Network Working Group D. Farinacci
Request for Comments: 4610 Y. Cai
Category: Standards Track Cisco Systems
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. Please 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 (C) The Internet Society (2006).
This specification allows Anycast-RP (Rendezvous Point) to be used
inside a domain that runs Protocol Independent Multicast (PIM) only.
Other multicast protocols (such as Multicast Source Discovery
Protocol (MSDP), which has been used traditionally to solve this
problem) are not required to support Anycast-RP.
Anycast-RP as described in [I1] is a mechanism that ISP-based
backbones have used to get fast convergence when a PIM Rendezvous
Point (RP) router fails. To allow receivers and sources to
Rendezvous to the closest 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
This memo extends the Register mechanism in PIM so Anycast-RP
functionality can be retained without using MSDP.
Farinacci & Cai Standards Track [Page 1]RFC 4610 Anycast-RP using PIM August 20061.1. 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].
o A unicast IP address is chosen to use as the RP address. This
address is statically configured, or distributed using a dynamic
protocol, to all PIM routers throughout the domain.
o A set of routers in the domain is chosen to act as RPs for this RP
address. These routers are called the Anycast-RP set.
o Each router in the Anycast-RP set is configured with a loopback
interface using the RP address.
o Each router in the Anycast-RP set also needs a separate IP address,
to be used 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 set is configured with the addresses
of all other routers in the Anycast-RP set. This must be
consistently configured in all RPs in the set.
The following diagram illustrates a domain using 3 RPs where
receivers are joining to the closest RP according to where unicast
routing metrics take them and 2 sources sending packets to their
The rules described in this section 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
/ \ |
/ \ |
R1 R1' R2
Farinacci & Cai Standards Track [Page 2]RFC 4610 Anycast-RP using PIM August 2006
Assume the above scenario is completely connected where R1, R1', and
R2 are receivers for a group, and S1 and S3 send to that group.
Assume RP1, RP2, and RP3 are all assigned the same IP address, which
is used as the Anycast-RP address (let's say the IP address is RPA).
Note, the address used for the RP address in the domain (the
Anycast-RP address) needs to be different than the addresses used by
the Anycast-RP routers to communicate with each other.
The following procedure is used when S1 starts sourcing traffic:
o S1 sends a multicast packet.
o The designated router (DR) directly attached to S1 will form a PIM
Register message to send to the Anycast-RP address (RPA). The