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 -- Malte v. dem Hagen Abteilung Technik - Network Operations Centre ----------------------------------------------------------------- Host Europe GmbH - http://www.hosteurope.de/ Welserstrasse 14 - D-51149 Köln - Germany Telefon 0800-4 67 83 87 - Telefax 01805-66 32 33 HRB 28495 Amtsgericht Koeln - UST ID DE187370678 GF: Uwe Braun - Alex Collins - Mark Joseph - Patrick Pulvermüller -----------------------------------------------------------------