V-221139

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.

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 Ethernet2/4
 no switchport
 ip address 10.2.22.3/24 
 ip pim sparse-mode
 ip igmp version 3
 ip igmp report-policy ALLOWED_SOURCES

Step 2: Verify that the report policy permits only sources that have been approved by the organization.

route-map ALLOWED_SOURCES permit 10
 match ip multicast source x.1.2.6/32 
route-map ALLOWED_SOURCES permit 20
 match ip multicast source x.1.2.7/32 
route-map ALLOWED_SOURCES deny 30
 match ip multicast source 0.0.0.0/0

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

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