Understanding Internet Protocol

This chapter discusses how to enable computers on the LAN or the Internet to communicate through Layer 3 IP addressing. Internet Protocol version 4 or IPv4 is the most frequently used communications protocol. IP resides on the Network layer of the OSI model, and IP addresses consist of four numbers, each between 0 and 255. The protocol suite is built into most operating systems and is used by most Internet connections in the United States and many other countries. As mentioned in Lesson 1, it is composed of a network portion and a host portion, which are defined by the subnet mask. For an IP address to function there must be a properly configured IP address and compatible subnet mask. To connect to the Internet, you also need a gateway address and DNS server address. Advanced examples of IP configurations include sub‐netting, NAT, and CIDR. To better understand IPv4 addresses, they have been categorized as five IP classes. Some have been reserved for private use, whereas the rest are utilized by public connections. This classification system helps to define what networks can be used on the LAN and what IP addresses can be used on the Internet. IPv4 addresses are further classified as either public or private. Public IP addresses are ones that are exposed to the Internet; any other computers on the Internet can potentially communicate with them. Private IP addresses are hidden from the Internet and any other networks. They are usually behind an IP proxy or firewall device.