[c-nsp] An attribute with less priority than local preference for choosing a best path.

Drew Weaver drew.weaver at thenap.com
Fri Jun 3 12:02:54 EDT 2022

As always thank you.


-----Original Message-----
From: Jon Lewis <jlewis at lewis.org> 
Sent: Friday, June 3, 2022 12:02 PM
To: Drew Weaver <drew.weaver at thenap.com>
Cc: 'cisco-nsp at puck.nether.net' <cisco-nsp at puck.nether.net>
Subject: Re: [c-nsp] An attribute with less priority than local preference for choosing a best path.

On Fri, 3 Jun 2022, Drew Weaver wrote:

> Hello,
> We have a few edge routers with multiple connections to multiple geographically diverse locations from the same AS number (for example we have a router that connects to Lumen in both Cleveland and Cincinnati).
> Since the routes from both peers have mostly the same AS PATHs all of the traffic was going through one of the connections.
> In order to control that I was using:
> if community matches-any LUMEN-CLEVE then
>    set local-preference 150
>  endif
> Makes perfect sense that any route tagged with a community in the list LUMEN-CLEVE would be preferred regardless of the AS-PATH.
> My question is what is considered the right attribute to modify that won't override the AS-PATH length?
> Would it be better to adjust MED?

Yep.  That's what we use to nudge traffic when everything else ties.  Make sure you also have consistent origin though...you may need to look at setting origin on all routes received from transits/peers to the same value to keep individual drains from winning due to their setting origin igp.

  Jon Lewis, MCP :)           |  I route
  StackPath, Sr. Neteng       |  therefore you are
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