for each interface in the outgoing associated with it: one for each interface in the outgoing
interface list, one for the multicast routing entry itself, and interface list, one for the multicast routing entry itself, and
one for the Joiner-bit. Each (S,G) and (*,G) entry also has an one for the Joiner-bit. Each (S,G) and (*,G) entry also has an
Assert timer and an Assert-rate-limit timer. In addition, DR's Assert timer and an Assert-rate-limit timer. In addition, DR's
have a Register-bit-timer for each (S,G) entry and every router have a Register-bit-timer for each (S,G) entry and every router
has a single Join/Prune timer. has a single Join/Prune timer.
Because some of the outgoing interfaces in an (S,G) entry are Because some of the outgoing interfaces in an (S,G) entry are
copied from the (*,G) outgoing interface list, they may not have copied from the (*,G) outgoing interface list, they may not have
explicit (S,G) join messages from some of the downstream routers explicit (S,G) join messages from some of the downstream routers
(i.e., where members are joining to the (*,G) tree only). Thus, (i.e., where members are joining to the (*,G) tree only). Thus,
when a timer is reset for an outgoing interface listed in a when a timer is reset for an outgoing interface listed in a
(*,G) entry, the timers are reset for that interface in each (*,G) entry, the timers are reset for that interface in each
existing (S,G) entry whose oif list contains that interface [*] existing (S,G) entry whose oif list contains that interface [*]
The same rule applies to (*,G) and (S,G) entries when resetting
an oif timer on a (*,*,RP) entry.
_________________________ _________________________
[*] If there are sources in the prune list of the (*,G) [*] If there are sources in the prune list of the (*,G)
join, then the timers for the arriving interface will join, then the timers for the arriving interface will
first be reset for those sources, and then this inter- first be reset for those sources, and then this inter-
face will be deleted from these same entries; producing face will be deleted from these same entries; producing
a correct result, even though the updating of the ti- a correct result, even though the updating of the ti-
mers was unnecessary. An implementation could optimize mers was unnecessary. An implementation could optimize
[Page 38]
The same rule applies to (*,G) and (S,G) entries when resetting
an oif timer on a (*,*,RP) entry.
_________________________
this by checking the prune list before processing the this by checking the prune list before processing the
join list. join list.
[Page 39]
Timer DefVal Notes Timer DefVal Notes
Joiner-bit 90 Started : When Joiner bit is cleared Joiner-bit 90 Started : When Joiner bit is cleared
per route entry Reset by: Receiving Join from higher-IP neighbor on iif per route entry Reset by: Receiving Join from higher-IP neighbor
on iif
Action : Set Joiner bit Action : Set Joiner bit
Join/Prune 60 Started : When booting Join/Prune 60 Started : When booting
Reset by: Nothing Reset by: Nothing
Action : Send Join/Prune to each RPF neighbor, restart timer Action : Send Join/Prune to each RPF neighbor,
restart timer
oif 180 Started : When adding oif to oiflist oif 180 Started : When adding oif to oiflist
per (*,*,RP) oif Restarted by: Receiving (*,*,RP) Join on that iface per (*,*,RP) oif Restarted by: Receiving (*,*,RP) Join on that
iface
Action : Remove oif from oiflist Action : Remove oif from oiflist
oif 180 Started : When adding oif to oiflist oif 180 Started : When adding oif to oiflist
per (*,G) oif Restarted by: Receiving (*,G) Join or IGMP per (*,G) oif Restarted by: Receiving (*,G) Join or IGMP
Host-Membership-Report for G on that iface, or Host-Membership-Report for G on that iface, or
restartedting oif timer in (*,*,RP). restartedting oif timer in (*,*,RP).
Action : Remove oif from oiflist Action : Remove oif from oiflist
oif 180 Started : When adding oif to oiflist oif 180 Started : When adding oif to oiflist
per (S,G) oif Restarted by: Receiving (S,G) Join on that per (S,G) oif Restarted by: Receiving (S,G) Join on that
skipping to change at line 1621 skipping to change at page 41, line 41
(*,*,RP). (*,*,RP).
