V-269899

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 report messages, allowing hosts to only join multicast groups from sources that have been approved.

Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation.

Step 1: Verify that SSM is in use. If not, this requirement is not applicable.

!
ip access-list ssm-1
 seq 10 permit ip any 236.0.0.0/8
 
!
ip pim ssm-range ssm-1

Step 2: Verify that each interface applies an appropriate inbound IGMP filter that permits or denies IGMP messages.

!
interface vlan100
 no shutdown
 ip access-group IGMP_FILTER in
 
!
ip access-list IGMP_FILTER
 seq 10 deny 2 224.0.0.22  239.8.0.0/16 ttl eq 1
 seq 20 permit 2 224.0.0.0/24 238.5.0.0/16
 seq 30 permit ip any any

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