Question : DNS Failing

Ok, I have a tricky one! I have got a server running Windows 2003 server with SP2. This server is the core of the network, controlling DHCP, DNS, Exchange service and Backups. There are only around 10 users connecting up.

For a while now the DNS seems to stop working! I have been trawling the net for similar problems and trying numerour fixes but it is still there! It is completely random, happening anytime of the day for random ammounts of time! For instance, yesterday from midday to around 4.30 it was fine then the problem started again! The external DNS of all the machines and the server stops working. The service itself is still running and reports no errors!! Restarting the DNS service when it is down does not help! There is a Cisco 857 controlling the net connection.

I have the Forwarders to the 2 external isp dns addresses setup. The DHCP server is distributing the following settings:

(Ip of Server is 192.168.8.2)
003 Router - 192.168.8.1
006 DNS Servers - 192.168.8.2, IP1 of external isp ip, IP2 of external isp ip
015 DNS Dmain Name - DOMANINNAME.LOCAL
044 WINS/NBNS Servers - 192.168.8.2
046 WINS/NBT Node Type - 0x8

Additional settings:
Address Pool - 192.168.8.20 - 192.168.8.100 (Lease Duration 3 Days)

I believe all the reverse lookup zones/forward lookup zones are correct. I have checked all the settings against other servers with the same setup and all appear to be correct. The root hints seem fine also!

One other note i have to add to this is that when i initially started looking into this problem, all of the computers on the network had this DNS failure but the server could connect to the internet fine!! I found some redundant external IP addresses in the forwarders for example an old BT (unreachable ip) and for some reason a PLESK ip address (unreachable) I suspect some in the office has had a crack at changing some settings and caused this problem and is keeping quiet! After resetting the DNS etc to the correct settings the server does exactly the same as the machines on the network.

I can connect to sites via their IP addresses fine and ALL other internet based services that dont require DNS name resolution work fine. Email is fine also!!

This problem is starting to drive me slightly mental!! Any possible solutions would be much appreciated!!

Thanks

Answer : DNS Failing

Now, even if Roothints fail then trust me...This is the time to take the troubleshooting to the next level..;)...If you are familiar with taking traces...nothing like it...I want to see what happens when you use Forwarders...Does the DNS Query send by you is getting a response or not. Network Trace will show us clearly what is happening on the wire..

You can use WireShark or netmon 3.1 to take the trace.