IGMP Snooping Commands 45319IGMP Snooping CommandsDell Networking N2000/N3000/N4000 Series SwitchesSnooping of Internet Group Management Protocol (IGMP) messages is afeature that allows Dell Networking switches to forward multicast trafficintelligently on the switch. Multicast traffic is traffic that is destined to a hostgroup. Host groups are identified by the destination MAC address, i.e. therange 01:00:5e:00:00:00-01:00:5e:7f:ff:ff:ff for IPv4 multicast traffic or33:33:xx:xx:xx:xx for IPv6 multicast traffic. Based on the IGMP query andreport messages, the switch forwards traffic only to the ports that request themulticast traffic. This prevents the switch from broadcasting the traffic to allports and possibly affecting network performance.IGMP snooping switches build forwarding lists by monitoring for, and insome cases intercepting, IGMP messages. Although the software processingthe IGMP messages could maintain state information based on the full IPgroup addresses, the forwarding tables in Dell Networking are mapped to linklayer addresses.The Multicast Forwarding Database (MFDB) manages the forwardingaddress table for Layer 2 multicast protocols, such as IGMP Snooping.The IGMP Snooping code in the CPU ages out IGMP entries in the MFDB.If a report for a particular group on a particular interface is not receivedwithin a certain time interval (query interval), the IGMP Snooping codedeletes that interface from the group. The value for query interval time isconfigurable using management.If an IGMP Leave Group message is received on an interface, the IGMPSnooping code sends a query on that interface and waits a specified length oftime (maximum response time). If no response is received within that time,that interface is removed from the group. The value for maximum responsetime is configurable using management.In addition to building and maintaining lists of multicast groupmemberships, the snooping switch also maintains a list of multicast routers.When forwarding multicast packets, they should be forwarded on ports thathave joined using IGMP and also on ports on which multicast routers areattached. The reason for this is that in IGMP there is only one active query
