MULTICAST · MSDP

Multicast: sources in another domain with MSDP

Two PIM sparse-mode domains each keep their own RP: R2 (2.2.2.2) for domain A, where SRC sends, and R3 (3.3.3.3) for domain B, where PC4 has joined 239.1.1.1. RP-B never hears about SRC, so PC4 gets nothing. Peer the two RPs with MSDP so RP-A announces the source in a Source-Active message and RP-B joins it across the border.

Multicast track · Cisco · 5 objectives

Open in simulator More Multicast labs

Objectives

The simulator ticks each one as soon as the network meets it.

On R2 (RP-A) configure ip msdp peer 3.3.3.3 connect-source loopback0 remote-as 65002.
On R3 (RP-B) configure ip msdp peer 2.2.2.2 connect-source loopback0 remote-as 65001.
On R2, show ip msdp summary: peer 3.3.3.3 is Up.
From SRC ping 239.1.1.1: PC4 replies.
On R3, show ip msdp sa-cache lists (10.1.1.10, 239.1.1.1) from RP 2.2.2.2, and show ip mroute shows that (S,G) entry with the M flag (created by MSDP).

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Before you start

Each RP only knows the sources that register with it. MSDP connects RPs over TCP port 639: when a source registers, its RP sends a Source-Active (S, G, RP) to its MSDP peers. An RP that has receivers for G joins (S,G) toward the source, across the domain border, and its last-hop routers then switch to the shortest-path tree. Peer on loopbacks with connect-source, so each side connects from the address the other side configured.

Concept

MSDP: sources in another PIM domain

Each PIM sparse-mode domain has its own RP, and an RP only learns the sources that register with it. MSDP (Multicast Source Discovery Protocol) peers RPs over TCP port 639, so a source in one domain is announced to the RPs of the others in a Source-Active (SA) message.

Concept

PIM sparse mode (ASM): shared tree, register, SPT

Sparse mode sends a stream only where it is requested. Receivers’ routers join a shared tree rooted at a rendezvous point (RP); the source’s router registers the stream to the RP; once the stream arrives, the receiver’s router joins the source directly on the shortest-path tree (SPT).