On Sat, Aug 22, 2009 at 6:52 AM, Adam Greene<maillist@webjogger.net> wrote:
Another option could be to announce one /17 to each upstream provider and use conditional BGP to announce the other /17 to the provider that's still active in the event that one provider goes down.
Maybe I'm wrong, but I think this method will only work when handling local failures. If there is a failure in a remote network which causes ISP A to be unreachable from a third party, your routers will not adjust the announcements since ISP A and B are still reachable to you, but the third party will not be able to reach the network nearer to ISP A through the ISP B connection because ISP B doesn't have an announcement to that network. (This is assuming that ISP A and ISP B are not peers). Hector