Useful Commands for Debugging IGMP Snooping

Cisco Catalyst 3750G is used in examples.

Display a snooping configuration information for all VLANs on a switch:

#show ip igmp snooping
Global IGMP Snooping configuration:
-----------------------------------
IGMP snooping              : Enabled
IGMPv3 snooping (minimal)  : Enabled
Report suppression         : Enabled
TCN solicit query          : Disabled
TCN flood query count      : 2
Last Member Query Interval : 1000

Vlan 704:
--------
IGMP snooping                       : Enabled
IGMPv2 immediate leave              : Disabled
Explicit host tracking              : Enabled
Multicast router learning mode      : pim-dvmrp
Last Member Query Interval          : 1000
CGMP interoperability mode          : IGMP_ONLY

Display information about an IP address and a port for received IGMP query messages:

#show ip igmp snooping querier
Vlan      IP Address        IGMP Version   Port                
----------------------------------------------------------------
704       194.44.18.50      v2             Gi1/0/27

Display information on dynamically learned and manually configured multicast router interfaces:

#show ip igmp snooping mrouter
Vlan    ports
----    -----
 704    Gi1/0/27(dynamic)

Display a multicast table information:

#show ip igmp snooping groups
Vlan      Group             Type        Version     Port List
----------------------------------------------------------------
704       239.255.128.1     igmp        v2          Gi1/0/18, Gi1/0/27
704       239.255.128.2     igmp        v2          Gi1/0/18, Gi1/0/27

Enabling an IGMP snooping debug mode:

#debug ip igmp snooping group 
group debugging is on

#terminal monitor 

Report for group:

Mar 24 09:21:11: IGMPSN: group: Received V2 report for group 239.255.128.1 received on Vlan 704, port Gi1/0/18
Mar 24 09:21:11: IGMPSN: group: Adding client ip 192.168.4.10, port_id Gi1/0/18, on vlan 704

Leave for group:

Mar 24 09:21:53: IGMPSN: group: Leave for group 239.255.128.1 received on Vlan 704, port Gi1/0/18
Mar 24 09:21:53: IGMPSN: group: Sending Group-Specific Query for group 239.255.128.1 on Vlan 704, port Gi1/0/18
Mar 24 09:21:54: IGMPSN: group: Deleting group 239.255.128.1
Mar 24 09:21:54: IGMPSN: group: Deleting gce 0100.5e7f.8001
Mar 24 09:21:54: IGMPSN: group: Sending Leave for group 239.255.128.1, source 192.168.4.10 on Vlan 704

Host membership query:

Mar 24 09:22:10: IGMPSN: IGMPv2 General Query received on Vlan 704, port Gi1/0/27

Useful literature:

1. Multicast Does Not Work in the Same VLAN in Catalyst Switches