The SPB-PIM GW functional component for MSDP resides in the SPB-PIM Gateway Controller node (Controller).
Controllers from an SPB network discover sources through MSDP sessions with RPs from a PIM network. Once the SA packed is received at the MSDP module of the Controller, the IP routing table is examined to determine which peer is the next hop towards the originating RP of the SA message. Once the SA RPF test passes, the SA packet is saved in the foreign cache and passed to the Controller.
The Controller nodes also distribute the sources from an SPB domain to a PIM domain through an MSDP session with RPs in the PIM network. Similar to RP, when a Controller in the SPB domain learns of a new (S,G), through a directly connected source or ISIS, the Controller saves the new (S,G) in its local SA cache. The Controller then transmits an SA update message for this source to its MSDP peers in the PIM domain. The Controller that sends the SA to the MSDP is viewed as the RP (circuitless IP interface is used).
MSDP does not work with the traditional PIM implementation. MSDP communicates only with the Controller and should be configured as an IP endpoint.
A circuitless IP interface (CLIP) is used in the context of global router or VRF, hence at least one CLIP in each VRF should be configured.
MSDP should use a single CLIP address as the source for establishing all MSDP connections in the same VRF.
For SPB sources, this CLIP is used as the RP in all SA messages advertised.
MSDP source IP address should be one of the CLIP interfaces pre-configured on the global router or VRF.
Note
MSDP transmits encapsulated multicast data packets inside forwarded MSDP messages. If the received SA is an encapsulated SA, then the switch parses the TTL value of the encapsulated data and compares it against the configured value. If the configured value is less than or equal to the parsed value, then the switch forwards the encapsulated data along with the SA, otherwise the switch forwards the SA alone by stripping the encapsulate data. By default, MSDP forwards encapsulated data along with the SA message. MSDP does not forward the encapsulated data to the local receivers.
When MSDP generates SA messages for SPB sources, the local cache miss data cannot be encapsulated into the SA messages that are sent to the peers.
The switch supports forwarding SA messages with encapsulated data from sources to MSDP peers but not from MSDP peers to the receivers.
For more information on MSDP configuration, see Multicast Source Discovery Protocol configuration.