V-256045

Discussion

Real-time multicast traffic can entail multiple large flows of data. Large unicast flows tend to be fairly isolated (i.e., someone doing a file download here or there), whereas multicast can have broader impact on bandwidth consumption, resulting in extreme network congestion. Hence, it is imperative that there is multicast admission control to restrict which multicast groups hosts are allowed to join via IGMP or MLD.

Check Content

Review the configuration of the Arista DR to verify it is filtering IGMP or MLD report messages, allowing hosts to join only groups that have been approved.

Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation. This requirement is not applicable to Any Source Multicast (ASM) because the filtering is being performed by the Rendezvous Point router.

Step 1: Verify the ACL filters the unauthorized IGMP groups. The ACL below is blocking the IGMP group sourced 232.0.0.0/8. Execute the command "sh ip access-list".

ip access-list FILTER_IGMP
  10 deny igmp 232.0.0.0/8 any
  20 permit ip any any

Step 2: Verify the ACL is configured on internal host-facing interfaces (IGMP process) to filter IGMP.

router igmp
  ip igmp access-group FILTER_IGMP

or 

interface ethernet 3
 ip access-group FILTER_IGMP

If the Arista DR is not filtering IGMP or MLD report messages, this is a finding.