Interesting DNS issue - cannot resolve name!

[Dman33]

Here is an interesting one... perhaps I am missing something obvious.
On our LAN, we have two subnets: 10.30.0.x (New York) and 172.16.10.x (DC)
From my workstation in New York, I am trying to ping a server in DC. I cannot by name, but can by IP. So now I launch nslookup. nslookup is showing the correct local DNS server and when I type in the hostname of the machine in DC that I need to resolve it returns the correct IP address. I expected nslookup to not work, but it does!

Now, if nslookup is working fine, and I can ping the destination by IP address, why is it that I cannot ping by name? I am missing something...

[Jeffbx]

To narrow it down:

- Are you doing NSLOOKUP on the same DNS server that your PC uses to resolve addresses?
- Does NSLOOKUP return the correct address on your primary AND secondary (and any additional) DNS servers? Make sure they're all returning the same address
- Are you pinging the FQDN or just the machine name? (i.e., 'ping machinename.DClan.com' or 'ping machinename')
- Is this limited to one machine, or every machine on the subnet?
- Do you have any entries in your HOSTS file?

[Dman33]

To narrow it down:

- Are you doing NSLOOKUP on the same DNS server that your PC uses to resolve addresses?
Yes. All checks out okay.

- Does NSLOOKUP return the correct address on your primary AND secondary (and any additional) DNS servers? Make sure they're all returning the same address
Yes. All provide the correct address.

- Are you pinging the FQDN or just the machine name? (i.e., 'ping machinename.DClan.com' or 'ping machinename')
Tried both. Neither work.

- Is this limited to one machine, or every machine on the subnet?
It has been consistant with all machines but... see below.

- Do you have any entries in your HOSTS file?
nope.

Stange thing is that this problem was in the morning however after a few hours suddenly the server would resolve. So this morning when I came in it was not resolving again (I leave my PC on overnight but logged out).

This time I did an ipconfig /flushdns and it started working. I am setting the TTL on the local machine DNS resolver cache to 4 hours instead of 24 hours... that might do the trick.

[Jeffbx]

One more: when you ping by name, do you get no response, or unknown host?

[Dman33]

One more: when you ping by name, do you get no response, or unknown host?
Unknown host.
From what I have been gathering online, it seems that the DNS resolver cache is the problem. Since the destination server is located across a VPN link, it is possible the local machine is recording occasional negative entries for the host in the cache. If these build up, it will start returning unknown host. I can set the local machine to not record negative entries (registry setting, requires reboot after) and see if the problem ever comes back.