Catalyst 2960-XR Switch IP Multicast Routing Configuration Guide, Cisco IOS Release 15.0(2)EX1

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Catalyst 2960-XR Switch IP Multicast Routing Configuration Guide, Cisco IOS Release 15.0(2)EX1

Chapter Title

Understanding Cisco's Implementation of IP Multicast Routing

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Updated:
August 7, 2013

Chapter: Understanding Cisco's Implementation of IP Multicast Routing

Understanding Cisco's Implementation of IP Multicast Routing

Cisco’s Implementation of IP Multicast Routing

Cisco IOS software supports the following protocols to implement IP multicast routing:

  • Internet Group Management Protocol (IGMP) is used among hosts on a LAN and the routers (and multilayer switches) on that LAN to track the multicast groups of which hosts are members.
  • Protocol-Independent Multicast (PIM) protocol is used among routers and multilayer switches to track which multicast packets to forward to each other and to their directly connected LANs.
  • Distance Vector Multicast Routing Protocol (DVMRP) is used on the multicast backbone of the Internet (MBONE). The software supports PIM-to-DVMRP interaction.
  • Cisco Group Management Protocol (CGMP) is used on Cisco routers and multilayer switches connected to Layer 2 Catalyst switches to perform tasks similar to those performed by IGMP.
Figure 1. IP Multicast Routing Protocols. The following figure shows where these protocols operate within the IP multicast environment.

According to IPv4 multicast standards, the MAC destination multicast address begins with 0100:5e and is appended by the last 23 bits of the IP address. For example, if the IP destination address is 239.1.1.39, the MAC destination address is 0100:5e01:0127.

A multicast packet is unmatched when the destination IPv4 address does not match the destination MAC address. The switch forwards the unmatched packet in hardware based on the MAC address table. If the destination MAC address is not in the MAC address table, the switch floods the packet to the all port in the same VLAN as the receiving port.

Information About IGMP

To participate in IP multicasting, multicast hosts, routers, and multilayer switches must have the Internet Group Management Protocol (IGMP) operating. This protocol defines the querier and host roles:

  • A querier is a network device that sends query messages to discover which network devices are members of a given multicast group.
  • A host is a receiver that sends report messages (in response to query messages) to inform a querier of a host membership.

A set of queriers and hosts that receive multicast data streams from the same source is called a multicast group. Queriers and hosts use IGMP messages to join and leave multicast groups.

Any host, regardless of whether it is a member of a group, can send to a group. However, only the members of a group receive the message. Membership in a multicast group is dynamic; hosts can join and leave at any time. There is no restriction on the location or number of members in a multicast group. A host can be a member of more than one multicast group at a time. How active a multicast group is and what members it has can vary from group to group and from time to time. A multicast group can be active for a long time, or it can be very short-lived. Membership in a group can constantly change. A group that has members can have no activity.

IGMP Versions

The switch supports IGMP version 1, IGMP version 2, and IGMP version 3. These versions are interoperable on the switch. For example, if IGMP snooping is enabled and the querier's version is IGMPv2. and the switch receives an IGMPv3 report from a host, then the switch can forward the IGMPv3 report to the multicast router.

IGMP Version 1

IGMP version 1 (IGMPv1) primarily uses a query-response model that enables the multicast router and multilayer switch to find which multicast groups are active (have one or more hosts interested in a multicast group) on the local subnet. IGMPv1 has other processes that enable a host to join and leave a multicast group. For more information, see RFC 1112.

IGMP Version 2

IGMPv2 extends IGMP functionality by providing such features as the IGMP leave process to reduce leave latency, group-specific queries, and an explicit maximum query response time. IGMPv2 also adds the capability for routers to elect the IGMP querier without depending on the multicast protocol to perform this task. For more information, see RFC 2236.


Note

IGMP version 2 is the default version for the switch.

Default IGMP Configuration

This table displays the default IGMP configuration for the switch.

Table 1 Default IGMP Configuration

Feature

Default Setting

Multilayer switch as a member of a multicast group

No group memberships are defined.

