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I have several ssh connections to a server that is in the same LAN as my desktop machine. Some sessions have X forwarding enabled, some don't. Both types of sessions occasionally hang for a couple of seconds, i.e. don't react to mouse and/or keyboard and also don't update their displayed content. After this short delay, they work as normal, the sessions don't crash or anything.

I'm running lubuntu 13.04 on my desktop and Scientific Linux 6.3 on the server. Nothing special was done with the sshd on the server or the ssh client on the desktop. Neither machine is even remotely close to being at full load. Any ideas?

Update: tcpdump shows that my desktop machine continues to send packets to the server (about 10 packets or so), the server just doesn't answer anymore for some time. There are two more guys working on the same server and they don't have this problem.

Update 2: It seems that not only the ssh sessions lag, but sometimes, the connection to the internet will also stop working for some time. I didn't notice before because I wasn't surfing at the time. The internet outage seems to be unrelated (in time) to the ssh outage. Also: This is not your typical wireless problem -- the machine doesn't even have a wireless card.

Update 3: A different NIC doesn't solve the problem.

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what client are you using? try 'ssh -v' to see any warning or error messages – golimar Jun 24 '13 at 7:36
client is OpenSSH_6.1p1 Debian-4, OpenSSL 1.0.1c 10 May 2012, but I get no error messages. – arne Jun 24 '13 at 7:50

As explained in it might be about periodic key re-exchange, which causes that. During the process, "normal" connection activity is paused.

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