Wifi – How to host an ssh server

port-forwardingwifi

I have a broadband internet connection. I have an wireless modem (Airtel India). I don't have a static ip address. I want to host a ssh/web/ftp server to be visible to the outside world just for testing and learning purpose so I can ask my friend to connect to my current ip address and test. My modem has an admin interface which allows to port forward and open ports. modem Configuration

I set up ssh server as shown and checked if port 22 is open using this website ,
Port Scan

And port 22 is open. I have an openssh server running and it works if i do,
ssh balki@192.168.1.5 which is my local ip address but doesn't work if i do ssh balki@122.xx.xx.xx where 122.xx.xx.xx is my external ip address of my modem which i checked from whatismyipaddress.com.
Since it looks like the port is open, I wonder if there is some setting I need to change in my server config to expose my server. How should I go about solving this?

Best Answer

It can be that your router does not support you connecting from your internal network to your external IP address, unfortunately some routers cannot route that.

You can try visiting this website: http://portscan.me it will perform a portscan on the IP address you're coming from, so given that you come from the same IP address as your server, then you should be able to see whether or not port 22 is open to the world.

The scan might take a few mins to complete.

Related Solutions

SSH – Adding Port Forwardings Programmatically on a ControlMaster SSH Session

That's quite simple, actually. Simply add the ctl_cmd -O forward to your existing command, thus:

ssh -M -L5555:localhost:22 remotehost

becomes:

ssh -O forward -M -L5555:localhost:22 remotehost

The ssh man page discusses the -O ctl_cmd option:

-O ctl_cmd
        Control an active connection multiplexing master process.  When the -O option is
        specified, the ctl_cmd argument is interpreted and passed to the master process.
        Valid commands are: “check” (check that the master process is running), “forward”
        (request forwardings without command execution), “exit” (request the master to
        exit), and “stop” (request the master to stop accepting further multiplexing
        requests).

This, of course, assumes you've either enabled ControlMaster yes in your ~/ssh/config file or -M on the command line.

SSH Reverse Port Forwarding with PuTTy – how to specify bind address

There are two checkboxes when setting up the PuTTY tunnel,

Local ports accept connections from other hosts
Remote ports do the same (SSH-2 only)

the second of those does what you need.

I just tested it,

PuTTY tunnels dialog,

Tick Remote ports ...
Put 8080 into Source port
Put 127.0.0.1:80 into Destination port
Select 'Remote' radio button
Click Add
Connect

Works fine, here's the resulting netstat,

# netstat -an | grep 8080
tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN
tcp6       0      0 :::8080                 :::*                    LISTEN

You can also use plink.exe that comes with PuTTY, for example,

plink -R *:8080:localhost:80 user@remote.host.example

which works fine as well.

# netstat -an | grep 8080
tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN
tcp6       0      0 :::8080                 :::*                    LISTEN

If you're still getting 127.0.0.1:8080 on the host, then GatewayPorts is still set to no in your sshd config.

Also, don't forget to update the firewall on the target server to allow external connections to port 8080.

Best Answer

Related Solutions

SSH – Adding Port Forwardings Programmatically on a ControlMaster SSH Session

SSH Reverse Port Forwarding with PuTTy – how to specify bind address

Related Topic