V-216629

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 DR to verify that it is filtering IGMP or MLD Membership Report messages, allowing hosts to join only those groups that have been approved.

Step 1: Verify that all host facing interfaces are configured to filter IGMP Membership Report messages (IGMP joins) as shown in the example below.

interface GigabitEthernet0/0
 ip address 10.3.3.3 255.255.255.0
 ip pim sparse-mode
 ip igmp access-group IGMP_JOIN_FILTER
 ip igmp version 3

Step 2: Verify that the Access Control List (ACL) denies unauthorized groups or permits only authorized groups. The example below denies all groups from 239.8.0.0/16 range.

ip access-list standard IGMP_JOIN_FILTER
 deny   239.8.0.0 0.0.255.255
 permit any

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

If the DR is not filtering IGMP or MLD Membership Report messages, this is a finding.