## 18.10. Secure TCP/IP Connections with SSH Tunnels

It is possible to use SSH to encrypt the network connection between clients and a Postgres Pro Enterprise server. Done properly, this provides an adequately secure network connection, even for non-SSL-capable clients.

First make sure that an SSH server is running properly on the same machine as the Postgres Pro Enterprise server and that you can log in using `ssh` as some user. Then you can establish a secure tunnel with a command like this from the client machine:

    ssh -L 63333:localhost:5432 joe@foo.com

The first number in the `-L` argument, 63333, is the port number of your end of the tunnel; it can be any unused port. (IANA reserves ports 49152 through 65535 for private use.) The second number, 5432, is the remote end of the tunnel: the port number your server is using. The name or IP address between the port numbers is the host with the database server you are going to connect to, as seen from the host you are logging in to, which is `foo.com` in this example. In order to connect to the database server using this tunnel, you connect to port 63333 on the local machine:

    psql -h localhost -p 63333 postgres

To the database server it will then look as though you are really user `joe` on host `foo.com` connecting to `localhost` in that context, and it will use whatever authentication procedure was configured for connections from this user and host. Note that the server will not think the connection is SSL-encrypted, since in fact it is not encrypted between the SSH server and the Postgres Pro Enterprise server. This should not pose any extra security risk as long as they are on the same machine.

In order for the tunnel setup to succeed you must be allowed to connect via `ssh` as `joe@foo.com`, just as if you had attempted to use `ssh` to create a terminal session.

You could also have set up the port forwarding as

    ssh -L 63333:foo.com:5432 joe@foo.com

but then the database server will see the connection as coming in on its `foo.com` interface, which is not opened by the default setting `listen_addresses = 'localhost'`. This is usually not what you want.

If you have to “hop” to the database server via some login host, one possible setup could look like this:

    ssh -L 63333:db.foo.com:5432 joe@shell.foo.com

Note that this way the connection from `shell.foo.com` to `db.foo.com` will not be encrypted by the SSH tunnel. SSH offers quite a few configuration possibilities when the network is restricted in various ways. Please refer to the SSH documentation for details.

### Tip

Several other applications exist that can provide secure tunnels using a procedure similar in concept to the one just described.