AS 701 local-pref answer.

Mon Dec 17 02:06:53 UTC 2001

> Date: Sun, 16 Dec 2001 17:28:30 -0800 (PST)
> From: David Barak <thegameiam at 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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