Redundant Phantom Rendez-vous Point / Longest Match

Because multicast source information is no longer available in Bidir, the Anycast/MSDP mechanism used to provide redundancy in sparse-mode is not an option for Bidir.
That mechanism relied on the announcement of active sources through MSDP, which is not available in Bidir.
In Bidir, redundancy consists of a primary/ secondary model, there is no load sharing as was possible with the Anycast-rendezvous point sparse-mode case (it’s impossible to load share without maintaining source information).

The preferred method for providing Bidir rendezvous point redundancy can be designed using loopback networks with different mask length.
This mechanism relies on unicast routing longest match route lookups to guarantee a consistent path to the rendezvous point.
In this case the rendezvous point address is still a “phantom” address (that is, it is not associated with any physical entity).
It is only necessary to ensure that a route to the rendezvous point exists, to maintain rendezvous point reachability. For this we will employ loopback interfaces in the primary and secondary routers with different netmask lengths.
The way the primary/secondary relationship works in this situation is by advertising routes for the rendezvous point with different netmasks.