IGMP Snooping

This module describes how to enable and configure the Ethernet Virtual Connection (EVC)-based IGMP Snooping feature globally and on bridge domains.

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Information About IGMP Snooping

IGMP Snooping

Multicast traffic becomes flooded because a device usually learns MAC addresses by looking into the source address field of all the frames that it receives. A multicast MAC address is never used as the source address for a packet. Such addresses do not appear in the MAC address table, and the device has no method for learning them.

IP Multicast Internet Group Management Protocol (IGMP), which runs at Layer 3 on a multicast device, generates Layer 3 IGMP queries in subnets where the multicast traffic must be routed. IGMP (on a device) sends out periodic general IGMP queries.

IGMP Snooping is an Ethernet Virtual Circuit (EVC)-based feature set. EVC decouples the concept of VLAN and broadcast domain. An EVC is an end-to-end representation of a single instance of a Layer 2 service being offered by a provider. In the Cisco EVC framework, bridge domains are made up of one or more Layer 2 interfaces known as service instances. A service instance is the instantiation of an EVC on a given port on a given device. A service instance is associated with a bridge domain based on the configuration.

Traditionally, a VLAN is a broadcast domain, and physical ports are assigned to VLANs as access ports; the VLAN tag in a packet received by a trunk port is the same number as the internal VLAN broadcast domain. With EVC, an Ethernet Flow Point (EFP) is configured and associated with a broadcast domain. The VLAN tag is used to identify the EFP only and is no longer used to identify the broadcast domain.

When you enable EVC-based IGMP snooping on a bridge domain, the bridge domain interface responds at Layer 2 to the IGMP queries with only one IGMP join request per Layer 2 multicast group. Each bridge domain represents a Layer 2 broadcast domain. The bridge domain interface creates one entry per subnet in the Layer 2 forwarding table for each Layer 2 multicast group from which it receives an IGMP join request. All hosts interested in this multicast traffic send IGMP join requests and are added to the forwarding table entry. During a Layer 2 lookup on a bridge domain to which the bridge domain interface belongs, the bridge domain forwards the packets to the correct EFP. When the bridge domain interface hears the IGMP Leave group message from a host, it removes the table entry of the host.

Layer 2 multicast groups learned through IGMP snooping are dynamic. However, you can statically configure Layer 2 multicast groups. If you specify group membership for a multicast group address statically, your static setting supersedes any automatic manipulation by IGMP snooping. Multicast group membership lists can consist of both user-defined and IGMP snooping-learned-settings.

Restrictions for IGMP Snooping

  • IGMP snooping is only supported on a Bridge Domain when OTV is enabled on ASR 1000 routers.

  • If IGMP snooping is configured on a Bridge Domain with OTV enabled, then the IGMP snooping process limits the multicast traffic. In this scenario, the snooping tables are populated.

  • If IGMP snooping is configured on a Bridge Domain without OTV, the IGMP snooping process does not limit multicast traffic. In this scenario, the snooping tables are not populated and the multicast traffic floods the entire VLAN.

How to Configure IGMP Snooping

Enabling IGMP Snooping

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip igmp snooping

    4.    bridge-domain bridge-id

    5.    ip igmp snooping

    6.    end


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 snooping


    Example: 
    Device(config)# ip igmp snooping
     

    Globally enables IGMP snooping after it has been disabled.

     
    Step 4 bridge-domain bridge-id


    Example: 
    Device(config)# bridge-domain 100
     

    (Optional) Enters bridge domain configuration mode.

     
    Step 5 ip igmp snooping


    Example: 
    Device(config-bdomain)# ip igmp snooping
     

    (Optional) Enables IGMP snooping on the bridge domain interface being configured.

    • Required only if IGMP snooping was previously explicitly disabled on the specified bridge domain.

     
    Step 6 end


    Example: 
    Device(config-bdomain)# end
     

    Returns to privileged EXEC mode.

