V-256038

Discussion

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.

Check Content

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.