V-283857

Discussion

The current multicast paradigm can let any host join any multicast group at any time by sending an IGMP or MLD membership report to the DR. In a Protocol Independent Multicast (PIM) Sparse Mode network, the DR will send a PIM Join message for the group to the Rendezvous Point (RP). Without any form of admission control, this can pose a security risk to the entire multicast domain, specifically the multicast routers along the shared tree from the DR to the RP that must maintain the mroute state information for each group join request. Hence, it is imperative that the DR is configured to limit the number of mroute states that must be maintained to mitigate the risk of IGMP or MLD flooding.

Check Content

Review the DR configuration to verify it is limiting the number of mroute states via IGMP or MLD.

Verify the maximum number of IGMP or MLD groups and maximum group sources is configured using the command below:

- show router igmp interface "TO-CE" detail | match "Max Groups Allowed"
Max Groups Allowed : 200                Max Groups Till Now: 0

- show router mld interface "TO-CE" detail | match "Max Groups Allowed"
Max Groups Allowed     : 200              Max Groups Till Now: 0

Note: If both global and per-interface state limiters are configured, the limits configured for per-interface state limiters are still enforced but are constrained by the global limit.

If the DR is not limiting multicast join requests via IGMP or MLD on a global or interface basis, this is a finding.