     

    Configuring IGMP Snooping Globally

    Perform this task to modify the global configuration for IGMP snooping.

    Before You Begin

    IGMP snooping must be enabled. IGMP snooping is enabled by default.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    ip igmp snooping robustness-variable variable

      4.    ip igmp snooping tcn query solicit

      5.    ip igmp snooping tcn flood query count count

      6.    ip igmp snooping report-suppression

      7.    ip igmp snooping explicit-tracking-limit limit

      8.    ip igmp snooping last-member-query-count count

      9.    ip igmp snooping last-member-query-interval interval

      10.    ip igmp snooping check { ttl | rtr-alert-option }

      11.    exit


    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 snooping robustness-variable variable


      Example:
      Device(config)# ip igmp snooping robustness-variable 3
       

      (Optional) Configures IGMP snooping robustness variable.

       
      Step 4 ip igmp snooping tcn query solicit


      Example:
      Device(config)# ip igmp snooping tcn query solicit
       

      (Optional) Enables device to send TCN query solicitation even if it is not the spanning-tree root.

       
      Step 5 ip igmp snooping tcn flood query count count


      Example:
      Device(config)# ip igmp snooping tcn flood query count 4
       

      (Optional) Configures the TCN flood query count for IGMP snooping.

       
      Step 6 ip igmp snooping report-suppression


      Example:
      Device(config)# ip igmp snooping report-suppression
       

      (Optional) Enables report suppression for IGMP snooping.

       
      Step 7 ip igmp snooping explicit-tracking-limit limit


      Example:
      Device(config)# ip igmp snooping explicit-tracking-limit 200
       

      (Optional) Limits the number of reports in the IGMP snooping explicit-tracking database.

       
      Step 8 ip igmp snooping last-member-query-count count


      Example:
      Device (config)# ip igmp snooping last-member-query-count 5
       

      (Optional) Configures how often Internet Group Management Protocol (IGMP) snooping will send query messages in response to receiving an IGMP leave message. The default is 2 milliseconds.

       
      Step 9 ip igmp snooping last-member-query-interval interval


      Example:
      Device (config)# ip igmp snooping last-member-query-interval 200
       

      (Optional) Configures the length of time after which the group record is deleted if no reports are received. The default is 1000 milliseconds.

       
      Step 10 ip igmp snooping check { ttl | rtr-alert-option }


      Example:
      Device (config)# ip igmp snooping check ttl
       

      (Optional) Enforces IGMP snooping check.

       
      Step 11 exit


      Example:
      Device (config)# exit
       

      Exits global configuration mode and returns to privileged EXEC mode.

       

      Configuring IGMP Snooping on a Bridge Domain Interface

      Perform this task to modify the IGMP snooping configuration on a bridge domain interface.

      Before You Begin

      • The bridge domain interface must be created. See the "Configuring Bridge Domain Interfaces" section of the Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide.

      • IGMP snooping must be enabled on the interface to be configured. IGMP snooping is enabled by default.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    bridge-domain bridge-id

        4.    ip igmp snooping immediate-leave

        5.    ip igmp snooping robustness-variable variable

        6.    ip igmp snooping report-suppression

        7.    ip igmp snooping explicit-tracking

        8.    ip igmp snooping explicit-tracking-limit limit

        9.    ip igmp snooping last-member-query-count count

        10.    ip igmp snooping last-member-query-interval interval

        11.    ip igmp snooping access-group {acl-number | acl-name}

        12.    ip igmp snooping limit num [except {acl-number | acl-name}]

        13.    ip igmp snooping minimum-version {2 | 3}

        14.    ip igmp snooping check { ttl | rtr-alert-option }

        15.    ip igmp snooping static source source-address interface port-type port-number

        16.    end


      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 bridge-domain bridge-id


        Example:
        Device(config)# bridge-domain 100
         

        Enters bridge domain configuration mode.

         
        Step 4 ip igmp snooping immediate-leave


        Example:
        Device(config-bdomain)# ip igmp snooping immediate-leave
         

        (Optional) Enables IGMPv2 immediate-leave processing.

