Using OpenSSH through a firewall, even with the KeepAlive option, causes the connection to be dropped due to inactivity. The site in the URL includes a patch to add a Heartbeat option to keep the connection open using SSH_MSG_IGNORE packets; it also adds a watchdog feature. The Heartbeat feature apparently doesn't work in conjunction with ServerAliveInterval, which may be a problem. Alternatively, the Debian version of OpenSSH has a "ProtocolKeepAlive" option to do much the same thing (using "SSH-NULL" packets?) I haven't found where to get hold this patch.
post something that *doesnt* interfere with existing options ;)
