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Ok I'm pulling my hair out over this one. We have a wireless network with many clients all working well except two Ubuntu clients running 10.10 that can't access the internet via a browser at the same time. They can both still ping, use Skype etc but can't browse.

As soon as the one that can browse exits the network browsing returns for the other and vice versa. As ping and Skype was working I assumed some kind of DNS problem but moving over to OpenDNS didn't solve it, nor did restarting networking or using wired rather than wireless.

We also switched out the router, and it still persisted so I'm sure this isn't a network issue. The two clients are both laptops and work fine together on a wireless network at another office (which we don't control).

I'm thinking something must be cached from the other network they both use that's causing this but have no idea what.

Does anyone have any ideas? I just don't know where to go from here.

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Have you verified that they aren't both using the same IP address on your network? Run /sbin/ifconfig -a on both machines to check. Just a guess, I don't have a solid idea what might be going on. Are you trying to access the same website? What website is it? –  Phil Hollenback Jan 7 '11 at 6:42
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have you also checked to make sure ubuntu isnt faking the MAC address and thus having a duplicate MAC? –  Jimsmithkka Jan 7 '11 at 7:12
    
The IP's are different. And it happens for any website. Also noticed one more thing, if I reset the router and start over, whichever machine connects first (after the reset) is the one that can always browse, the one that connects second is the one that can only browse when the other is disconnected. –  ChrisInCambo Jan 7 '11 at 9:35
    
Looking in ifconfig, the MAC's are also different. –  ChrisInCambo Jan 7 '11 at 9:36
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2 Answers

if you don't detect duplicates (MAC address, IP-address) through ifconfig -a, you might also want to check the routing table on the clients through /sbin/route

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Thanks for the suggestion but it didn't throw anything up. –  ChrisInCambo Jan 7 '11 at 9:53
    
- proxy problems? - with both clients connected, does /usr/bin/nslookup www.google.ch yield correct results? - running wireshark on a mirror port (if available) could provide a hint. –  sa_zh Jan 7 '11 at 13:13
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What do you mean that it cannot browse ? It takes forever to load a page (permanent white screen) or it comes with an error message (e.g cannot connect to somewhere) ?

something you could do is to create a dummy web page inside your network and try to access (This way you 'll see if the problem is located in the AP or somewhere else)

What about other protocols ? Try to download something (at the same time) from an FTP server.

My best thought is that there is a stupid rule in the AP, related with http redirection.

P.S do you use any authentication ?

P.S 2 : check if you use any proxy on these laptops

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They get time out errors. In Firefox the status bar just sits there saying "Connecting" until it times out. Neither computer is using a proxy, neither is the network, I can't speak for the ISP. Other protocols work as they can both ping the web and use Skype, so it's just HTTP with the problem. –  ChrisInCambo Jan 8 '11 at 0:13
    
Also we have this same problem across two routers, both of which have been factory reset. So I doubt it's the AP (I'm guessing AP means access point?) –  ChrisInCambo Jan 8 '11 at 0:15
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