IP Multicast: IGMP Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
Configuring Router-Port Group Management Protocol
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Configuring Router-Port Group Management Protocol

Router-Port Group Management Protocol (RGMP) is a Cisco protocol that restricts IP multicast traffic in switched networks. RGMP is a Layer 2 protocol that enables a router to communicate to a switch (or a networking device that is functioning as a Layer 2 switch) the multicast group for which the router would like to receive or forward traffic. RGMP restricts multicast traffic at the ports of RGMP-enabled switches that lead to interfaces of RGMP-enabled routers.

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 at the end of this module.

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 RGMP

Before you enable RGMP, ensure that the following features are enabled on your router:

  • IP routing
  • IP multicast
  • PIM in sparse mode, sparse-dense mode, source specific mode, or bidirectional mode

If your router is in a bidirectional group, make sure to enable RGMP only on interfaces that do not function as a designated forwarder (DF). If you enable RGMP on an interface that functions as a DF, the interface will not forward multicast packets up the bidirectional shared tree to the rendezvous point (RP).

You must have the following features enabled on your switch:

  • IP multicast
  • IGMP snooping

Note


Refer to the Catalyst switch software documentation for RGMP switch configuration tasks and command information.


Information About RGMP

IP Multicast Routing Overview

The software supports the following protocols to implement IP multicast routing:

  • Internet Group Management Protocol (IGMP) is used between hosts on a LAN and the routers on that LAN to track the multicast groups of which hosts are members.
  • Protocol Independent Multicast (PIM) is used between routers so that they can track which multicast packets to forward to each other and to their directly connected LANs.
  • Cisco Group Management Protocol (CGMP) is a protocol used on routers connected to Catalyst switches to perform tasks similar to those performed by IGMP.
  • RGMP is a protocol used on routers connected to Catalyst switches or networking devices functioning as Layer 2 switches to restrict IP multicast traffic. Specifically, the protocol enables a router to communicate to a switch the IP multicast group for which the router would like to receive or forward traffic.

The figure shows where these protocols operate within the IP multicast environment.

Figure 1. IP Multicast Routing Protocols


Note


CGMP and RGMP cannot interoperate on the same switched network. If RGMP is enabled on a switch or router interface, CGMP is automatically disabled on that switch or router interface; if CGMP is enabled on a switch or router interface, RGMP is automatically disabled on that switch or router interface.


RGMP Overview

RGMP enables a router to communicate to a switch the IP multicast group for which the router would like to receive or forward traffic. RGMP is designed for switched Ethernet backbone networks running PIM sparse mode (PIM-SM) or sparse-dense mode.


Note


RGMP-enabled switches and router interfaces in a switched network support directly connected, multicast-enabled hosts that receive multicast traffic. RGMP-enabled switches and router interfaces in a switched network do not support directly connected, multicast-enabled hosts that source multicast traffic. A multicast-enabled host can be a PC, a workstation, or a multicast application running in a router.


The figure shows a switched Ethernet backbone network running PIM in sparse mode, RGMP, and IGMP snooping.

Figure 2. RGMP in a Switched Network

In the figure, the sources for the two different multicast groups (the source for group A and the source for group B) send traffic into the same switched network. Without RGMP, traffic from source A is unnecessarily flooded from switch A to switch B, then to router B and router D. Also, traffic from source B is unnecessarily flooded from switch B to switch A, then to router A and router C. With RGMP enabled on all routers and switches in this network, traffic from source A would not flood router B and router D. Also, traffic from source B would not flood router A and router C. Traffic from both sources would still flood the link between switch A and switch B. Flooding over this link would still occur because RGMP does not restrict traffic on links toward other RGMP-enabled switches with routers behind them.

By restricting unwanted multicast traffic in a switched network, RGMP increases the available bandwidth for all other multicast traffic in the network and saves the processing resources of the routers.

The figure shows the RGMP messages sent between an RGMP-enabled router and an RGMP-enabled switch.

Figure 3. RGMP Messages

The router sends simultaneous PIM hello (or a PIM query message if PIM Version 1 is configured) and RGMP hello messages to the switch. The PIM hello message is used to locate neighboring PIM routers. The RGMP hello message instructs the switch to restrict all multicast traffic on the interface from which the switch received the RGMP hello message.


Note


RGMP messages are sent to the multicast address 224.0.0.25, which is the local-link multicast address reserved by the Internet Assigned Numbers Authority (IANA) for sending IP multicast traffic from routers to switches. If RGMP is not enabled on both the router and the switch, the switch automatically forwards all multicast traffic out the interface from which the switch received the PIM hello message.


The router sends the switch an RGMP join <G> message (where G is the multicast group address) when the router wants to receive traffic for a specific multicast group. The RGMP join message instructs the switch to forward multicast traffic for group <G> out the interface from which the switch received the RGMP hello message.


Note


The router sends the switch an RGMP join <G> message for a multicast group even if the router is only forwarding traffic for the multicast group into a switched network. By joining a specific multicast group, the router can determine if another router is also forwarding traffic for the multicast group into the same switched network. If two routers are forwarding traffic for a specific multicast group into the same switched network, the two routers use the PIM assert mechanism to determine which router should continue forwarding the multicast traffic into the network.


The router sends the switch an RGMP leave <G> message when the router wants to stop receiving traffic for a specific multicast group. The RGMP leave message instructs the switch to stop forwarding the multicast traffic on the port from which the switch received the PIM and RGMP hello messages.


Note


An RGMP-enabled router cannot send an RGMP leave <G> message until the router does not receive or forward traffic from any source for a specific multicast group (if multiple sources exist for a specific multicast group).


