DNS Resolution Issue

Posted on 2006-06-26
Last Modified: 2010-03-18

Periodically we will have an issue with some, not all of our clients(XP Pro) connecting to the Exchange Server(2003 Standard), sometimes it will be immediately upon booting up or after having being connected all day, they will lose the connection.  They can still access network resources and the internet, but can not connect to the exchange server.  When I ping the internal IP(192.168.x.x) of the exch. server the request times out.  When I ping the hostname(exchangeserver) I get the extertnal IP assigned to the server.  In order to reconnect the affected clients I need to run ipconfig /flushdns and ipconfig /registerdns.  After I run the utility they are connected and when I ping the internal IP(192.168.x.x) it returns the hostname and ping properly.  Please help as this is driving me insane.  TIA

Question by:NCIA
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LVL 57

Expert Comment

by:Pete Long
ID: 16985367
Do you have WINS running on anything?
LVL 11

Expert Comment

ID: 16985467
does ip config show they are using a DC as a DNS server?
could there be multiple DHCP server? is your dhcp server configured correctly?

do the users have some type of VPN client?
LVL 77

Accepted Solution

Rob Williams earned 500 total points
ID: 16985493
Workstations should only point to your internal DNS servers for DNS. If you have the ISP's DNS added as well, this could be the issue.
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Author Comment

ID: 16985768
I do not have WINS running...

Yes it shows a DC is the DNS server, there is only one DHCP server, as far as I know my dhcp server configured correctly, there are currently no VPN clients installed.

I had the primary DNS set up as the internal...and secondary set up as the external(ISP).  If this is the issue why are the clients not accessing the internal DNS first to resolve the querry?  Also if this is the case it seems that they will still lose the connection, just no longer point to the external IP when they do?  I thought that the reason to have the external IP listed was for internet access/resolution.  I have removed the ISP DNS listing to test this idea....

thanks for the ideas....
LVL 77

Expert Comment

by:Rob Williams
ID: 16985800
One would think it would always use the first DNS server first, but for some reason it doesn't always. I don't know if it is a timing issue or what. In any case once it uses the external it likely changes your cashed DNS, and is why you need to run ipconfig /flushdns

Basic rule; the workstations and all servers should only point to your internal DNS server/s and the ISP should be added under Forwarders in the DNS management console.
LVL 11

Expert Comment

ID: 16985811
point them ONLY to AD integrated DNS servers.  Let the DNS servers do the lookups.

you should have 2 DNS servers for redundancy also.
LVL 77

Expert Comment

by:Rob Williams
ID: 16985833
By the way once you make the change you should run ipconfig  /flushdns
LVL 11

Expert Comment

ID: 16985858
as a matter of fact, i completly block that port to anyone but my admin workstation, and our DNS servers outgoing. (and all incoming)

I set alerts to warn me if anyone is trying to do DNS lookups.  no reason for clients to do that via default gateway.  Its a good way to keep an eye out for viruses, spyware, etc..


Expert Comment

ID: 16992712
I think it seems to be a problem with exchange server and the dns. what i would like to know is that output of ipconfig/all of exchange with complete info and error/warnings on exchange server related to dns registration. Also the status of dhcp client service on the exchange server. Please provide me the info
LVL 77

Expert Comment

by:Rob Williams
ID: 17161531
Thanks  NCIA,

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