        Note   

        When both immediate-leave processing and the query count are configured, fast-leave processing takes precedence.

         
        Step 5 ip igmp snooping robustness-variable variable


        Example:
        Device(config-bdomain)# ip igmp snooping robustness-variable 3
         

        (Optional) Configures the IGMP snooping robustness variable. The default is 2.

         
        Step 6 ip igmp snooping report-suppression


        Example:
        Device(config-bdomain)# ip igmp snooping report-suppression
         

        (Optional) Enables report suppression for all hosts on the bridge domain interface.

         
        Step 7 ip igmp snooping explicit-tracking


        Example:
        Device(config-bdomain)#  ip igmp snooping explicit-tracking
         

        (Optional) Enables IGMP snooping explicit tracking. Explicit tracking is enabled by default.

         
        Step 8 ip igmp snooping explicit-tracking-limit limit


        Example:
        Device(config-bdomain)# ip igmp snooping explicit-tracking-limit 200
         

        (Optional) Limits the number of reports in the IGMP snooping explicit-tracking database.

         
        Step 9 ip igmp snooping last-member-query-count count


        Example:
        Device(config-bdomain)# ip igmp snooping last-member-query-count 5
         

        (Optional) Configures the interval for snooping query messages sent in response to receiving an IGMP leave message. The default is 2 milliseconds.

        Note   

        When both immediate-leave processing and the query count are configured, fast-leave processing takes precedence.

         
        Step 10 ip igmp snooping last-member-query-interval interval


        Example:
        Device(config-bdomain)#  ip igmp snooping last-member-query-interval 2000
         

        (Optional) Configures the length of time after which the group record is deleted if no reports are received. The default is 1000 milliseconds.

         
        Step 11 ip igmp snooping access-group {acl-number | acl-name}


        Example:
        Device(config-bdomain)# ip igmp snooping access-group 1300
         

        Configures ACL-based filtering on a bridge domain.

         
        Step 12 ip igmp snooping limit num [except {acl-number | acl-name}]


        Example:
        Device(config-bdomain)# ip igmp snooping 4400 except test1
         

        (Optional) Limits the number of groups or channels allowed on a bridge domain.

         
        Step 13 ip igmp snooping minimum-version {2 | 3}


        Example:
        Device(config-bdomain)# ip igmp snooping minimum-version 2
         

        (Optional) Configures IGMP protocol filtering.

         
        Step 14 ip igmp snooping check { ttl | rtr-alert-option }


        Example:
        Device(config-bdomain)# ip igmp snooping check ttl
         

        (Optional) Enforces IGMP snooping check.

         
        Step 15 ip igmp snooping static source source-address interface port-type port-number


        Example:
        Device(config-bdomain)# ip igmp snooping static source 192.0.2.1 interface gigbitethernet 1/1/1
         

        (Optional) Configures a host statically for a Layer 2 LAN port.

         
        Step 16 end


        Example:
        Device(config-bdomain)# end
         

        Returns to privileged EXEC mode.

         

        Configuring an EFP

        Perform this task to configure IGMP snooping features on an EFP.

        Before You Begin

        The EFP and bridge domain must be previously configured. Configuring a service instance on a Layer 2 port creates a pseudoport or Ethernet Flow Point (EFP) on which you configure Ethernet Virtual Connection (EVC) features. See the “Configuring Ethernet Virtual Connections on the Cisco ASR 1000 Router” section of the Carrier Ethernet Configuration Guide for configuration information.

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    router-guard ip multicast efps

          4.    interface type number

          5.    service instance id ethernet

          6.    router-guard multicast

          7.    ip igmp snooping tcn flood

          8.    ip igmp snooping access-group {acl-number | acl-name}

          9.    ip igmp snooping limit num [except {acl-number | acl-name}]

          10.    end


        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 router-guard ip multicast efps


          Example:
          Device(config)# router-guard ip multicast efps
           

          (Optional) Enables the router guard for all EFPs.

