topic Re: PORT FORWARD SSH in Operating System - HP-UX

PORT FORWARD SSH

Inter_1 — Thu, 01 Mar 2007 16:12:34 GMT

Server1
Port 2222

Server2
Port 22

How can I forward the Port 22 from Server to Port 2222 to Server1. I want also that the Server1 to use 2222 to interact with the Port 22 of Server2.

Thanks

Re: PORT FORWARD SSH

hpuxrox — Thu, 01 Mar 2007 16:28:37 GMT

So what your saying is, when you connect to port 22 via ssh on Server1 you want to really access server2? And, when you access port 2222 on server2 you will be accessing server one. Accentually, you will be able to connect to both machines from just one of the machines.

On Server1
ssh -L2222:server1:22 server2 sleep 1000000

On Server2
ssh -L22:server1:2222 server2 sleep 1000000

Re: PORT FORWARD SSH

hpuxrox — Thu, 01 Mar 2007 16:34:21 GMT

Be sure to verify your sshd_config file for the following settings

# Port forwarding
AllowTcpForwarding yes

# If port forwarding is enabled, specify if the server can bind to INADDR_ANY.
# This allows the local port forwarding to work when connections are received
# from any remote host.
GatewayPorts no

Re: PORT FORWARD SSH

Matti_Kurkela — Fri, 02 Mar 2007 08:59:03 GMT

If you have sshd running on a server, you cannot use port 22 as a forwarding source, because sshd is already occupying that port.
If a port is occupied by a process listening on it, you cannot re-use that port number.

When using the -L option the syntax is
-L::

The is where the ssh sets up a listening socket on the local host (where the command is executed). Then the data is taken (using the encrypted SSH tunnel) to the destination host of the SSH connection.

*From there* it is forwarded to :. This last step is *not* protected by the SSH encryption, so it's good to make this step as short as possible.

So, if you enter on server1 a command like:
ssh -L 2222:localhost:22 server2 sleep 1000000

it actually makes sense (the "localhost" is interpreted according to server2's point of view).

After this, if you connect to server1:22, you'll get server1 as normal. But if you connect to server1:2222, it will behave just as if you'd connected to server2:22.

However, unless you use the -g option, connections to server1:2222 will be refused unless they are originating from server1.

Re: PORT FORWARD SSH

Inter_1 — Fri, 02 Mar 2007 09:16:47 GMT

Thank you for your answers. I have done the changes as you suggested, but I would like to know how can I test that is working or not?

Re: PORT FORWARD SSH

Matti_Kurkela — Mon, 05 Mar 2007 13:05:31 GMT

Err... connect to the ports and see whether you get the connectivity you required?

Was this a trick question? :-)

Re: PORT FORWARD SSH

Inter_1 — Mon, 05 Mar 2007 14:14:58 GMT

That was not a tricky question. Some time the brain doesn't function proper and the easy things looks difficult :)

Re: PORT FORWARD SSH

Inter_1 — Mon, 05 Mar 2007 14:16:03 GMT

thanks