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I have two desktop computers a laptop and a smartphone. All of them connect perfectly to my router (WRT54GL with Tomato firmware), but randomly (once a week maybe) something odd happens:

For over an hour or so one of the desktop computers (Windows 7 Pro x64) will just refuse to connect properly to the router. Only that computer and only to that network. I can connect all the other machines to the router perfectly and I can connect properly to other networks with that machine. What I mean by "not being able to connect properly" I mean that the OS will just tell me "not able to connect to.." or that it will connect but then say that it has no Internet access or it connects but will then take minutes to load any website, even the router web interface.

I've tried to change from WPA2 to WEP and back to WPA2, I've tried different network adapters (one internal PCI card and one USB external card), removing networks from Windows and adding again... without making any difference. It works for some days but at the end, it ends happening at some time.

I just have no clue on what could be going on here. I first thought it was the network adapter, then the router, then Windows...

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Have you checked the security logs on the AP itself to see if the desktop is doing something to cause the AP shut it out? – Izzy Jan 17 '11 at 23:19
How would that look in tomato firmware? I looked at it and didn't find anything suspicious, but I just don't know what am I looking for. I just saw a lof of dhcp-/MACs/IPs, you know. – bluehallu Jan 18 '11 at 0:19

Make sure your wireless network card drivers are updated. I've seen so many intermittent and entirely flaky wireless network behavior caused by out-of-date drivers. It's a standard response to a question like yours, but super important.

To work off of Izzy's suggestion, when you are in the middle of experiencing the problem, connect to the router web interface and see what machines are currently connected to the router. That may give you a hint as to whether the problem machine is actually communicating with the router. It may also show whether you have a duplicate IP/DHCP issue.

Also, go commandline (might have to be an Administrator) and try ipconfig /release then ipconfig /renew

share|improve this answer
Will keep you updated. It's gone since 30 mins or so ago, so I can't test anything until god knows when (will be the less convenient moment, I've found this issue to be a perfect Murphy law example). Btw, I'm telling you when it happens, changing the wireless adapter won't change the situation, and honestly, I doubt it's a duplicated bug between two different brand cards. What are those commands supposed to do? Restarting the computer or the router won't help, why would an ipconfig renewal do? – bluehallu Jan 18 '11 at 0:16
ipconfig gives you direct control over when the NIC grabs its DHCP assignment. Forcing it to release and re-request an IP may help. A computer restart may just use the cached, previous IP. A router restart might not resend/reassign an IP at all (because the computer isn't requesting a new one). I've found ipconfig to work even when Windows Vista/7 Network Control Panel has issues. – JCotton Jan 27 '11 at 20:09

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