THE CCNP EXAM TOPICS COVERED IN THIS
CHAPTER INCLUDE THE FOLLOWING:
Describe the process of Network Address Translation (NAT).
Configure Network Address Translation (NAT).
Troubleshoot nonfunctional remote access systems.
As the Internet grows and individuals increasingly need more than
one IP address to use for Internet access from their home and
office PCs, their phones (Voice over IP, VOIP), their office’s network
printers, and many other network devices, the number of available IP addresses is diminishing.
To add insult to injury, the early designers of TCP/IP—back when the Internet project
was being created by the Advanced Research Projects Agency (ARPA)—never anticipated the
explosion of users from private industry that has occurred.
ARPA’s goal was to design a protocol that could connect all the United States Defense
Department’s major data systems and enable them to talk to one another. The ARPA designers
created not only a protocol that would enable all the Defense Department’s data systems to
communicate with one another, but one that the entire world now relies on to communicate
over the Internet.
Unfortunately, because of the unexpected popularity of this protocol, the distribution of IP
addresses was inadequately planned. As a result, many IP addresses are unusable, and many are
placed in networks that will never use all the addresses assigned to them. For example, every
organization with a Class A network, which provides 16,777,214 addresses per Class A assignment,
would find it difficult to use more than half of the addresses available, and those that are
not used are wasted.
All the Class A and Class B addresses are already assigned to organizations. There are 65,534
Class B addresses available in each Class B address range. If a new organization needs more than
one Class C address range, which provides only 254 addresses, they must get another Class C
address range.
IP version 6 will eventually alleviate IP addressing problems because it increases the address
space from 32 bits to 128 bits, but its adoption has been slow because of the problems associated
with infrastructure and application support. Outside the United States, IPv6 is being paid
more attention because less IPv4 address space is available. Specifically, Japan has implemented
a large-scale IPv6 network because of the number of addresses needed and the availability of
IPv6 address space.
This chapter introduces you to Network Address Translation (NAT) and Port Address
Translation (PAT). Cisco routers and internal route processors use these two protocols to allow
the use of a limited number of registered IP addresses by a large number of users and devices.
As you progress through the chapter, you will learn the differences between NAT and PAT, as
well as their operational boundaries, how to configure them, and how to troubleshoot problems
associated with these two protocols.