There is a system B with the following open servers: I have a web server listening on port 80 and a ssh server listening on 22. However, only port 22 is publicly available. Now, I would like to create some kind of tunnel, so that I can access B:80 from A. However, my client computer A that would like to connect to the system B is not publicly open, either.
So, all I have is a client computer A from where I would like to access the server B and, there, an open port 22. On A, no port is open or can be opened.
What (I think) I would need is to open locally (on A) some port that connects in some way through port 22 of B to port 80 on B.
Is this possibly without using any man-in-the-middle open servers with multiple ports?
Answer
(Note: Jakuje answered while I was composing my answer. It's more elaborate from the start, so I'm posting it anyway.)
If I get you right, all you need is to forward a local port through SSH. I assume you have SSH access to B
.
Linux command to run on A
:
ssh -NL 2345:127.0.0.1:80 B
Now you can connect to the port 2345
on A
and it should be equivalent to connecting to the 80
port on B
from the B
itself.
Few remarks:
-N
causesssh
not to execute a command on the remote (B
) side; perfect for port forwarding.- The number
2345
is arbitrarily chosen; it may be any number from1024
to65535
(binding to a port lower than1024
requires root access usually). If you happen to hit the already occupied port, then try another number. - The
127.0.0.1
address I used requires your web server onB
to listen on theloopback
interface. If it listens on some other address(es) only, use it instead. This address should be a valid address of your server as seen from within the systemB
. It doesn't matter at all what this address means toA
nor if it means something in the first place. - If you need computer
C
to connect to the2345
forwarded port onA
then you should get familiar withssh -g
option. Readman ssh
.
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