Configuring Basic IP Multicast Routing

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

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.

Prerequisites for Basic IP Multicast Routing

The following are the prerequisites for configuring basic IP multicast routing:

  • You must configure the PIM version and the PIM mode in order to perform IP multicast routing. The switch populates its multicast routing table and forwards multicast packets it receives from its directly connected LANs according to the mode setting. You can configure an interface to be in the PIM dense mode, sparse mode, or sparse-dense mode.

    On a switch running the IP base image, if you try to configure a VLAN interface with PIM dense-mode, sparse-mode, or dense-sparse-mode, the configuration is not allowed.

  • Enabling PIM on an interface also enables IGMP operation on that interface. (To participate in IP multicasting, the multicast hosts, routers, and multilayer device must have IGMP operating. )

    If you enable PIM on multiple interfaces, when most of these interfaces are not on the outgoing interface list, and IGMP snooping is disabled, the outgoing interface might not be able to sustain line rate for multicast traffic because of the extra replication.

Related Concepts
Information About Basic IP Multicast Routing
Related Tasks
Configuring Basic IP Multicast Routing

Restrictions for Basic IP Multicast Routing

The following are the restrictions for IP multicast routing:

  • The switch supports homogeneous stacking, but does not support mixed stacking.

Information About Basic IP Multicast Routing

IP multicasting is an efficient way to use network resources, especially for bandwidth-intensive services such as audio and video. IP multicast routing enables a host (source) to send packets to a group of hosts (receivers) anywhere within the IP network by using a special form of IP address called the IP multicast group address.

The sending host inserts the multicast group address into the IP destination address field of the packet, and IP multicast routers and multilayer switches forward incoming IP multicast packets out all interfaces that lead to members of the multicast group. 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.

Related Tasks
Configuring Basic IP Multicast Routing
Related References
Default IP Multicast Routing Configuration
Prerequisites for Basic IP Multicast Routing

Multicast Routing and Switch Stacks

For all multicast routing protocols, the entire stack appears as a single router to the network and operates as a single multicast router.

In a switch stack, the active switch performs these functions:

  • It is responsible for completing the IP multicast routing functions of the stack. It fully initializes and runs the IP multicast routing protocols.

  • It builds and maintains the multicast routing table for the entire stack.

  • It is responsible for distributing the multicast routing table to all stack members.

The stack members perform these functions:

  • They act as multicast routing standby devices and are ready to take over if there is a active switch failure.

    If the active switch fails, all stack members delete their multicast routing tables. The newly elected active switch starts building the routing tables and distributes them to the stack members.

  • They do not build multicast routing tables. Instead, they use the multicast routing table that is distributed by the active switch.

Default IP Multicast Routing Configuration

This table displays the default IP multicast routing configuration.

Table 1 Default IP Multicast Routing Configuration

Feature

Default Setting

Multicast routing

Disabled on all interfaces.

PIM version

Version 2.

PIM mode

No mode is defined.

PIM stub routing

None configured.

PIM RP address

None configured.

PIM domain border

Disabled.

PIM multicast boundary

None.

Candidate BSRs

Disabled.

Candidate RPs

Disabled.

Shortest-path tree threshold rate

0 kb/s.

PIM router query message interval

30 seconds.
Related Concepts
Information About Basic IP Multicast Routing
Related Tasks
Configuring Basic IP Multicast Routing

Configuring sdr Listener Support

The MBONE is the small subset of Internet routers and hosts that are interconnected and capable of forwarding IP multicast traffic. Other multimedia content is often broadcast over the MBONE. Before you can join a multimedia session, you need to know what multicast group address and port are being used for the session, when the session is going to be active, and what sort of applications (audio, video, and so forth) are required on your workstation. The MBONE Session Directory Version 2 (sdr) tool provides this information. This freeware application can be downloaded from several sites on the World Wide Web, one of which is http://www.video.ja.net/mice/index.html.

SDR is a multicast application that listens to a well-known multicast group address and port for Session Announcement Protocol (SAP) multicast packets from SAP clients, which announce their conference sessions. These SAP packets contain a session description, the time the session is active, its IP multicast group addresses, media format, contact person, and other information about the advertised multimedia session. The information in the SAP packet is displayed in the SDR Session Announcement window.

How to Configure Basic IP Multicast Routing

Configuring Basic IP Multicast Routing

By default, multicast routing is disabled, and there is no default mode setting.

This procedure is required.

