Ubuntu Linux Gateway Example

The following are the steps necessary to create a general purpose gateway to AMPRNet using an Ubuntu Linux Server.

Not everyone needs a gateway!

You only need to setup a gateway if:

• You want to access AMPRNet resources that are not accessible from the Global Internet.
• You want to provide access to AMPRNet over RF (via packet or using WiFi).

Design

The basic design consists of a standard PC running Ubuntu 12.04 (LTS) and three network connections:

1. The first connection is to your ISP so you can reach the Internet.
2. The second connection is used to connect your normal "non-ham" devices to the Internet.
3. The third connection is used to connect your "ham" devices so they can see and be seen by other AMPRNet devices.

The following diagram shows the layout of the connections. (Click on the image to enlarge).

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Prerequisites (What do I need to get started?)

Hardware

I'm running my gateway on an old Dell Optiplex GX260 (a Pentium 4 with 512 MB of RAM and a 20 GB Hard drive). You don't need much of a system if your Internet Service Provider's bandwidth is 100Mb/s or less.

Along with the built in Ethernet network interface, I've installed two additional 10/100 Ethernet network cards I purchased from Amazon.

Software

On the Dell I've installed Ubuntu 12.04 LTS (the 32-bit server version). With one exception all of the software you will need for the gateway you can get with the server.

IP Addresses

What is an IPv4 Address ?

An IPv4 address is a unique 32-bit binary number that is assigned to every publicly connected Internet device.

To make the address easy for humans to read, it is usually represented as a four decimal numbers separated by periods (i.e. 192.0.0.2).

More information on IPv4 addresses can be found in this Wikipedia article.

Static IPv4 from your ISP

What is a "Static" IP ?

Normally your ISP assigns your router a public IPv4 address dynamically from a pool of IPv4 addresses shared by many customers.

This means that your Public IPv4 address can change periodically and without notice. Usually this isn't a big issue for most normal users, however it can cause problems when trying implement an AMPRNet gateway.

While it is possible to make AMPRNet gateways work with a dynamically assigned address, there could be a significant time lag between the time your Public IPv4 address changes and when others on AMPRNet learn about the new address. During this time your AMPRNet subnet may be unreachable.

Therefore, I recommend asking your ISP for a "static" IPv4 address. A "static" IPv4 address is one that doesn't change. Usually your ISP will set you up with one for a small setup fee and monthly recurring fee. It is well worth the small cost to insure a stable gateway.

When you ask for a "static" IPv4 address, your ISP will provide you with the following information that you will need to configure your server.

That information is:

IP Address

The "static" IP Address itself.

Netmask

The netmask is used to determine what part of the IPv4 address is the "network" portion and what portion is the "host" (Think POSTAL Code vs. House Number)

Default Gateway

The default gateway is an IP address that you send traffic to reach the rest of the Internet

DNS Server Addresses

DNS server addresses are IP addresses of systems that look up the IP address for the name enter. (When you type "google.com" into your browser, the DNS Servers look up the IP address for "google.com" to know where to send your search request.