Action : Remove oif from oiflist Action : Remove oif from oiflist
(*,*,RP) entry 180 Started : When entry is created (*,*,RP) entry 180 Started : When entry is created
per (*,*,RP) Restarted by: Restartedting timer on any oif per (*,*,RP) Restarted by: Restartedting timer on any oif
Action : Delete entry Action : Delete entry
(*,G) entry 180 Started : When entry is created (*,G) entry 180 Started : When entry is created
per (*,G) Restarted by: Receiving (*,G) prune, per (*,G) Restarted by: Receiving (*,G) prune,
restarting timer on any oif, or receiving an restarting timer on any oif, or receiving an
Assert with RP-bit set. Assert with RPT-bit set.
Action : Delete entry and any associated Action : Delete entry and any associated
(S,G)RP-bit entries (S,G)RPT-bit entries
(S,G) entry 180 Started : When entry is created (S,G) entry 180 Started : When entry is created
aka S-timer Restarted by: Forwarding data packet, aka S-timer Restarted by: Forwarding data packet,
per (S,G) receiving Register, receiving (S,G) RP-bit per (S,G) receiving Register, receiving (S,G)RPT-bit
prune, restarting timer on any oif, prune, restarting timer on any oif,
or receiving an Assert without RP-bit set. or receiving an Assert without RPT-bit set.
Action : Delete entry Action : Delete entry
Register-bit 60 Started : When Register bit is cleared by Register-bit 60 Started : When Register bit is cleared by
per (S,G) receiving a Register-Stop per (S,G) receiving a Register-Stop
Restarted by: Receiving Register-Stop Restarted by: Receiving Register-Stop
[Page 40]
Action : Set Register bit Action : Set Register bit
Assert 180 Started : Receiving an Assert where the Assert 180 Started : Receiving an Assert where the
per (S,G) upstream RPF neighbor is not your unicast RPF per (S,G) upstream RPF neighbor is not your unicast RPF
and (*,G) neighbor. and (*,G) neighbor.
Restarted by: Receiving an Assert where the Restarted by: Receiving an Assert where the
upstream RPF neighbor is not your unicast upstream RPF neighbor is not your unicast
RPF neighbor. RPF neighbor.
Action : Change RPF neighbor to unicast RPF neighbor Action : Change RPF neighbor to unicast RPF
neighbor
Assert-Rate-limit 5 Started : When an Assert is sent Assert-Rate-limit 5 Started : When an Assert is sent
per (S,G) Restarted by: Nothing per (S,G) Restarted by: Nothing
and (*,G) Action : Allow asserts to be triggered by and (*,G) Action : Allow asserts to be triggered by
data packets data packets
*Timers relating to neighbor discovery 3.8.2 Timers relating to neighbor discovery
Timer DefVal Notes Timer DefVal Notes
Query 30 Started : When booting Query 30 Started : When booting
Restarted by: Nothing Restarted by: Nothing
Action : Send Query on all ifaces, restart timer Action : Send Query on all ifaces, restart timer
Neighbor 90 Started : When receive first Query from neighbor Neighbor 90 Started : When receive first Query from neighbor
per neighbor Restarted by: When receive subsequent Queries per neighbor Restarted by: When receive subsequent Queries
Action : Delete neighbor entry Action : Delete neighbor entry
*Timers relating to RP information 3.8.3 Timers relating to RP information
[Page 41]
Timer DefVal Notes Timer DefVal Notes
C-RP-Adv 60 Started : When booting if you're a Cand-RP C-RP-Adv 60 Started : When booting if you're a Cand-RP
Restarted by: Nothing Restarted by: Nothing
Action : Send C-RP-Adv, restart C-RP-Adv timer Action : Send C-RP-Adv, restart C-RP-Adv timer
RP 180 Started : When adding an RP to the RP-Set if RP 180 Started : When adding an RP to the RP-Set if
per RP you are BSR per RP you are BSR
Restarted by: Receiving C-RP-Adv Restarted by: Receiving C-RP-Adv
Action : Remove RP from RP-Set Action : Remove RP from RP-Set
RP-Set 180/60 Started : Set to 180 when booting if RP-Set 180/60 Started : Set to 180 when booting if
you're a C-BSR you're a C-BSR
Restarted by: Restarted to 180 when receive Restarted by: Restarted to 180 when receive
RP-Set from preferred router if you're a C-BSR RP-Set from preferred router if you're a C-BSR
Action : Send RP-Set and restart timer to 60 secs Action : Send RP-Set and restart timer to 60
secs
3.9 Summary of flags used 3.9 Summary of flags used
Following is a summary of all the flags used in our scheme. Following is a summary of all the flags used in our scheme.
