[44819] in North American Network Operators' Group
Re: AS 701 local-pref answer.
daemon@ATHENA.MIT.EDU (E.B. Dreger)
Sun Dec 16 21:07:30 2001
Date: Mon, 17 Dec 2001 02:06:53 +0000 (GMT)
From: "E.B. Dreger" <eddy+public+spam@noc.everquick.net>
To: David Barak <thegameiam@yahoo.com>
Cc: nanog@merit.edu, mleber@he.net, smentzer@mentzer.org,
rekoil@semihuman.com, gmartine@nic.gip.net
In-Reply-To: <20011217012830.3887.qmail@web14914.mail.yahoo.com>
Message-ID: <Pine.LNX.4.20.0112170149290.22495-100000@www.everquick.net>
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Errors-To: owner-nanog-outgoing@merit.edu
> Date: Sun, 16 Dec 2001 17:28:30 -0800 (PST)
> From: David Barak <thegameiam@yahoo.com>
> AS 701 always announces the best route, as their
> routers know it. Their average AS-path length is
This is silly. Local-pref is one of the methods by which a
router learns the "best route". The question was: If not by
local-pref, then by what?
> under 2, so it doesn't seem to be a problem. If a
And if someone pads their adverts to 701 at their egress?
Suddenly the "best route" to the downstream is via the peer.
Sorry, it doesn't matter if "average as-path length is under 2"
or not... the point is that (unless BGP weight comes into play),
after reachability, as-path length is the first route selection
mechanism after reachability.
> customer of AS 701 wants to insure that his/her route
> is advertised in all cases, s/he could send a
> community which AS701 edge devices could use to
> manipulate local-preference upward. [this was covered
IOW, the bottom line answer is: reliance on as-path length,
but local-pref is tunable via communities.
Eddy
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