           
          Step 4 interface type number


          Example:
          Device(config)# interface BDI100
           

          (Optional) Specifies the bridge domain interface to be configured.

           
          Step 5 service instance id ethernet


          Example:
          Device(config-if)# service instance 333 ethernet
           

          (Optional) Enters Ethernet service configuration mode for configuring the EFP.

           
          Step 6 router-guard multicast


          Example:
          Device(config-if-srv)# router-guard multicast
           

          (Optional) Configures a router guard on an EFP.

           
          Step 7 ip igmp snooping tcn flood


          Example:
          Device(config-if-srv)# no ip igmp snooping tcn flood
           

          (Optional) Disables TCN flooding on an EFP. TCN flooding is enabled by default.

           
          Step 8 ip igmp snooping access-group {acl-number | acl-name}


          Example:
          Device(config-if-srv)# ip igmp snooping access-group 44
           

          (Optional) Configures ACL-based filtering on an EFP.

           
          Step 9 ip igmp snooping limit num [except {acl-number | acl-name}]


          Example:
          Device(config-if-srv)# ip igmp snooping limit 1300 except test1
           

          (Optional) Limits the number of IGMP groups or channels allowed on an EFP.

           
          Step 10 end


          Example:
          Device(config-if-srv)# end
           

          Returns to privileged EXEC mode.

           

          Verifying IGMP Snooping

          SUMMARY STEPS

            1.    enable

            2.    show igmp snooping [count [bd bd-id]]

            3.    show igmp snooping groups bd bd-id [ count | ip-address [verbose] [hosts | sources | summary ]]

            4.    show igmp snooping membership bd bd-id

            5.    show igmp snooping mrouter [bd bd-id]

            6.    show igmp snooping counters [bd bd-id]


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 enable


            Example:
            Device> enable
             

            Enables privileged EXEC mode.

            • Enter your password if prompted.

             
            Step 2 show igmp snooping [count [bd bd-id]]


            Example:
            Device(config)# show igmp snooping
             

            Displays configuration for IGMP snooping, globally or by bridge domain.

             
            Step 3 show igmp snooping groups bd bd-id [ count | ip-address [verbose] [hosts | sources | summary ]]


            Example:
            Device(config)# show igmp snooping groups bd 100
             

            Displays snooping information for groups by bridge domain.

             
            Step 4 show igmp snooping membership bd bd-id


            Example:
            Device(config)# show igmp snooping membership bd 100
             

            Displays IGMPv3 host membership information.

             
            Step 5 show igmp snooping mrouter [bd bd-id]


            Example:
            Device(config)# show igmp snooping mrouter
             

            Displays multicast ports, globally or by bridge domain.

             
            Step 6 show igmp snooping counters [bd bd-id]


            Example:
            Device(config)# show snooping counters
             

            Displays IGMP snooping counters, globally or by bridge domain.

             

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            Feature Information for IGMP Snooping

            The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

            Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.
            Table 1 Feature Information for Configuring IGMP Snooping

            Feature Name

            Releases

            Feature Information

            IGMP Snooping

            Cisco IOS XE Release 3.5S

            15.2(4)S

            IGMP snooping is an IP multicast constraining mechanism based on the Ethernet Virtual Connection (EVC) infrastructure. IGMP snooping examines Layer 3 information (IGMP Join/Leave messages) in the IGMP packets sent between hosts and routers.

            The following commands were introduced or modified: ip igmp snooping, ip igmp snooping check, ip igmp snooping explicit-track ing limit, ip igmp snooping immediate leave, ip igmp snooping last-member-query count, ip igmp snooping last-member-query interval, ip igmp snooping report-suppression, ip igmp snooping robustness-variable, ip igmp snooping static, ip igmp snooping tcn flood (if-srv), ip igmp snooping tcn flood query, ip igmp snooping tcn flood query solicit, router guard ip multicast efps