An Insight into Junos' Multicast Source Discovery Protocol (MSDP)

Multicast Source Discovery Protocol (MSDP) is a key protocol in IP multicast. It is used to share multicast source information between different multicast domains. This blog post will provide a detailed insight into Junos' MSDP, which is a crucial topic for students studying for the JNCIS-ENT certification.

What is MSDP?

MSDP is a protocol that allows multicast sources for a group to be known to all rendezvous points (RPs) in different multicast domains. It establishes peer relationships with other MSDP-enabled devices to exchange active multicast source information. This allows multicast traffic to be forwarded across multiple domains, which is particularly useful in large-scale networks.

How does MSDP work?

MSDP works by establishing TCP connections with other MSDP peers and exchanging Source-Active (SA) messages. These messages contain information about the active sources and the groups they are sending to. When an RP receives an SA message, it creates (S, G) state and starts forwarding the multicast traffic to the receivers in its domain.

Configuring MSDP on Junos

Let's look at how to configure MSDP on a Junos device. The following example shows a basic configuration for MSDP:

protocols {
    msdp {
        group {
            peer {
                description "MSDP Peer";

In this configuration, the group statement specifies the multicast group range that the MSDP process can accept. The local-address statement specifies the source address for the MSDP messages. The peer statement configures an MSDP peer and the connect-source statement specifies the source address for the TCP connection to the MSDP peer.

Verifying MSDP Configuration

You can verify the MSDP configuration and operation using the show msdp command. Here is an example:

user@router> show msdp
Peer Address     AS    State Up/Dn Time  SA Count  In/Out     64512 Connect 00:00:00        0     0/0

In this output, the State column shows the state of the MSDP peer. If it shows Connect, it means the MSDP peer is trying to establish a connection. The SA Count column shows the number of SA messages received from the peer.


MSDP is a crucial protocol for multicast routing in large-scale networks. It allows multicast sources to be known across different multicast domains, enabling multicast traffic to be forwarded efficiently. Understanding and configuring MSDP is a key skill for network engineers and is a crucial topic for the JNCIS-ENT certification.

Remember, practice is key when it comes to mastering networking protocols. So, make sure to get hands-on experience with configuring and troubleshooting MSDP on Junos devices. Good luck with your studies!


© Ben Jacobson.RSS