North American Network Operators Group

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Re: "Simple" Multi-Homing ? (was Re: CIDR Report)

  • From: Chris Williams
  • Date: Tue May 16 11:21:16 2000

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
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..)