Well this one has been causing me to pull my hair out for a couple of weeks. I was using the Cisco VPN client for Linux put got really tried of having to recompile it every time I did a Kernel update. So I switched over to vpnc the VPN stuff which works under network manager in Ubuntu. At first it seemed to work nice, but I found the connection was 'freezing' after I sshed into a server over the VPN. An example of this would be ssh to server, then run ls which works fine, then run ls -l and the connection 'freezes'. If I open another terminal sesssion to the server it would open fine, but ls and then ls -l would 'freeze' the connection. So after some digging our found out it had have something to do with my MTU setting. I still have a Windows VM and tested out the VPN their and used putty to ssh to the server and had no issues. I tried setting the MTU on my eth0 or wlan0 but no joy. Finally I found I needed to set the MTU on the tun0 connection like this to get it to work:
sudo ifconfig tun0 mtu 576
This mtu is very small, but I think its a setting on their side that maybe someones forgot to update since the days of dail-up connections. I am also glad to report the VPN connection is now working 'sharp-sharp'. :-)
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