Complicated ssh tunneling task.

[dmartini@uni-hohenheim.de]

Hello list, 
 
consider the following setup: 
 
         |                    | 
boxA----boxB------boxC---------boxD 
         |                    | 
LAN      |     Internet       |Home computer, connected to  
         |                    |Internet via modem    
 
boxA sits on a LAN, running OpenBSD 3.3. On this box I can get root 
privileges. It has an IP address only for use in private networks 
(RFC 1918, 10.195.x.x). So its IP address will never be visible to the 
internet, to which boxA is connected via: 
 
boxB. This one is a bridge and firewall, running Novell Netware, doing 
NAT for the LAN. Additionally, it will only pass http traffic from the 
inside of the LAN, via Novell Border Manager http proxy on port 8080. 
I cannot get root on this machine. 
 
boxC is running Solaris, has an officially assigned IP-address, has 
running sshd on it, and has an account for me, but not a root account. 
 
boxD is my home box, running OpenBSD 3.3, connected to the internet 
via dialup modem. Its IP address is dynamically assigned. Root access 
for me is no problem. 
 
If I'm dialed in, I can login from boxD to boxC with ssh. 
I can login from boxA to boxC with ssh using corkscrew from the ports 
collection to pierce the proxy. 
 
Question is: 
Can I establish a ssh connection from boxA to boxC and use this connection  
later on, to connect from boxD to boxA via boxC? 
Or are there even other, better ways to connect from boxD to boxA in  
this scenario (perhaps using nc?)? 
 
Note, that while establishing a connection from boxA to boxD using ssh 
and forwarding the traffic through this tunnel would be possible, it is 
not desirable, because boxD would have to be dialed up all the time, 
which would be much too expensive. Setting up a cron job to connect boxA  
to boxD at a certain time is also not possible, because boxA would have 
to know boxD's (dynamic) IP address. 
 
Regards, 
Daniel