Before You Begin

You must configure the PIM version and the PIM mode. The switch populates its multicast routing table and forwards multicast packets it receives from its directly connected LANs according to the mode setting.

In populating the multicast routing table, dense-mode interfaces are always added to the table. Sparse-mode interfaces are added to the table only when periodic join messages are received from downstream devices or when there is a directly connected member on the interface. When forwarding from a LAN, sparse-mode operation occurs if there is an RP known for the group. If so, the packets are encapsulated and sent toward the RP. When no RP is known, the packet is flooded in a dense-mode fashion. If the multicast traffic from a specific source is sufficient, the receiver’s first-hop router might send join messages toward the source to build a source-based distribution tree.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip multicast-routing distributed

    4.    interface interface-id

    5.    ip pim version [1 | 2]

    6.    ip pim {dense-mode | sparse-mode | sparse-dense-mode}

    7.    end

    8.    show running-config

    9.    copy running-config startup-config


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example: 
    Switch> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.

     

    Step 2configure terminal


    Example: 
    
Switch# configure terminal
     

    Enters the global configuration mode.

     
    Step 3ip multicast-routing distributed


    Example: 
    
Switch(config)# ip 
multicast-routing distributed
     

    Enables IP multicast distributed switching

    Note    To disable multicasting, use the no ip multicast-routing distributed global configuration command.
     
    Step 4interface interface-id


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

    Specifies the Layer 3 interface on which you want to enable multicast routing, and enters interface configuration mode.

    The specified interface must be one of the following:

    • A routed port—A physical port that has been configured as a Layer 3 port by entering the no switchport interface configuration command. You will also need to enable IP PIM sparse-dense-mode on the interface, and join the interface as a statically connected member to an IGMP static group. For a configuration example, see Example: Interface Configuration as a Routed Port

    • An SVI—A VLAN interface created by using the interface vlan vlan-id global configuration command. You will also need to enable IP PIM sparse-dense-mode on the VLAN, join the VLAN as a statically connected member to an IGMP static group, and then enable IGMP snooping on the VLAN, the IGMP static group, and physical interface. For a configuration example, see Example: Interface Configuration as an SVI

    These interfaces must have IP addresses assigned to them.

     
    Step 5ip pim version [1 | 2]


    Example: 
    
Switch(config-if)# ip pim version 2
     

    Configures the PIM version on the interface.

    By default, Version 2 is enabled and is the recommended setting.

    An interface in PIMv2 mode automatically downgrades to PIMv1 mode if that interface has a PIMv1 neighbor. The interface returns to Version 2 mode after all Version 1 neighbors are shut down or upgraded.

    Note   

    To return to the default PIM version, use the no ip pim version interface configuration command.

     
    Step 6ip pim {dense-mode | sparse-mode | sparse-dense-mode}


    Example: 
    
Switch(config-if)# ip pim 
sparse-dense-mode
     

    Enables a PIM mode on the interface.

    By default, no mode is configured.

    The keywords have these meanings:

    • dense-mode—Enables dense mode of operation.

    • sparse-mode—Enables sparse mode of operation. If you configure sparse mode, you must also configure an RP.

    • sparse-dense-mode—Causes the interface to be treated in the mode in which the group belongs. Sparse-dense mode is the recommended setting.

    Note   

    To disable PIM on an interface, use the no ip pim interface configuration command.

     
    Step 7end


    Example: 
    
Switch(config-if)# end
     

    Returns to privileged EXEC mode.

     
    Step 8show running-config


    Example: 
    
Switch# show running-config
     

    Verifies your entries.

     
    Step 9copy running-config startup-config


    Example: 
    Switch# copy running-config startup-config
     

    (Optional) Saves your entries in the configuration file.

     
    Related Concepts
    Information About Basic IP Multicast Routing
    Related References
    Default IP Multicast Routing Configuration
    Prerequisites for Basic IP Multicast Routing

    Configuring Optional IP Multicast Routing Features

    Defining the IP Multicast Boundary

    You define a multicast boundary to prevent Auto-RP messages from entering the PIM domain. You create an access list to deny packets destined for 224.0.1.39 and 224.0.1.40, which carry Auto-RP information.

    This procedure is optional.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    access-list access-list-number deny source [source-wildcard]

      4.    interface interface-id

      5.    ip multicast boundary access-list-number

      6.    end

      7.    show running-config

      8.    copy running-config startup-config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example: 
      Switch> enable
       

      Enables privileged EXEC mode. Enter your password if prompted.