Bit Used in Definition Bit Used in Definition
Border Register Register is coming from a PIM border router. Border Register Register is coming from a PIM multicast border router.
Joiner Route entry Periodic Join/Prunes should be sent for this entry. Joiner Route entry Periodic Join/Prunes should be sent for this entry.
Register (S,G) entry Encapsulate packets from directly connected Register (S,G) entry Encapsulate packets from directly connected
sources in Register messages unicast to the RP sources in Register messages unicast to the RP
for that group. for that group.
RP Route entry Entry represents state on the RP-tree. RP Route entry Entry represents state on the RP-tree.
RP Join/Prune Join is associated with the shared tree and therefore RP Join/Prune Join is associated with the shared tree and therefore
the Join/Prune message is propagated along the RP-tree. the Join/Prune message is propagated along the
RP-tree.
RP Assert The data packet was routed down the shared tree; thus, RP Assert The data packet was routed down the shared tree; thus,
the path indicated corresponds to the RP tree. the path indicated corresponds to the RP tree.
SPT (S,G) entry Packets have arrived on the iif towards S, SPT (S,G) entry Packets have arrived on the iif towards S,
and the iif is different from the (*,G) iif. and the iif is different from the (*,G) iif.
WC Join Included address is an RP and the receiver expects to WC Join Included address is an RP and the receiver expects to
receive packets from all sources via this (shared tree) receive packets from all sources via this (shared
tree)
path. Thus, the Join/Prune applies to a (*,G) entry. path. Thus, the Join/Prune applies to a (*,G) entry.
WC Route entry Wildcard entry; if there is no more specific match for WC Route entry Wildcard entry; if there is no more specific match for
a particular source, packets will be forwarded according a particular source, packets will be forwarded
according
to this entry. to this entry.
[Page 42]
3.10 Security 3.10 Security
{ Editors Note: this section is to be completed.} Editors Note: this section is to be completed.
All PIM control messages may use [5] to address security All PIM control messages may use [5] to address security
concerns. concerns.
[Page 43]
4 Packet Formats 4 Packet Formats
This section describes the details of the packet formats for PIM This section describes the details of the packet formats for PIM
control messages. control messages.
All PIM control messages have protocol number 103. All PIM control messages have protocol number 103.
Basically, PIM messages are either unicast (e.g. Registers and Basically, PIM messages are either unicast (e.g. Registers and
Register-Stop), or multicast hop-by-hop to `ALL-PIM-ROUTERS' Register-Stop), or multicast hop-by-hop to `ALL-PIM-ROUTERS'
group `224.0.0.13' (e.g. Join/Prune, Asserts, etc.). group `224.0.0.13' (e.g. Join/Prune, Asserts, etc.).
skipping to change at line 1755 skipping to change at page 46, line 5
5 = Assert 5 = Assert
6 = Graft (used in PIM-DM only) 6 = Graft (used in PIM-DM only)
7 = Graft-Ack (used in PIM-DM only) 7 = Graft-Ack (used in PIM-DM only)
8 = Candidate-RP-Advertisement 8 = Candidate-RP-Advertisement
Addr length Addr length
Address length in bytes. Throughout this section this Address length in bytes. Throughout this section this
would indicate the number of bytes in the Address field of would indicate the number of bytes in the Address field of
an address, including unicast and group addresses. an address, including unicast and group addresses.
[Page 44]
Checksum Checksum
The checksum is the 16-bit one's complement of the one's The checksum is the 16-bit one's complement of the one's
complement sum of the entire PIM message, (excluding the complement sum of the entire PIM message, (excluding the
data portion in the Register message). For computing the data portion in the Register message). For computing the
checksum, the checksum field is zeroed. checksum, the checksum field is zeroed.
[Page 45]
4.1 Encoded Source and Group Address formats 4.1 Encoded Source and Group Address formats
1 Unicast address: Only the address is included. The length 1 Unicast address: Only the address is included. The length
of the unicast address in bytes is specified in the `Addr of the unicast address in bytes is specified in the `Addr
length' field in the header. length' field in the header.
2 Encoded-Group-Address: Takes the following format: 2 Encoded-Group-Address: Takes the following format:
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
skipping to change at line 1796 skipping to change at page 48, line 5
Addr length * 8. If the message is sent for a single Addr length * 8. If the message is sent for a single
group then the Mask length should equal Addr length * group then the Mask length should equal Addr length *
8 (i.e. 32 for IPv4 and 128 for IPv6). 8 (i.e. 32 for IPv4 and 128 for IPv6).
