IP Multicast Optimization: IGMP State Limit

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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

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.


Note

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.

Related Tasks
Configuring Global IGMP State Limiters
Related References
Configuring IGMP State Limiters Example

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 (*, group address)> on <interface type number> by host <ip address>
    • %IGMP-6-IGMP_CHANNEL_LIMIT: IGMP limit exceeded for <channel (source address, group address)> on <interface type number> by host <ip 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.

How to Configure IGMP State Limit

Configuring IGMP State Limiters


Note

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.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip igmp limit number

    4.    end

    5.    show ip igmp groups


DETAILED STEPS
     Command or ActionPurpose
    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.

     
    Related Concepts
    IGMP State Limit
    Related References
    Configuring IGMP State Limiters Example

    Configuring Per Interface IGMP State Limiters

    Perform this optional task to configure a per interface IGMP state limiter.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    ip igmp limit number [except access-list]

      5.    Do one of the following:

      • exit
      • end

      6.    show ip igmp interface [type number]

      7.    show ip igmp groups


    DETAILED STEPS
       Command or ActionPurpose
      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 GigabitEthernet0/0
       

      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.

       

      Configuration examples for IGMP State Limit

      Configuring IGMP State Limiters Example

      The following example shows how to configure IGMP state limiters to provide multicast CAC in a network environment where all the multicast flows roughly utilize the same amount of bandwidth.

      This example uses the topology illustrated in the figure.


      Note

      Although the following illustration and example uses routers in the configuration, any device (router or switch) can be used.

      Figure 1. IGMP State Limit Example Topology

      In this example, a service provider is offering 300 Standard Definition (SD) TV channels. Each SD channel utilizes approximately 4 Mbps.

      The service provider must provision the Gigabit Ethernet interfaces on the PE router connected to the Digital Subscriber Line Access Multiplexers (DSLAMs) as follows: 50% of the link’s bandwidth (500 Mbps) must be available to subscribers of the Internet, voice, and video on demand (VoD) service offerings while the remaining 50% (500 Mbps) of the link’s bandwidth must be available to subscribers of the SD channel offerings.

      Because each SD channel utilizes the same amount of bandwidth (4 Mbps), per interface IGMP state limiters can be used to provide the necessary CAC to provision the services being offered by the service provider. To determine the required CAC needed per interface, the total number of channels is divided by 4 (because each channel utilizes 4 Mbps of bandwidth). The required CAC needed per interface, therefore, is as follows:

      500Mbps / 4Mbps = 125 mroutes

      Once the required CAC is determined, the service provider uses the results to configure the per IGMP state limiters required to provision the Gigabit Ethernet interfaces on the PE router. Based on the network’s CAC requirements, the service provider must limit the SD channels that can be transmitted out a Gigabit Ethernet interface (at any given time) to 125. Configuring a per interface IGMP state limit of 125 for the SD channels provisions the interface for 500 Mbps of bandwidth, the 50% of the link’s bandwidth that must always be available (but never exceeded) for the SD channel offerings.

      The following configuration shows how the service provider uses a per interface mroute state limiter to provision interface Gigabit Ethernet 0/0/0 for the SD channels and Internet, Voice, and VoD services being offered to subscribers: 

      interface GigabitEthernet0/0/0
description --- Interface towards the DSLAM ---
.
.
.
ip igmp limit 125
      Related Concepts
      IGMP State Limit
      Related Tasks
      Configuring Global IGMP State Limiters

      Additional References

      Related Documents

      Related Topic

      Document Title

      Cisco IOS commands

      Cisco IOS Master Commands List, All Releases

      Cisco IOS IP Multicast commands

      Cisco IOS IP Multicast Command Reference

      MIBs

      MIB

      MIBs Link

      No new or modified MIBs are supported by this feature, and support for existing standards has not been modified by this feature.

      To locate and download MIBs for selected platforms, Cisco IOS XE releases, and feature sets, use Cisco MIB Locator found at the following URL:

      http:/​/​www.cisco.com/​go/​mibs

      Technical Assistance

      Description

      Link

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      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

      Feature History and Information for IGMP State Limit

      Release

      Modification

      Cisco IOS XE 3.3SE

      This feature was introduced.