       

      Step 2configure terminal


      Example: 
      
Switch# configure terminal
       

      Enters the global configuration mode.

       
      Step 3access-list access-list-number deny source [source-wildcard]


      Example: 
      Switch(config)# 
access-list 12 deny 224.0.1.39
access-list 12 deny 224.0.1.40
       

      Creates a standard access list, repeating the command as many times as necessary.

      • For access-list-number, the range is 1 to 99.

      • The deny keyword denies access if the conditions are matched.

      • For source, enter multicast addresses 224.0.1.39 and 224.0.1.40, which carry Auto-RP information.

      • (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.

      The access list is always terminated by an implicit deny statement for everything.

       

      Step 4interface interface-id


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

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

       

      Step 5ip multicast boundary access-list-number


      Example: 
      Switch(config-if)# ip multicast boundary 12
       

      Configures the boundary, specifying the access list you created in Step 2.

      Note   

      To remove the boundary, use the no ip multicast boundary interface configuration command.

       

      Step 6end


      Example: 
      
Switch(config)# end
       

      Returns to privileged EXEC mode.

       
      Step 7show running-config


      Example: 
      
Switch# show running-config
       

      Verifies your entries.

       
      Step 8copy running-config startup-config


      Example: 
      Switch# copy running-config startup-config
       

      (Optional) Saves your entries in the configuration file.

       
      Related References
      Example: Defining the IP Multicast Boundary to Deny Auto-RP Information

      Configuring Multicast VRFs

      For complete syntax and usage information for the commands, see the switch command reference for this release and the Cisco IOS IP Multicast Command Reference.

      For more information about configuring a multicast within a Multi-VRF CE, see the IP Routing: Protocol-Independent Configuration Guide, Cisco IOS Release 15S.

         Command or ActionPurpose
        Step 1configure terminal


        Example: 
        
Switch# configure terminal
         

        Enters the global configuration mode.

         
        Step 2ip routing


        Example: 
        
Switch(config)# ip routing
         

        Enables IP routing mode.

         
        Step 3ip vrf vrf-name


        Example: 
        
Switch(config)# ip vrf vpn1
         

        Names the VRF, and enter VRF configuration mode.

         
        Step 4rd route-distinguisher


        Example: 
        
Switch(config-vrf)# rd 100:2
         

        Creates a VRF table by specifying a route distinguisher. Enter either an AS number and an arbitrary number (xxx:y) or an IP address and an arbitrary number (A.B.C.D:y)

         
        Step 5route-target {export | import | both} route-target-ext-community


        Example: 
        
Switch(config-vrf)# route-target import 100:2
         

        Creates a list of import, export, or import and export route target communities for the specified VRF. Enter either an AS system number and an arbitrary number (xxx:y) or an IP address and an arbitrary number (A.B.C.D:y). The route-target-ext-community should be the same as the route-distinguisher entered in Step 4.

         
        Step 6import map route-map


        Example: 
        
Switch(config-vrf)# import map importmap1
         

        (Optional) Associates a route map with the VRF.

         
        Step 7ip multicast-routing vrf vrf-name distributed


        Example: 
        
Switch(config-vrf)# ip multicast-routing vrf vpn1 distributed
         

        (Optional) Enables global multicast routing for VRF table.

         
        Step 8interface interface-id


        Example: 
        
Switch(config-vrf)# interface gigabitethernet 1/0/2
         

        Specifies the Layer 3 interface to be associated with the VRF, and enter interface configuration mode. The interface can be a routed port or an SVI.

         
        Step 9ip vrf forwarding vrf-name


        Example: 
        
Switch(config-if)# ip vrf forwarding vpn1
         

        Associates the VRF with the Layer 3 interface.

         
        Step 10ip address ip-address mask


        Example: 
        
Switch(config-if)# ip address 10.1.5.1 255.255.255.0
         

        Configures IP address for the Layer 3 interface.

         
        Step 11ip pim sparse-dense mode


        Example: 
        
Switch(config-if)# ip pim sparse-dense mode
         

        Enables PIM on the VRF-associated Layer 3 interface.

         
        Step 12end


        Example: 
        
Switch(config)# end
         

        Returns to privileged EXEC mode.

         
        Step 13show ip vrf [brief | detail | interfaces] [vrf-name]


        Example: 
        
Switch# show ip vrf detail vpn1
         

        Verifies the configuration. Displays information about the configured VRFs.

