[c-nsp] BGP route influence question related to multi-path iBGP

[David Hubbard]

Hello all, I have a setup where one BGP AS exists at two physical locations, with an edge router at each location peered to different upstreams.  The two edge routers are interconnected with a 40gig and 10gig link, each with its own interface/address, so there are two iBGP sessions between the same two routers.  The intent of the 10gig is only to be used as backup, and when I first brought it up, the routers of course began treating them as equal cost paths (from BGP perspective) and used both.  The way I initially worked around that was via a route map on both sides that assigns a higher non-default weight to advertisements coming in via the iBGP session on the 40gig link.

The issue with this is weight of course comes before other factors in best path selection, including AS path length, so I’m seeing less desirable routes end up in my route tables, likely just based on which edge router gets an update first and sends it to the other.

Is there a better way for these two to be set up so they can have a backup path that is only used if the primary is down, without negatively influencing normal best path selection?

Thanks,

David