manually expiring cached dns entries on nameservers

[Ketil Froyn]

On Thu, 2004-06-17 at 16:38, Rein Petersen wrote:
> Hi All,
> I'm trying to assist a friend who has incorrectly updated his mx
> entries for his site. As people have been unsuccessfully trying to
> send mail from various networks, new cached entries that are incorrect
> are going to continue to misroute mail until they expire (an
> unfortunately long time). I am hoping that there may be a way for me
> to update caching dns servers on other networks - or at least tell
> them to drop whatever cached records they are holding...
> 
> Is this possible and if so, how?

There is one (quite limited) method to update a cache, but it probably
isn't what you are looking for, and it doesn't sound like it is
practical in your case. 

To update an A record in a cache by this method, you will need access to
query the cache in question (in your case, a list of caches and access
to all of them). The method is to set up a bogus domain which is
delegated to the name that was wrong, and query the caches for the bogus
subdomain. This should cause the new A record to be passed as glue, and
the cache will update. Updating MX records is probably a bit more
difficult...

Here's an example. Let's say a cache has an A record for www.example.com
that is wrong. To fix it, this is what you need in your zone file:

www.example.com A 192.168.0.1 ; this is the new correct IP
bogus.example.com NS www.example.com ; this is a new bogus record

Now, when you query the cache for bogus.example.com, it will ask your
authoritative server, which should pass www.example.com with the correct
IP as glue. The cache will then be updated with the new www.example.com
record, discarding the old one, and the bogus.example.com record can be
removed from the zone.

Good luck...

Ketil Froyn
ketil at froyn.name
http://ketil.froyn.name/