ProxyCommand
             Specifies the command to use to connect to the server.  The com-
             mand string extends to the end of the line, and is executed with
             the user's shell.  In the command string, '%h' will be substi-
             tuted by the host name to connect and '%p' by the port.  The com-
             mand can be basically anything, and should read from its standard
             input and write to its standard output.  It should eventually
             connect an sshd(8) server running on some machine, or execute
             sshd -i somewhere.  Host key management will be done using the
             HostName of the host being connected (defaulting to the name
             typed by the user).  Setting the command to ``none'' disables
             this option entirely.  Note that CheckHostIP is not available for
             connects with a proxy command.

             This directive is useful in conjunction with nc(1) and its proxy
             support.  For example, the following directive would connect via
             an HTTP proxy at 192.0.2.0:

                ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p