raft Manuscript Draft Ma VLSM and CIDR cript Draft Manuscript Dra Manuscript Draft Manuscri raft Manuscript Draft Ma uscript Draft Manuscript raft Manuscript Draft Ma script Draft Manuscript D ft Manuscript Draft Manu ript Draft Manuscript Dra Manuscript Draft Manuscri t Draft Manuscript Draft M nuscript Draft Manuscript
CHAPTER 6

Objectives
■

Upon completion of this chapter, you should be able to answer the following questions: What are the differences between classful and classless IP addressing? What is VLSM, and what are the benefits of classless IP addressing?
■

■

What is the role of the classless interdomain routing (CIDR) standard in making efficient use of scarce IPv4 addresses?

Key Terms

This chapter uses the following key terms. You can find the definitions in the Glossary at the end of the book. classful IP addressing page 280 prefix aggregation page 285 network prefix page 286 contiguous page 294

discontiguous address assignment page 280 supernet page 280

private addressing page 281 high-order bits page 282

supernetting page 294

This is a prepublication draft of the manuscript. The final book will publish in December and will be available for purchase at http://www.ciscopress.com/title/9781587132063.

raft Manuscript Draft Ma cript Draft Manuscript Dra Manuscript Draft Manuscri raft Manuscript Draft Ma uscript Draft Manuscript raft Manuscript Draft Ma script Draft Manuscript D ft Manuscript Draft Manu ript Draft Manuscript Dra Manuscript Draft Manuscri t Draft Manuscript Draft M nuscript Draft Manuscript
280 Routing Protocols and Concepts, CCNA Exploration Companion Guide

Prior to 1981, IP addresses used only the first 8 bits to specify the network portion of the address, limiting the Internet—then known as ARPANET—to 256 networks. Early on, it became obvious that this was not going to be enough address space.

In