A remote (incoming) tunnel forwards traffic coming to a remote port to a specified local port.
sshg3 on the command line, the syntax of the
remote tunneling command is as follows:
client$ sshg3 -R [protocol/][listen-address:]listen-port:dst-host:dst-port \ username@sshserver
[protocol/] specifies which protocol is to be
used in the tunneled connection, it can be
tcp (optional argument). The default is
[listen-address:] defines which interface on the remote
server will be listened to (optional argument). By default all interfaces
listen-port is the number of the port on the
remote server, and connections coming to this port will be tunneled to
dst-host:dst-port define the destination host
address and the port to which the connection is tunneled from the
sshserver is the IP address or the host name of
the Secure Shell server.
The IP addresses and host names of the destination host and the sshserver can be defined using regular expressions that follow the egrep syntax. No wildcards are supported.
Setting up remote tunneling allocates a listener port on the remote server. Whenever a connection is made to this listener, the connection is tunneled over Secure Shell to the local client and another connection is made from the client to a specified destination host and port. The connection from the client onwards will not be secure, it is a normal TCP connection.
Every user with access to the remote server host will be able to use remote tunnel.
Figure 7.4 shows the different hosts and ports involved in remote port forwarding.
For example, if you issue the following command, all traffic which comes to port 1234 on the server will be tunneled to port 23 on the client. See Figure 7.5.
sshclient$ sshg3 -R 1234:localhost:23 username@sshserver
The forwarding address in the command is resolved at the (local)
end point of the tunnel. In this case
localhost refers to
the client host.
Tunnels can also be defined for connection profiles in the Connection Broker configuration file. The defined tunnels are opened automatically when a connection with the profile is made.
The following is an example from a
<profile id="id1" host="sshserver.example.com"> ... <tunnels> <remote-tunnel type="tcp" listen-port="1234" dst-host="localhost" dst-port="23" /> ... </tunnels> </profile>