4.4 Multicast RIB Commands

The Multicast RIB provides a separate table of unicast destinations which is used for Multicast Reverse Path Forwarding decisions. It is used with a multicast source’s IP address, hence contains not multicast group addresses but unicast addresses.

This table is fully separate from the default unicast table. However, RPF lookup can include the unicast table.

WARNING: RPF lookup results are non-responsive in this version of Quagga, i.e. multicast routing does not actively react to changes in underlying unicast topology!

Command: ip multicast rpf-lookup-mode mode

Command: no ip multicast rpf-lookup-mode [mode]

mode sets the method used to perform RPF lookups. Supported modes:

‘urib-only’

Performs the lookup on the Unicast RIB. The Multicast RIB is never used.

‘mrib-only’

Performs the lookup on the Multicast RIB. The Unicast RIB is never used.

‘mrib-then-urib’

Tries to perform the lookup on the Multicast RIB. If any route is found, that route is used. Otherwise, the Unicast RIB is tried.

‘lower-distance’

Performs a lookup on the Multicast RIB and Unicast RIB each. The result with the lower administrative distance is used; if they’re equal, the Multicast RIB takes precedence.

‘longer-prefix’

Performs a lookup on the Multicast RIB and Unicast RIB each. The result with the longer prefix length is used; if they’re equal, the Multicast RIB takes precedence.

The mrib-then-urib setting is the default behavior if nothing is configured. If this is the desired behavior, it should be explicitly configured to make the configuration immune against possible changes in what the default behavior is.

WARNING: Unreachable routes do not receive special treatment and do not cause fallback to a second lookup.

Command: show ip rpf addr

Performs a Multicast RPF lookup, as configured with ip multicast rpf-lookup-mode mode. addr specifies the multicast source address to look up.

> show ip rpf 192.0.2.1
Routing entry for 192.0.2.0/24 using Unicast RIB
  Known via "kernel", distance 0, metric 0, best
  * 198.51.100.1, via eth0

Indicates that a multicast source lookup for 192.0.2.1 would use an Unicast RIB entry for 192.0.2.0/24 with a gateway of 198.51.100.1.

Command: show ip rpf

Prints the entire Multicast RIB. Note that this is independent of the configured RPF lookup mode, the Multicast RIB may be printed yet not used at all.

Command: ip mroute prefix nexthop [distance]

Command: no ip mroute prefix nexthop [distance]

Adds a static route entry to the Multicast RIB. This performs exactly as the ip route command, except that it inserts the route in the Multicast RIB instead of the Unicast RIB.