changing ISP

[Barry Margolin]

In article <37779b13.0 at pfaff.ethz.ch>, Stef  <stef at sos.ethz.ch> wrote:
>I have my own DNS. My ISP is changing his subnet, so my machine and
>the virtual hosts on it will get a new IP adress. Can I just have two
>IP addresses TTL long before the change will take place and keep them
>TTL long after the change? So I have records like:
>
>my.host.               IN A  100.100.100.100
>                       IN A  200.200.200.200
>
>where 100.100.100.100 is the old IP and 200.200.200.200 the new
>one. Will web browers, mail servers, ftp clients etc. always try both
>IP numbers when they try to connect, or will they give up if the first
>one is not working?

Lots of applications will just use one address and give up.  It's up to the
programmer who coded the application to decide how to use multiple
addresses, and many don't bother.

>Is there another way this should be done?

On the day before the change, lower your TTL, e.g.

my.host.  900 IN A 100.100.100.100

Then when it changes, update the A record:

my.host.  IN A 200.200.200.200

The old record will only be cached for 15 minutes, so within 15 minutes of
your change it should propagate out.

You'll also need to lower the Refresh time in your SOA record so that your
secondary servers will pick up the change quickly.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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