Tunnelling UDP Traffic Through An SSH Connection

Overview

This section describes how to use NST to tunnel a UDP traffic conversation through a SSH connection. For our example we will tunnel IPMItool traffic (UDP Port: "623") through an SSH connection to a Sun Fire X4200 server's Integrated Lights Out Manager (ILOM) service processor network interface. Three systems are involved, 2 NST probes and the X4200 server. Reference information was taken from: "Performing UDP tunneling through an SSH connection".

Tunnel A TCP Forward Port Through SSH

First we need to establish the tunnel for a "non-used" TCP port from the local NST probe to the remote NST probe SSH server which shares the same LAN as the destination X4200 server.

Establish An SSH Connection With TCP Port Forwarding

[root@probe tmp]# /usr/bin/ssh -p 31222 -L 9999:localhost:9999 root@55.44.22.178;

root@55.44.22.178's password:
Last login: Thu Mar 22 11:18:59 2007 from cpe-72-222-76-188.nycaper.res.rdr.com

===============================================
= Linux Network Security Toolkit (NST v1.5.0) =
===============================================

[root@probe-biostar ~]#

In this example SSH traffic is being NATed through a firewall. The SSH filtered port at the dirty side of the firewall is: "31222". We have chosen to use TCP port forwarding for the "non-used" TCP port: "9999". The remote NST probe's IP Address is: "55.44.22.178". On the local NST probe, TCP port: "9999" is bound to the localhost IP Address: "127.0.0.1".

Use: "nc" To Translate TCP To UDP Forward On The SSH Server Side

On the remote NST probe (SSH server side), we need to open a TCP port listener on the TCP port: "9999" which will forward all network traffic to UDP port: "623" for the IP Address assigned to the X4200 server's ILOM network interface.

We will first need to create a "fifo". The "fifo" will be necessary to maintain a two-way communication channel between the TCP port listener and the UDP port. A simple shell pipe would NOT work. It would only communicate left process' standard output to right process' standard input. We will use the Linux command mkfifo to establish the "fifo".

FIFO Creation

[root@probe-biostar ~]# /usr/bin/mkfifo "/tmp/fifo";

[root@probe-biostar ~]# /bin/ls -al "/tmp/fifo";

prw-r--r-- 1 root root 0 Mar 22 19:37 /tmp/fifo

[root@probe-biostar ~]#

Next will will use "nc" (netcat) the "TCP/IP Swiss Army Knife" to perform the TCP/IP to UDP translation.

FIFO Creation

[root@probe-biostar ~]# /usr/bin/nc -l 9999 < "/tmp/fifo" | /usr/bin/nc -u 172.16.1.18 623 > "/tmp/fifo";