ssh keep alive

[John Masters]

This may not be the correct place to post this but I have run out of
ideas.

On my iMac I have installed my favourite Linux distro Ubuntu Intrepid
Ibex via VMWare Fusion. It works! End of story - almost.
On the self same iMac I have ssh and sshd installed and the config files
are, in all relevant respects, the same as those on Intrepid on VMWare. 

In both machines I can ssh-add my key and connect to my remote server
(running Debian Etch). However, leaving the connection open causes the
terminal to hang after exactly one hour on the iMac yet the connection
stays up for days on the Virtual Ubuntu machine.

I have tried the Mac lists for an answer but no luck so am hoping for a
pointer from the experts here.
-- 
Regards, John