H3C Technologies H3C S7500E Series Switches - Manual (Page 56)

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z When the number of multicast groups a port has joined reaches the maximum number
configured, the system deletes all the forwarding entries persistent to that port from the
IGMP snooping forwarding table, and the hosts on this port need to join the multicast
groups again.
z If you have configured static or simulated joins on a port, however, when the number of
multicast groups on the port exceeds the configured threshold, the system deletes all the
forwarding entries persistent to that port from the IGMP snooping forwarding table and
applies the static or simulated joins again, until the number of multicast groups joined by
the port comes back within the configured threshold.
Configuring Multicast Group Replacement
For some special reasons, the number of multicast groups that can be joined on the current
switch or port may exceed the number configured for the switch or the port. In addition, in some
specific applications, a multicast group newly joined on the switch needs to replace an existing
multicast group automatically. A typical example is “channel switching”, namely, by joining a
new multicast group, a user automatically switches from the current multicast group to the new
one.
To address such situations, you can enable the multicast group replacement function on the
switch or certain ports. When the number of multicast groups joined on the switch or a port has
joined reaches the limit:
z If the multicast group replacement feature is enabled, the newly joined multicast group
automatically replaces an existing multicast group with the lowest address.
z If the multicast group replacement feature is not enabled, new IGMP reports will be
automatically discarded.
Configuring multicast group replacement globally
Follow these steps to configure multicast group replacement globally:
To do... Use the command... Remarks
Enter system view system-view —
Enter IGMP snooping view igmp-snooping —
Enable multicast group
replacement
overflow-replace [ vlan
vlan-list ]
Required
Disabled by default
Configuring multicast group replacement on a port or a group of ports
Follow these steps to configure multicast group replacement on a port or a group of ports: