The ABCs of IP

IP addresses are unique sets of numbers assigned to devices that connect to a network. These sets of numbers are used to send and receive information on the network and to find other devices. An IP address is very much like a home address that others use to send you mail and for you to send mail from—it's a unique identifier of your location.


Find the Address
IP addresses are represented as a set of dotted decimal numbers. Go ahead and click on the Start button. In the "Search" or "Run" field type in CMD. At the command prompt (which is the C:\> (there may be extra words after the first >. Type after the last >B.) Type in ipconfig /all.





Is that the address other networks use to find my laptop on the Internet? No. That is an IP address that is given to me by my ISP. You can find that IP address by going into your router's interface and checking the WAN (Wide Area Network) IP address or by accessing the interface of your cable, DSL, or FIOS modem. You typically don't need to know or deal with the WAN IP address unless you are doing tasks like hosting your own web or email server, and we will save those details for a future article.

In contrast, my address is my LAN (Local Area Network) IP address. It is used for internal networking purposes, meaning it is the way my laptop is identified and forwards and receives traffic between all of the devices connected on my home network.

ABC (and D and E)
IP addresses are broken into different classes.

Class A IP addresses are used for huge networks, like those deployed by Internet Service Providers (ISPs). Class A IP addresses support up to 16 million hosts (hosts are devices that connect to a network (computers, servers, switches, routers, printers…etc.) and a Class A network can be divided into 128 different networks.

Class B IP addresses are used for medium and large-sized networks in enterprises and organizations. They support up to 65,000 hosts on 16,000 individual networks.


Class D and E addresses are least used. Class D is reserved for a not widely used, and reserved for special cases largely for services and applications to stream audio and video to many subscribers at once. Class E addresses are reserved for research purposes by those responsible for Internet networking and IP address research, management, and development.





Beyond the Basics
