ssh locking up

[Brian McGroarty <ink@enteract.com>]

I've got a Windows machine and a Woody box behind my office firewall.

I use both to connect to my ISP's shell machines, and to map a port to
the remote news server.

The firewall/NAT and the remote machine are all FreeBSD - no MS Proxy
madness involved here.

My problem:

I can keep a session open for weeks with the Windows machine, running
SecureSSH. But ssh from the Linux box invariably locks up (but remains
connected) after 15 minutes to an hour.

Any clue why the Debian machine can't keep ssh active?