Reference Guide

Multicast Features | 621
In Figure 31-2, 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 limiting Receiver 1, so
both IGMP reports are accepted, and two corresponding entries are created in the routing table.
FTOS Behavior: Do not enter the command ip igmp access-group before creating the access-list. If you do, upon
entering your first deny rule, FTOS clears multicast routing table and re-learns 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 command
ip igmp
access-group
before creating the access-list, prevent FTOS from clearing the routing table by entering a permit any
rule with high sequence number before you enter any other rules.