Group multicast Address Group multicast Address
contains the group address, and has number of bytes contains the group address, and has number of bytes
equal to that specified in the Addr length field. equal to that specified in the Addr length field.
3 Encoded-Source-Address: Takes the following format: 3 Encoded-Source-Address: Takes the following format:
[Page 46]
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsrvd |S|W|R| Mask Len | Source Address ... | | Rsrvd |S|W|R| Mask Len | Source Address ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Source Address | | ... Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+~+~+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+~+~+-+
Reserved Reserved
Transmitted as zero, ignored on receipt. Transmitted as zero, ignored on receipt.
S,W,R See Section7 ef{Join_format} for details. S,W,R See Section 4.5 for details.
Mask Length Mask Length
Mask length is 8 bits. The value is the number of Mask length is 8 bits. The value is the number of
contiguous bits left justified used as a mask which contiguous bits left justified used as a mask which
describes the address. The mask length must be less describes the address. The mask length must be less
than or equal to Addr Length * 8. If the message is than or equal to Addr Length * 8. If the message is
sent for a single source then the Mask length should sent for a single source then the Mask length should
equal Addr length * 8. In version 2 of PIM, it is equal Addr length * 8. In version 2 of PIM, it is
strongly recommended that this field be set to 32 for strongly recommended that this field be set to 32 for
IPv4. IPv4.
Source Address Source Address
The address length is indicated from the Addr length The address length is indicated from the Addr length
field at the beginning of the header. For IPv4, the field at the beginning of the header. For IPv4, the
address length is 4 octets. address length is 4 octets.
[Page 47]
4.2 Query Message 4.2 Query Message
It is sent periodically by routers on all interfaces. It is sent periodically by routers on all interfaces.
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 | Addr length | Checksum | |PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Holdtime | | Reserved | Holdtime |
skipping to change at line 1848 skipping to change at page 50, line 5
PIM Version, Type, Addr length, Checksum PIM Version, Type, Addr length, Checksum
Described above. Described above.
Reserved Reserved
Transmitted as zero, ignored on receipt. Transmitted as zero, ignored on receipt.
Holdtime Holdtime
The amount of time a receiver should keep the neighbor The amount of time a receiver should keep the neighbor
reachable, in seconds. reachable, in seconds.
[Page 48]
4.3 Register Message 4.3 Register Message
It is sent by the Designated Router (DR) to the RP when a It is sent by the Designated Router (DR) to the RP when a
multicast packet needs to be transmitted on the RP-tree. Source multicast packet needs to be transmitted on the RP-tree. Source
IP address is set to the address of the DR, destination IP IP address is set to the address of the DR, destination IP
address is to the RP's address. address is to the RP's address.
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 | Addr length | Checksum | |PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B| Reserved | |B| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
Multicast data packet Multicast data packet
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PIM Version, Type, Addr length, Checksum PIM Version, Type, Addr length, Checksum
Described above. { Note that the checksum for Registers Described above. Note that the checksum for Registers
is done only on the PIM header, excluding the data packet is done only on the PIM header, excluding the data packet
portion.} portion.
B The Border bit. Set to zero by all DRs. Set to `1' by the B The Border bit. Set to zero by all DRs. Set to `1' by the
PIM Multicast Border Routers, when registering for external PIM Multicast Border Routers, when registering for external
sources. sources.
Multicast data packet Multicast data packet
The original packet sent by the source. The original packet sent by the source.
[Page 49]
4.4 Register-Stop Message 4.4 Register-Stop Message
A Register-Stop is unicast from the RP to the sender of the A Register-Stop is unicast from the RP to the sender of the
Register message. Source IP address is the address to which the Register message. Source IP address is the address to which the
register was addressed. Destination IP address is the source register was addressed. Destination IP address is the source
address of the register message. address of the register message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at line 1912 skipping to change at page 52, line 5
Format described above. Note that for Register-Stops the Format described above. Note that for Register-Stops the
Mask Len field should contain Addr length * 8 (32 for Mask Len field should contain Addr length * 8 (32 for
IPv4), if the message is sent for a single group. IPv4), if the message is sent for a single group.
