Background -- TCP/IP and Acorn Access
Most people set up an Acorn home network for one of two reasons:
Both of these things are supported by Acorn's own software, and additionally by some 3rd party applications. When you buy a DCI-4 ethernet card, you usually get the option of having Acorn Access in the podule's ROM. This is Acorn's Disc and Printer sharing system. Fortunately, Acorn have also decided to release this to everyone in the form of the New !Boot application. Since this is well proliferated now (eg Acorn User CDs) and has a whole host of other benefits for your machine, I'll make a big assumption that you're using this from now on. If you've got a good reason not to, or you've got a discless machine to connect, mail me and I'll write some more details about that.
- To share discs/printers between machines
- To access the Internet from multiple machines, whilst only one has a 'real' Internet connection
Acorn Access, at a basic level, is trivial to set up. You load the modules (or they're loaded automatically from your ethernet card at bootup) and that's about all there is to it. The software can assign it's own settings and locate other computers on the network all by itself. So why this document? Because if you want to do full tcp/ip networking, you have to change these settings and carefully set up the network software yourself. You need to know some basic details of TCP/IP networks:
With all this background information now understood, we can begin to set up our home network!
- Each node (usually a computer) on a network has a lowlevel 6 element network address -- for example 00:02:07:02:fd:e8 This is known as a MAC address and is fixed in the ethernet card's hardware as it is built. Your card's address is unique in the whole world. On most cards, you can see your MAC address by typing * Podules and you'll see something like this:
Expansion card 0: ANT Ethernet (00:02:07:02:fd:e8) Acorn Access / AUN (DCI4)
You don't actually need to know this, or be concerned about it, but it's worth knowing what a MAC address is.
- Each node that wishes to use TCP/IP protocols must be assigned an IP (Internet Protocol) address. This is a 4 element address which must be unique for every machine on the network -- for example 192.168.1.1 If your computer is connected to the Internet, then this IP is assigned by your Internet access provider either statically, when you create your account, or dynamically, each time you connect to the Internet. For internal networks, which are not connected to the Internet, you can freely choose your own IPs (via certain rules). However, to play things safe, and to keep things flexible if you do ever connect to the Internet, it's best that you use some of the reserved IPs. Typical small networks should use 192.168.*.* and so in this document, I'll assume 192.168.1.1 to 192.168.1.254 -- this set s a single Class C subnet and if you stick to these numbers, you'll have no problems.
- Given an IP, we need to work out if that IP is local to our network, or should be routed somewhere to get to other networks. To determine this, we use a Net Mask. This is a logical bit mask for your IP address, which specifies which parts of it mean "network" and which parts mean "host". There are strict rules about how IP addresses and NetMasks are associated, but in the simple case of a home network using 192.168.1.* the NetMask will be 255.255.255.0 which means that the "192.168.1" part is the network identifier, with the final number being the host identifier. Again, stick to 192.168.1.* as your IP range, and use 255.255.255.0 as the mask, and you'll have no problems!
- Connections between networks are called Gateways -- sometimes you'll hear these referred to as routers too. They have two, or more, network connections, each with a different IP, and can forward packets from one network to another. On a home network you won't usually have a true Gateway as such, even if you have a computer which has a modem connected to the Internet. This is because, typically, you won't actually directly communicate to a machine on the Internet from anything other than the machine with the modem. You'll use a Proxy...
- A Proxy is a software component which takes your requests and passes them on to another place. You can use a proxy server on a machine which you have connected to the Internet, to allow other machines without true Internet connections, to effectively access services on the Internet. The most common proxy is a web proxy which allows machines on your private network to view web pages on the Internet. Acorn's !WebServe software is a proxy server.
- DNS -- Domain Name Server, is a piece of software which makes using the network much easier for humans. It translates symbolic textual names (such as www.paradise-uk.net) in to the actual numbers (the IP address) used by the computer to address that machine (eg 220.127.116.11). For small local networks, you can also set up a simple text file which has these mappings.
- It's a good idea to set a loopback / localhost interface on each machine. This way, a machine can communicate with itself via TCP/IP without using the network card, and using network bandwidth. The naming and IPs for this are always the same: "localhost" and "127.0.0.1"
This page was written by Ian Jeffray and hosted on his website until 2002, it is now available here with permission
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