如何在两个接口之间建立Telnet连接隧道？

Question

I have the following network:

PC1 --|¯¯¯¯¯¯¯¯¯|                            |¯¯¯¯¯¯¯¯¯|-- board2
PC2 --| gateway |-- (eth0) [server] (eth1) --| gateway |
PC3 --|_________|                            |_________|-- board1

As you can see, the server (running Linux) has 2 interfaces so that the PCs and embedded boards are not on the same subnetwork.

I would like to develop a simple application (or use an existing one) that tunnels incomming Telnet connections from eth0 (using a specific port) to boards through eth1 .

I don't have root privileges on the server, but I have a regular Unix account. I don't want the PCs to actually "log in" to the server; I just want them to pass through it to connect to the boards. The server has Python, PHP and Perl installed.

I want to support multiple connections. The port number could be used to forward the connection to the right board (say I have 10 boards, then the tunnel listens on ports 3000 to 3009).

I can imagine a simple Web application to do that, but I want a native Telnet connection that will support CTRL+C and all that stuff and allow you to use any terminal emulator on the PCs (ie PuTTY or another one), which run Windows.

Any help would be much appreciated.

Answer 1

It sounds like you're looking for a TCP proxy . A proxy accepts connections on one port, connects to another ip/port, and then passes traffic back and forth.

If you have xinetd on your system you already have what you need. The redirect directive for a service causes xinetd to open a connection to another host/port and act as a proxy. See this document for an example.

balance is another very simple proxy tool that will do what you need. This is probably easier to run as a non- root user, especially since it's configured entirely on the command line.

Since you're not root on your server you'll need to run these on ports > 1024, but otherwise you should be all set.