Unicast-Source Address Unicast-Source Address
IP host address of source from multicast data packet in IP host address of source from multicast data packet in
register. The length of this field in bytes is specified in register. The length of this field in bytes is specified in
the Addr length field. A special wild card value (0.0.0.0), the Addr length field. A special wild card value (0.0.0.0),
can be used to indicate any source. can be used to indicate any source.
[Page 50]
4.5 Join/Prune Message 4.5 Join/Prune Message
It is sent by routers towards upstream sources and RPs. A join It is sent by routers towards upstream sources and RPs. A join
creates forwarding state and a prune destroys forwarding state. creates forwarding state and a prune destroys forwarding state.
Joins are sent to build shared trees (RP trees) or source trees Joins are sent to build shared trees (RP trees) or source trees
(SPT). Prunes are sent to prune source trees when members leave (SPT). Prunes are sent to prune source trees when members leave
groups as well as sources that do not use the shared tree. groups as well as sources that do not use the shared tree.
[Page 51]
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 | Addr length | Checksum | |PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unicast-Upstream Neighbor Address | | Unicast-Upstream Neighbor Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Num groups | Holdtime | | Reserved | Num groups | Holdtime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Multicast Group Address-1 | | Encoded-Multicast Group Address-1 |
skipping to change at line 1969 skipping to change at page 54, line 4
| . | | . |
| . | | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Joined Source Address-n | | Encoded-Joined Source Address-n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Pruned Source Address-1 | | Encoded-Pruned Source Address-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . | | . |
| . | | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[Page 52]
| Encoded-Pruned Source Address-n | | Encoded-Pruned Source Address-n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PIM Version, Type, Addr length, Checksum PIM Version, Type, Addr length, Checksum
Described above. Described above.
Upstream Neighbor Address Upstream Neighbor Address
The IP address of the RPF or upstream neighbor. The IP address of the RPF or upstream neighbor.
Reserved Reserved
skipping to change at line 1996 skipping to change at page 54, line 29
Number of Groups Number of Groups
The number of multicast group sets contained in the The number of multicast group sets contained in the
message. message.
Encoded-Multicast group address Encoded-Multicast group address
For format description see Section For format description see Section
4.1. A wild card group in the (*,*,RP) join is represented 4.1. A wild card group in the (*,*,RP) join is represented
by a 224.0.0.0 in the group address field and `4' in the by a 224.0.0.0 in the group address field and `4' in the
mask length field. A (*,*,RP) join also has the WC-bit and mask length field. A (*,*,RP) join also has the WC-bit and
the RP-bit set. the RPT-bit set.
Number of Joined Sources Number of Joined Sources
Number of join source addresses listed for a given group. Number of join source addresses listed for a given group.
Join Source Address-1 .. n Join Source Address-1 .. n
This list contains the sources that the sending router This list contains the sources that the sending router
will forward multicast datagrams for if received on the will forward multicast datagrams for if received on the
interface this message is sent on. interface this message is sent on.
See format section 4.1. The fields explanation for the See format section 4.1. The fields explanation for the
Encoded-Source-Address format follows: Encoded-Source-Address format follows:
Reserved Reserved
Described above. Described above.
[Page 53]
S The Sparse bit is a 1 bit value, set to 1 for PIM-SM. S The Sparse bit is a 1 bit value, set to 1 for PIM-SM.
It is used for PIM v.1 compatability. It is used for PIM v.1 compatability.
W The WC bit is a 1 bit value. If 1, the join or prune W The WC bit is a 1 bit value. If 1, the join or prune
applies to the (*,G) or (*,*,RP) entry. If 0, the join applies to the (*,G) or (*,*,RP) entry. If 0, the join
or prune applies to the (S,G) entry where S is Source or prune applies to the (S,G) entry where S is Source
Address. Joins and prunes sent towards the RP should Address. Joins and prunes sent towards the RP should
have this bit set. have this bit set.
R The RP bit is a 1 bit value. If 1, the information R The RPT-bit is a 1 bit value. If 1, the information
about (S,G) is sent towards the RP. If 0, the about (S,G) is sent towards the RP. If 0, the
information should be sent about (S,G) toward S, where information should be sent about (S,G) toward S, where
S is Source Address. S is Source Address.
Mask Length, Source Address Mask Length, Source Address
Described above. Described above.
