Getting more from broadband 1: Networking

You'll want to make sure that the maximum number of people benefit from your broadband connection, so what's the best way to share it?

Many PC networking technologies are available but, for smaller and peer-to-peer (P2P) PC networking requirements, there's an obvious choice: Ethernet.

The convenience of simple plug-in connections and a relatively high speed have made Ethernet popular, while market competition has brought costs down to the point where a small P2P home network can now be built for under £100.

USB networking is also possible with some digital subscriber lines (DSL) services, but at present it's too complicated to be worthwhile.

Choosing your network equipment
Ethernet 10/100Mbps client adaptors are typically Peripheral Component Interconnect (PCI) cards, although PC Card and USB adaptors are available. Brand name cards, such as those from Intel and 3Com, command a significant premium over generic alternatives, offering the reassurance of support and perceived quality.

In a home network, advanced features - and the associated price hike - offered by big-name adaptors are unnecessary.

Upper-limit throughput capacity is also not an issue. Even at the £10 to £15 level, you can buy a competent PCI Fast Ethernet adaptor. In fact, the only serious concern when buying adaptors for PCs is support for your chosen operating system. All offer Windows support, but not all are so well supported by Linux.

It's rare to find a card that can't be used at all in a Linux machine, although you might have to compile drivers or even a new kernel if you stray too far away from mainstream products.

Cable choice is limited to Category 5 or the recently announced Category 6. Only if you're building network cabling into walls, conduits and the like should you consider using Category 6 to provide future proofing. Otherwise, use cheaper Category 5.

The last physical component of the network is the switching equipment, which links the clients together. For Ethernet, this will be either a hub or a switch. On a hub, all ports of the hub see all traffic passing through the hub.

More expensive switches, on the other hand, automatically learn which machines are connected to each port and each port only sees traffic destined for machines connected to it. As a rule of thumb, use switches in preference to hubs. In larger networks, you'll have to introduce switches to avoid too much unnecessary data being transmitted across the entire network.

Switches appropriate for home network use are small, unmanaged devices, which are plug-and-play. Larger switches offer advanced functionality such as virtual local area networks (Lans), traffic filtering and web and console management.

All of that is overkill for home and many small office networks, but small, silent switches from companies like Netgear and Linksys are ideal. Only in more complicated and larger network topologies are more advanced switches likely to be required.

Designing the physical network
The golden rule of designing a network is not to overcomplicate. For a home or small office network, a simple 'flat' network design is sufficient. If this includes an internet connection, one PC will have two network connections: one to the internet and one to the home network. Each of the other PCs will be connected to the same switch.

If you need to support multiple PCs in multiple rooms, you can either run cables back from each PC to a central switch or install additional switches in each room and connect the switches instead.

Configuring the network
Once everything is wired up, each PC needs to be configured. This means assigning an Internet Protocol (IP) address, subnet mask, gateway and Domain Name System server addresses. Doing this for each PC can be laborious, especially if any of the information changes.

A neat way around this is to use the Dynamic Host Control Protocol (DHCP). Using this, a central server assigns IP addresses (and associated network configuration) as required. Server versions of Windows and all common Linux distributions include DHCP servers.

IP addresses on the public internet are assigned specifically, so you shouldn't invent IP addresses for machines connected to it. For internal networks, internet-valid IP addresses aren't required for each host.

Instead, the gateway machine connecting the local network to the internet is assigned a valid public IP address and handles internet-bound traffic on behalf of machines behind it on the Lan.

This is known as Native Address Translation (sometimes called Network, rather than Native) or Nat. Network traffic bound for the internet from the local network has its IP address translated to that of the gateway on the way out, while reply traffic returning to the gateway is tracked and passed on to the correct machine behind it.

With the Windows operating system, this mechanism is called Internet Connection Sharing. With Linux, the technique is called IP Masquerading.

A rather useful side effect is that machines behind the gateway are effectively invisible to the public internet. Private IP address ranges for use on internal networks are defined here.

A combination of DHCP, Nat and firewalls run on a dedicated gateway host on ADSL or cable modem line would make an excellent gateway for a small office or home network. A P100 with 32MB of Ram, for example, is more than up to this task in a Linux system; 64MB of Ram should be fitted for Windows.

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