CCNA CHAPTER 6 - HAL 173

Addressing is a key function of network layer protocols. Addressing enables data communi-cation between hosts on the same network or on different networks. Internet Protocol ver-sion 4 (IPv4) provides hierarchical addressing for packets that carry your data.

Designing, implementing, and managing an effective IPv4 addressing plan ensures that net-works can operate effectively and efficiently. This chapter examines in detail the structure of IPv4 addresses and their application to the construction and testing of IP networks and subnetworks.

IPv4 Addresses

For communication to take place between hosts, the appropriate addresses must be applied to these devices. Managing the addressing of the devices and understanding the IPv4 address structure and its representation are essential.

Anatomy of an IPv4 Address

Each device on a network must be uniquely defined by a network layer address. At this layer, the packets of the communication are also identified with the source and destination addresses of the two end systems. With IPv4, each packet uses a 32-bit source address and a 32-bit destination address in the Layer 3 header.

These addresses are represented in the data network as binary patterns. Inside the devices, digital logic is applied for the interpretation of these addresses. For the human network, a string of 32 bits is difficult to interpret and even more difficult to remember. For this reason, IPv4 addresses are represented using dotted decimal format.

Dotted Decimal

IPv4 addresses are easier to remember, write, and verbally communicate than strings of 32 bits. Representing IPv4 addresses as dotted decimals begins by separating the 32 bits of the address into bytes. Each byte of the binary pattern, called an octet, is separated with a dot. The bytes are called an octet, because each of the decimal numbers represents 1 byte, or 8 bits.

For example, the following address:

10101100000100000000010000010100

is expressed in dotted decimal as

172.16.4.20

Keep in mind that devices use binary logic. The dotted decimal format makes it easier for people to use and remember addresses.