MTR Support for Multicast
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MTR Support for Multicast

Last Updated: July 23, 2010

The MTR Support for Multicast feature provides Multitopology Routing (MTR) support for multicast and allows you to control the path of multicast traffic in the network. This module describes how to configure MTR support for multicast.

Finding Feature Information

Your software release may not support all the features documented in this module. 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 Table at the end of this document.

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.

Restrictions for MTR Support for Multicast

Only a single multicast topology can be configured, and only the topology base command can be entered when the multicast topology is created.

Information About MTR Support for Multicast

Multicast Topology Support for MTR

Cisco IOS software supports legacy (pre-MTR) IP multicast behavior by default. MTR support for IP multicast must be explicitly enabled. Legacy IP multicast uses reverse path forwarding on routes in the unicast RIB (base unicast topology) to build multicast distribution trees (MDTs).

MTR introduces a multicast topology that is completely independent from the unicast topology. MTR integration with multicast allows the user to control the path of multicast traffic in the network.

The multicast topology maintains separate routing and forwarding tables. The following list summarizes MTR multicast support that is integrated into Cisco IOS software:

  • Conventional longest match support for multicast routes.
  • RPF support for Protocol Independent Multicast (PIM).
  • Border Gateway Protocol (BGP) MDT subaddress family identifier (SAFI) support for Inter-AS Virtual Private Networks (VPNs) (SAFI number 66).
  • Support for static multicast routes is integrated into the ip route topology command (modifying the ip mroute command).

As in pre-MTR software, you enable multicast support by configuring the ip multicast-routing command in global configuration mode. You enable MTR support for multicast by configuring the ip multicast rpf multitopology command. The global-address-family command is entered with the IPv4 address family and multicast subaddress family. You then enter thetopology command with the base keyword, and global topology configuration parameters are applied in this mode.

For detailed steps, see the Configuring a Multicast Topology for MTR section.

How to Configure MTR Support for Multicast

Configuring a Multicast Topology for MTR


Note
  • Only a single multicast topology can be configured, and only the base keyword can be entered when the multicast topology is created in Step 6.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ip multicast-routing [vrf name]

4.    ip multicast rpf multitopology

5.    global-address-family ipv4 [multicast | unicast]

6.    topology {base | topology-name}

7.    route-replicate from {multicast | unicast} [topology {base | name}] protocol [route-map name | vrf name]

8.    use-topology unicast {base | topology-name}

9.    shutdown

10.    end

11.    show topology [cache [topology-id] | ha [[detail | interface | lock | router] [all | ipv4 | ipv6 | vrf vpn-instance]]]


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 multicast-routing [vrf name]


Example:

Router(config)# ip multicast-routing

 

Enables IP multicast routing.

 
Step 4
ip multicast rpf multitopology


Example:

Router(config)# ip multicast rpf multitopology

 

Enables MTR support for IP multicast routing.

 
Step 5
global-address-family ipv4 [multicast | unicast]


Example:

Router(config)# global-address-family ipv4 multicast

 

Enters global address family configuration mode to configure the global topology.

  • The address family for the class-specific topology is specified in this step. The subaddress family can be specified. Unicast is the default if no subaddress family is entered.
 
Step 6
topology {base | topology-name}


Example:

Router(config-af)# topology base

 

Configures the global topology instance and enters address family topology configuration mode.

  • Only the base keyword can be accepted for a multicast topology.
 
Step 7
route-replicate from {multicast | unicast} [topology {base | name}] protocol [route-map name | vrf name]


Example:

Router(config-af-topology)# route-replicate from unicast topology VOICE ospf 100 route-map map1

 

(Optional) Replicates (copies) routes from another multicast topology RIB.

  • The protocol argument is configured to specify the protocol which is the source of the route. Routes can be replicated from the unicast base topology or a class-specific topology.
Note    However, route replication cannot be configured from a class-specific topology that is configured to forward the base topology (incremental forwarding). You can replicate routes from a multicast RIB to a multicast RIB or replicate routes from a unicast RIB to a multicast RIB, but you cannot replicate routes from a multicast RIB to a unicast RIB.
  • Replicated routes can be filtered through a route map before they are installed into the multicast RIB.
 
Step 8
use-topology unicast {base | topology-name}


Example:

Router(config-af-topology)# use-topology unicast VIDEO

 

(Optional) Configures a multicast topology to perform RPF computations using a unicast topology RIB.

