Information
IGMP snooping operates on a Layer 2 device as a multicast constraining mechanism designed to enhance multicast forwarding efficiency. It creates Layer 2 multicast forwarding entries by processing IGMP packets exchanged between hosts and routers. Without IGMP snooping, the switch would flood multicast packets to all hosts within a VLAN. By enabling IGMP snooping, the Layer 2 device forwards multicast packets associated with known multicast groups only to the receivers that have expressed interest, thereby conserving bandwidth on segments of the network where no hosts have requested the multicast traffic.
The device may encounter invalid multicast entries if malicious users send IGMP reports, which can disrupt multicast services for legitimate users. To address this, configuring a multicast group policy using an access control list (ACL) allows the Layer 2 device to control which multicast groups hosts can join. The device filters IGMP reports according to the policy and adds the host's port to the outgoing port list only if the report is permitted by the policy. This ensures that multicast traffic flows only to authorized groups, providing better security and optimized resource utilization.
Solution
To apply ACL to IGMP Snooping -
switch(config)# ip igmp snooping apply access list <ACL-NAME>
Impact:
If an IGMPv3 packet contains multiple group addresses, the switch processes only the permitted group addresses per the ACL rules. Such packets are forwarded to the querier and PIM router, even if some group addresses are blocked. This prevents delays in learning permitted groups.If all group addresses in an IGMPv3 packet are denied by the ACL, the packet is not forwarded to the querier or PIM router, causing existing join messages for those groups to time out.For IGMPv2, if the packet does not match any rule or matches a deny rule, the packet is dropped, ensuring unauthorized multicast traffic is blocked.
Item Details
Category: ACCESS CONTROL, SECURITY ASSESSMENT AND AUTHORIZATION, MEDIA PROTECTION, SYSTEM AND COMMUNICATIONS PROTECTION
References: 800-53|AC-3, 800-53|AC-5, 800-53|AC-6, 800-53|CA-7, 800-53|MP-2, 800-53|SC-4, CSCv7|14.6, CSCv7|14.7
Control ID: cabf91c6a950c896521cdbdad42861c93d9401d756f25c244db5fa8418a3c85a