How Not to Multihome
Stephen Satchell
list at satchell.net
Wed Oct 10 12:06:58 UTC 2007
Justin M. Streiner wrote:
>
> On Tue, 9 Oct 2007, Patrick W. Gilmore wrote:
>
>> Justin, if Provider A _has_ permission from Provider B to announce a
>> prefix, do you believe Provider A should be allowed to announce the
>> prefix?
>
> As long as all of the relevant parties know about it and are OK with it,
> that's fine. It's just not my first choice for solving the customer's
> multihoming dilemma, that's all :)
>
> jms
>
Back when I was a NOC monkey (that stopped a month ago), I had exactly
that situation. I had MCI and SBC as upstreams. Before multihoming, my
network was split in two segments, one for each substream. This made
things like DNS interesting.
When I got my ASN, I got agreement from both MCI and SBC to announce my
/21 allocations from them over both upstream circuits. As a result, I
was able to go back to a single inside network, a single pair of DNS
servers, and no more cross-router traffic via the Internet cloud.
I then got my ARIN allocation and went through the Fiscal Quarter From
Hell renumbering everything into the new number block. I dropped MCI
(long story) and lit up Idacomm, but kept SBC link and numbers.
When I left the ISP, my routers had been announcing my suballocation of
SBC space for more than a year. With their permission. Their only
requirement is that I have proper routing objects in a routing registry
so SBC could see that the route I was announcing was valid. (What was
VERY interesting was that I was using the ARIN registry, and SBC was
not. The resulting bru-ha-ha uncovered a synchronization problem that
ARIN had, and that ARIN fixed.)
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