A proxy act as an intermediary host where you could tunnel your connection through the proxy to access another host. Tunneling your SSH connection via a proxy, among other things, could allow you to access hosts in a private network or under a NAT. As such, a proxy avoids the need to set up a more complex infrastructure such as a VPN.

OpenSSH's SSH client supports connecting through both SOCKS and HTTPS proxy. It is achieved with the use of ProxyCommand option alongside third-party programs such as nc or netcat.

Steps to connect SSH client via SOCKS or HTTPS proxy:

  1. Create SOCKS or HTTPS proxy if you dont already have one.

  2. Test if the SOCKS or HTTPS proxy is reachable from the SSH client's host.

    $ nc -zv 127.0.0.1 2222 Connection to 127.0.0.1 2222 port [tcp/*] succeeded!
    -v      Produce more verbose output. -z      Only scan for listening daemons, without sending any data to         them.  Cannot be used together with -l.

  3. Use ProxyCommand as option for SSH client.

    $ ssh -o ProxyCommand='nc -X4 -x 127.0.0.1:2222 %h %p' [email protected]
    -X proxy_protocol         Use proxy_protocol when talking to the proxy server.  Supported         protocols are 4 (SOCKS v.4), 5 (SOCKS v.5) and connect (HTTPS         proxy).  If the protocol is not specified, SOCKS version 5 is         used.  -x proxy_address[:port]         Connect to destination using a proxy at proxy_address and port.         If port is not specified, the well-known port for the proxy pro‐         tocol is used (1080 for SOCKS, 3128 for HTTPS).  An IPv6 address         can be specified unambiguously by enclosing proxy_address in         square brackets.  A proxy cannot be used with any of the options         -lsuU.

  4. Add ProxyCommand to SSH client configuration file for persistence.

    $ cat .ssh/config Host remotehost     hostname 192.168.1.10     user remoteuser     ProxyCommand nc -X4 -x 127.0.0.1:2222 %h %p

  5. Connect again using SSH client with just the Host name as parameter.

    $ ssh remotehost