What Are IP Addresses in Home Networking? - dummies

What Are IP Addresses in Home Networking?

By Lawrence C. Miller

Every device on a home network must be uniquely identified with an IP (Internet Protocol) address. An IP address consists of four sets of numbers from 0 to 255, separated by a decimal, such as:

Although the numbers in an IP address may appear random, there is a method to the madness. Each of the four numbers that comprise an IP address is known as an octet because it consists of 8 bits. With 8 bits, there are 256 possible combinations from 0 to 255.

IP addresses are assigned to organizations by the Internet Assigned Numbers Authority (IANA). That’s right, organizations. So how do you, an individual, get your very own IP address? Your Internet service provider (ISP) can lease a permanent IP address to you, but that isn’t really necessary, unless you’re running your own Web or e-mail server on your home network.

More often, your ISP dynamically assigns an IP address to you from a pool of addresses that IANA has assigned to your ISP. If your high-speed Internet connection is more or less always connected, you essentially get a permanent IP address anyway.

Of course, there’s no guarantee that you’ll always get that same IP address (for example, if your router is reset or your ISP has a timeout set on your connection you may get a different IP address assigned), so if you’re running your own Web or e-mail server, you’ll need to get a permanent IP address from your ISP and manually configure it on your server.

Your ISP will give you only one IP address, and that one address is assigned to your modem or router. You still need to assign a unique IP address to each of your network devices. Fortunately, IANA reserves three ranges of IP addresses for private use: to to to

These IP addresses are never routed over the Internet, so you can use them on your home network as you see fit. But IP addressing can get very complicated very fast, so it’s best to keep your IP numbering scheme as simple as possible.

The easiest way to do this is to make the first three groups (or octets) of numbers in your IP address the same, and focus only on the last group. In the last group, start numbering the routers, computers, and other devices on your network from 1 to 254. For example, if you have a variety of devices on your network, you might assign them IP addresses.


Because private IP addresses cannot be routed over the Internet, your router or firewall must translate your private IP addresses to a public IP address (or IP addresses), which can be sent over the Internet. This is known as Network Address Translation (NAT) or Port Address Translation (PAT).

NAT translates a private IP address (such as to a public IP address (such as PAT translates a range of private IP addresses (such as to to a single public IP address. Most home routers and firewalls sold today are preconfigured to perform NAT, or you can easily enable it, usually through a check box option or setup wizard depending on your router or firewall model.

Although NAT and PAT are distinctly different, the overall function (that is, translating IP addresses) is the same. Many router and firewall vendors do not distinguish between NAT and PAT in the user interface and simply refer to the address translation function as NAT.