How are IP Addresses assigned?

As we mentioned earlier, IP addresses are assigned by the IANA, network administrators, ISPs, or yourself. What we didn’t mention is that there are different ways of assigning IP addresses.

Static IP addresses

A static IP address is a number that is permanently assigned to a certain computer and does not change. Once a computer has been assigned its IP address, it will keep it indefinitely. The advantage of a static IP is that the computer will always have the same IP address on the network and will be easy to identify in the future once its IP address is known. The disadvantage is that the party that assigns the IP has to do this manually and keep good track of them to make sure that it does not get assigned to another computer as well by accident. You will find static IP addresses used by some cable modem providers, in small company networks, and of course on the Internet where every site has its own unique permanent IP address until it is removed or moved to another web server and assigned a new IP.

Dynamic IP addresses

A dynamic IP address is a number that is assigned to different computers at different times. This means that every time a computer is connected to a network, it is assigned a random IP address from a pool of IP addresses depending on whatever IP is available and is not currently in use. For example if your company network uses dynamic IP addresses, it means that when you start your computer and it wants to log into the network, it will get a new IP address. Or every time you connect to the Internet using a dial-up connection through your modem to your ISP, the ISP will assign an available IP address to your computer for the time of your online session. When you disconnect your computer from your ISP and connect again the next time, you’ll be assigned a different IP address depending on what IP’s are available at that time.

This is done with a technology called Dynamic Host Configuration (DHCP). The server for the network has a number of IP’s available to assign to hosts on the network and distributes them to computers as needed as they connect to the network.

The advantage of dynamic IP’s is that the server automatically keeps track of them and makes sure that each computer has a unique address. There is no need to keep track of them manually. Another advantage is that it allows computers to move between subnets and always have a valid IP without manual reconfiguration. A lease time can be assigned to a dynamic IP for automatic expiration to disconnect a computer from the network after a certain time.

To find out whether your computer has a dynamic or static IP, go to Start/Settings/Control Panel and double-click the Network icon. In the resulting window, make sure the Configuration tab is selected and double-click the TCP/IP protocol entry to see the TCP/IP Properties. Select the IP address tab. If “Obtain an IP address automatically” is selected, you’re set up with a dynamic IP. If “Specify an IP address is selected” then you’ll see your IP address displayed in the field below and it means you have a static IP address.


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