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Re: How Not to Multihome
Justin M. Streiner wrote:
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.)