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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.
For the latest feature information and caveats, see 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 for Router-Port Group Management Protocol" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
•Feature Information for Router-Port Group Management Protocol
Before you configure RGMP, you should understand the following concepts:
•IP Multicast Routing Overview
The Cisco IOS XE 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.
•Distance Vector Multicast Routing Protocol (DVMRP) is the protocol used on the MBONE (the multicast backbone of the Internet). The Cisco IOS XE software supports PIM-to-DVMRP interaction.
•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.
Figure 1 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 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.
Figure 2 shows a switched Ethernet backbone network running PIM in sparse mode, RGMP, and IGMP snooping.
Figure 2 RGMP in a Switched Network
In Figure 2, 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.
Figure 3 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.
To configure RGMP, perform the tasks described in this section. The first task is required; the remaining tasks are optional.
•Enabling RGMP (required)
•Verifying RGMP Configuration (optional)
•Monitoring and Maintaining RGMP (optional)
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.
To enable RGMP, use the following commands on all routers in your network beginning in global configuration mode:
See the "RGMP Configuration Example" section for an example of how to configure RGMP.
To verify that RGMP is enabled on the correct interfaces, use the show ip igmp interface EXEC command:
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.
To enable RGMP debugging, use the following command in privileged EXEC mode:
Figure 4 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
This section provides an RGMP configuration example that shows the individual configurations for the routers and switches shown in Figure 5.
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
The following sections provide references related to RGMP.
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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 |
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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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: |
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No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature. |
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Table 1 lists the release history of the features in this module.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.