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I am having an issue where one host on my network cannot FTP or ping external sites but the rest can. My setup is with a single router with wireless and ethernet. With my host on the wireless I can FTP and ping fine but with my host on ethernet I can't ping or FTP external sites.

What makes this a bit strange to me is that I can wget from the ethernet host fine and it is resolving names correctly. Also I CAN ping the internet gateway immediately beyond my router so it doesn't seem like it's the routers doing. At this stage I'm at a bit of a loss as to how to diagnose the problem further.

Both hosts described are linux. The ethernet host that can't connect is a server with no GUI and it is the only wired host so I can't wireshark capture what is going on. Also router has no firewall enabled.

Anyone have any ideas as to what could be happening here?

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This sounds, as if it might be related to MTU issues!

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that's quite a vague statement, any ideas as to how I might be able to diagnose MTU issues? – radman Nov 17 '10 at 21:55

Well this turns out to be a pretty lame solution, but turning the host in question off and on again has fixed the problem. I am still a bit bamboozled as to how it got into a bad state or what exactly was wrong.

I have opened another question here asking about the output of tracert for the machine in question if anyone is interested.

Turns out that I had peerguardian for linux running on the machine and it was assassinating all incoming packets :P

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