V-217090

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.

Verify that a group policy has been configured to filter IGMP join requests as shown in the example below.

protocols {
    igmp {
        interface ge-1/0/1.0 {
            group-policy MULTICAST_JOIN_POLICY;
        }
    }

Verify that the policy only allows join requests for those sources that have been approved.

policy-options {
    …
    …
    …
    }
    policy-statement MULTICAST_JOIN_POLICY {
        term BAD_SOURCES {
            from {
                source-address-filter x.x.x.x/32 exact;
                source-address-filter x.x.x.x/24 orlonger;
            }
            then reject;
        }
        …
        …
        …
        }
        term ALLOW_APPROVED {
            then accept;
        }
    }

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

If the DR is not filtering IGMP or MLD report messages to only allow joins for approved sources, this is a finding.