[110489] in North American Network Operators' Group
Re: question about BGP default routing
daemon@ATHENA.MIT.EDU (Edward B. DREGER)
Tue Jan 6 14:34:40 2009
Date: Tue, 6 Jan 2009 19:34:36 +0000 (GMT)
From: "Edward B. DREGER" <eddy+public+spam@noc.everquick.net>
To: nanog@merit.edu
In-Reply-To: <722214.74526.qm@web57414.mail.re1.yahoo.com>
Errors-To: nanog-bounces@nanog.org
cK> Date: Tue, 6 Jan 2009 07:40:16 -0500 (EST)
cK> From: chloe K
cK> Why it needs default routes when running BGP?
If you have a full table, you do not need default. It's even desirable
to drop road-to-nowhere packets inside your network, before they clog up
your connections.
However, consider that you may encounter some problems -- such as
insufficient RAM to deal with growing table size -- that leave you
forced to take a partial table. Then what?
If you're running BGP, you probably have more than one upstream, so you
don't want static defaults (unless the next hop is a serial interface).
To deal with this, you can have your providers originate default _and_
send a full table.
Under normal circumstances, use a route map that nukes 0/0. If you find
yourself in a jam, replace the route map with one that allows 0/0 and
discard long paths, AS_PATHs that you consider troublesome, et cetera.
You still have the benefit of directing certain routes to a specific
provider, but with a smaller (partial) table.
Finally, note that not every router needs full tables. Consider a
peering router that exchanges traffic between a network's peers and
customers.
Eddy
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