3Com Switch 4500 26-Port Configuration Manual page 162

160 C 8: IGMP S
HAPTER NOOPING
Diagnosis 3: Multicast forwarding table set up on the bottom layer is wrong.
1 Enable IGMP Snooping group in user view and then input the command
igmp-snooping group
layer and that created by IGMP Snooping is consistent. You may also input the
display mac vlan
table under vlanid in the bottom layer and that created by IGMP Snooping is
consistent.
2 If they are not consistent, refer to Technical Support for assistance.
to check if MAC multicast forwarding table in the bottom
command in any view to check if MAC multicast forwarding
display