Not the usual ssh tunneling thread

OK, I've beaten my head against the wall on this one for a few days, and decided it's just not possible to do - but I'll toss it up here just in case I'm missing something obvious.

I've got two servers that I want to sync, but there are a couple of very robust firewalls between them. Normally, I'd jut tunnel - but there are also some directionality restrictions. Like so:


A <--- B <--- C ---> D --> E


I need to get data from A to E. C can ssh to B and D, but B and D can't ssh to C. B can ssh to A, but A can't ssh to B; D can get to E, but E can't get to D.

So to get from C to A or C to E is relatively easy - reverse tunnels. But I don't see any possible way of getting from A to E. If the connection went all in one direction, I'd just set up four tunnels. But this way, data gets to C and I don't see any way of getting it out of there.

Suggestions, alternatives, and RTFM references appreciated...

-- tim --

I actually do this quite often, but it is not necessarily "trivial". ;-)

# Open a local forward from C to A through B
me@C ~]$  ssh -L1234:IP-of-A:22 IP-of-B

# Connect to A from C through the local tunnel and \
configure a reverse forward to D
me@C ~]$  ssh -R4321:IP-of-D:22 -p 1234 localhost

# Connect from A to D through the 2nd tunnel and \
configure a local forward to E
me@A ~]$  ssh -L2222:IP-of-E:22 -p 4321 localhost

# Connect from A to E through the local forward on A
me@A ~]$  ssh -p 2222 localhost

I think that should do it. I am not in a position to confirm with my use and once I got it working I heavily leveraged ~/.ssh/config so I do not have to remember it all so meticulously. Also, you can "piggy-back" the SSH connections without actually have to use a shell, but should save that for after you get it working this way. You will need multiple shells; I use screen when I need to do something like this until I get it all worked out and more automated.

Once you are able to successfully ssh from A to E using the various tunnels/directions, you can pretty much shove whatever you want through it using rsync, scp, sftp, sshfs, tar, np, ... it really is up to you at that point.

That makes my head hurt, and looks like exactly what I need. You've figured out what was stumping me - everything I was doing had C going in two directions at once.

Thanks VERY much - can't wait to try it out!