Intermittent DNS Problems

Unanswered Question
May 16th, 2007

I have a small network managed network that about every three days at least one computer will not resolve DNS. It can be the same computer, but the problem typically happens between three or four different machines. I can ping my default gateway, ping numerical IP address, but not for instance. The Internet broswer fails to load any web pages. Then maybe 20 minutes to 2 hours the problem is gone and they problem computer is functioning normally. There are no error messages at the command line when the ping fails? Any help appreciated.

I have this problem too.
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acomiskey Wed, 05/16/2007 - 12:28

Where is the dns server and can you ping it while this is occuring?

virgilhunt Wed, 05/16/2007 - 12:56

I am not 100% sure. The techs who manage this network have given me several and all have intermittently failed. I will ping the server at the next outage and see if I can get past my pix firewall to it or not. Thanks. Please advise if this is what you meant? Thanks again.

virgilhunt Fri, 05/18/2007 - 08:01

I can ping both DNS servers when I have an outage, no problems?

virgilhunt Fri, 05/18/2007 - 08:16

No they are not. I have used several different DNS server numbers and problem still recures.


Just give a try to clear DNS cache from the client. You can use ipconfig / flushdns for Windows OS. If there is no Answer from server even after that you may consider starting traffic capture using ethereal or Wireshark etc at server and client to view packets.

From Client side you should use UDP ping for port 53 pointing towards DNS server

using utilities like UDP ping.

Steps mentioned above will NOT resolve the issue, however it will be helpful for troubleshooting. You can attach the traffic capture to the forum if you need some assistance.



virgilhunt Fri, 05/25/2007 - 05:40

I think we solved my problem and I'll post here what it is so those that offered assistance can gain from this. Our Pix 501 was configured for 10 hosts and our network had grown to 13 hosts. So, sometimes it would allow all out, othertimes it blocked one or two hosts. Once the data table was refreshed in the Pix it would allow the host to get past. They are working out the details with our contract on getting this upgraded?


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