Routing Configuration Guide, Cisco IOS XE Catalyst SD-WAN Release 17.x

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MSDP Routing Protocol Support

Updated: March 9, 2026

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Overview

This topic explains how the protocol facilitates the interconnection of multiple sparse-mode domains by exchanging source information between rendezvous points. It describes the conversion process between Source Active messages and overlay management routes to support inter-domain traffic.

A Multicast Source Discovery Protocol (MSDP) is a multicast routing protocol that:

  • facilitates interconnection of multiple Protocol Independent Multicast Sparse-Mode (PIM-SM) domains,

  • enables a rendezvous point (RP) in a PIM-SM domain to maintain MSDP peering relationships with MSDP-enabled routers in other domains, and

  • allows Cisco IOS XE Catalyst SD-WAN devices, from Cisco IOS XE Catalyst SD-WAN Release 17.11.1a, to interoperate with other devices by converting Source Active (SA) messages received from MSDP peers into OMP routes, and vice-versa.

MSDP enables multicast sources in one PIM-SM domain to be discovered by other PIM-SM domains through the exchange of SA messages between MSDP peers.

When MSDP is enabled on Cisco IOS XE Catalyst SD-WAN devices, a rendezvous point (RP) in a PIM-SM domain maintains MSDP peering relationships with MSDP-enabled routers in other domains. When configured for interoperability, these devices convert Source Active (SA) messages received from MSDP peers into OMP routes and vice-versa. For more information about MSDP, see MSDP.

The following illustration depicts MSDP interoperability between Cisco IOS XE Catalyst SD-WAN devices in Cisco Catalyst SD-WAN and devices in a non-SD-WAN setup.

Figure 1. MSDP Interoperability

Single Homed Network

In the sample topology, the Cisco IOS XE Catalyst SD-WAN device R20 at site 2 has MSDP interoperability enabled. At the non-SD-WAN site, R3 serves as the rendezvous point (RP) for its PIM domain. MSDP peering is established between R3 and R20.

When source H2 sends multicast traffic to R4, R4 registers the data with R3. R3 then sends an MSDP Source Active (SA) message to R20. Because MSDP interoperability is enabled, R20 converts the received MSDP SA message into an OMP SA route and advertises it to all Cisco IOS XE Catalyst SD-WAN devices at other sites through the Cisco SD-WAN Controller.

When R10, a Cisco IOS XE Catalyst SD-WAN device at site 1, receives this OMP SA route, it converts the route into an MSDP SA message and advertises it to its MSDP peer R2 at the non-SD-WAN site. If R2 has receivers interested in the multicast group advertised in the MSDP SA message, it sends a (S,G) join towards the source. This process establishes an inter-domain source tree across the Cisco Catalyst SD-WAN.

As multicast packets arrive at R2 (the RP), R2 forwards them down its shared tree to group members within its domain. R20 withdraws the advertised OMP SA route only when the MSDP SA message expires.

Dual-Homed Network

A dual-homed network has two Cisco IOS XE Catalyst SD-WAN devices configured for MSDP interoperability. At the dual-homed Cisco Catalyst SD-WAN site 3, MSDP peering must be established among the Cisco IOS XE Catalyst SD-WAN devices R30, R40, and the non-SD-WAN device R5.

When the source registers its traffic with the RP R5, R5 sends an MSDP SA message to both R30 and R40. Upon receiving the MSDP SA message, R30 converts it into OMP SA routes and advertises these to all Cisco IOS XE Catalyst SD-WAN devices at other sites, as well as to R40 within site 3.

To prevent routing loops, an MSDP SA filter must be configured between R30 and R40 to drop SA messages that originate from other Cisco IOS XE Catalyst SD-WAN devices and sites via the Overlay Management Protocol (OMP).

At site 1, the Cisco IOS XE Catalyst SD-WAN device R10 receives two OMP SA routes for the same Source Group (S, G) and caches both routes. R10 then converts the OMP SA route into an MSDP SA message and advertises it to its MSDP peer R2 at the non-SD-WAN site. If R2 has receivers interested in the multicast group advertised in the MSDP SA message, it sends a (S, G) join towards the source. This sequence establishes an inter-domain source tree across the Cisco Catalyst SD-WAN.

MSDP supports the following scenarios where Cisco IOS XE Catalyst SD-WAN devices at the Cisco Catalyst SD-WAN sites are configured for MSDP interoperability with other devices located in the non-SD-WAN sites.

  • Source devices located at the Cisco Catalyst SD-WAN sites, and receivers at the Cisco Catalyst SD-WAN and non-SD-WAN sites.

  • Source devices located in the non-SD-WAN sites, and receivers at the Cisco Catalyst SD-WAN and non-SD-WAN sites.

  • In Dual border sites, where two devices are configured for MSDP interoperability in Cisco Catalyst SD-WAN where sources and receivers are located in the Cisco Catalyst SD-WAN sites.

  • In dual border sites, where two devices are configured for MSDP interoperability in non-SD-WAN, and where sources and receivers are located at the non-SD-WAN sites.

  • A Replicator can be any Cisco IOS XE Catalyst SD-WAN device located in the Cisco Catalyst SD-WAN site. For more information about Replicators, see the Replicators section in PIM.

Benefits of support for MSDP to interconnect Cisco SD-WAN and non-SD-WAN

Facilitates MSDP interoperability between devices located at the Cisco SD-WAN sites and devices at the non-SD-WAN sites.

Restrictions for support for MSDP to interconnect Cisco SD-WAN and Non-SD-WAN

  • Only one MSDP mesh group is supported per site in Cisco Catalyst SD-WAN.

  • The MSDP peer devices must be located at the same site and cannot be spread across sites.