Cisco IP Multicast Optimization: IGMP State Limit User Guide PDF (EN)

IGMP State Limit

IP Multicast Optimization: IGMP State Limit Prerequisites for IGMP State Limit, on page 1 Restrictions for IGMP State Limit, on page 1 Information About IGMP State Limit, on page 1 How to Configure IGMP State Limit, on page 3 Configuration examples for IGMP State Limit, on page 4 Additional References, on page 6 Feature History for IP Multicast Optimization: IGMP State Limit, on page 6 Prerequisites for IGMP State Limit • IP multicast is enabled and the Protocol Independent Multicast (PIM) interfaces are configured using the tasks described in the "Configuring Basic IP Multicast" module of the IP Multicast: PIM Configuration Guide . • ALL ACLs must be configured.

For information, see the see the " Creating an IP Access List and Applying It to an Interface " module of the Security Configuration Guide: Access Control Lists guide. Restrictions for IGMP State Limit You can configure only one global limit per device and one limit per interface. Information About IGMP State Limit This section provides information about IGMP state limit. IGMP State Limit The IGMP State Limit feature allows for the configuration of IGMP state limiters, which impose limits on mroute states resulting from IGMP membership reports (IGMP joins) on a global or per interface basis. Membership reports exceeding the configured limits are not entered into the IGMP cache.

This feature can be used to prevent DoS attacks or to provide a multicast CAC mechanism in network environments where all the multicast flows roughly utilize the same amount of bandwidth. IP Multicast Optimization: IGMP State Limit 1

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Mechanics of IGMP State Limiters

IGMP state limiters impose limits on the number of mroute states resulting from IGMP, IGMP v3lite, and URL Rendezvous Directory (URD) membership reports on a global or per interface basis. Note IGMP State Limit Feature Design • Configuring IGMP state limiters in global configuration mode specifies a global limit on the number of IGMP membership reports that can be cached. • Configuring IGMP state limiters in interface configuration mode specifies a limit on the number of IGMP membership reports on a per interface basis. • Use ACLs to prevent groups or channels from being counted against the interface limit. A standard or an extended ACL can be specified.

A standard ACL can be used to define the (*, G) state to be excluded from the limit on an interface. An extended ACLs can be used to define the (S, G) state to be excluded from the limit on an interface. An extended ACL also can be used to define the (*, G) state to be excluded from the limit on an interface, by specifying 0.0.0.0 for the source address and source wildcard--referred to as (0, G)--in the permit or deny statements that compose the extended access list. • You can only configure one global limit per device and one limit per interface. Mechanics of IGMP State Limiters The mechanics of IGMP state limiters are as follows:

• Each time a router receives an IGMP membership report for a particular group or channel, the Cisco IOS software checks to see if either the limit for the global IGMP state limiter or the limit for the per interface IGMP state limiter has been reached. • If only a global IGMP state limiter has been configured and the limit has not been reached, IGMP membership reports are honored. When the configured limit has been reached, subsequent IGMP membership reports are then ignored (dropped) and a warning message in one of the following formats is generated: %IGMP-6-IGMP_GROUP_LIMIT: IGMP limit exceeded for (*, group address)> on type number> by host address> %IGMP-6-IGMP_CHANNEL_LIMIT:

IGMP limit exceeded for (source address, group address)> on type number> by host address> • If only per interface IGMP state limiters are configured, then each limit is only counted against the interface on which it was configured. • If both a global IGMP state limiter and per interface IGMP state limiters are configured, the limits configured for the per interface IGMP state limiters are still enforced but are constrained by the global limit. IP Multicast Optimization: IGMP State Limit IGMP State Limit Feature Design IP Multicast Optimization: IGMP State Limit 2

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Configuring Per Interface IGMP State Limiters

How to Configure IGMP State Limit This section describes how to configure IGMP state limit. Configuring IGMP State Limiters IGMP state limiters impose limits on the number of mroute states resulting from IGMP, IGMP v3lite, and URD membership reports on a global or per interface basis. Configuring Global IGMP State Limiters Perform this optional task to configure one global IGMP state limiter per device. Procedure Configuring Per Interface IGMP State Limiters Perform this optional task to configure a per interface IGMP state limiter. IP Multicast Optimization: IGMP State Limit How to Configure IGMP State Limit Command or Action Purpose Step 1 enable Example:

Device> enable Enables privileged EXEC mode. • Enter your password if prompted. Step 2 configure terminal Example: Device# configure terminal Enters global configuration mode. Step 3 ip igmp limit number Example: Device(config)# ip igmp limit 150 Configures a global limit on the number of mroute states resulting from IGMP membership reports (IGMP joins). Step 4 end Example: Device(config-if)# end Ends the current configuration session and returns to privileged EXEC mode. Step 5 show ip igmp groups Example: Device# show ip igmp groups (Optional) Displays the multicast groups with receivers that are directly connected to the device and that were learned through IGMP. IP Multicast Optimization:

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Configuration examples for IGMP State Limit

Procedure Configuration examples for IGMP State Limit This section show configuration examples of IGMP state limit. IP Multicast Optimization: IGMP State Limit Configuration examples for IGMP State Limit Command or Action Purpose Step 1 enable Example: Device> enable Enables privileged EXEC mode. • Enter your password if prompted. Step 2 configure terminal Example: Device# configure terminal Enters global configuration mode. Step 3 interface type number Example: Device(config)# interface GigabitEthernet 1/0/0 Enters interface configuration mode. • Specify an interface that is connected to hosts. Step 4 ip igmp limit number [except access-list] Example:

Device(config-if)# ip igmp limit 100 Configures a per interface limit on the number of mroutes states created as a result of IGMP membership reports (IGMP joins). Step 5 Do one of the following: • exit • end Example: Device(config-if)# exit Device(config-if)# end • (Optional) Ends the current configuration session and returns to global configuration mode. Repeat steps 3 and 4 to configure a per interface limiter on another interface. • Ends the current configuration session and returns to privileged EXEC mode. Step 6 show ip igmp interface [type number] Example:

Device# show ip igmp interface (Optional) Displays information about the status and configuration of IGMP and multicast routing on interfaces. Step 7 show ip igmp groups Example: Device# show ip igmp groups (Optional) Displays the multicast groups with receivers that are directly connected to the device and that were learned through IGMP. IP Multicast Optimization: IGMP State Limit 4

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