The Arista multicast Designated Router (DR) must be configured to increase the shortest-path tree (SPT) threshold or set it to infinity to minimalize source-group (S, G) state within the multicast topology where Any Source Multicast (ASM) is deployed.

ASM can have many sources for the same groups (many-to-many). For many receivers, the path via the RP may not be ideal compared with the shortest path from the source to the receiver. By default, the last-hop router will initiate a router from the shared tree to a source-specific SPT to obtain lower latencies. This is accomplished by the last-hop router sending an (S, G) Protocol Independent Multicast (PIM) Join toward S (the source).

When the last-hop router begins to receive traffic for the group from the source via the SPT, it will send a PIM Prune message to the RP for the (S, G). The RP will then send a Prune message toward the source. The SPT routerover becomes a scaling issue for large multicast topologies that have many receivers and many sources for many groups because (S, G) entries require more memory than (*, G). Hence, it is imperative to minimize the amount of (S, G) state to be maintained by increasing the threshold that determines when the SPT routerover occurs.

Review the Arista multicast last-hop router configuration to verify the SPT routerover threshold is increased (default is "0") or set to infinity (never router over).

router pim sparse-mode ipv4 spt threshold infinity

If any Arista multicast router is not configured to increase the SPT threshold or set to infinity to minimalize (S, G) state, this is a finding.

Configure the Arista multicast router to increase the SPT threshold or set it to infinity to minimalize (S, G) state within the multicast topology where ASM is deployed.

LEAF-1A(config)#router pim sparse-mode LEAF-1A(config-router-pim-sparse)#ipv4 LEAF-1A(config-router-pim-sparse-ipv4)#spt threshold infinity