Basic Networking And LAN's
Computer Networks - Understanding The Basics
Updated: 27th December 2007
It’s only recently that I’ve delved deep into the world of networking. It’s a topic I left alone for quite some time. I new the basics about IP addressing, default gateways and how to use a unmanaged switch, but I never paid attention to the more complex aspects of networking such as port forwarding, netmasks and long distance connections.
That is until recently, and I must say it’s given me a lot to learn. On the surface, it seems networking just ‘does it itself’, without the need to configure most modern out of the box routers – but that’s because TCP/IP – the internet protocol of discussion, is highly maintainable.
I felt this document needed a good revision, after attempting to make changes; it became obvious it just needed re-writing. Now that I have my CCNA (come on, I had to mention it sometime soon!), I feel there’s a lot more to be said on the topic of networking.
Anyway, enough waffle – lets get to it. This article assumes you have dabbled in networking and are keen to see how the pieces fit.
Why Network?
This is becoming an old question now as even the most IT illiterate users can see the obvious benefits to networking up PC’s. Sharing printers, storage space, and other removable media are such benefits, and let’s not forget blogging, YouTube and social networking sites all exist because we can access remote machines thanks to the Internet. Networking is simply a must for modern technical trade, emails are fast becoming legal documents and the speed and ease of communicating using video messaging are taking hold fast in the IT sector. Of course, connectivity does mean more risk, but that’s life.
There are millions of reasons to network computers, though I assume readers of this already know why they want to!
However before computers can become networked… they must agree on a common language.
Computer Talk
As mentioned, computers need to agree on a language they both understand. It’s important they both do understand as otherwise communication cannot take place. All the Windows operating systems and indeed almost all Linux distributions use the protocol known as TCP/IP. There are other protocols that computers can use to exchange information such as Novell’s IPX but we will stick with the most common and widely accepted choice – it’s also the choice of the Internet, so it’s a good place to start ;)
TCP/IP is actually two protocols in one. The TCP part stands for ‘Transmission Control Protocol’ and provides a reliable method of transporting information from one host to another. The IP part stands for ‘Internet Protocol’ and allows packets to be routed across an environment that depends on many different types of hardware.
We’ll be focusing on the IP part which allows your machine access to your ISP, but before any of that can happen; you’ll need an IP address. If you want to know more about how TCP/IP works over the Internet, check out our ‘All About The Internet’ section.
Fortunately (for now anyway) IP addresses are easy to come by, especially if you’re an ISP customer as your ISP will already have one for you. Most modern ISP’s own enough IP addresses to give each of their subscribers one and that is exactly what they do. However they don’t give it to you – the lease it to you.
A word about ISP's
ISP stands for ‘Internet Service Provider’. They are typically phone companies (though not always) who provide you with access into the Internet. ISP’s don’t own the Internet, though they do have a lot of influence over its future, and some of the larger ISP’s (BT, AT&T) carry the majority of the Internet’s traffic.For the sharp ones among you, I mentioned that most ISP’s have enough addresses for one per house-hold. However most people nowadays have more then one PC – and everything that wants to connect via TCP/IP – weather that be printers, phones, routers, servers etc all need an IP address… so how does the Internet handle all these extra devices? You can find out the gritty details in ‘All About The Internet’ section, as this guide will only touch on the subject.
Getting An IP
But for now let’s focus on the basics to networking. We’ve established that all Internet connected devices – and indeed any device wishing to belong to an IP network needs its own IP addresses. In the older days of dialup things were easy. Your computer would be directly attached to the phone company’s equipment via the phone line, and your computer would be given an Internet IP address. You would keep the IP address for as long as you were online, then when you disconnected, the IP address was freed for other people to use. It’s important that ISP’s make sure they don’t run out of addresses!
However, now we have broadband and always-on services, your home network always needs an IP address. The box that is assigned this address is your home router. Home routers come in all shapes and sizes. Sometimes you’ll be given a USB device, which connects directly to your machine. In this case, it’s just like dialup – your computer is given the IP address and things are sorted, however you can’t connect anymore machines to the Internet connection. Something that’s not very desirable these days.
So to recap, every computer on a network (including the Internet) has an address - An IP address. A typical IP address will look like this: 192.168.1.100.
