Network Working Group D. Farinacci Request for Comments: 4610 Y. Cai Category: Standards Track Cisco Systems August 2006 Anycast-RP Using Protocol Independent Multicast (PIM)
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for
improvements. Plea refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited. Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This specification allows Anycast-RP (Rendezvous Point) to be ud
inside a domain that runs Protocol Independent Multicast (PIM) only. Other multicast protocols (such as Multicast Source Discovery
Protocol (MSDP), which has been ud traditionally to solve this
problem) are not required to support Anycast-RP.
1. Introduction
Anycast-RP as described in [I1] is a mechanism that ISP-bad
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backbones have ud to get fast convergence when a PIM Rendezvous
Point (RP) router fails. To allow receivers and sources to
Rendezvous to the clost RP, the packets from a source need to get
to all RPs to find joined receivers.
This notion of receivers finding sources is the fundamental problem
of source discovery that MSDP was intended to solve. However, if one would like to retain the Anycast-RP benefits from [I1] with less
protocol machinery, removing MSDP from the solution space is an
option.
This memo extends the Register mechanism in PIM so Anycast-RP
functionality can be retained without using MSDP.
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1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [N2].
2. Overview
o A unicast IP address is chon to u as the RP address. This
address is statically configured, or distributed using a dynamic
protocol, to all PIM routers throughout the domain.
o A t of routers in the domain is chon to act as RPs for this RP address. The routers are called the Anycast-RP t.
o Each router in the Anycast-RP t is configured with a loopback
interface using the RP address.
o Each router in the Anycast-RP t also needs a parate IP address, to be ud for communication between the RPs.
o The RP address, or a prefix that covers the RP address, is injected into the unicast routing system inside of the domain.
o Each router in the Anycast-RP t is configured with the address of all other routers in the Anycast-RP t. This must be
consistently configured in all RPs in the t.
3. Mechanism
The following diagram illustrates a domain using 3 RPs where
receivers are joining to the clost RP according to where unicast
routing metrics take them and 2 sources nding packets to their
respective RPs.
肛门痛什么原因
The rules described in this ction do not override the rules in
[N1]. They are intended to blend with the rules in [N1]. If there
is any question on the interpretation, precedent is given to [N1].
S1-----RP1 RP2 RP3------S3
/ \ |
/
\ |
计算机局域网
R1 R1’ R2
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Assume the above scenario is completely connected where R1, R1’, and R2 are receivers for a group, and S1 and S3 nd to that group.
Assume RP1, RP2, and RP3 are all assigned the same IP address, which is ud as the Anycast-RP address (let’s say the IP address is RPA). Note, the address ud for the RP address in the domain (the
Anycast-RP address) needs to be different than the address ud by the Anycast-RP routers to communicate with each other.
The following procedure is ud when S1 starts sourcing traffic:
o S1 nds a multicast packet.
o The designated router (DR) directly attached to S1 will form a PIM Register message to nd to the Anycast-RP address (RPA). The
unicast routing system will deliver the PIM Register message to the nearest RP, in this ca RP1.
工程实训o RP1 will receive the PIM Register message, decapsulate it, and nd the packet down the shared-tree to get the packet to receivers R1
and R1’.
o RP1 is configured with RP2 and RP3’s IP address. Since the
Register message did not come from one of the RPs in the anycast-RP t, RP1 assumes the packet came from a DR. If the Register is not addresd to the Anycast-RP address, an error has occurred and it
should be rate-limited logged.
o RP1 will then nd a copy of the Register message from S1’s DR to
both RP2 and RP3. RP1 will u its own IP address as the source
address for the PIM Register message.
o RP1 MAY join back to the source-tree by triggering a (S1,G) Join
message toward S1. However, RP1 MUST create (S1,G) state.
o RP1 nds a Register-Stop back to the DR. If, for some reason, the Register messages to RP2 and RP3 are lost, then when the Register
suppression timer expires in the DR, it will rend Registers to
allow another chance for all RPs in the Anycast-RP t to obtain
the (S,G) state.
