[110251] in North American Network Operators' Group
Re: Failover solution using BGP
daemon@ATHENA.MIT.EDU (Malte von dem Hagen)
Tue Dec 30 20:49:15 2008
Date: Wed, 31 Dec 2008 02:49:04 +0100
From: Malte von dem Hagen <mvh@hosteurope.de>
To: "Braun, Mike" <MBraun@firstam.com>
In-Reply-To: <CCC465742E47CC4090095AE1FF1C5B5910DAEDF3@CREDPWY01SXCH02.credit.credco.net>
Cc: nanog@nanog.org
Reply-To: mvh@hosteurope.de
Errors-To: nanog-bounces@nanog.org
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Hi,
Am 31.12.2008 01:19 Uhr, Braun, Mike schrieb:
> Why not just AS prepend your secondary site if the services to the
> Internet are the same at both sites and tied to the same IP addresses?
because that simply does not work (reliably). It would depend on
AS-paths of the same length from every possible source.
Simple, reliable and quite stylish is another way:
Choose primary and secondary location by announcing more specifics at
Sacramento, e.g. all networks as /20 subnets. As "longest match always
wins", any source seeing both routes for an IP address will choose
Sacramento.
The only way traffic could reach LA would be a missing route to
Sacramento. In any other case, Sacramento is chosen. Thus, if Sacramento
(manually or automatically) stops announcing the /20s, LA's /18 and /19
will be chosen.
CAVE: This is no failover solution for single services, just for whole
subnets depending on the announcement at Sacramento.
CAVE2: My suggestion creates inconsistent announcements for the source
AS. That may or may not be a problem.
Kind regards,
Malte
--=20
Malte v. dem Hagen
Abteilung Technik - Network Operations Centre
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