Looking at this address, you can see it breaks down into 4 sections (known as octets) separated by a period: 192.168.1.100. Each number can not exceed 255 and there must be 4 sets of octets to make a valid IP address. Computers refer to each other by calling these addresses. Below are some examples of valid and invalid IP's:
| Examples of valid IP addresses: | Invalid IP addresses and the reasons why: | |||
|---|---|---|---|---|
| 213.163.211.2 | 342.124.452.23 | The first and third set of numbers exceed 255. | ||
| 172.16.2.1 | 124.34.64 | There are only 3 sets of numbers (octets). | ||
| 81.54.23.112 | 231-34.12.142 | Cannot contain a dash or symbols other then periods. | ||
| 127.0.0.1 | 0.0.0.0 | Not a valid IP, meaning the system has no IP address. | ||
The more popular option is a multi-port router (technically a multi-layer switch). These devices from the likes of Netgear, D-Link, Linksys etc are all much better options, and although they look complicated to configure – they actually do a very good job of simplifying all the tasks they need to complete – there are two main tasks that every home router does:
1. Obtains an Internet IP address from your ISP2. Routes traffic from your internal network out through the phone line to the Internet
The first function if fairly simple, once you supply your ISP username and password – the router goes and connects. Your ISP is running a DHCP server which leases a free IP address, and there you have it – one device is already online.
Note:
I’ll just clear up some of the terminology surrounding ‘home router’. This could be any device given to you by your ISP to connect to a DSL service, it can include Wireless (known as an access point) but isn’t essential – it’s still a router with or without. If it has multiple Ethernet ports enabling you to connect more then one computer, it’s also a switch – or ‘multi-layer switch’. All these terms are interchangeable but for simplicity, we’ll stick with router. The term ‘hub’ is technically incorrect as these are much older devices similar to switches by less efficient and as far as I’m aware, have never been given out to customers of DSL services.Next is the fun part. DHCP is the protocol used to serve IP addresses to clients that do not have one. Now that your router has an IP from your ISP’s DHCP server – how does your home PC’s get an IP? Simple, your router is also a DHCP server!
Your router will only allow IP addresses to be leased through its Ethernet ports or Wireless – so there’s no risk of screwing with the ISP. Any clients who connect either via cable or wireless will automatically receive an IP address from your very own DHCP server, the router doesn’t just stop there, it also tells your client PC’s where the default network can be located.
Note:
Every IP devices needs a default gateway if it wants to communicate with the outside world. Since the entire goal of this is to get onto the Internet, all your clients will need a default gateway – a device that knows where the Internet is physically located. This happens to also be your router, so along with the IP address of each client – your router also sends out its own IP address as the default gateway in its DHCP messages. Whenever a client needs to find the Internet – it sends the traffic to your router.Your router now becomes the focal point for your network; it’s the gateway between your internal network and the Internet. It’s also a great place to have a firewall, and for this reason most home routers do come with firewalls built in.
So far it may all seem a little daunting, and that really is just the basics. We’ll stop here and give you a diagram to help, along with information of IP address that has been assigned.
From the image, you can see the router is directly connected to the Internet and has been given an IP address of 81.10.10.13, and the two PC’s have been given internal IP addresses. You can also assume that the PC’s have a default gateway of 192.168.1.1 (the router).
This is the basic setup of any home LAN using Ethernet\wireless and DSL. Knowing this hopefully will help you troubleshoot connectivity problems if you happen to loose access to the Internet. It’s extremely useful to know the IP address of your home router, as if your PC cannot access the router, then the problem is local – not internet. Most routers come with setup instructions asking you to type the routers name or IP address into your browser to configure it. You can perform the same test should you have problems, and in almost all cases, if you can access the router, you can see if it’s still connected to your ISP with a valid IP address.
Wireless
Everyone loves wireless, and it has taken the market by storm. Though I still hear many complaints about its performance and ease of setup, my reply is always the same – the technology is still very new, and like all new things – will have bugs and kinks. Wireless works by using radio frequencies to transmit and receive data. Most home routers also have wireless onboard. It doesn’t affect the way the router interacts with the ISP – it’s just simply another way for clients to connect to it. They will require an IP address and default gateway, all of which is handled by your DHCP service within the router.
Wireless however is not perfect. It will drop from time to time whenever radio interference is present – if it drops a lot… then you obviously have a lot of radio interference. This can be in the form of Microwaves, (wireless radio waves travelling through a microwave that’s on will get scrambled), radiators (seem to just block wireless at the best of times), other access points and radio operated telephones\doorbells. Fortunately it was expected this could happen – and your router should have an option to switch to a different channel, there are several to choose from. Find one that’s best for you (don’t change the option via wireless. You’ll be disconnected!), and give each one a try for a few days until you find the one that works best. Sometimes wireless just doesn’t like a part of nature, these have come to be known as ‘black spots’ and network engineers don’t even investigate them anymore… if wireless doesn’t work – tuff ;)
Resources
I thought I’d end with giving you some information about popular products and services that I’ve come to trust over the years. We’ll start with good old fashioned routers; my choice of home routers so far is Linksys.
Linksys are a division of Cisco – the behemoth of networking on planet Earth. So it stands to reason they know their stuff. It certainly shows, Linksys was conceived to target the consumer with affordable networking products. Some of their most basic line products have more functionality then most market leaders, though they aren’t the most user friendly in the world.