HI, On Tue, Oct 11, 2011 at 05:02:45PM +0000, Vincent Aniello wrote: > > Can you be a bit more specific about the config? > > We have two routers, the first router has two Internet connections, > ISP A and ISP B. The second router has a backup connection to ISP > A. All three connections take a full BGP routing table and the > two routers peer with each other via iBGP. The connections to the > ISPs are Ethernet. We recently had a failure of ISP B and the > Ethernet interface stayed up, but the BGP peer went down, which is > what prompted this question.
Actually this is really what BFD was invented for: fast low-weight
hellos to make sure that the link is still operational, and if not,
quick signalisation to the routing protocols (here: BGP) that it's
broken.
The fact that ISPs currently don't usually offer BFD doesn't mean it
couldn't or shouldn't be done. It just means customers are not asking
often enough.
(OTOH, even if your BFD/BGP session would notice in 0.5 seconds that
the link failed, it would still take a few minutes for The Whole
Internet to reconverge - so don't expect miracles from global BGP.
If you want *fast* failover, get two links to the same ISP, and use
BGP+BFD there - only local convergence needed, not global)
gert
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Gert Doering - Munich, Germany [email protected]
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