o RP2 receives the Register message from RP1, decapsulates it, and
also nds the packet down the shared-tree to get the packet to
receiver R2.
o RP2 nds a Register-Stop back to RP1. RP2 MAY wait to nd the
Register-Stop if it decides to join the source-tree. RP2 should
wait until it has received data from the source on the source-tree Farinacci & Cai Standards Track [Page 3]
before nding the Register-Stop. If RP2 decides to wait, the
Register-Stop will be nt when the next Register is received. If RP2 decides not to wait, the Register-Stop is nt now.流浪远方
o RP2 MAY join back to the source-tree by triggering a (S1,G) Join
message toward S1. However, RP2 MUST create (S1,G) state.
o RP3 receives the Register message from RP1, decapsulates it, but
since there are no receivers joined for the group, it can discard
the packet.
o RP3 nds a Register-Stop back to RP1.
o RP3 creates (S1,G) state so when a receiver joins after S1 starts
nding, RP3 can join quickly to the source-tree for S1.
o RP1 process the Register-Stop from each of RP2 and RP3. There is no specific action taken when processing Register-Stop messages.
The procedure for S3 nding follows the same as above but it is RP3 that nds a copy of the Register originated by S3’s DR to RP1 and
RP2. Therefore, this example shows how sources anywhere in the
domain, associated with different RPs, can reach all receivers, also associated with different RPs, in the same domain.
4. Obrvations and Guidelines about This Proposal
o An RP will nd a copy of a Register only if the Register is
received from an IP address not in the Anycast-RP list (i.e., the
Register came from a DR and not another RP). An implementation
MUST safeguard against inconsistently configured Anycast-RP ts in each RP by copying the Time to Live (TTL) from a Register message
to the Register messages it copies and nds to other RPs.
o Each DR that PIM registers for a source will nd the message to
the Anycast-RP address (which results in the packet getting to the clost physical RP). Therefore, there are no changes to the DR
logic.
o Packets flow to all receivers no matter what RP they have joined
to.
o The source gets Registered to a single RP by the DR. It’s the
responsibility of the RP that receives the PIM Register messages
from the DR (the clost RP to the DR bad on routing metrics) to get the packet to all other RPs in the Anycast-RP t.
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o Logic is changed only in the RPs. The logic change is for nding copies of Register messages. Register-Stop processing is
unchanged. However, an implementation MAY suppress nding
经典睡前故事大全Register-Stop messages in respon to a Register received from an
RP.
o The rate-limiting of Register and Register-Stop messages are done
end-to-end. That is from DR -> RP1 -> {RP2 and RP3}. There is no need for specific rate-limiting logic between the RPs.
o When topology changes occur, the existing source-tree adjusts as it does today according to [N1]. The existing shared-trees, as well, adjust as they do today according to [N1].
o Physical RP changes are as fast as unicast route convergence,
retaining the benefit of [I1].
o An RP that doesn’t support this specification can be mixed with RPs that do support this specification. However, the non-supporter RP should not have sources registering to it, but may have receivers
joined to it.
o If Null Registers are nt (Registers with an IP header and no IP
payload), they MUST be replicated to all of the RPs in the
Anycast-RP t so that source state remains alive for active
sources.
o The number of RPs in the Anycast-RP t should remain small so the amount of non-native replication is kept to a minimum.
许多拼音o Since the RP, who receives a Register from the DR, will nd copies of the Register to the other RPs at the same time it nds a
Register-Stop to the DR, there could be packet loss and lost state in the other RPs until the time the DR nds Register messages
again.
5. Interaction with MSDP Running in an Anycast-PIM Router
The objective of this Anycast-PIM proposal is to remove the
dependence on using MSDP. This can be achieved by removing MSDP
peering between the Anycast-RPs. However, to adverti internal
sources to routers outside of a PIM routing domain and to learn
external sources from other routing domains, MSDP may still be
required.
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