The router sends the switch an RGMP bye message when RGMP is disabled on the router. The RGMP bye message instructs the switch to forward the router all IP multicast traffic on the port from which the switch received the PIM and RGMP hello messages, as long as the switch continues to receive PIM hello messages on the port.

How to Configure RGMP

Enabling RGMP

To enable RGMP, use the following commands on all routers in your network beginning in global configuration mode:


Note


CGMP and RGMP cannot interoperate on the same switched network. If RGMP is enabled on a switch or router interface, CGMP is automatically disabled on that switch or router interface; if CGMP is enabled on a switch or router interface, RGMP is automatically disabled on that switch or router interface.


SUMMARY STEPS

    1.    interface type number

    2.    ip rgmp


DETAILED STEPS
      Command or Action Purpose
    Step 1 interface type number
     

    Specifies the router interface on which you want to configure RGMP and enters interface configuration mode.

     
    Step 2 ip rgmp
     

    Enables RGMP on a specified interface.

     
    What to Do Next

    See the "RGMP_Configuration_Example" section for an example of how to configure RGMP.

    Verifying RGMP Configuration

    To verify that RGMP is enabled on the correct interfaces, use the show ip igmp interfacecommand:

    Router> show ip igmp interface
    gigabitethernet1/0 is up, line protocol is up
      Internet address is 10.0.0.0/24
        IGMP is enabled on interface
      Current IGMP version is 2
        RGMP is enabled
      IGMP query interval is 60 seconds
      IGMP querier timeout is 120 seconds
      IGMP max query response time is 10 seconds
      Last member query response interval is 1000 ms
      Inbound IGMP access group is not set
      IGMP activity: 1 joins, 0 leaves
      Multicast routing is enabled on interface
      Multicast TTL threshold is 0
      Multicast designated router (DR) is 10.0.0.0 (this system)
      IGMP querying router is 10.0.0.0 (this system)
      Multicast groups joined (number of users):
          224.0.1.40(1) 

    Note


    If RGMP is not enabled on an interface, no RGMP information is displayed in the show ip igmp interface command output for that interface.


    Monitoring and Maintaining RGMP

    To enable RGMP debugging, use the following command in privileged EXEC mode:

    Command

    Purpose

    Router# debug ip rgmp

    Logs debug messages sent by an RGMP-enabled router.

    Using the command without arguments logs RGMP Join <G> and RGMP leave <G> messages for all multicast groups configured on the router. Using the command with arguments logs RGMP join <G> and RGMP leave <G> messages for the specified group.

    The figure shows the debug messages that are logged by an RGMP-enabled router as the router sends RGMP join <G> and RGMP leave <G> messages to an RGMP-enabled switch.

    Figure 4. RGMP Debug Messages

    Configuration Examples for RGMP

    RGMP Configuration Example

    This section provides an RGMP configuration example that shows the individual configurations for the routers and switches shown in the figure.

    Figure 5. RGMP Configuration Example

    Router A Configuration

       ip routing
       ip multicast-routing distributed
       interface gigabitethernet 1/0/0
         ip address 10.0.0.1 255.0.0.0
         ip pim sparse-dense-mode
         no shutdown
       interface gigabitethernet 1/1/0
         ip address 10.1.0.1 255.0.0.0
         ip pim sparse-dense-mode
         ip rgmp
         no shutdown

    Router B Configuration

       ip routing
       ip multicast-routing distributed
       interface gigabitethernet 1/0/0
         ip address 10.2.0.1 255.0.0.0
         ip pim sparse-dense-mode
         no shutdown
       interface gigabitethernet 1/1/0
         ip address 10.3.0.1 255.0.0.0
         ip pim sparse-dense-mode
         ip rgmp
         no shutdown

    Router C Configuration

       ip routing
       ip multicast-routing distributed
       interface gigabitethernet 1/0/0
         ip address 10.4.0.1 255.0.0.0
         ip pim sparse-dense-mode
         no shutdown
       interface gigabitethernet 1/1/0
         ip address 10.5.0.1 255.0.0.0
         ip pim sparse-dense-mode
         ip rgmp
         no shutdown

    Router D Configuration

       ip routing
       ip multicast-routing distributed
       interface gigabitethernet 1/0/0
         ip address 10.6.0.1 255.0.0.0
         ip pim sparse-dense-mode
         no shutdown
       interface gigabitethernet 1/1/0
         ip address 10.7.0.1 255.0.0.0
         ip pim sparse-dense-mode
         ip rgmp
         no shutdown

    Switch A Configuration

       Switch> (enable) set igmp enable
       Switch> (enable) set rgmp enable

    Switch B Configuration

       Switch> (enable) set igmp enable
       Switch> (enable) set rgmp enable

    Additional References

    The following sections provide references related to RGMP.

    Related Documents

    Related Topic

    Document Title

    PIM-SM and SSM concepts and configuration examples

    “ Configuring Basic IP Multicast ” module

    IP multicast commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

    Cisco IOS IP Multicast Command Reference

    Standards

    Standard

    Title

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

    --

    MIBs

    MIB

    MIBs Link

    None

    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

    RFCs

    RFC

    Title

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

    --

    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/​techsupport

    Feature Information for Router-Port Group Management Protocol

    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 Router-Port Group Management Protocol

    Feature Name

    Releases

    Feature Information

    Router-Port Group Management Protocol

    Cisco IOS XE Release 2.1

    Router-Port Group Management Protocol (RGMP) is a Cisco protocol that restricts IP multicast traffic in switched networks. RGMP is a Layer 2 protocol that enables a router to communicate to a switch (or a networking device that is functioning as a Layer 2 switch) the multicast group for which the router would like to receive or forward traffic. RGMP restricts multicast traffic at the ports of RGMP-enabled switches that lead to interfaces of RGMP-enabled routers