[c-nsp] mpls route target export question

[Nick Chettle]

Using multiple RD's is important for convergence when you are using route-reflectors as a route-reflector will only advertise the "best" BGP route to it's clients. If you use the same RD for a VPN across two (Or more) PE's then the route-reflector will see that route as the same and only pick the one it considers the best. If you use unique RD's the route-reflector will not consider the routes the same and will advertise both of them.

Taking this even further, you may also want to investigate the command "maximum-paths ibgp unequal-cost" which can be used to protect against route-reflector failure. For example, you could use "maximum-paths ibgp unequal-cost 2 import 4" to ensure your VRF's will import 4 BGP routes. If a route-reflector fails (I'm assuming there are 2 for this) you will still have the 2 routes in your VRF.

HTH

Nick

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of David Freedman
Sent: 05 August 2010 15:29
To: cisco-nsp at puck.nether.net
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] mpls route target export question

We generally do one RD, RT per VRF, same RD across multiple PEs the VRF
is configured (extended import/export policies aside)

We also attach standard communities to VRF prefixes (yes, astonishing
thing to do) since our standard community scheme does all the stuff like
identifying the originating router/site/customer/routing policy etc..

We currently use a system of route reflectors and have no issue where we
have multi-PE homed CE (other than where we do as-override where we set
SoO per PE)

would be interested on some expansion of oli's comments on convergence,
and why differing RDs for the same prefix would be a good thing (I'm
imagining perhaps if you want to do multipath then they are considered
multiple paths as opposed to simply just selecting one because RD is the
same?)

Dave.

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