BGP Traffic Engineering question


If you have several transit providers connected to your network and much of your traffic is generally directed by the "BGP tiebreaker" (i.e. lowest IP address) is there a way, without specifying on a per-prefix basis to prefer the "tie breaker winner" slightly less often? I don't want to "completely flip" the preference so that it just saturates a different link, I am just trying to see if there is any good way to influence the "natural" selection method.

We have 6 transit providers, and Level3 always wins because it is 4/8, normally this isn't a problem because we have traffic engineering systems (route science/avaya) which move traffic away from that link, but if we need to reboot the RS, or something catastrophic happens we would like it to spread out a little more evenly.

Anyone have any thoughts on this?


Isn't Route Science EOL?


Sure, it still works however (for now).


Assuming Cisco, set "bgp always-compare-med", "bgp deterministic-med", and
in your route-map in, "set origin igp" and "set metric X". You can then
vary X as you see fit as an alternate tie-breaker. As long as you never set
the metric the same on two different paths for the same prefix, it'll never
fall back to router-id.

Depending on the transit provider, you can often match bgp communities to
determine which are customer routes or the region where the announcement was
heard, which you can then use as a tie-breaker when setting the metric.
Barring that, as-path access-lists matching specific path fragments can do
the same thing, but seems to take more work to maintain as relationships
change over time.

                                     -- Aaron

Aaron Hopkins wrote: