Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 722

ip igmp access-group access-list-name Dell Networking OS Behavior: Do not enter the ip igmp access-group command before creating the access-list. If you do, after entering your first deny rule, the system clears multicast routing table and relearns all groups, even those not covered by the rules in the access-list, because there is an implicit deny all rule at the end of all access-lists. Therefore, configuring an IGMP join request filter in this order might result in data loss. If you must enter the ip igmp access-group command before creating the access-list, prevent the system from clearing the routing table by entering a permit any rule with high sequence number before you enter any other rules. In the following example, virtual local area network (VLAN) 400 is configured with an access list to permit only IGMP reports for group 239.0.0.1. Though Receiver 2 sends a membership report for groups 239.0.0.1 and 239.0.0.2, a multicast routing table entry is created only for group 239.0.0.1. VLAN 300 has no access list Multicast Features 722