Home Network IP Address Guide

Every device attached to your home network has an IP address, but what is a IP address and why is it needed?

First image 4 computers linked together on a network. Now if computer A want to send data to computer D . How does computer D know that the data is intended for computer D and not for computers B or C?

The answer is that each computer has an address. To be accurate the computer has two addresses, one known as the MAC or physical address which is actually the address of the network card and cannot be changed. The other address is the IP address or network address which can be changed.

The IP address is the important address as far as we are concerned as it is a logical address meaning it is assigned by us, and can be changed. It is this address that is used, not only for getting data between two computers on your home network, but also between your computer and any other computer in the world.

The IP address appears like this:

192.168.0.1

The address has four components each component is separated by a dot(.). So it is of this form:

a.b.c.d

Where the value of a,b,c or d is 0-255 decimal. Now as far as we are concerned, all you need to remember when assigning these addresses to a computer, is that,
each computer has a unique address.

Assigning Computer Addresses

So if we had our network of 4 computers then we would give each an address like this:

 

Computer	IP address
computer A	192.168.0.1
computer B	192.168.0.2
computer C	192.168.0.3
computer D	192.168.0.4

If we have look at this address assignment on a Windows machine then this is what we see:

 

The first thing you should notice is that there are several other entries besides the IP address.

The only one that is absolutely necessary is the subnet mask.

Getting into the nitty gritty of sub-netting is a course on its own, but as far as we are concerned all we need to do is to make sure that each computer has the same sub-net address; in this case 255.255.255.0.

 So our computer address assignment table would now look like this:

Computer	IP address	Subnet Mask
computer A	192.168.0.1	255.255.255.0
computer B	192.168.0.2	255.255.255.0
computer C	192.168.0.3	255.255.255.0
computer D	192.168.0.4	255.255.255.0

Default Gateway

You may also notice that the default gateway address is undefined. So what is the default Gateway?

The default gateway is the way out of your network to the Internet. It is in effect the address of the router box that connects you to the Internet. So if we assume our router has an address of 192.168.0.100 then our address table now looks like this:

Computer	IP address	Subnet Mask	Default Gateway
computer A	192.168.0.1	255.255.255.0	192.168.0.100
computer B	192.168.0.2	255.255.255.0	192.168.0.100
computer C	192.168.0.3	255.255.255.0	192.168.0.100
computer D	192.168.0.4	255.255.255.0	192.168.0.100

Notice how the default Gateway address and the subnet mask are the same for each of our computers and only the IP address is different. If you aren’t connected to the Internet thenthere is no need for a default Gateway entry.

Checking the Configuration

On a windows machine open a command line and type ipconfig and the following is displayed

Here the default gateway is 192.168.1.1. This is the IP address of the Router.

Problems With Manual Address Assignments

Manually assigning addresses as described above is seldom done because of how easy it is to make mistakes. It is also not useful for people with laptops who move from an office network to a home network and vice versa.

Even though it is not normally done you should be aware of how to do it.

Automatic Address Assignments

If you examine the TCP/IP properties dialogue box above you will see and option radio box “obtain an IP address automatically”. This is normally enabled along with the option “obtain DNS server address automatically“.

By enabling both of these the computer picks up its IP address, subnet mask, default gateway address and DNS server address automatically from a DHCP server.

A DHCP (dynamic host configuration Protocol) server is an integral part of the NAT router used to connect to the Internet and requires no configuration on your part.

If you are configured for automatic address assignments and you experience networking problems then you can check that you have been assigned a IP address etc by opening a command line and typing ipconfig .

If no IP address has been assigned then the IP address will be either:

0.0.0.0 or 169.254.x.y

The 169.254.x.y address range was introduced in windows 2000 and allows windows XP machines to automatically allocated themselves IP addresses in the absence of a DHCP server.

What it usually means is that the local computers can communicate with each other but not the Internet.