best way to change IPs

[Simon Hobson]

TAC Support wrote:

>About every year or 2 we change wholesalers and have to update our IP
>range (1 class c)
>
>Inevitably there is a period where sites dont work and mail disappears -
>this year I would like to minimize the problems.
>
>I have had a search of the archives and came up with this
>
>As long as you're comfortable running without a secondary server for the
>amount of time it takes to update and move the server to the new ip
>address, you shouldn't have to go about registering a new server.  As
>long as all the domains use the same name (ns2.domain.com) as their name
>server, all you have to do is change the ip of ns2.domain.com. at the
>registrar, and change the ip in the zone of domain.com.
>
>So is this the recommended procedure i.e. change the secondary name server
>(NS2) to the new IP range at the register and change the records on that
>server to reflect the change while leaving the primary server with the old
>range and records for a few days. Then change the IP of NS1 at the
>register and change the records on NS1 to reflect the change.
>
>Is there nothing to do to NS1 during the changeover period?

You can reduce, but not entirely eliminate, the problems with a 
little advance planning. One thing you can do is to reduce your TTL 
values as you approach the cutover date - this means that anyone with 
your site data cached will keep it for less time and so have a 
shorter period where your service 'just disappear'.

If you can multihome your network during the changeover (so your mail 
server for example is accessible on both the old and new address) 
then that is even better. In that scenario, you would add your new 
network addresses, and then change your DNS zone data to suit. 
Separately, you can move one of your DNS servers to it's new address, 
change your NS records to suit, and change the registrars entries, 
and after a few days, you should be able to move the other DNS 
server. All this with barely any downtime at all. You could change 
both servers at one, but why tempt fate ?


If you can't multihome, then it's a bit harder. In advance, cut down 
your TTL values - until just prior to cutover they are perhaps just a 
few minutes. The idea is to have no-one else in the internet caching 
your old DNS data for long. You need to start this well in advance, 
so if for example you had data with a 4 week TTL, you'd need to cut 
this down (perhaps to a week) at least 4 weeks before cutover. As you 
get closer, cut them back further. Change the NS entry for ONE server 
at your registry several days in advance. It won't be accessible at 
the new address, so clients will simply ignore it for now, but you 
want the data to be fully propagated prior to the changeover.

At changeover time, you switch networks, and also change your DNS 
zone data. At this point, you will have one DNS server accessible at 
the new address, and one still referenced at the old address. Within 
minutes, anyone accessing your services will have got the new DNS 
data - you can of course restore your TTL values !

Finally, you change the NS setting for the other server at the 
registry, and after a few days, that will be fully propagated and you 
are done.

Simon

-- 

NOTE: This is a throw-away email address which will reach me for as 
long as it stays spam-free, remove date for real address.

Simon Hobson, Technology Specialist
Colony Gift Corporation Limited
Lindal in Furness, Ulverston, Cumbria, LA12 0LD
Tel 01229 461100, Fax 01229 461101

Registered in England No. 1499611
Regd. Office : 100 New Bridge Street, London, EC4V 6JA.