Foundation Topics

This chapter covers the details of NAT using three major sections. The first section explains the challenges to the IPv4 address space caused by the Internet revolution of the 1990s. The second section explains the basic concept behind NAT, how several variations of NAT work, and how the Port Address Translation (PAT) option conserves the IPv4 address space. The final section shows how to configure NAT from the Cisco IOS Software command-line interface (CLI), and how to troubleshoot NAT.

For those of you following the optional reading plan for which you move back and forth between this book and CCENT/CCNA ICND1 640-822 Official Cert Guide, note that Chapter 23 of that book also covers NAT and PAT, with the configuration performed from the Security Device Manager (SDM). This chapter necessarily covers some of the same underlying concepts, but with a much fuller description of the concepts and configuration.