Understanding IP Addresses

At the root of any network running TCP/IP is a unique identifier known as an IP address. In the same way that your home is identified by a street name (more general) and numeric address (more specific), a computer on a TCP/IP network is identified by an IP address like 192.168.1.100. Similar to your home address, part of an IP address identifies a particular network, and another part represents a unique computer (referred to as a host in TCP/IP jargon) on that network.

Because of the way in which hosts running TCP/IP identify and communicate with one another,
you cannot just blindly pick numbers to assign as IP addresses. In order for two computers on the same network to communicate, they must be assigned addresses that begin with the same network number, and then the host portion of each address must be unique. For example, if you were to give one computer an IP address of 10.10.10.10 and another on the same network an IP address of 11.11.11.11, the two could never communicate – from their internal calculations, the two hosts would “see” each other as being on different networks, and would not attempt to communicate directly.

Distinguishing network numbers isn’t quite as easy as starting IP addresses with a common number like “192”. IP addresses are divided into what are known as “classes”, and the first number in an IP address is used to determine how much of the IP address is the network portion, and how much is the host portion. For example, when an IP address starts with the number 10, only the first section (known as an octet) represents the network, and the last three octets are used to identify a host. However, when an IP address starts with the number 213, the first three octets uniquely identify the network, and only the last octet identifies a host.

The reason for IP addresses being separated into different classes is to allow for networks of different sizes on the Internet – some networks are small, while others are much larger. The table below outlines the three main address classes used on the Internet. The value in the first octet of the address is used to determine the address class. For this information you can subsequently determine which portion of an IP address identifies a network, and which a host.

Address Class First Octet Range Network Portion (N) and Host Portion (H)
Class A 1-126 N.H.H.H
Class B 128-191 N.N.H.H
Class C 192-223 N.N.N.H

Looking at the table above, you would now know that the IP address 167.204.7.1 is a Class B address, and that 167.204 identifies the network, while 7.1 uniquely identifies the host. So, if two hosts on the same network were configured with the IP addresses 167.204.7.1 and 167.204.99.2 respectively, they would be able to communicate using TCP/IP.

You may have noticed that the number “127” appears to be missing from the table above. It is, and this is on purpose. IP addresses starting with 127 are reserved for a special diagnostic function on a TCP/IP network, and are known as “loopback” addresses. When you ping the address 127.0.0.1, you are effectively pinging the same machine from which the command is issued. If you receive a reply, it means that TCP/IP is functioning on that computer. However, it still doesn’t mean that your configuration settings are correct.

Getting to Know TCP/IP

The truth be told, both NWLink and NetBEUI are easier to configure than TCP/IP. Just because they’re easier to get up and running, that doesn’t make them better. Since TCP/IP is the protocol used on the Internet, it best to take the time to properly configure your home network to use TCP/IP rather than the other two. In fact, for almost all home or small networks, you’re almost better offer pretending that TCP/IP is the only protocol that exists.

One of the reasons that users have commonly avoided TCP/IP back when home networks first came on the scene was that it takes a little more understanding to install and configure correctly. Instead of just “turning it on”, you need to configure systems with settings like IP addresses, subnet masks, default gateways, and DNS server settings. While it is possible to make your computers acquire or generate this information automatically, those methods can involve additional configuration or be subject to limitations. The main focus of this article is to help you understand how TCP/IP works, and how to manually configure the correct settings for your network. The “automatic” stuff will all be looked at later in the series, once you understand how to make it all work manually.

Network Protocols

Much like people, computers need to be speaking a common language to communicate. If you were speaking Spanish and we only spoke English, we would certainly hear each you talking, but we wouldn’t really understand what you were saying. In the same way, computers need to
be running a common “protocol” in order to share information. A protocol is essentially like a language, a formal set of communication standards that network devices follow in order to exchange information. A variety of network protocols exist, but four are far more common than others – TCP/IP, IPX/SPX, NetBEUI, and AppleTalk.

The Transmission Control Protocol/Internet Protocol is actually a suite of different protocols that make communications between systems possible. As the “protocol of the Internet”, TCP/IP has become the defacto standard for networks worldwide. Where companies previously ran a whole slew of different protocols on their networks, almost all have now moved to TCP/IP only, or are moving in that direction. On your home network, TCP/IP is almost certainly the only protocol you’ll ever need to run, with very few exceptions.

The other three protocols mentioned all have (or at least had) their time and place. IPX/SPX is a protocol that was developed by Novell for use on NetWare networks – in other words, for networks that included NetWare servers. Even NetWare uses TCP/IP as its standard protocol today, so the chances of you needing to install it are very slim indeed. NetBEUI (NetBios Extended User Interface) is a very simple protocol that was used extensively on networks until the early 90s, mainly because it was easy to configure – simply install it, and two computers will chat away. Unfortunately, NetBEUI is limited to local networks, and won’t get you onto the Internet. Given that most home networks are implemented to share Internet access, NetBEUI is unlikely to be in your future either. Finally, AppleTalk was a protocol developed by Apple for use on their Macintosh systems. Although a solid protocol in it’s own right, Macs now run TCP/IP, and even Apple (the company) runs TCP/IP on their internal network.

At the end of the day, the message should be clear – 99.9% of the time, the only protocol that home networkers will need is TCP/IP. In future articles, this subject will be looked at in much more detail.

Configuring Your Home Networking Router’s DHCP Settings

Almost all home routers will have their built-in DHCP server feature turned on by default. When enabled, the DHCP component will allocate IP addresses and related options (subnet mask, default gateway) to client systems configured to obtain their IP addresses automatically.

Although the DHCP component simplifies the allocation of IP addresses, you should disable the feature if you plan on configuring client TCP/IP settings manually. In fact, some advanced router features cannot function with DHCP enabled. Furthermore, most routers are configured to allocate up to 50 or more IP addresses to clients as necessary. If you plan to continue using the DHCP feature, consider changing the range of available addresses to a number that matches the number of client systems on your network for security purposes.

Logging In To Your Home Networking Router

In the most typical setup, your hardware router will be located somewhere between your PC and your broadband modem. Most users now opt for router models that include an integrated 4-port switch, but others may have devices (the router and their PCs) connected to a separate hub or switch. By default, most hardware routers will ship with a preconfigured IP address like 192.168.1.1 (check the guide that came with yours) and will be set up to allocate IP addresses to client systems automatically via DHCP.

Because of the default setup, you’ll need your PC’s network card configured correctly in order to connect to the router’s administrative interface. In most cases, accessing your network card’s TCP/IP properties and setting it to obtain an IP address automatically will suffice. You can check and see what IP address you were allocated by issuing the ipconfig /all command. If you’re address comes up as starting with “169.254”, your system isn’t receiving an address from the router, so try the ipconfig /renew command. If you’re still out of luck, press the reset button on your router to restore it to its factory default settings, and then try again.

If your system can ping the router’s address, you’re in luck. To access its administrative interface, fire up your browser and enter the device’s IP address, for example http://192.168.1.1. You will generally be prompted to log on, so you’ll need to check your user manual for the appropriate username and password for your model. If you can’t find your manual, visit www.phenoelit.de/dpl/dpl.html. This site lists the default username and password combinations for virtually all home networking routers.