Represented in the form of Represented in the form of < WC-bit >< RPT-bit ><
< WCbit >< RPbit >< Mask length>< Source address>: Mask length >< Source address>:
A source address could be a host IP address : A source address could be a host IP address :
< 0 >< 0 >< 32 >< 192.1.1.17 > < 0 >< 0 >< 32 >< 192.1.1.17 >
A source address could be the RP's IP address : A source address could be the RP's IP address :
< 1 >< 1 >< 32 >< 131.108.13.111 > < 1 >< 1 >< 32 >< 131.108.13.111 >
A source address could be a subnet address to prune from A source address could be a subnet address to prune from
skipping to change at line 2059 skipping to change at page 56, line 4
Number of Pruned Sources Number of Pruned Sources
Number of prune source addresses listed for a group. Number of prune source addresses listed for a group.
Prune Source Address-1 .. n Prune Source Address-1 .. n
This list contains the sources that the sending router This list contains the sources that the sending router
does not want to forward multicast datagrams for when does not want to forward multicast datagrams for when
received on the interface this message is sent on [*] received on the interface this message is sent on [*]
_________________________ _________________________
[*] If the Join/Prune message boundary exceeds the max- [*] If the Join/Prune message boundary exceeds the max-
[Page 54]
4.6 RP-Set 4.6 RP-Set
The RP-Set messages are multicast to `ALL-PIM-ROUTERS' group, The RP-Set messages are multicast to `ALL-PIM-ROUTERS' group,
out all interfaces having PIM neighbors (excluding the one over out all interfaces having PIM neighbors (excluding the one over
which the message was received). RP-Set messages are sent with which the message was received). RP-Set messages are sent with
TTL value of 1. RP-Set messages originate at the BSR, and are TTL value of 1. RP-Set messages originate at the BSR, and are
forwarded by intermediate routers. forwarded by intermediate routers.
RP-Set message is divided up into `semantic fragments', if the RP-Set message is divided up into `semantic fragments', if the
original message exceeds the maximum packet size boundaries. original message exceeds the maximum packet size boundaries.
The semantics of a single `fragment' is given below: The semantics of a single `fragment' is given below:
_________________________ _________________________
imum packet size, then the join and prune lists for the imum packet size, then the join and prune lists for the
same group must be included in the same packet. same group must be included in the same packet.
[Page 55]
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 | Addr length | Checksum | |PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment Tag | Hash Mask len | BSR-priority | | Fragment Tag | Hash Mask len | BSR-priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unicast-BSR-Address | | Unicast-BSR-Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded-Group Address-1 | | Encoded-Group Address-1 |
skipping to change at line 2121 skipping to change at page 58, line 4
| . | | . |
| . | | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unicast-RP-Address-m | | Unicast-RP-Address-m |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PIM Version, Type, Addr length, Checksum PIM Version, Type, Addr length, Checksum
Described above. Described above.
Fragment Tag Fragment Tag
[Page 56]
A randomly generated number, acts to distinguish the A randomly generated number, acts to distinguish the
fragments belonging to different RP-Set messages; fragments fragments belonging to different RP-Set messages; fragments
belonging to same RP-Set message carry the same `Fragment belonging to same RP-Set message carry the same `Fragment
Tag'. Tag'.
Hash Mask len Hash Mask len
The length (in bits) of the mask to use in the hash The length (in bits) of the mask to use in the hash
function. For IPv4 we recommend a value of 30. For IPv6 we function. For IPv4 we recommend a value of 30. For IPv6 we
recommend a value of 126. recommend a value of 126.
skipping to change at line 2168 skipping to change at page 59, line 5
The address of the Candidate RPs, for the corresponding The address of the Candidate RPs, for the corresponding
_________________________ _________________________
[*] A router does not replace its old RP-Set for a [*] A router does not replace its old RP-Set for a
given group prefix until/unless it receives `RP-Count' given group prefix until/unless it receives `RP-Count'
addresses for that prefix; the addresses could be car- addresses for that prefix; the addresses could be car-
ried over several fragments. If only part of the RP-Set ried over several fragments. If only part of the RP-Set
for a given group prefix was received, the router dis- for a given group prefix was received, the router dis-
cards it, without updating that specific group prefix's cards it, without updating that specific group prefix's
RP-Set. RP-Set.
[Page 57]
group prefix. The length of this field in bytes is group prefix. The length of this field in bytes is
specified in Addr length. specified in Addr length.
[Page 58]
4.7 Assert Message 4.7 Assert Message
The Assert message is sent when a multicast data packet is The Assert message is sent when a multicast data packet is
received on an outgoing interface corresponding to the (S,G) or received on an outgoing interface corresponding to the (S,G) or
(*,G) associated with the source. (*,G) associated with the source.
