The Illustrated Network- P16:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices.:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been. | CHAPTER 4 IPv4 and IPv6 Addressing 119 IPv4 address space. Class E addresses are experimental and some of them have been used for that purpose but they are seldom seen today. In practice only the Class D addresses are still used on the Internet in a classful manner. Class D addresses are the IPv4 multicast addresses to and we ll talk about those as needed. We will nonetheless talk about classful IPv4 addressing in this book especially later on in this chapter when subnetting is considered and when mentioning the routing protocol RIPvl. However the significance of classful IPv4 addressing is strictly historical. Classful addressing comes up occasionally and at least some introduction is necessary. This chapter and this book emphasizes classless IP addresses the current way of interpreting the 32-bit IPv4 address space. This scheme assumes that no classes exist and is how routers on the Internet interpret IPv4 addresses. In classless addressing the IPv4 network mask or prefix determines the boundary between the network and host portion of the IP address instead of the initial IP address bits. On a host it is still often called a network mask because hosts don t care about classful or classless but it is called a prefix on a router. Hosts really don t deal with the differences between classful and classless IP addresses. Routers on the other hand must. Because this book deals with networks as a whole including routers some understanding of both classful and classless IPv4 addressing is beneficial. Dotted Decimal IPv4 addresses are most often written in dotted decimal notation. In this format each 8-bit byte in the 32-bit IPv4 address is converted from binary or hexadecimal to a decimal number between 0 0000 0000 or 0x00 and 255 1111 1111 or 0xFF . The numbers are then written as four decimal numbers with dots between them . For example 1010 1100 0001 0000 1100 1000 0000 0010 0xAC 10 C8 02 becomes . And 1011 1111 1111 1111 .