Access to multicast groups

All groups are allowed on an interface.

IGMP version

Version 2 on all interfaces.

IGMP host-query message interval

60 seconds on all interfaces.

IGMP query timeout

60 seconds on all interfaces.

IGMP maximum query response time

10 seconds on all interfaces.

Multilayer switch as a statically connected member

Disabled.

Configuring Optional IGMP Features

Configuring the Switch as a Member of a Group

You can configure the switch as a member of a multicast group and discover multicast reachability in a network. If all the multicast-capable routers and multilayer switches that you administer are members of a multicast group, pinging that group causes all of these devices to respond. The devices respond to ICMP echo-request packets addressed to a group of which they are members. Another example is the multicast trace-route tools provided in the software.


Caution

Performing this procedure might impact the CPU performance because the CPU will receive all data traffic for the group address.

This procedure is optional.

SUMMARY STEPS

    1.    configure terminal

    2.    interface interface-id

    3.    ip igmp join-group group-address

    4.    end

    5.    show ip igmp interface [ interface-id]

    6.    copy running-config startup-config


DETAILED STEPS
      Command or Action Purpose
    Step 1 configure terminal


    Example:
    
            
            
Switch# configure terminal
     

    Enters the global configuration mode.

     
    Step 2 interface interface-id


    Example:
    
            
            
Switch(config)# interface gigabitethernet 1/0/1
     

    Specifies the interface on which you want to enable multicast routing, and enters interface configuration mode.

     
    Step 3 ip igmp join-group group-address


    Example:
    
            
            
Switch(config-if)# ip igmp join-group 225.2.2.2
     

    Configures the switch to join a multicast group.

    By default, no group memberships are defined.

    For group-address, specify the multicast IP address in dotted decimal notation.

    Note   

    To cancel membership in a group, use the no ip igmp join-group group-address interface configuration command.
     
    Step 4 end


    Example:
    
            
            
Switch(config-if)# end
     

    Returns to privileged EXEC mode.

     
    Step 5 show ip igmp interface [ interface-id]


    Example:
    
            
            
Switch# show ip igmp interface
     

    Verifies your entries.

     
    Step 6 copy running-config startup-config


    Example:
    
            
            
Switch# copy running-config startup-config
     

    (Optional) Saves your entries in the configuration file.

     
    Related References
    Example: Configuring the Switch as a Member of a Multicast Group

    Controlling Access to IP Multicast Group

    The switch sends IGMP host-query messages to find which multicast groups have members on attached local networks. The switch then forwards to these group members all packets addressed to the multicast group. You can place a filter on each interface to restrict the multicast groups that hosts on the subnet serviced by the interface can join.

    This procedure is optional.

    SUMMARY STEPS

      1.    configure terminal

      2.    interface interface-id

      3.    ip igmp access-group access-list-number

      4.    exit

      5.    access-list access-list-number {deny | permit} source [source-wildcard]

      6.    end

      7.    show ip igmp interface [ interface-id]


    DETAILED STEPS
        Command or Action Purpose
      Step 1 configure terminal


      Example:
      
            
            
Switch# configure terminal
       

      Enters the global configuration mode.

       
      Step 2 interface interface-id


      Example:
      Switch(config)# interface GigabitEthernet 1/0/12
       

      Specifies the interface to be configured, and enters interface configuration mode.

       
      Step 3 ip igmp access-group access-list-number


      Example:
      Switch(config-if)# ip igmp access-group 10
       

      Specifies the multicast groups that hosts on the subnet serviced by an interface can join.

      By default, all groups are allowed on an interface.

      For access-list-number, specify an IP standard access list number.

      The range is 1 to 199.

      Note   

      To disable groups on an interface, use the no ip igmp access-group interface configuration command.

       
      Step 4 exit


      Example:
      
            
            
Switch(config-if)# exit
       

      Returns to global configuration mode.

       
      Step 5 access-list access-list-number {deny | permit} source [source-wildcard]


      Example:
      
            
            
Switch(config)# access-list 10 permit
       

      Creates a standard access list.

