Network Layer and IP Adresses

The Network layer, or OSI Layer 3, provides services to exchange the individual pieces of data over the network between identified end devices. To accomplish this end-to-end transport, Layer 3 uses four basic processes:
• Addressing
• Encapsulation
• Routing
• Decapsulation
Addressing is a key function of Network layer protocols that enables data communication between hosts on the same network or on different networks. Internet Protocol version 4 (IPv4) provides hierarchical addressing for packets that carry our data.
Designing, implementing and managing an effective IPv4 addressing plan ensures that our networks 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.
Learning Objectives
Upon completion of this chapter, you will be able to:
• Identify the role of the Network layer as it describes communication from one end device to another end device.
• Examine the most common Network layer protocol, Internet Protocol (IP), and its features for providing connectionless and best-effort service.
• Understand the principles used to guide the division, or grouping, of devices into networks.
• Understand the hierarchical addressing of devices and how this allows communication between networks.
• Understand the fundamentals of routes, next-hop addresses, and packet forwarding to a destination network.
Each device on a network must be uniquely defined. At the Network layer, the packets of the communication need to be identified with the source and destination addresses of the two end systems. With IPv4, this means that each packet has a 32-bit source address and a 32-bit destination address in the Layer 3 header.
These addresses are used in the data network as binary patterns. Inside the devices, digital logic is applied for their interpretation. For us in the human network, a string of 32 bits is difficult to interpret and even more difficult to remember. Therefore, we represent IPv4 addresses using dotted decimal format.