How to create an ssh chain A->B->C to do http over ssh across the chain?

[Mitchell Laks <mlaks@post.harvard.edu>]

Hi,

Here is the situation. You have machines A->B->C. You want to create a ssh tunnel directly
from A to C.

Machine A can see machine B and machine B can see C, but A can't see C directly.
A and B are on a local network and only B has 'limited net access'.

I know how to ssh in from A to B and  then again from B to C. But I want a direct tunnel.
This would work for http over ssh or perhaps to run  X say. 

Thus I know how to browse while logged on B through using C via a ssh tunnel from B to C. 

Thus:

In firefox, you use localhost:8080 
in the socks host settings for manual proxy configuration.
then you set up a ssh tunnel

ssh -ND 8080 yourlogin@C.com.

Or can set up X etc.

Now how can you extend that tunnel from  machine B  back to machine A so that
you can use the  same tunnel from B to C.

Is there a way to set up a ?"socks tunnel" on B to accomodate a "ssh in" from A?

Thus we would be able to use the same firefox set up for A to  get to C.

Thanks,

Mitchell