# Configuring IPv6 Multicast Attributes

You can configure IPv6 multicast to control the flow of multicast traffic with the following tasks:

- Enabling IPv6 Multicast
- Defining IPv6 Static Routes for Reverse-Path Forwarding
- Enabling and Disabling RPF Checks for IPv6
- Specifying Unicast Routes for RPF in IPv6
- Defining Permanent IPv6 Multicast Forwarding Entries

## Enabling IPv6 Multicast

IPv6 multicast works on virtual routers. By default, IPv6 multicast is disabled on a virtual router. To enable IPv6 multicast on a virtual router, access the context for a virtual router, and then issue the ipv6 multicast-routing command.

To enable IPv6 multicast routing on the default virtual router:

- Issue the ipv6 multicast-routing command in Global Configuration mode.
  host1(config)#ipv6 multicast-routing

Use the no version to disable IPv6 multicast routing on the virtual router (the default). In the disabled state, all multicast protocols are disabled, and the virtual router forwards no multicast packets.

## Defining IPv6 Static Routes for Reverse-Path Forwarding

You can use the ipv6 rpf-route command to define RPF to verify that a router receives a multicast packet on the correct incoming interface.

To customize the static IPv6 routes that the router may use for RPF:

- Issue the ipv6 rpf-route command in Global Configuration mode.
  host1(config)#ipv6 rpf-route 1000::/64 ATM2/1.200

Use the no version to remove the static route.

## Enabling and Disabling RPF Checks for IPv6

By default, the router accepts multicast packets for each (S,G) pair on an IIF, which satisfies the RPF check (RPF-IIF). When the router performs RPF checks, only the interface that first accepts traffic for an (S,G) pair accepts subsequent traffic for that pair. If traffic stops coming on that interface and starts arriving on another interface, the router does not accept or forward the traffic.

Some network configurations require the router to accept traffic on any interface. To do so, you can disable the RPF check on a specified set of (S,G) pairs by issuing the ipv6 multicast-routing disable-rpf-check command.

When you disable RPF checks, the router accepts multicast packets for (S,G) pairs on any incoming interface. When the router has added the new route to its multicast routing table, it accepts multicast packets for these pairs on any interface in the virtual router and forwards them accordingly. Multicast routes established before you issue this command are not affected.

To enable and disable RPF checks:

- Enable RPF checks for all (S,G) pairs (the default situation).
  host1(config)#no ipv6 multicast-routing disable-rpf-check
- Disable RPF checks for the (S,G) pair specified using a standard IPv6 access list.
  host1(config)#ipv6 multicast-routing disable-rpf-check denver-list

## Specifying Unicast Routes for RPF in IPv6

You can use the ipv6 route-type command to specify that BGP or OSPF IPv6 routes should be available for RPF. Routes available for RPF appear in the multicast view of the routing table.

To specify that BGP IPv6 routes are available for both unicast protocols and multicast protocols to perform RPF checks:

host1(config)#router bgp host1(config-router)#ipv6 route-type both

## Defining Permanent IPv6 Multicast Forwarding Entries

An mroute is a multicast traffic flow, a (S,G) entry used for forwarding multicast traffic. By default, forwarding mroutes (with a valid RPF incoming interface) are timed out if data for them is not received for 210 seconds. However, you can specify an mroute as permanent by using the ipv6 multicast-routing permanent-mroute command.

To specify that any newly created mroutes that match the specified access-list do not time out:

- Issue the ipv6 multicast-routing permanent-mroute command in Global Configuration mode.
  host1(config)#ipv6 multicast-routing permanent-mroute routesv61

Use the no version to prevent any new mroutes from becoming permanent. To remove existing permanent mroutes, use the clear ipv6 mroute command.

| The ipv6 multicast-routing permanent-mroute command does not change existing mroutes. Permanent mroutes are removed if a topology change occurs that affects the mroute. Permanent mroutes may be removed due to certain protocol actions (for example, PIM sparse mode switching from shared to shortest path tree). Outgoing interface lists of permanent mroutes may change due to protocol actions.

#### Related Documentation

- IPv6 Multicast Overview
- Before You Begin
- Deleting IPv6 Multicast Forwarding Entries
- Monitoring Available IPv6 Routes for Reverse-Path Forwarding
- Monitoring IPv6 Multicast Forwarding Entries
- Monitoring Active IPv6 Multicast Routes
- Monitoring Join Interface Details when IPv6 OIF Mapping is Configured
- Monitoring IPv6 Multicast Statistics
- Monitoring Summary Information of IPv6 Multicast Routes
- Monitoring IPv6 Multicast Status on a Virtual Router
- clear ipv6 mroute
- ipv6 multicast-routing
- ipv6 multicast-routing disable-rpf-check
- ipv6 multicast-routing permanent-mroute
- ipv6 route-type
- ipv6 rpf-route