Simon Chen wrote: > Hi all, > > Happy new year... > > I have a question regarding multi-homing, mostly from stub network's > operational point of view. My big question is: what kind of failures > do you usually see from your providers? Link down? Link up, but > withdraw some routes? Link up, no route change, but blackholing > partial or all traffic? Anything else? >
I am a multihomed network with no downstream customers. Speaking only for myself over the last 5 years I have only had loss of link conditions as the majority problem such as: * DLCI deleted (LEC "accidentally canceled" a FRT1 once) * Loss of signal (almost always LEC problems) * Loss of frame (almost always long haul problems) It's worth noting all my circuits are T1, T3, or OC-x and less likely to have an "up/up but not passing traffic" state like an Ethernet handoff could do. And only once: * Sprint vs. Cogent peering spat (I'm a Sprint customer) The last one would have been a huge problem for default route or single homed users - and why I always recommend full tables - but for me I didn't care since the affected paths disappeared via Sprint but were still there via my other upstream. > To state this problem in detail: I use a static default route on Ra to > forward traffic to provider A, or receive 0/0 from provider A via BGP. > For some reason, provider A can no longer reach a /24. My network > cannot be notified (unless, I receive a full internet routing table). > In this case, all I know is that my traffic to /24 is blackholed > through provider A. In this case, is there an automatic way for my > stub network to switch over to provider B? Do I have to do the > detection and switch over manually? I don't think VRRP can help here, > right? You're asking for what BGP does. You could ping every prefix you care about and do it by hand, I guess. If this is a major concern for you I'd say full tables are in your best interest so you can let BGP do what it does best. (Disclaimer: there may be some trick I'm not aware of because I always prefer to let BGP do its job.) ~Seth
