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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