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Re: how to relocate servers transparently

On June 18, 2004 12:49 am, Nate Duehr wrote:

> No, this isn't right.  You must lower the TTL time at a bare minimum 2 *
> (Current TTL) ahead of time.  Why?  Because nameservers out in the real
> world will not even query your nameservers again until the TTL has
> expired, meaning that if you change it today, the FIRST time another
> nameserver that has already cached your records will ask for it again is
> after the *current* TTL expires.  Now take the case where one nameserver
> is a forwarder for another (rare, but there are environments where it's
> needed) and the one behind the forwarder could take up to 2 * TTL to
> come ask for new information.

Can you explain that a little further?  If my nameserver caches a record with 
TTL 86400, and someone asks for it again an hour later I hand them the record 
from my cache using TTL 82800 (not 86400).  This is certainly what bind does, 
if other caching nameservers do it differently then it's a bug IMHO.

I would be very surprised if it is different when DNS queries are being 
forward from one DNS server to another.  Or did you mean something else?

Fraser Campbell <fraser@wehave.net>                 http://www.wehave.net/
Georgetown, Ontario, Canada                               Debian GNU/Linux

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