Information
PIM is a routing protocol used to build multicast distribution trees for forwarding multicast traffic across the network infrastructure. PIM traffic must be limited to only known PIM neighbors by configuring and binding a PIM neighbor filter to interfaces that have PIM enabled.
If a PIM neighbor filter is not applied to interfaces that have PIM enabled, unauthorized switches can join the PIM domain, discover and use the rendezvous points, and advertise their rendezvous points into the domain. This can result in a denial of service by traffic flooding or in the unauthorized transfer of data.
Solution
Configure neighbor ACLs to only accept PIM control plane traffic from documented PIM neighbors. Bind neighbor ACLs to all PIM-enabled interfaces.
Step 1: Configure ACL for PIM neighbors.
SW2(config)#ip access-list standard PIM_NEIGHBORS
SW2(config-std-nacl)#permit 10.1.2.6
SW2(config-std-nacl)#exit
Step 2: Apply the ACL to all interfaces enabled for PIM.
SW2(config)#int g1/1
SW2(config-if)#ip pim neighbor-filter PIM_NEIGHBORS