SSH Tunnel, how to know the server port information post tunneling

Question

I am trying to google a method to achieve this but unable to find one.

Basically, I have created an SSH tunnel to several remote hosts through a bastion host using a command like this.

ssh -L 9000:ourprodserver.domain.com:1521 \
    -L 9001:otherprodserver.domain.com:1521 \
-A -l [email protected] somebastionhost.domain.net

Now, how do I know the connection details mapping to the local port whenever the tunnel is active.

i.e I want to be able to create a list of this form.

L_port         Remote_host            R_port
9000       ourprodserver.domain.com   1521
9001       otherprodserver.domain.com 1521

Is it possible?

Answer 1

A simple solution exists, but it will only list the currently active tunnel connections: it's using the ssh escape sequence ~#

If the tunnel is not used, it won't be shown.

From the help (shown with ~? inside an active ssh connection):

~# - list forwarded connections

Example output will be :

user@somebastionhost$ ~#
The following connections are open:
  #4 client-session (t4 r0 i0/0 o0/0 fd 9/10 cc -1)
  #5 direct-tcpip: listening port 9000 for ourprodserver.domain.com port 1521, connect from 127.0.0.1 port 48954 to 127.0.0.1 port 9000 (t3 nr0 i0/0 o0/0 fd 12/12 cc -1)

On the client side, you can get an idea of the open tunnels, even the inactive ones, by listing TCP sockets it has opened:

lsof -n -p <pidof-ssh-client> -a -iTCP -a -sTCP:LISTEN

Although this doesn't fully answer your question, it may be a starting point.