.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.\" $OpenBSD: ssh.1,v 1.245 2006/01/06 13:29:10 jmc Exp $
+.\" $OpenBSD: ssh.1,v 1.246 2006/01/12 14:44:12 jmc Exp $
.Dd September 25, 1999
.Dt SSH 1
.Os
Request rekeying of the connection
(only useful for SSH protocol version 2 and if the peer supports it).
.El
-.Sh X11 AND TCP FORWARDING
+.Sh TCP FORWARDING
+Forwarding of arbitrary TCP connections over the secure channel can
+be specified either on the command line or in a configuration file.
+One possible application of TCP forwarding is a secure connection to a
+mail server; another is going through firewalls.
+.Pp
+In the example below, we look at encrypting communication between
+an IRC client and server, even though the IRC server does not directly
+support encrypted communications.
+This works as follows:
+the user connects to the remote host using
+.Nm ,
+specifying a port to be used to forward connections
+to the remote server.
+After that it is possible to start the service which is to be encrypted
+on the client machine,
+connecting to the same local port,
+and
+.Nm
+will encrypt and forward the connection.
+.Pp
+The following example tunnels an IRC session from client machine
+.Dq 127.0.0.1
+(localhost)
+to remote server
+.Dq server.example.com :
+.Bd -literal -offset 4n
+$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
+$ irc -c '#users' -p 1234 pinky 127.0.0.1
+.Ed
+.Pp
+This tunnels a connection to IRC server
+.Dq server.example.com ,
+joining channel
+.Dq #users ,
+nickname
+.Dq pinky ,
+using port 1234.
+It doesn't matter which port is used,
+as long as it's greater than 1023
+(remember, only root can open sockets on privileged ports)
+and doesn't conflict with any ports already in use.
+The connection is forwarded to port 6667 on the remote server,
+since that's the standard port for IRC services.
+.Pp
+The
+.Fl f
+option backgrounds
+.Nm
+and the remote command
+.Dq sleep 10
+is specified to allow an amount of time
+(10 seconds, in the example)
+to start the service which is to be tunnelled.
+If no connections are made within the time specified,
+.Nm
+will exit.
+Once opened,
+a SSH connection will remain active
+until all actively forwarded connections have closed.
+.Sh X11 FORWARDING
If the
.Cm ForwardX11
variable is set to
options above) and
the user is using an authentication agent, the connection to the agent
is automatically forwarded to the remote side.
-.Pp
-Forwarding of arbitrary TCP/IP connections over the secure channel can
-be specified either on the command line or in a configuration file.
-One possible application of TCP/IP forwarding is a secure connection to an
-electronic purse; another is going through firewalls.
.Sh ENVIRONMENT
.Nm
will normally set the following environment variables: