how to relocate servers transparently

[Rhesa Rozendaal <lists.debian@rhesa.com>]

Hello all,

I'm looking for some practical advice on moving servers from one 
colocation to another.

In a couple of weeks, we need to move our servers to a different 
colocation, which means all the ip addresses will change.
The servers are running regular stuff: web, mail, ftp, and two dns servers.

In the past I witnessed such a move, and there were a lot of problems 
with the DNS. As it turned out, many DNS servers out there kept caching 
the old ip addresses for over 3 days, causing a lot of connection issues 
for many users. Beforehand we did lower the ttl on all the domains prior 
to the move, but many dns servers seemed to ignore that. On top of that, 
we moved both our dns servers at the same time, which was a big mistake too.

So, what I'd like to hear from you is practical advice on how to avoid 
connection problems after the move is complete.
Will it be enough to keep 1 dns server behind? I'm afraid it won't be, 
given the dns caching problem mentioned above. Is there a way to have 
that 1 dns server act as a proxy or port forwarder in some way? Can that 
be done between two different class A networks?

Btw, the servers are running debian stable (woody).

Thanks in advance,

Rhesa Rozendaal