[c-nsp] VRF randomly, stably install only one from multiple route sets

[Everton da Silva Marques]

Desired scenario:

  Remote VRF-1 exports routes R1.
  Remote VRF-2 exports routes R2.
  Remote VRF-3 exports routes R3.

  Central VRF-C imports only one from (R1, R2, R3),
  without any preference. Once C selects Ri, it
  stably sticks with Ri as long as Ri remains available.
  Only if Ri becomes unavaiable, C would switch
  to another Rj available and distinct from Ri;
  afterwards, if Ri availability is ever restored,
  C still stably keeps Rj as long as Rj remains available.

Questions:

  1) Is that possible to achieve by properly
  configuring VRF's statements? If so, how?

  2) Would disabling "multipath ibgp" on the
  VRF-C's PE, so that only the oldest active Ri
  get installed on VRF-C's local forwarding table,
  provide the behavior described above?

  3) Can anyone point another way to achieve
  the same behavior?

Please advise.