Amateur Radio
AX-25 Networks for Rookies

Get your Linux computer networking across amateur radio
frequencies by following this "AX-25 & IP made easy" project.

by Jamie Saker, W0JRS
w0jrs@arrl.net
Revised February 28, 2001
Copyright 2001. James R. Saker Jr.

Table of Contents

Section 1 (this page)
- Introduction
- Why are we doing this?

Section 2: Let's Get Started

Introduction

I've worked on Linux since it came out on two 5.25 floppies (remember those?), have built several TCP/IP networks, administered DNS, held my own with UNIX security and done the obligatory other stuff (kernels, sshd, etc). So when I started messing with amateur radio, I figured it'd be a "no brainer" to get my Linux boxes playing over amateur frequencies.

Then I read the documentation.

The first observation is that these things were OLD. Like, 1990's generation old! :-) The next realization was that the kernels and distributions referenced were ancient... 2.0.what? Redhat 5.??? But for some strange reason, very little updated information was available, and what was available was obscure and expert-friendly..

A lot of what I found seemed to indicate a "chicken and egg" situation - those that were playing with LinuxHam stuff were complaining that not enough others were doing it, but the technical level required to sort through the outdated mess and figure out what it meant in modern Linux terms was beyond most. I decided to document my travels through this obscure universe and see if I couldn't make it easier for others who're following me.

Why are we doing this?

When I wrote this, I was working from a set of assumptions about why I valued IP over amateur radio using Linux systems. Realizing you might have a different set of assumptions, or a different purpose in mind, let me explain some of these assumptions so you can decide if this is for you before making the investment of your time and energy.

Q: What will this do for me?

It will allow you to build your own part of the Internet, connecting to computers you set up as well as ones other people set up, without using a commercial provider's backbone to do so. While it's convenient to use commercial networks (and since I run one, I wouldn't want to talk you out of that anyway!), there are times where it is valuable to have an alternative, including:

• disasters: amateur radio is a critical component in disaster planning, mitigation, management and recovery. In many respects, we are the "communications of last resort." Internet communications should be no different and we should be up to the challenge of sending critical noncommercial information through digital means as well as by using voice communications.
  
• experimentation and education: want to learn how Internets really work? You can build one from the ground up using amateur frequencies.
  
• special projects: amateur wireless IP can be a tool for other projects, such as remote data gathering (when APRS isn't enough!), remote communications, etc.
  
• independence: many folks receive great satisfaction by being less dependent upon "the infrastructure," be it the power grid, the food system, commercial networks, the government, etc. If this drives you at all, you'll find many other folks out there with a similar interest. 

Q: Why use Linux?

While there are a lot more Windows PCs out there (one wrote this document and is in use every day in my home and office) and Windows systems definitely have their role in the world, Linux also things it is very good at. Being a very low cost server or router happens to be one of those things.

In our project, we're going to make Linux act as if it is a router of TCP/IP and AX.25 traffic. Since Linux gives us ultimate control (and ultimate ability to mess up!), it's an ideal platform for amateur experimentation.

After we've got the protocol routing basics down, we're going to fire up a few applications that we will serve off of our Linux system. Without an application to use, there wouldn't be much need to do all this work!

After that's done, we'll work on making our applications work for other people not necessarily on our Linux system. Please note that like ANY operating system installation, the more services you open up for people to use, the more responsibility you have in making sure that use meets your expectations. If you don't care to learn about Internet security and don't wish to make a commitment to continually educating yourself on the security requirements of your system and the applications you run on it, then stop here, go get yourself a copy of Windows and a commercial security product and let them take care of these things for you. 

Any server operating system (Linux, freeBSD, openBSD, Windows 2000 Server, etc.) can be a target for crackers if you don't take the responsibility of securing your system. If you're not interested in being a responsible server administrator, don't create an insecure host that'll be an easy target for crackers to gain access to and use for their illegal exploits.

Q: What is the objective of this project?

The goal of this project is to make a Linux system capable of running TCP/IP and the required underlying protocol, AX-25, over amateur radio equipment and frequencies.

Q: What is being left out in this project?

Various other protocols can be operated on top of AX-25, such as Rose and NetRom. These are not referenced in this project due to the scope being exclusively focused on activating IP services over AX-25.

Q: What are we going to do?

1. Prepare our system.

2. Build and test our kernel.

3. Install our supporting software.

4. Configure the software.

5. Hook up our amateur radio equipment.

6. Test and run our system.

7. Celebrate and show off our setup to friends.

Q: What do I need to know?

This all said, there are a few things you'll need to have under your belt to handle this, or at least have a friend who does who you can talk into helping you do (beers work well, I've found). They include:

• You need an amateur radio license! If you don't have one, get one. It's a lot more than the "old guys talking to each other using boat anchor radios with vacuum tubes" you might have thought. It's better described as a medium that supports hundreds of different hobbies. Some people chase or spot storms and provide communications during a disaster. Some talk around the world, participate in contests reaching difficult places (or setting up operations on the most remote places on earth). Some even bounce signals off the moon, use amateur satellites, and have the most bizarre antennas in the neighborhood. There are also people using digital modes - TCP/IP, PSK-31, APRS, packet and other modes at anything between 300 baud to several Mbps, covering a few feet to around the world. Plus, if you're reading this site and aren't a ham, I've got news for you. You're already different than 99% of the earth's population. You'll probably find other "different people" just like you in ham radio.
  
• Knowing the basics of setting up a Linux system. I'm using Redhat 6.2 for this project (and won't reference 7.0 until Redhat gets a bunch of the mess cleaned up, but that's another matter). You should be confortable with shell access to your Redhat system, familiar with all the nuances of root administration, be competent in your UNIX skills (e.g. using vi, locating files, etc.), and know where to find information on things you don't, like configuring kernels. Since there are entire FAQs out there on this subject, I won't waste your time nor mine covering this subject, but will instead tell you what you do need to change specific to our project when you do configure your kernel and system.
  
• Know the details of operating your radio equipment, including making any necessary cables to hook up your system to your TNC or soundcard, and to your radio.
  
• Have read the bandplan that affects your country and locality. If you're a licensed ham in the United States, you can review this information here. Some states also have coordination guidelines. Learn them first and determine what's the local practice before transmitting.

Q: What do I need to have?

Redhat 6.2 server installation on Intel architecture. I recommend the server config because it'll have many of the applications you'll want around for your amateur radio IP system. If you've got a Gnome or KDE workstation install and know what you're doing, that's fine too. I haven't tried this on other Linux architectures - either other distributions or other processor architectures. If you try it, please drop me a note and let me know of your results.

Operational serial ports available for TNC, or compatible soundboard and familiarity with the requirements of getting this operational for amateur use. (This is beyond the scope of the Rookies project, but I may cover it in another document at some point. For now, we'll stick with a standard Kantronics KPC-3+ for our TNC).

Ethernet cables and operational Internet connection. If you're doing dialup from your Linux box, I'll leave that to you to get configured. I'm assuming you have IP available via an Ethernet connection for this document and will reference it as such (as configuring PPP over modem adapter is beyond the scope of this document). If you don't have Ethernet and aren't familiar with setting up dialup on your Linux box, find a friend with fixed-wireless broadband, cable modem, or an office with LAN connectivity to the Internet to get this going since we'll need to access files off of the Internet to do our installation.

Ready to go? Let's move on to the next page and get started...

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