Moving to different dns server.

Kevin Darcy kcd at daimlerchrysler.com
Wed Dec 22 23:28:22 UTC 1999


Bhargava wrote:

> Hi
> I have a problem. Now we have a dsl link. We want to move to anothe isp and
> T1 line with redundancy. Can U help me which is the best way to change over
> to different set of IP address. With least down time. This is more about MX
> record.If i give secondary as second set of ip address. What will be the
> effect of it.

Add an MX record for the new address in addition to the old address, and allow
time for it to propagate. If a mailer can't connect to one of the addresses,
it'll try the other. Once you're moved, then delete the MX record with the old
address.

Unfortunately, things aren't quite as automatic with A records. You could
temporarily create a round-robin with both the old and the new addresses, but
many clients aren't smart enough to try anything but the first address in the
list, so during the time the round-robin is visible, the clients will
experience seemingly random failures connecting to you (although if they keep
trying, they'll eventually get through).

To mitigate all of this, you can reduce the TTL values on the records that you
know are going to change. This will increase the traffic to the authoritative
DNS servers for your domain(s), because it defeats caching, but it means that
your changes will be visible much more quickly. After the switchover, of
course, you'll want to restore normal TTL values.

One more idea: if HTTP is one of the protocols affected, you might consider
pointing your DNS names to a hosting provider who just has a HTTP redirect to
your real website(s); then you could just have them switch the redirect at the
appropriate time, and it will be quite transparent to the users. Once you're
all moved, then you probably wouldn't need the redirect any more.


- Kevin




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