  • The base or a class-specific unicast topology can be configured. When this command is configured, the multicast topology uses routes in the specified unicast topology table to build multicast distribution trees.
Note    This multicast RIB is not used when this command is enabled, even if the multicast RIB is populated and supported by a routing protocol.
 
Step 9
shutdown


Example:

Router(config-af-topology)# shutdown

 

(Optional) Temporarily disables a topology instance without removing the topology configuration (while other topology parameters are configured and other routers are configured with MTR).

 
Step 10
end


Example:

Router(config-af-topology)# end

 

(Optional) Exits address family topology configuration mode and enters privileged EXEC mode.

 
Step 11
show topology [cache [topology-id] | ha [[detail | interface | lock | router] [all | ipv4 | ipv6 | vrf vpn-instance]]]


Example:

Router# show topology detail

 

(Optional) Displays information about class-specific and base topologies.

 

What to Do Next

The topology is not activated until classification is configured. Proceed to the Configuring MTR Traffic Classification section to configure classification for a class-specific topology.

Configuration Examples for MTR Support for Multicast

Example Route Replication Configuration

The following example shows how to enable multicast support for MTR and to configure a separate multicast topology: 

ip multicast-routing
ip multicast rpf multitopology
!
global-address-family ipv4 multicast
 topology base
 end

The following example shows how to configure the multicast topology to replicate OSPF routes from the VOICE topology. The routes are filtered through the BLUE route map before they are installed in the multicast routing table. 

ip multicast-routing
ip multicast rpf multitopology
!
access-list 1 permit 192.168.1.0 0.0.0.255
!
route-map BLUE
 match ip address 1
 exit 
!
global-address-family ipv4 multicast
 topology base
 route-replicate from unicast topology VOICE ospf route-map BLUE

Example Using a Unicast RIB for Multicast RPF Configuration

The following example shows how to configure the multicast topology to perform RPF calculations on routes in the VIDEO topology RIB to build multicast distribution trees: 

ip multicast-routing
ip multicast rpf multitopology
!
global-address-family ipv4 multicast
 topology base
 use-topology unicast VIDEO
 end

Example Multicast Verification

The following example shows that the multicast topology is configured to replicate routes from the RIB of the VOICE topology: 

Router# show topology detail 
Topology: base
  Address-family: ipv4
  Associated VPN VRF is default
  Topology state is UP
  Associated interfaces:
    Ethernet0/0, operation state: UP
    Ethernet0/1, operation state: DOWN
    Ethernet0/2, operation state: DOWN
    Ethernet0/3, operation state: DOWN
    Loopback0, operation state: UP
          
Topology: VIDEO
  Address-family: ipv4
  Associated VPN VRF is default
  Topology state is UP
  Topology fallback is enabled
  Topology maximum route limit 1000, warning limit 90% (900)
  Associated interfaces:
Topology: VOICE
  Address-family: ipv4
  Associated VPN VRF is default
  Topology state is UP
  Topology is enabled on all interfaces
  Associated interfaces:
    Ethernet0/0, operation state: UP
    Ethernet0/1, operation state: DOWN
    Ethernet0/2, operation state: DOWN
    Ethernet0/3, operation state: DOWN
    Loopback0, operation state: UP
Topology: base
  Address-family: ipv4 multicast
  Associated VPN VRF is default
  Topology state is DOWN
  Multicast multi-topology mode is enabled.
  Route Replication Enabled:
    from unicast topology VOICE all route-map BLUE
  Associated interfaces:

Additional References

Related Documents

Related Topic Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

Multitopology Routing (MTR) commands

Cisco IOS Multitopology Routing Command Reference

IP multicast commands

Cisco IOS Multicast Command Reference

IP multicast concepts and tasks

IP Multicast Configuration Guide Library

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Feature Information for MTR Support for Multicast

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 1Feature Information for MTR Support for Multicast
Feature Name Releases Feature Information

MTR Support for Multicast

12.2(33)SRB

15.0(1)M

This feature provides Multitopology Routing (MTR) support for multicast and allows you to control the path of multicast traffic in the network.

The following commands were introduced or modified: clear ip route multicast, ip multicast rpf multitopology, show ip route multicast, use-topology.

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