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 | Addr length | Checksum | |PIM Ver| Type | Addr length | Checksum |
skipping to change at line 2206 skipping to change at page 60, line 38
Encoded-Group Address Encoded-Group Address
The group address to which the data packet was addressed, The group address to which the data packet was addressed,
and which triggered the Assert. Format previously and which triggered the Assert. Format previously
described. described.
Unicast-Source Address Unicast-Source Address
Source IP address from IP multicast datagram that Source IP address from IP multicast datagram that
triggered the Assert packet to be sent. The length of this triggered the Assert packet to be sent. The length of this
field in bytes is specified in Addr length. field in bytes is specified in Addr length.
R RP bit is a 1 bit value. If the IP multicast datagram that R RPT-bit is a 1 bit value. If the IP multicast datagram
triggered the Assert packet is routed down the RP tree, that triggered the Assert packet is routed down the RP
then the RP bit is 1; if the IP multicast datagram is tree, then the RPT-bit is 1; if the IP multicast datagram
routed down the SPT, it is 0. is routed down the SPT, it is 0.
Metric Preference Metric Preference
Preference value assigned to the unicast routing protocol Preference value assigned to the unicast routing protocol
that provided the route to Host address. that provided the route to Host address.
Metric The unicast routing table metric. The metric is in units Metric The unicast routing table metric. The metric is in units
applicable to the unicast routing protocol used. applicable to the unicast routing protocol used.
[Page 59]
4.8 Graft Message 4.8 Graft Message
Used in dense-mode. Refer to PIM dense mode specification. Used in dense-mode. Refer to PIM dense mode specification.
4.9 Graft-Ack Message 4.9 Graft-Ack Message
Used in dense-mode. Refer to PIM dense mode specification. Used in dense-mode. Refer to PIM dense mode specification.
[Page 60]
4.10 Candidate-RP-Advertisement 4.10 Candidate-RP-Advertisement
Candidate-RP-Advertisements are periodically unicast from the Candidate-RP-Advertisements are periodically unicast from the
C-RPs to the BSR. C-RPs to the BSR.
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 | Addr length | Checksum | |PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at line 2270 skipping to change at page 63, line 4
information, the C-RP puts a default value of `0' in this information, the C-RP puts a default value of `0' in this
field. field.
Holdtime Holdtime
The amount of time the advertisement is valid. This field The amount of time the advertisement is valid. This field
allows advertisements to be aged out. allows advertisements to be aged out.
Unicast-RP-Address Unicast-RP-Address
The address of the interface to advertise as a Candidate The address of the interface to advertise as a Candidate
RP. The length of this field in bytes is specified in Addr RP. The length of this field in bytes is specified in Addr
[Page 61]
length. length.
Encoded-Group Address-1..n Encoded-Group Address-1..n
The group prefixes for which the C-RP is advertising. The group prefixes for which the C-RP is advertising.
Format previously described. Format previously described.
[Page 62] 5 Appendix I: Major Changes and Updates to the Spec
5 Appendix I: Changes and Updates to the Spec
This appendix populates the major changes in the specification This appendix populates the major changes in the specification
document as compared to `draft-ietf-idmr-pim-spec-01.ps,txt'. document as compared to `draft-ietf-idmr-pim-spec-01.ps,txt'.
5.1 Major Changes 5.1 Major Changes
List of changes since March '96 IETF: List of changes since March '96 IETF:
1. (*,*,RP) Joins state and data forwarding check; replaces (*,G- 1. (*,*,RP) Joins state and data forwarding check; replaces (*,G-
Prefix) Joins state for interoperability. (*,G) negative cache Prefix) Joins state for interoperability. (*,G) negative cache
introduced for the (*,*,RP) state supporting mechanisms. introduced for the (*,*,RP) state supporting mechanisms.
2. Semantic fragmentation for the RP-Set message. 2. Semantic fragmentation for the RP-Set message.
3. Appendix II on interoperability details with DVMRP in List of changes incurred since version 1 of the spec.:
preparation.
List of changes incurred since version 1 of the spec:
1. Proposal and refinement of bootstrap router (BSR) election 1. Proposal and refinement of bootstrap router (BSR) election
mechanisms mechanisms
2. Introduction of hash functions for Group to RP mapping 2. Introduction of hash functions for Group to RP mapping
3. New RP-liveness indication mechanisms based upon the the 3. New RP-liveness indication mechanisms based upon the the
Bootstrap Router (BSR) and the RP-Set messages. Bootstrap Router (BSR) and the RP-Set messages.
