DNS Cache needing frequent flushing

Posted on 2011-03-09
Medium Priority
Last Modified: 2012-05-11
We have a SBS 2003 Domain with approx 55 computers.  I am finding that the workstations are requiring me to run 'ipconfig /flushdns' frequently in order to allow for connection to a small SQL based time and billing software database.  General slowness often is associated as well.  Every few days or so, users will lose the ability to connect to the database through the software and their general network access becomes somewhat sluggish.  When this happens, i simply run 'ipconfig /flushdns' from the command prompt and all returns to normal.  I have gone through the DNS server configuration on the server, and everyhing seems ok.

Anyone have any idea what I might be missing that would clear this up on an ongoing basis?

Question by:urbanstyles

Expert Comment

ID: 35087201
You could give this a try.


Author Comment

ID: 35087385
I will try that, but two issues come to mind. 1)This is SBS 2003 and 2) the problem exists with local lookups, not public domains.

That being said, we'll give it a shot and see.
LVL 59

Accepted Solution

Darius Ghassem earned 668 total points
ID: 35087510
Check into this link.


On SBS server do you have more then one NIC enabled? Make sure SBS server is only pointing to itself for DNS in the TCP\IP properties

On clients make sure they are only pointing to SBS server for DNS.
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LVL 13

Assisted Solution

connectex earned 668 total points
ID: 35087622
Before going to in to any indepth troubleshooting I recommend you download and run the SBS BPA. Here's the download link: http://www.microsoft.com/downloads/en/details.aspx?familyid=3874527A-DE19-49BB-800F-352F3B6F2922&displaylang=en. Once you've corrected any issues it reports then post back here. Or you can post the report is you can't correct them yourself. The BPA will often point out missed items/configuration that can or will cause is SBS to have issues.
LVL 78

Assisted Solution

by:Rob Williams
Rob Williams earned 664 total points
ID: 35087993
This is often caused by incorrectly configured DNS.
Make sure the SBS's NIC points ONLY to itself for DNS. (i.e. do not add a router or ISP as alternate)
Re-running the CEICW will make sure any changes are applied where ever necessary including the DHCP scope.
Make sure the clients, which should be using the SBS for DHCP, point ONLY to the SBS for DNS.
ISP's get added as forwarders, not on the NIC/s

Author Comment

ID: 35088386
I have checked the server NIC (only one enabled) it did in fact have the router as a secondary DNS.  I have rectified that.  I think my logic in providing the backup was to avoid the 1 second delay in the forwarding to the router, but it makes sense you explain it.

I believe the clients also have the router as a secondary address.  I will rectify this as well and see if it helps.

Will post back on results.

Thanks thus far.

Author Comment

ID: 35088504
I ran the report and Offload Tasks was enabled which is listed as a possible cause of communication issues.  I have rectified this and will observe results.

LVL 78

Expert Comment

by:Rob Williams
ID: 35088670
Your logic of having the router as alternate DNS is sound, but I am afraid Windows DNS does not work as one would expect. Basic Windows will use which ever responds first. If that is the router, which is effectively the ISP you can get slow logons, name resolution issues, and on occasion incorrect DNS replies. I think you will find that may resolve a few issues.

As for TCP Task Offloading; good to disable that as well but I think you will find that relates more to performance issues.

Author Closing Comment

ID: 35209430
Thanks guys, the DNS reconfiguration seems to be holding as I've no reported issues in the past week or so.  I will keep an eye on things, but all seems to be well.

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