Re: Switching ISP's and DNS records


Subject: Re: Switching ISP's and DNS records
From: Michael Fowler (michael@shoebox.net)
Date: Thu Apr 25 2002 - 17:00:09 AKDT


On Wed, Apr 24, 2002 at 04:00:54PM -0800, Mike Barsalou wrote:
> One of the things that I run across on a fairly regular basis is people
> wanting to switch ISP's who host their DNS records. Most of the time I hear
> people saying about how their mail etc hiccuped for a few days while this
> took place.
>
> Would you folks consider this normal?
>
> What steps can you take to avoid these problems?

I couldn't really say it's normal, as most of my experience has been with
moving servers to new IP addresses and locations. Moving an individual
site would require some cooperation on the part of each service provider.

On a side note, moving just to new IP addresses is almost a non-issue, as
it's just a matter of configuring your interfaces and servers to respond on
both. There's still a bit of work involved, but it's almost invariably easy
and hiccup-free.

The several times I've had to move IP addresses and locations I had
administrative access on both ends. It probably made things much easier, as
I didn't have to coordinate these things with another admin, and the
software on each end was similar.

There are many services that need to be moved over, and each one has its
quirks. For example, the web space; you can set one of the web servers up
to proxy requests to the site to the other, which is necessary to keep
dynamic content correct. However, you lose your logging; because the
connections to one server (say, server X), are proxied to the other (server
Y), Y's log files show X having accessed the site, not the original client.

Mail is a bit easier to deal with; you just need to decide which server is
going to receive the mail, and forward all mail to it. Then forward all of
your access protocol ports (POP3, IMAP, etc.) to it. Syncing the spools, so
that the client never misses mail, is best done by shutting down both mail
daemons and moving the spools to the server getting the mail.

Anyways, those are a few examples, and probably more than you were asking
about. All in all it's not an easy process, at least on the scale I've
done it, and in the way I've done it.

With the TTL change Arthur mentioned much of the hiccup for an individual
site can be lessened greatly, but when moving multiple sites there always a
few that refuse to be updated on your timetable.

Michael

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Administrator                      www.shoebox.net
Programmer, System Administrator   www.gallanttech.com
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