4. Removal of reachability messages, RP reports and multiple RPs 4. Removal of reachability messages, RP reports and multiple RPs
per group. per group.
5.2 Packet Format Changes 5.2 Packet Format Changes
Packet Format incurred updates to accommodate different address Packet Format incurred updates to accommodate different address
lengths, and address aggregation. lengths, and address aggregation.
1 The `Addr length' field was added to the PIM fixed header 1 The `Addr length' field was added to the PIM fixed header
[Page 63]
to specify the address length in bytes of the underlying to specify the address length in bytes of the underlying
protocol, see section 4. protocol, see section 4.
2 The Encoded source and group address formats were 2 The Encoded source and group address formats were
introduced, with the use of a `Mask length' field to allow introduced, with the use of a `Mask length' field to allow
aggregation, section 4.1. aggregation, section 4.1.
3 Packet formats are no longer IGMP messages; rather PIM 3 Packet formats are no longer IGMP messages; rather PIM
messages. messages.
PIM message types and formats were also modified: PIM message types and formats were also modified:
[{ Note: most changes were made to the May 95 version, unless [ Note: most changes were made to the May 95 version, unless
otherwise specified}]. otherwise specified].
1 Obsolete messages: 1 Obsolete messages:
a. Register-Ack [Feb. 96] (a) Register-Ack [Feb. 96]
b. Poll and Poll Response [Feb. 96] (b) Poll and Poll Response [Feb. 96]
c. RP-Reachability [Feb. 96] (c) RP-Reachability [Feb. 96]
d. RPlist-Mapping [Feb. 96] (d) RPlist-Mapping [Feb. 96]
2 New messages: 2 New messages:
a. Candidate-RP-Advertisement [change made in October 95] (a) Candidate-RP-Advertisement [change made in October 95]
RP-Set [Feb. 96]
b. RP-Set [Feb. 96]
3 Modified messages: 3 Modified messages:
[Page 64] (a) Join/Prune [Feb. 96]
a. Join/Prune [Feb. 96]
b. Register [Feb. 96]
c. Register-Stop [Feb. 96]
[Page 65]
6 Appendix II: Interoperability with Dense Mode Protocols
{ Editors Note: This section is to be completed.} (b) Register [Feb. 96]
[Page 66] (c) Register-Stop [Feb. 96]
7 Acknowledgments 6 Acknowledgments
Tony Ballardie, Scott Brim, Jon Crowcroft, Bill Fenner, Paul Tony Ballardie, Scott Brim, Jon Crowcroft, Bill Fenner, Paul
Francis, Joel Halpern, Horst Hodel, Polly Huang, Stephen Francis, Joel Halpern, Horst Hodel, Polly Huang, Stephen
Ostrowski, and Lixia Zhang provided detailed comments on Ostrowski, and Lixia Zhang provided detailed comments on
previous drafts. The authors of [6] and membership of the IDMR previous drafts. The authors of [6] and membership of the IDMR
WG provided many of the motivating ideas for this work and WG provided many of the motivating ideas for this work and
useful feedback on design details. useful feedback on design details.
This work was supported by the National Science Foundation, This work was supported by the National Science Foundation,
ARPA, cisco Systems and Sun Microsystems. ARPA, cisco Systems and Sun Microsystems.
skipping to change at line 2399 skipping to change at line 2399
Protocol specification. Internet Draft, November 1995. Protocol specification. Internet Draft, November 1995.
4. S.Deering. Host extensions for ip multicasting, aug 1989. 4. S.Deering. Host extensions for ip multicasting, aug 1989.
RFC1112. RFC1112.
5. R.Atkinson. Security architecture for the internet protocol, 5. R.Atkinson. Security architecture for the internet protocol,
August 1995. RFC-1825. August 1995. RFC-1825.
6. A.J. Ballardie, P.F. Francis, and J.Crowcroft. Core based trees. 6. A.J. Ballardie, P.F. Francis, and J.Crowcroft. Core based trees.
In Proceedings of the ACM SIGCOMM, San Francisco, 1993. In Proceedings of the ACM SIGCOMM, San Francisco, 1993.
[Page 67]
Expire in six months
 End of changes. 

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