BGP Path Selection

Russell Briggs russb at puffer.quadrunner.com
Mon Aug 30 19:34:14 UTC 1999


in-line reply

On Mon, Aug 30, 1999 at 07:53:36PM +0200, Alex Bligh said:
> 
> Bryan,
> 
> > 	I keep hearing bitching about how broken the BGP path selection 
> > 	process as 1) defined in the protocol spec and 2) as implemented 
> > 	by vendors, is.
> 
> Well this is a yet-another-knob-request. I have for a while now thought
> it would be useful to have an attribute which is kept local to the AS,
> and is if you like an "exit-penalty". This could be added to your IGP
> distance at the decision stage process. It's difficult to combine
> internal IGP metrics (especially if you use next-hop-self style peerings
> internally so lose the distance on the interface itself) *and* add
> make intelligent use of different quality interconnects (especially
> if these are interfaces on the same router).
> 
> Consider the case where you are prepared to send traffic from SOME parts
> of the country "around the long way" to avoid a particularly crappy
> interconnect, point, but not from ALL parts of the country.
> 
> On your point (2) I reckon Cisco implements the standard pretty
> well (i.e. where it diverges it's for reasonable reasons), or at

  Um, Cisco uses as length and igp metrics in the route selection 
  process.  This is hardly in compliance with the RFC. 

> least it does when you've switched on "bgp deterministic-med" which
> gives you a good indication of how MED decisions are taken without
> this knob switched on.
> 
> -- 
> Alex Bligh
> GX Networks (formerly Xara Networks)
> 
> 

-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
  Russell Briggs                                     TEL: 512-322-9200
  Senior Network Engineer                            CEL: 512-633-5983
  Onramp Access, Inc.                                FAX: 512-476-2878
  russb at quadrunner.com                               http://www.onr.com/

----- End forwarded message -----

-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
  Russell Briggs                                     TEL: 512-322-9200
  Senior Network Engineer                            CEL: 512-633-5983
  Onramp Access, Inc.                                FAX: 512-476-2878
  russb at quadrunner.com                               http://www.onr.com/




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