[77039] in North American Network Operators' Group
Re: IBGP Question --- Router Reflector or iBGP Mesh
daemon@ATHENA.MIT.EDU (Iljitsch van Beijnum)
Wed Jan 12 06:20:52 2005
In-Reply-To: <0e0901c4f87d$99768ba0$6401a8c0@alexh>
Cc: Daniel Roesen <dr@cluenet.de>, NANOG list <nanog@merit.edu>
From: Iljitsch van Beijnum <iljitsch@muada.com>
Date: Wed, 12 Jan 2005 12:20:22 +0100
To: "Alexei Roudnev" <alex@relcom.net>
Errors-To: owner-nanog-outgoing@merit.edu
On 12-jan-05, at 9:06, Alexei Roudnev wrote:
> Are you sure? RR should just distribute routes.
> RR do not make any route decisions, and (btw) iBGP do not make route
> decisions - they are mostly based on IGP routing.
Route reflectors only propagate their idea of the best route for a
destination. If this decision is based on eBGP-learned information such
as the AS path this doesn't matter because all routers in the AS would
make the same decision anyway, but if the IGP metric comes into play
(which invariably happens in large networks) then all the reflector
clients only see the route that is best based on the IGP metrics the
reflector sees.
(Obviously the IGP metric will be different at the client, but the
client doesn't see the other routes, so it can't make a different
decision. The real fun starts when the next (intra-AS) hop isn't a
reflector client and the packet now takes a different path than the
reflector client thought it would take.)
