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29-9
Cisco ASA 5500 Series Configuration Guide using ASDM
Chapter 29 Configuring Multicast Routing
Customizing Multicast Routing
Limiting the Number of IGMP States on an Interface
You can limit the number of IGMP states resulting from IGMP membership reports on a per-interface
basis. Membership reports exceeding the configured limits are not entered in the IGMP cache, and traffic
for the excess membership reports is not forwarded.
To limit the number of IGMP states on an interface, perform the following steps:
Step 1 In the main ASDM window, choose Configuration > Device Setup > Routing > Multicast > IGMP >
Protocol.
Step 2 Choose the interface you want to limit from the table on the Protocol pane, and click Edit.
The Configure IGMP Parameters dialog box appears.
Step 3 In the Group Limit field, enter the maximum number of host that can join on an interface. Valid values
range from 0 to 500. The default value is 500. Setting this value to 0 prevents learned groups from being
added, but manually defined memberships are still permitted.
Step 4 Click OK.
Modifying the Query Messages to Multicast Groups
The ASA sends query messages to discover which multicast groups have members on the networks
attached to the interfaces. Members respond with IGMP report messages indicating that they want to
receive multicast packets for specific groups. Query messages are addressed to the all-systems multicast
group, which has an address of 224.0.0.1, with a time-to-live value of 1.
These messages are sent periodically to refresh the membership information stored on the ASA. If the
ASA discovers that there are no local members of a multicast group still attached to an interface, it stops
forwarding multicast packet for that group to the attached network, and it sends a prune message back
to the source of the packets.
By default, the PIM designated router on the subnet is responsible for sending the query messages. By
default, they are sent once every 125 seconds.
When changing the query response time, by default, the maximum query response time advertised in
IGMP queries is 10 seconds. If the ASA does not receive a response to a host query within this amount
of time, it deletes the group.
To change the query interval, query response time, and query timeout value, perform the following steps:
Step 1 In the main ASDM window, choose Configuration > Device Setup > Routing > Multicast > IGMP >
Protocol.
Step 2 Choose the interface you want to limit from the table on the Protocol pane, and click Edit.
The Configure IGMP Parameters dialog box appears.
Step 3 In the Query Interval field, enter the interval, in seconds, at which the designated router sends IGMP
host-query messages. Valid values range from 1 to 3600 seconds. The default value is 125 seconds.
If the ASA does not hear a query message on an interface for the specified timeout value, then the
ASA becomes the designated router and starts sending the query messages.
Step 4 In the Query Timeout field, enter the period of time, in seconds, before which the ASA takes over as the
requester for the interface after the previous requester has stopped doing so. Valid values range from 60
to 300 seconds. The default value is 255 seconds.