The points you make in your first two paragraphs are issues we had already considered. My original question really focuses on your third paragraph. How can we get by with partial routes if failover is our primary goal? It seems to me that we must receive full routes from at least the preferred ISP. Then we could get by with partial routes or even a default route for the secondary ISP. This means that we need at least one router powerful enough to handle the whole table.
These considerations, along with some others, lead us to conclude that BGP is not an optimal solution for us, but then you piqued my curiosity when you said we didn't need the whole table. I think that is only partially true. -----Original Message----- From: Bruce Robertson [mailto:[EMAIL PROTECTED] Sent: Tuesday, October 07, 2003 9:40 AM To: Robinson, Eric R. Subject: Re: [RLUG] An Alternative to Multihoming with BGP? > Bruce, I am a BGP plebian. Please explain how I can get by with partial > routes. I don't see how that can work. The only thing required for BGP failover is that you are advertising your routes through both ISPs, with preference given to one of the ISPs. You don't actually have to receive any routes whatsoever. You can install two default routes, and set up the one pointing to the preferred ISP with a higher priority. If the link goes down, it will automatically switch to the backup. Of course, this isn't perfect. It only fails over if the link physically goes down. If the ISP loses connectivity upstream from you, you'll still be pointing at them. You'll have this problem with your DNS solution, as well. There's no automated way for your DNS switcher to know that it should switch the DNS. The only way around this problem is to carry full BGP routes. That way, if the ISP loses connectivity, they'll lose their routes, and will stop advertising them to you. In practice, this is pretty safe, as long as your ISPs carry full routes and are multihomed. For example, it's been years since our routes have lost full routes for any reason other than routine maintenance. An optimization you can do is carry partial routes. For example, if you used GBIS as the backup, we could advertise just GBIS routes to you. That way, local traffic would stay local. And if you lost the GBIS connection, the connectivity would be preserved through the primary connection. -- Bruce Robertson, President/CEO +1-775-348-7299 Great Basin Internet Services, Inc. fax: +1-775-348-9412 http://www.greatbasin.net _______________________________________________ RLUG mailing list [EMAIL PROTECTED] http://www.rlug.org/mailman/listinfo/rlug
