From: James (james@towardex.com)
Date: Wed Oct 13 2004 - 18:06:01 GMT-3
On Wed, Oct 13, 2004 at 01:43:54PM -0700, John Matus wrote:
> when you are setting the local preference for traffic exiting your AS to
> another AS, is it necessary in the route map to have the as path listed?
>
> route-m local pref permit 10
> match as-path 1
> set local pref 200
>
> ip as-path access-l permit ^54$.................54 being the AS that you are
> routing to?...the reason i ask is i'm not sure what would happen if you were
> connected to multiple AS's with more than on exit point...how would the
> process know which AS you are referring too? <ok, now that i'm thinking about
> it, the connected neighbor that calls the route-map "neighbor 1.2.3.4 route-m
> localpref in'" can only belong to 1 AS any was.......but i'm still wondering
> if it is good practice to indicate the as-path in the route-map>........
It depends, John. If you are looking to set local pref on all routes heard
from a specific neighbor (e.g. a BGP session from an ISP with pretty cheap like
20$/meg bandwidth that you want to prefer) then simply doing this works for
you, and works for your router with the least minimal CPU usage in bgp process:
!
route-map lp-set permit 5
set local 200
!
router bgp blah
nei a.b.c.d route-map lp-set in
!
If you are looking to selectively grab for a specific AS path, for example
you only want to increase preference for your ISP's originated routes, but
not the internet routes, then that's where AS-PATH list comes in.
If you have no need for this, and just looking for simple local-pref setting
on all routes received from a neighbor, filtering through as-path is completely
unnecessary and puts useless cpu burden on your router trying to process all
150k (150,000 as in real life internet routes) prefixes.
HTH,
-J
-- James Jun TowardEX Technologies, Inc. Technical Lead Network Design, Consulting, IT Outsourcing james@towardex.com Boston-based Colocation & Bandwidth Services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net
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