ISP Switch / DNS problem

[Michael Kjorling]

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On Apr 9 2002 07:41 -0700, mrm00k at yahoo.com wrote:

> We are switching ISP's and we host our own DNS server. The IP address
> of the DNS server will be changed.
>
> I don't know how to eliminate name resolution problems during the
> cutover. I am told that if switch my internic registration to point to
> the new ip of the DNS server that it will take several days for the
> changes to complete. During that time, any nameservers that have the
> old information cached will not resolve.
>
> People must make changes like this all the time. Is there a "typical"
> procedure for this ?
>
> Thanks,
> Mike

Any chance you can be multihomed for a few days? If so, just leave it
at the old IP address, but lower the TTL to a few hours at most. When
the new connection comes online, update your DNS and the glue records
in the root servers, and reset the TTL to whatever it was before. Once
the changes have propagated, shut down the old ISP's connection. Using
sane TTLs you can safely shut down the old connection three days after
having updated your DNS and the root servers with the new data.

It's a little trickier if you can't be multihomed during a transition
period for whatever reason. When switching ISPs, though, I would say
that is an unlikely situation - but it was the situation when I
renumbered from a /29 to an altogether different /28. At that point I
had the firewall as well which needed to be updated as well, so it
took a little bit more planning. In the end, a short downtime during
such transitions is probably inevitable - but as far as DNS is
concerned, having off site slaves does help. Make sure they have up to
date copies of all zones before you begin, though.


Michael Kjörling

- -- 
Michael Kjörling  --  Programmer/Network administrator  ^..^
Internet: michael at kjorling.com -- FidoNet: 2:204/254.4   \/
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