[ssh] ssh keep-alive tip

 
1. ssh -o TCPKeepAlive=yes mark@localhost
 
or
 
2. 
Remember that 
ServerAliveInterval
is limited by
ServerAliveCountMax
and that ServerAliveCountMax is set to 3 by default!
That is, if you set ServerAliveInterval to 60 and ServerAliveCountMax is left to default value (3), after the client has sent 3 keep alive packets it will disconnect. That makes 60 x 3 = 180 seconds.
So if you want more time away, you set ServerAliveInterval to 60 and ServerAliveCountMax to the numer you want (for example: 100). The client will send one keep alive packet every 0 seconds for 100 times or, if you prefer, 100 keep alive packets, one every 60 seconds.  
You set this up in your $HOME/.ssh/config file.
Most of these options are explained in man ssh_config.
Thanks a lot to Cam for pointing us all in the right direction!!!!