      • For access-list-number, specify the access list created in Step 3.
      • The deny keyword denies access if the conditions are matched. The permit keyword permits access if the conditions are matched.
      • For source, specify the multicast group that hosts on the subnet can join.
      • (Optional) For source-wildcard, enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore.

      Recall that the access list is always terminated by an implicit deny statement for everything.

       
      Step 6 end


      Example:
      Switch(config-igmp-profile)# end
       

      Returns to privileged EXEC mode.

       
      Step 7 show ip igmp interface [ interface-id]


      Example:
      
            
            
Switch# show ip igmp interface
       

      Verifies your entries.

       
      Related References
      Example: Controlling Access to IP Multicast Groups

      Changing the IGMP Version

      By default, the switch uses IGMP Version 2, which provides features such as the IGMP query timeout and the maximum query response time.

      All systems on the subnet must support the same version. The switch does not automatically detect Version 1 systems and switch to Version 1. You can mix Version 1 and Version 2 hosts on the subnet because Version 2 routers or switches always work correctly with IGMPv1 hosts.

      Configure the switch for Version 1 if your hosts do not support Version 2.

      This procedure is optional.

      SUMMARY STEPS

        1.    configure terminal

        2.    interface interface-id

        3.    ip igmp version {1 | 2 | 3 }

        4.    end

        5.    show ip igmp interface [ interface-id]

        6.    copy running-config startup-config


      DETAILED STEPS
          Command or Action Purpose
        Step 1 configure terminal


        Example:
        
            
            
Switch# configure terminal
         

        Enters the global configuration mode.

         
        Step 2 interface interface-id


        Example:
        
            
            
Switch(config)# interface gigabitethernet 1/0/1
         

        Specifies the interface to be configured, and enters the interface configuration mode.

         
        Step 3 ip igmp version {1 | 2 | 3 }


        Example:
        
            
            
Switch(config-if)# ip igmp version 2
                  		Specifies the IGMP version that the switch uses.
        Note   

        If you change to Version 1, you cannot configure the ip igmp query-interval or the ip igmp query-max-response-time interface configuration commands.

        To return to the default setting, use the no ip igmp version interface configuration command.

         
        Step 4 end


        Example:
        
            
            
Switch(config-if)# end
         

        Returns to privileged EXEC mode.

         
        Step 5 show ip igmp interface [ interface-id]


        Example:
        
            
            
Switch# show ip igmp interface
         

        Verifies your entries.

         
        Step 6 copy running-config startup-config


        Example:
        
            
            
Switch# copy running-config startup-config
         

        (Optional) Saves your entries in the configuration file.

         

        Modifying the IGMP Host-Query Message Interval

        The switch periodically sends IGMP host-query messages to discover which multicast groups are present on attached networks. These messages are sent to the all-hosts multicast group (224.0.0.1) with a time-to-live (TTL) of 1. The switch sends host-query messages to refresh its knowledge of memberships present on the network. If, after some number of queries, the software discovers that no local hosts are members of a multicast group, the software stops forwarding multicast packets to the local network from remote origins for that group and sends a prune message upstream toward the source.

        The switch elects a PIM designated router (DR) for the LAN (subnet). The DR is the router or multilayer switch with the highest IP address for IGMPv2. For IGMPv1, the DR is elected according to the multicast routing protocol that runs on the LAN. The designated router is responsible for sending IGMP host-query messages to all hosts on the LAN. In sparse mode, the designated router also sends PIM register and PIM join messages toward the RP router.

        This procedure is optional.

        SUMMARY STEPS

          1.    configure terminal

          2.    interface interface-id

          3.    ip igmp query-interval seconds

          4.    end

          5.    show ip igmp interface [ interface-id]

          6.    copy running-config startup-config


        DETAILED STEPS
            Command or Action Purpose
          Step 1 configure terminal


          Example:
          
            
            
Switch# configure terminal
           

          Enters the global configuration mode.

