Background:
        sshd  openssh-2.9.9p2,openssh-3.0.2 only SSH2  (former ssh SSH1)
        ssh   openssh-2.9.9p2          (former openssh-2.2??)
        server   [C0] OS Linux  2.4.10-4GB-SMP
        firewall [C1] OS Linux  2.2.16 with ipchains masquerading [C2]
        client   [C2] OS Linux  2.2.16 behind [C1] 
        tcp/ip via pppoe on aDSL 
        
Since general upgrades to openssh-2.9.9p2 (same with sshd/openssh-3.0.2) the
SSH2 (RSA-auth) connection from [C2] client behind the firewall [C1]
to server [C0] freezes suddenly.  This occurs repeatable when return
packets get large (e.g. "ls -l" in big dirs, or "cvs update").  Before
the connection was set up properly and worked for small packets. 

At the same time ssh-connections between [C1] and [C0] are not
affected (both directions).

Packet-logging on ppp did not show anything.  Opening-up the firewall
rules did not help.

Any help is greatly appreciated

Thanks in advance