SSH Tunnel
SSH Tunnel
How to setup a basic SSH tunnel to access remote server resources that may be blocked by a firewall or simply inaccessible over the internet.
Understanding SSH Tunnels
Remote server that is running on port 80. Access this service from local computer, but a firewall is in the way.
Setup
| Host Type | IP Address | Description |
|---|---|---|
| Local | localhost | |
| Remote | 192.168.0.6 | Internal IP address of the local service |
To bypass the firewall restrictions, send the remote service over the SSH port via a tunnel.
SSH Tunnel Example
Confirm listening ports
Remote
Remote server running web server on port 80 and ssh on port 22.
> netstat -ntl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp6 0 0 :::22 :::* LISTEN
From the remote run the following command to establish a SSH tunnel:
> ssh -N -L localhost:8888:localhost:80 root@192.168.0.93
-Nis a flag to just forward ports and not execute remote commands-Lforwards local connections to the remote side- localhost is the host on the local machine that will bind to the remote service
- 8888 is the port that the local machine will listen on
- localhost is the internal IP address of the remote service
- 80 is the port of the remote service
- root is the SSH user of the remote server
- 192.168.0.93 is the public IP address of the remote server
The remote service at localhost:80 will be accessible on the local machine at http://127.0.0.1:8888.
-p 2222 of the remote server.Confirm listening ports
Local
Local is now established local connection port 8888 to remote system 192.168.0.93:80.
> netstat -ntl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 127.0.0.1:8888 0.0.0.0:* LISTEN
Shorthand
Remote command execution or pseudo terminal will be allocated for this connection.
> ssh -L 8888:localhost:80 root@192.168.0.93
Change the port number for other services.
- Don’t need to include localhost of the local machine because it is default
- Default SSH port is 22, so don’t need to specify this
-Nflag is optional. Functionality will be the same
Might be able to trace tunnel through lsof. Need to explore more.
> lsof -a -i -c '/^ssh$/'
Summary
Greate way to access remote services that are private and not exposed to the internt or that are running behind a firewall to access this service from local computer.
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