In the last year I worked for a company which had multihomed /24s and we never had any problem with parts of the internet being unreachable when our primary provider was down, at least not that anyone noticed. I suspect this is because of which providers were upstream -- the configuration was that we were directly peered with C&W, using C&W address space, and our backup was a tier 2 who peered with UUnet and Sprint. My theory is that when our connection to C&W was down, networks which filtered our /24 advertisement would send traffic destined for us to C&W (who was still advertising large aggregates which our /24s were under), and then once it reached C&W, C&W would use its own peering connections with UUnet and/or Sprint to deliver the traffic. Does this sound plausible, or am I missing something? Do a lot of multihomed /24ers get away with it by this principle? In what situations would something like this _not_ happen, aside from peering directly with a primary provider who would not accept advertisements for your small address block from outside? (which would be kind of pointless, anyway..)