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I have two machines.

WOPR: Ubuntu server edition 10.10 LTS 32 bit Adam Selene: Windows 7 home premium 64 bit / Ubuntu Desktop 10.10 LTS 64 bit

I want to be able to SSH from Adam Selene to WOPR, so I connect them to the same network.

Here's where things get weird. I cannot connect to WOPR in any way under normal circumstances. But, if WOPR is pinging Adam, then it starts responding to ping requests, HTTP gets, and SSH tunnels. I'm an amateur, and brand new to Ubuntu server, so I suspect there's a misconfiguration somewhere, but there's an off chance it's a bug in the OS. Does anyone know what might cause this behavior?

Thanks a lot!

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That sounds to me like an ARP cache problem. Basically all the systems on a LAN keep a mapping of IP addresses to the hardware "MAC" address of the ethernet card. The network switch also keeps track of the MAC address of the ethernet plugged into it so it can send only the required packets down the line rather than all packets it gets.

One reason this could be happening is you have two systems on the network with the same IP address. There could also be a problem with your hub or a bug in a ethernet card driver. To view the ARP cache, run "/sbin/arp" on the Linux box.

I would diagnose in this order:

  • Make sure all systems have a unique IP
  • Swap out the network hub and see if that helps
  • Update the ethernet card drivers on the systems
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  • +1 for thinking of something I had a stick too far up my butt to be bothered coming up with. I think there's a large chance this is just due to some amateur lack of knowledge, so I didn't bother thinking further.
    – Andrew Barber
    Jan 2, 2011 at 21:54
  • Well, you found the problem. The IPs were definitely different, I'd typed ifconfig so many times I was practically mesmerized by the word, but I switched my network hub and that fixed the problem right off the bat. Ima go read up on ARP caching now. Thanks a lot for the help!
    – ILikeFood
    Jan 4, 2011 at 4:03

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