ssh tunneling and "channel 2: open failed: administratively prohibited: open failed"

[Mike Cohler]

Jonathan Underwood <jonathan.underwood <at> gmail.com> writes:

> I am trying to connect to machine C via a tunnel to machine B from
> machine A, with machine A being the local machine.
> 
> Machine C is behind a firewall, and so direct ssh from A to C isn't possible.
> 
> At the command line, once ssh'd into machine B from machine A, I can
> ssh from machine B to machine A.
> 
> So, on machine A (local machine) I run in one terminal (Terminal 1):
> 
> ssh  -R 8888:C:22 username <at> B cat -
> 
> which asks me for my password on machine B, which I duly enter.
> 
> Then, on machine A, in a second terminal (Terminal 2) I run
> 
> ssh -p 8888 localhost

I had a similar problem a few months ago which took me some time to fathom the
solution needed.
I found the following for my case:
1) From machine A do "ssh -L 12345:C:5900 B" (where B and C are your machine
names in question) 
in a first terminal window.

This allows an ssh login from A to machine B where the firewall is, but once
connected is set up to forward in this case port 12345 from the originating
machine A to port 5900 on machine C. Once connected to machine B, then login to
machine C on the standard ssh port. Now the tunnel should be set up with the
correct port forwarding that you want - in this case anything going to poert
12345 on machine A will be forwarded through to 5900 on machine C which is the
standard vnc port.

2) Once this is running then start the vnc connection command in a second
terminal session on machine A going to port 12345, and this will then have the
vnc command running and communicating to port 5900 (default) on machine C via
the tunnel.

It did take me quite some time to work this out, but it has worked consistently
ever since.