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Fundamentals of Data Communication Networks by Oliver C. Ibe

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Chapter 6Network Layer Part I – IP Addressing

6.1 Introduction

The purpose of this chapter is to discuss IP addressing, which is one of the network layer services. The specific topics to be discussed include the following:

  • IP addresses
  • IPv4
  • IP network subnetting
  • IP quality of service (IP QoS)
  • Address resolution protocol (ARP)
  • Dealing with IPv4 address shortage
  • IPv6.

Recall that the network layer is concerned with addressing and routing. The Internet layer is the top part of the network layer. The Internet protocol, which is defined for this layer, is a simple connectionless datagram protocol that provides no error recovery and no delivery guarantee. In this section, we consider the addressing aspect of the layer.

6.2 IP Address

The current version of IP is IP version 4 (IPv4). The IPv4 header has the format shown in Figure 6.1.

Illustration of IPv4 Header Structure.

Figure 6.1 IPv4 Header Structure.

The length of IPv4 header is variable, and the fields are measured in terms of 32-bit words. The shortest IPv4 header is 20 bytes, and IP header length (IHL) would be 5 since 20 × 8/32 = 5. The fields are defined as follows:

  • Version: (4 bits) indicates the IP version number, which is 4
  • IHL (IP Header Length): (4 bits) indicates the number of 32-bit words that form the packet header
  • DSCP (Differentiated Services Code Point): (6 bits) used to define the quality of service (QoS) for different network applications ...

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