           
          Step 2 interface interface-id


          Example:
          
            
            
Switch(config)# interface gigabitethernet 1/0/1
           

          Specifies the interface on which you want to enable multicast routing, and enters interface configuration mode.

           
          Step 3 ip igmp query-interval seconds


          Example:
          
            
            
Switch(config-if)# ip igmp query-interval 75
           

          Configures the frequency at which the designated router sends IGMP host-query messages.

          By default, the designated router sends IGMP host-query messages every 60 seconds to keep the IGMP overhead very low on hosts and networks.

          The range is 1 to 18000.

          Note   

          To return to the default setting, use the no ip igmp query-interval interface configuration command.
           
          Step 4 end


          Example:
          
            
            
Switch(config-if)# end
           

          Returns to privileged EXEC mode.

           
          Step 5 show ip igmp interface [ interface-id]


          Example:
          
            
            
Switch# show ip igmp interface
           

          Verifies your entries.

           
          Step 6 copy running-config startup-config


          Example:
          
            
            
Switch# copy running-config startup-config
           

          (Optional) Saves your entries in the configuration file.

           

          Changing the IGMP Query Timeout for IGMPv2

          If you are using IGMPv2, you can specify the period of time before the switch takes over as the querier for the interface. By default, the switch waits twice the query interval period controlled by the ip igmp query-interval interface configuration command. After that time, if the switch has received no queries, it becomes the querier.

          This procedure is optional.

          SUMMARY STEPS

            1.    configure terminal

            2.    interface interface-id

            3.    ip igmp querier-timeout seconds

            4.    end

            5.    show ip igmp interface [ interface-id]

            6.    copy running-config startup-config


          DETAILED STEPS
              Command or Action Purpose
            Step 1 configure terminal


            Example:
            
            
            
Switch# configure terminal
             

            Enters the global configuration mode.

             
            Step 2 interface interface-id


            Example:
            
            
            
Switch(config)# interface gigabitethernet 1/0/1
             

            Specifies the interface on which you want to enable multicast routing, and enters interface configuration mode.

             
            Step 3 ip igmp querier-timeout seconds


            Example:
            
            
            
Switch(config-if)# ip igmp querier-timeout 120
             

            Specifies the IGMP query timeout.

            The default is 60 seconds (twice the query interval). The range is 60 to 300.

            Note   

            To return to the default setting, use the no ip igmp querier-timeout interface configuration command.
             
            Step 4 end


            Example:
            
            
            
Switch(config-if)# end
             

            Returns to privileged EXEC mode.

             
            Step 5 show ip igmp interface [ interface-id]


            Example:
            
            
            
Switch# show ip igmp interface
             

            Verifies your entries.

             
            Step 6 copy running-config startup-config


            Example:
            
            
            
Switch# copy running-config startup-config
             

            (Optional) Saves your entries in the configuration file.

             

            Changing the Maximum Query Response Time for IGMPv2

            If you are using IGMPv2, you can change the maximum query response time advertised in IGMP queries. The maximum query response time enables the switch to quickly detect that there are no more directly connected group members on a LAN. Decreasing the value enables the switch to prune groups faster.

            This procedure is optional.

            SUMMARY STEPS

              1.    configure terminal

              2.    interface interface-id

              3.    ip igmp query-max-response-time seconds

              4.    end

              5.    show ip igmp interface [ interface-id]

              6.    copy running-config startup-config


            DETAILED STEPS
                Command or Action Purpose
              Step 1 configure terminal


              Example:
              
            
            
Switch# configure terminal
               

              Enters the global configuration mode.

               
              Step 2 interface interface-id


              Example:
              
            
            
Switch(config)# interface gigabitethernet 1/0/1
               

              Specifies the interface on which you want to enable multicast routing, and enters interface configuration mode.

               
              Step 3 ip igmp query-max-response-time seconds


              Example:
              
            
            
Switch(config-if)# ip igmp query-max-response-time 15
               

              Changes the maximum query response time advertised in IGMP queries.

              The default is 10 seconds. The range is 1 to 25.

