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Internet Browsing Problem - DNS?

zimboman
zimboman asked
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Last Modified: 2013-11-16
Hi,
I have a rather strange intermittent problem, I am hoping someone can assist with.
I have a client, who has a small network of 10x WinXP PC's, and a SBS2003 server.

The PC's are using one Primary DNS entry, which is the IP of the SBS2003. I have setup the appropriate forwarders (IP's of the ISP's DNS servers), in the DNS on the server.

I am getting intermittent scenarios where the workstations cannot open a web page. It seems as if the DNS is incorrect, and the url cannot resolve.
I change the w/s DNS entry to primary as the ISP, and it works for a while then the same occurs. I am not sure if the DNS is at fault anymore...
I have a checkpoint Safe@Office 500 firewall, which unless you pay for expensive reporting subscriptions, does not really give you much on the fly information about what is happening...
The site uses an adsl VPN, to a remote site of about 4 PC's, which connect up to the head office, via Terminal Services - but from the very basic traffic logs, it does not seem like the VPN is overwhelming the adsl broadband connection. This issue also occurs at night, when there is limited internat traffic on the system...

Any ideas on where I can look?

Thanks
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Thanks,
I will try that tonight...
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Sorry for the long delay, I found out it was a rogue laptop - with a worm infestation.
The laptop was also randomly connected at night, hense the confusion.

Thanks for all your tips

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Commented:
I have awarded the majority of the points to demazter, as his solution was the most relevant, but thanks to ChiefIT - so f a trick I had not used before.
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