[nsp] eBGP routes not balancing

[Jeff Chan]

I went back and reviewed some of the old messages here and
noticed that the question was already answered by Jon Lewis:

> Date: Sat, 13 Sep 2003 18:25:08 -0400 (EDT)
> From: jlewis at lewis.org-nospam
> To: Kevin <kevin at honeycomb.net-nospam>
> Subject: Re: [nsp] BGP question
> Cc: "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net>
>
> On Fri, 12 Sep 2003, Kevin wrote:
> 
>> A lot of routes from both providers have equal AS paths.
>> If one bgp session gets reset all that traffic (the equal AS path
>> routes) goes out to provider2 and does'nt reset back to provider1,
>> providing that the bgp session to provider1 was the first one to come
>> up. I don't have any metrics, weights or localpref on any routes.
> 
> At some point, cisco changed the default of bgp bestpath compare-routerid
> to "bgp bestpath oldest-route" (AFAIK, that's not a valid command...just
> what I think they might call it if it were).  You can go back to the old
> behavior by adding bgp bestpath compare-routerid to your router bgp
> config.  At least that way, you know how things will route when all your
> connections are up...and you can play around with route-maps if you want
> to shift some traffic off the best routerid.  With "bestpath oldest-route"
> a BGP flap will screw up your balancing if you're just shifting traffic to
> certain AS's.

Which agrees with Michael Loftis' comment that older routes are
preferred.

So I think we'll give "bgp best path compare-routerid" a try.  It
may well balance the two connections better for us.  Presumably
there aren't major downsides.  I found an apparently recent
overview of Cisco's best path selection algorithm mentioning this
statement at:

  http://www.cisco.com/en/US/tech/tk365/tk80/technologies_tech_note09186a0080094431.shtml

"no bgp best path compare-routerid" seems to disable it.

Jeff C.