[GROW] draft-ietf-grow-diverse-bgp-path-dist: risk of inconsistent path selection

[Jakob Heitz <[e-mail]>]

Route selection tie breakers in RFC 4271 state:

      f) Remove from consideration all routes other than the route that
         was advertised by the BGP speaker with the lowest BGP
         Identifier value.

      g) Prefer the route received from the lowest peer address.

Suppose RR Planes use different BGP Identifier values.
If they use the same BGP Identifier, a similar argument
can be made for peer address.

To prevent clients in different clusters from choosing
different bestpaths based on tie breaker (f):

The RR Plane that advertises the best path MUST be configured
with a BGP Identifier higher than that of the RR Plane that
advertises the 2nd best. This must be higher than that of
the Plane that advertises the 3rd best and so on.

I'm not sure if this rule completely solves the problem.
If not, then the "Edge_Discriminator attribute" proposed
by draft-pmohapat-idr-fast-conn-restore may be required.
Also, this would need to be applied before rule (f).

--
Jakob Heitz.