3Com 5500-EI PWR Install Manual page 433

1) IGMP Snooping is not enabled.
Use the display current-configuration command to check the status of IGMP Snooping.
If IGMP Snooping is disabled, check whether it is disabled globally or in the specific VLAN. If it is
disabled globally, use the igmp-snooping enable command in both system view and VLAN view
to enable it both globally and on the corresponding VLAN at the same time. If it is only disabled on
the corresponding VLAN, use the igmp-snooping enable command in VLAN view only to enable it
on the corresponding VLAN.
2) Multicast forwarding table set up by IGMP Snooping is wrong.
Use the display igmp-snooping group command to check if the multicast groups are expected
ones.
If the multicast group set up by IGMP Snooping is not correct, contact your technical support
personnel.
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