SCP from A to C across B

[vuakko]

A: my machine, which has the files
B: a public gatekeeper for C among others.
C: machine, where I want the files. I can SSH here from B.

So there you have it. I have sshfs for B at A if it helps a thing.
The lazy solution would be to first copy the stuff to B and to
C from there, but that would be wimpy (bad aftertaste 'n all that).

Another complication: Machine A is masked by the ISP (trying to
get them drop it...) so I can't run sshd at A and manage the copy
from B.

[embobo]

Port forward from port X on B to port 22 on C and use "-P X" in your scp command line. You can accomplish the port forwarding with iptables or another ssh session.

[vuakko]

Thanks, that was kind of too easy then after all. I had just tried wrong forwarding tactics.

Full final solution for future reference (at A in two different shells):