[119242] in North American Network Operators' Group
Re: BGP Traffic Engineering question
daemon@ATHENA.MIT.EDU (Joe Maimon)
Tue Nov 10 15:47:25 2009
Date: Tue, 10 Nov 2009 15:46:07 -0500
From: Joe Maimon <jmaimon@ttec.com>
To: Aaron Hopkins <lists@die.net>
In-Reply-To: <alpine.LRH.2.00.0911101122250.3386@namshub.die.net>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Aaron Hopkins wrote:
> On Tue, 10 Nov 2009, Drew Weaver wrote:
>
>> 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?
>
> 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
>
Tutorial: Effective BGP Load Balancing Using "The Metric System"
Dani Roisman, Peak Web Consulting
http://tinyurl.com/yzlmmo8
