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Only one of the users in the network has this problem: at random times during the day, the user is unable to visit ANY websites.

He still has access to Network drives.

When pinging for Google or websites he never visited, we receive a ping back.

No VPN is connected when the problem occurs.

A reboot solves the problem.

He is working on Windows 7 Professional SP1.

Any ideas?

Thanks!

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Do they not load, load very slowly, or time out. Is he torrenting? –  tombull89 Mar 14 '13 at 21:52
    
Have you tried an alternative browser? –  Dave Mar 14 '13 at 22:32
    
They dont load at all. Tried with Firefox and Chrome @tombull89 –  Ebpo Mar 15 '13 at 13:04

3 Answers 3

up vote 0 down vote accepted

...at random times during the day, the user is unable to visit ANY websites.

Could be that something on his machine is blocking or attempting to use port 80. My first guesses would be malware or a bit torrent client. But there is also the outside chance that the user has web sharing services active on their machine? Or perhaps some kind of LAMP development tool—or Windows/Mac equivalent—running there as well.

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He is using XAMPP for web development... on port 80. I think we are onto something! –  Ebpo Mar 15 '13 at 13:02
1  
The problem happened again and we just down XAMPP. It was the culprit! Thanks again! –  Ebpo Mar 18 '13 at 13:07

To start with, is it a domain user or a local user? Did you try scanning for malware? I've seen this happen once with a user and he had a lot of infections in the user profile. Try switching with a other employee's PC to test if it is a profile issue or a pc issue. If so, reconfiguring his user profile might solve the problem.

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Here is a possible outlier issue. I've seen this exact same scenario in a network with multiple switches between a client and the internet router. The problem can come in if some device near the client has an IP conflict with the router LAN IP. The client ARP will bounce back and forth between mapping to the router MAC and the offending device MAC. If you suspect that is the case run arp -a from the client and look for the MAC of the gateway IP (from TCP/IP properties) and compare to the label on the device (or arp -a on another client that doesn't have this problem).

If you do find that your gateway IP is being associated with the wrong MAC address you can fix this by using arp -s to force the mapping. However, you should try and track down the offending device.

Definately an edge case, but can cause the symptoms reported. (And is a tricky one to pin point if you aren't paying attention)

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