3Com 8800 Configuration Manual page 292

3Com Switch 8800 Configuration Guide
If IGMP Snooping is not enabled, input the igmp-snooping enable command in
system view to enable IGMP Snooping. Then, use the same command in VLAN
view to enable IGMP Snooping in the corresponding VLAN.
2) Multicast forwarding table set up by IGMP Snooping is wrong.
Input the display igmp-snooping group command to display if the multicast
group is the expected one.
If the multicast group created by IGMP Snooping is not correct, turn to
professional maintenance personnel for help.
Continue with diagnosis 3 if the second step is completed.
3) Multicast forwarding table set up on the bottom layer is wrong.
In any view, execute the display mac-address vlan command to check whether
the MAC multicast forwarding table established in the VLAN identified by vlanid is
consistent with that established by IGMP Snooping.
If they are not consistent, please contact the maintenance personnel for help.
Chapter 24 IGMP Snooping Configuration
24-9