2.5 Fixing a host address, and two special addresses
In this part you will look at some nuts-and-bolts ideas that can be useful when setting up networks or diagnosing problems.
The ‘fixing a host address’ part of the title refers to the assigning of a fixed IP address to a networked device (or host, as it is often called). As you will see in a later session, IP addresses are generally assigned to networked devices automatically through a process called Dynamic Host Configuration Protocol (DHCP), and can change. Sometimes, though, you need a host’s IP address to be fixed. The first section of the video looks at how this can be done to a Microsoft Windows computer.
The remainder of the video looks at two classes of ‘special’ IP address. These addresses have diagnostic use, and are not used as normal IP addresses.
Now watch the video below, which is about 5 minutes long.
Now try to answer the questions below.
Activity 5 Test yourself
1. One of the main reasons to give a computer a fixed IP address is to enable it to communicate directly with another device that has a fixed IP address (for example, a printer). Via a direct connection, you can change the device’s IP address or other settings. The direct connection would typically be a length of Ethernet cable between the two devices.
Suppose you are given a printer that has a fixed IP address of 192.168.2.25 and a subnet mask of 255.255.255.0. Your network uses addresses that begin with 192.168.1 and has the same subnet mask. How do you enable the printer to work on your own network, given that you cannot find a way of doing a factory reset on the printer?
Give the Ethernet port of your own computer a fixed IP address that is compatible with the printer’s current address, for example 192.168.2.30. Join the computer to the printer with an Ethernet cable. Use the computer to change the settings of the printer to something compatible with your own network (or to receive IP addresses automatically), and connect the printer to your network. Restore your computer’s Ethernet port to receive IP addresses automatically.
2. A friend rings you to say that their computer is not receiving emails and cannot browse the web. You ask your friend to enter ipconfig at the computer’s command prompt to see whether it has an IP address. Your friend reports that the computer has an IP address, and says, ‘So that cannot be the problem’. Why should you ask what the IP address is?
If the automatic allocation of IP addresses has failed, then the computer might have allocated itself a link-local address, which begins with 169.254. This is not a usable address.
3. As a result of 2 above, your friend says, ‘The problem must either be the computer or the network’. What test do you suggest?
Ask your friend to ping 127.0.0.1 (or any other loopback address) at the command prompt and see whether there is a reply. If there is a response, then it suggests – but doesn’t prove – that the computer is all right.