         
        Step 14copy running-config startup-config


        Example: 
        Switch# copy running-config startup-config
         

        (Optional) Saves your entries in the configuration file.

         

        Advertising Multicast Multimedia Sessions Using SAP Listener

        Enable SAP listener support when you want to use session description and announcement protocols and applications to assist the advertisement of multicast multimedia conferences and other multicast sessions and to communicate the relevant session setup information to prospective participants.

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    ip sap cache-timeout minutes

          4.    interface type number

          5.    ip sap listen

          6.    end

          7.    clear ip sap [group-address | “ session-name ”]

          8.    show ip sap [group-address | “ session-name ”| detail]


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Router> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.

           
          Step 2 configure terminal


          Example:
          Router# configure terminal
           

          Enters global configuration mode.

           
          Step 3 ip sap cache-timeout minutes


          Example:
          Router(config)# ip sap cache-timeout 600
           

          (Optional) Limits how long a SAP cache entry stays active in the cache.

          • By default, SAP cache entries are deleted 24 hours after they are received from the network.

           
          Step 4 interface type number


          Example:
          Router(config)# interface ethernet 1
           

          Selects an interface that is connected to hosts on which IGMPv3 can be enabled.

           
          Step 5 ip sap listen


          Example:
          Router(config-if)# ip sap listen
           

          Enables the software to listen to session directory announcements.

           
          Step 6 end


          Example:
          Router(config-if)# end
           

          Ends the session and returns to EXEC mode.

           
          Step 7 clear ip sap [group-address | “ session-name ”]


          Example:
          Router# clear ip sap "Sample Session"
           

          Deletes a SAP cache entry or the entire SAP cache.

           
          Step 8 show ip sap [group-address | “ session-name ”| detail]


          Example:
          Router# show ip sap 224.2.197.250 detail
           

          (Optional) Displays the SAP cache.

           

          Monitoring and Maintaining Basic IP Multicast Routing

          Clearing Caches, Tables, and Databases

          You can remove all contents of a particular cache, table, or database. Clearing a cache, table, or database might be necessary when the contents of the particular structure are or suspected to be invalid.

          You can use any of the privileged EXEC commands in the following table to clear IP multicast caches, tables, and databases.

          Table 2 Commands for Clearing Caches, Tables, and Databases

          Command

          Purpose

          clear ip cgmp

          Clears all group entries the Catalyst switches have cached.

          clear ip igmp group {group [ hostname | IP address] | vrf name group [ hostname | IP address] }

          Deletes entries from the IGMP cache.

          clear ip mroute { * | [hostname | IP address] | vrf name group [ hostname | IP address] }

          Deletes entries from the IP multicast routing table.

          clear ip sap [group-address | “session-name”]

          Deletes the Session Directory Protocol Version 2 cache or an sdr cache entry.

          Displaying Multicast Peers, Packet Rates and Loss Information, and Path Tracing

          You can use the privileged EXEC commands in the following table to monitor IP multicast routers, packets, and paths.

          Table 3 Commands for Displaying Multicast Peers, Packet Rates and Loss Information, and Path Tracing

          Command

          Purpose

          mrinfo { [hostname | address] | vrf }

          Queries a multicast router or multilayer switch about which neighboring multicast devices are peering with it.

          mstat { [hostname | address] | vrf }

          Displays IP multicast packet rate and information loss.

          mtrace { [hostname | address] | vrf }

          Traces the path from a source to a destination branch for a multicast distribution tree for a given group.

          Additional References

          Related Documents

          Related Topic Document Title

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

          IP Multicast Command Reference, Cisco IOS Release 15.2(2)E (Catalyst 2960-XR Switch)

          Cisco IOS commands

          Cisco IOS Master Commands List, All Releases

          Cisco IOS IP multicast commands

          Cisco IOS IP Multicast Command Reference

          Error Message Decoder

          Description Link

          To help you research and resolve system error messages in this release, use the Error Message Decoder tool.

          https:/​/​www.cisco.com/​cgi-bin/​Support/​Errordecoder/​index.cgi

          Standards and RFCs

          Standard/RFC Title

          RFC 1112

          Host Extensions for IP Multicasting

          RFC 2236

          Internet Group Management Protocol, Version 2

          RFC 4601

          Protocol-Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification

          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

          Technical Assistance

          Description Link

          The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

          To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

          Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

          http:/​/​www.cisco.com/​support

          Feature History and Information for IP Multicast

          Release

          Modification

          Cisco IOS 15.0(2)EX1

          This feature was introduced.