VRF route import is an IP address-specific extended community, of an extended type, and is transitive across AS boundaries (RFC 4360, BGP Extended Communities Attribute).
To support MVPN, in addition to the import/export route target extended communities used by the unicast routing, each VRF on a PE must have an import route target extended community that controls imports of C-multicast routes into a particular VRF.
The c-multicast import RT uniquely identifies a VRF, and is constructed as follows:
The Global Administrator field of the c-multicast import RT must be set to an IP address of the PE. This address should be common for all the VRFs on the PE (this address may be the PE’s loopback address).
The Local Administrator field of the c-multicast import RT associated with a given VRF contains a 2 octets long number that uniquely identifies that VRF within the PE that contains the VRF.
A PE that has sites of a given MVPN connected to it communicates the value of the c-multicast import RT associated with the VRF of that MVPN on the PE to all other PEs that have sites of that MVPN. To accomplish this, a PE that originates a (unicast) route to VPN-IP addresses includes in the BGP updates message that carries this route the VRF route import extended community that has the value of the c-multicast import RT of the VRF associated with the route, except if it is known a priori that none of these addresses acts as multicast sources and/or RP, in which case the (unicast) route need not carry the VRF Route Import extended community.
All c-multicast routes with the c-multicast import RT specific to the VRF must be accepted. In this release, vrf-import and vrf-target policies do not apply to C-multicast routes.
The decision flow path is shown below.
if (route-type == c-mcast-route)
if (route_target_list includes C-multicast_Import_RT){
else
drop;
else
Run vrf_import and/or vrf-target;