Dell S4048T-ON, Configuration Manual

Page: 377 / 1146

Preventing a Host from Joining a Group
You can prevent a host from joining a particular group by blocking specific IGMP reports using an extended access list containing the
permissible source-group pairs.
NOTE: For rules in IGMP access lists,
source
is the multicast source, not the source of the IGMP packet. For IGMPv2, use the
keyword
any
for
source
(as shown in the following example) because the IGMPv2 hosts do not know in advance who the source
is for the group in which they are interested.
To apply the access list, use the following command.
• Apply the access list.
INTERFACE mode
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 Dell Networking OS clears the 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
ip igmp access-group
command before creating the
access-list, prevent the Dell Networking OS from clearing the routing table by entering a permit any rule with a 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 limiting Receiver 1, so both IGMP reports are accepted and two corresponding entries are
created in the routing table.
Internet Group Management Protocol (IGMP) 377