Reverse DNS issues

[Don Jones]

We have a class of IP addresses from our ISP which we currently run
DNS for and also would like to run reverse DNS.  In speaking with our
ISP, they have configured our subnet so we can run reverse DNS on our
own servers.  We have DNS configured with reverse zones configured as
well on our servers.  The problem we are having is that the only way
we can run a successful reverse lookup on our hosts when the ISPs DNS
servers have our information cached.  What I mean exactly if I were to
run a reverse lookup from an outside server, it always fails.  If I
then run a reverse lookup directly using our ISP's DNS server, it
works and then subsequently works for all outside DNS servers for a
couple of days.  Any idea what I can be missing here?  We are running
Windows 2000 DNS and our ISP is running Windows 2000 DNS as well.

Thanks in advance for any help.

Don