Allied Telesis AT-S63 - Manual (Page 214)

Chapter 17: IGMP Snooping
214 Section II: Advanced Operations
Note
The combined number of multicast address groups for IGMP and
MLD snooping cannot exceed 255.
4. Click Apply.
Changes to the IGMP snooping parameters are immediately
implemented on the switch.
5. To permanently save your changes, select the Save Config option in
the Configuration menu.