Source Active Caching

When a Multicast Source Discovery Protocol (MSDP) supported device that is also a Rendezvous Point (RP) receives a Source Active message, it checks the Protocol Independent Multicast (PIM) sparse multicast group table for receivers for that group. If there are receivers for that group being advertised in the Source Active message, the RP sends a Join message towards the source.

In

When in the full doc (IP Multicast) this cross reference will do to the figure titled PIM Sparse Domains Joined by MSDP devices in the Configuring Multicast Source Discovery Protocol topic.
PIM Sparse Domains Joined by MSDP Devices, if the MSDP device (which is an RP) in Domain 4 has a table entry for the receiver, the RP sends a Join message on behalf of the receiver back through the reverse-path forwarding (RPF) tree to the source, in this case the source in Domain 1.

Source Active caching is enabled in MSDP on RUCKUS devices. The RP caches the Source Active messages it receives even if the RP does not have a receiver for the group. Once a receiver arrives, the RP can then send a Join message to the cached source immediately.

The MSDP SA cache size is set by default to 4096 messages, but can be configured from 1024 message to 8192 messages using the system-max msdp-sa-cache command.

Added the following text for 10.0.20a

The size of the cache for Source Active messages per peer can also be configured by using the sa-limit in command. If a specific peer limit is 4000 but the system-max value is 2000 that means that the peer is able to receive only the 2000 SA cache for the specific peer.

Note: If the maximum cache size defined at the global level is less than the peer-specific maximum cache size, the global-level size takes precedence and the system restricts the peer cache to the global-level size.
Parent topic: Configuring Multicast Source Discovery Protocol