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SSH Tectia 
PreviousNextUp[Contents] [Index]

    About This Document >>
    Installing SSH Tectia Server for IBM z/OS >>
    Getting Started with SSH Tectia Server for IBM z/OS >>
    Configuring the Server >>
    Authentication >>
    System Administration >>
    File Transfer Using SFTP >>
    Secure File Transfer Using Transparent FTP Security >>
    Tunneling >>
        Local Tunnels
            Tunneling TN3270
        Remote Tunnels
        Agent Forwarding
    Troubleshooting SSH Tectia Server for IBM z/OS >>
    Man Pages and Default Configuration Files >>
    Log Messages >>

Local Tunnels

A local (outgoing) tunnel forwards traffic coming to a local port to a specified remote port.

With sshg3 on the command line, the syntax of the local tunneling command is the following:

$ sshg3 -L [protocol/][listen-address:]listen-port:dst-host:dst-port server

Setting up local tunneling allocates a listener port on the local client. Whenever a connection is made to this listener, the connection is tunneled over Secure Shell to the remote server and another connection is made from the server to a specified destination host and port. The connection from the server onwards will not be secure, it is a normal TCP connection.

Figure Local tunneling terminology shows the different hosts and ports involved in local port forwarding.


clientserver-tunnel-local2-4.gif
Figure : Local tunneling terminology

For example, when you issue the following command, all traffic coming to port 1234 on the client will be forwarded to port 23 on the server. See Figure Local tunnel.

$ sshg3 -L 1234:localhost:23 username@sshserver


clientserver-tunnel-basic-5.gif
Figure : Simple local (outgoing) tunnel

The forwarding address in the command is resolved at the (remote) end point of the tunnel. In this case localhost refers to the server host (sshserver).

If you have three hosts, for example, sshclient, sshserver, and imapserver, and you forward the traffic coming to the sshclient port 143 to the imapserver port 143, only the connection between sshclient and sshserver will be secured. The command you use would be similar to the following:

$ sshg3 -L 143:imapserver:143 username@sshserver

Figure Tunnel to an IMAP server shows an example where the Secure Shell server resides in the DMZ network. The connection is encrypted from the Secure Shell client to the Secure Shell server and continues unencrypted in the corporate network to the IMAP server.


clientserver-tunnel-out-6.gif
Figure : Local (outgoing) tunnel to an IMAP server

By default, the server allows local tunnels to all addresses for all users. To restrict tunneling for all or for specified users, see Section Securing Tunneling.

Tunneling TN3270

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