host does not resolve names it should

[Laszlo Boszormenyi <gcs@lsc.hu>]

Hi,

 I have a very strange problem. I have a Debian box at home, connected
to an ISP (full with Slackware boxes). As the ISP's sysadmin left, I
took the sysadmin role there.
The main problem is that the ISP has it's domain, but it can't be
resolved inside because there's a trick somewhere with everything:
if you ask for any domain inside, it is served by the internal DNS
servers, outside domains are also resolved; but not the ISP's domain
name, everyone get "Nameserver internal.dns.name not responding".
But hell, if every other names are resolved immediately, then what's
the trick that for that specific domain name the DNS server shows as
'not responding'?
The ISP uses tindydns on Slackware boxes. If anyone has any clue why
this may happen, please let me know.

Thanks,
Laszlo/GCS