              Note   

              To return to the default setting, use the no ip igmp query-max-response-time interface configuration command.
               
              Step 4 end


              Example:
              
            
            
Switch(config-if)# end
               

              Returns to privileged EXEC mode.

               
              Step 5 show ip igmp interface [ interface-id]


              Example:
              
            
            
Switch# show ip igmp interface
               

              Verifies your entries.

               
              Step 6 copy running-config startup-config


              Example:
              
            
            
Switch# copy running-config startup-config
               

              (Optional) Saves your entries in the configuration file.

               

              Configuring the Switch as a Statically Connected Member

              At various times, either there is not a group member on a network segment or a host that cannot report its group membership by using IGMP. However, you may want multicast traffic to be sent to that network segment. The following commands are used to pull multicast traffic down to a network segment:

              • ip igmp join-group—The switch accepts the multicast packets in addition to forwarding them. Accepting the multicast packets prevents the switch from fast switching.
              • ip igmp static-group—The switch does not accept the packets itself, but only forwards them. This method enables fast switching. The outgoing interface appears in the IGMP cache, but the switch itself is not a member, as evidenced by lack of an L (local) flag in the multicast route entry.

              This procedure is optional.

              SUMMARY STEPS

                1.    configure terminal

                2.    interface interface-id

                3.    ip igmp static-group group-address

                4.    end

                5.    show ip igmp interface [ interface-id]

                6.    copy running-config startup-config


              DETAILED STEPS
                  Command or Action Purpose
                Step 1 configure terminal


                Example:
                
            
            
Switch# configure terminal
                 

                Enters the global configuration mode.

                 
                Step 2 interface interface-id


                Example:
                
            
            
Switch(config)# interface gigabitethernet 1/0/1
                 

                Specifies the interface on which you want to enable multicast routing, and enters interface configuration mode.

                 
                Step 3 ip igmp static-group group-address


                Example:
                
            
            
Switch(config-if)# ip igmp static-group 239.100.100.101
                 

                Configures the switch as a statically connected member of a group.

                By default, this feature is disabled.

                Note   

                To remove the switch as a member of the group, use the no ip igmp static-group group-address interface configuration command.
                 
                Step 4 end


                Example:
                
            
            
Switch(config-if)# end
                 

                Returns to privileged EXEC mode.

                 
                Step 5 show ip igmp interface [ interface-id]


                Example:
                
            
            
Switch# show ip igmp interface gigabitethernet 1/0/1
                 

                Verifies your entries.

                 
                Step 6 copy running-config startup-config


                Example:
                
            
            
Switch# copy running-config startup-config
                 

                (Optional) Saves your entries in the configuration file.

                 

                Configuration Examples for IGMP Features

                Example: Configuring the Switch as a Member of a Multicast Group

                This example shows how to enable the switch to join multicast group 255.2.2.2:

                
         
         
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# ip igmp join-group 255.2.2.2
Switch(config-if)#
                Related Tasks
                Configuring the Switch as a Member of a Group

                Example: Controlling Access to IP Multicast Groups

                This example shows how to configure hosts attached to a port as able to join only group 255.2.2.2:

                Switch(config)# access-list 1 255.2.2.2 0.0.0.0
Switch(config-if)# interface gigabitethernet1/0/1
Switch(config-if)# ip igmp access-group 1
                Related Tasks
                Controlling Access to IP Multicast Group

                Where to Go Next

                You can configure the following for your IP multicast configuration:

                • CGMP feature support
                • PIM feature support
                • SSM feature support
                • IP Multicast Routing

                Additional References

                Related Documents

                Related Topic Document Title

                For complete syntax and usage information for the commands used in this book.

                Catalyst 2960-XR Switch IP Multicast Command Reference

                Standards and RFCs

                Standard/RFC Title

                RFC 1112

                Host Extensions for IP Multicasting

                RFC 2236

                Internet Group Management Protocol, Version 2

                MIBs

                MIB MIBs Link

                All supported MIBs for this release.

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

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

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