Chapter 1 introduced you to the various layers of the TCP/IP model. The CCNA  exam is almost entirely about the Internet and the Network Access layer. So this chapter will cover one of the most important subjects of networking – IP Addresses. As you already know, each host in the network has a logical address called the IP address. This address helps in routing packets from source to destination across internetworks. This chapter delves deep into IP addresses, subnet mask, subnetting and Variable Length Subnet Mask (VLSM). Finally this chapter looks at some troubleshooting techniques that are used to solve IP address related problems. The two current versions of IP addresses in use today are IPv4 and IPv6. This chapter focuses on IPv4. IPv6 is discussed in Chapter 12.