Administrator Guide

NOTE: The IN-L3-McastFib CAM partition is used to store multicast routes and is a separate hardware
limit that exists per port-pipe. Any software-configured limit may supersede by this hardware space
limitation. The opposite is also true, the CAM partition might not be exhausted at the time the system-
wide route limit the ip multicast-limit command sets is reached.
Preventing a Host from Joining a Group
You can prevent a host from joining a particular group by blocking specific IGMP reports. Create 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 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 system 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 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 623