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This chapter covers the following topics that you need to master as a CCNP:

Characteristics of NAT--This section covers Network Address Translation (NAT),
which is a tool that enables administrators to use the RFC 1918 private address space
for internal network numbering.

Simple NAT translation--In this section, you learn that a simple NAT translation
replaces the outbound or inbound destination address with another address.

Overloading--Overloading the address space is used with Internet connectivity.
Overloading NAT translates or replaces not only the IP address, but also the port
number in the TCP header. In this fashion, a single IP address can be used again and
again. The port number is used to map the translation, and the address space is thus
conserved. This method has become a very common method for Internet connectivity.

Overlapping networks--This section covers how overlapping networks using the
same IP addresses can be connected by doing a double translation of address space on
a single router.

TCP load distribution--NAT is also capable of doing a simple TCP load
distribution. NAT does this by advertising a single IP address and translating it to a
pool of addresses when the IP address is the inbound destination. In this fashion,
multiple hosts can be advertised as a single IP address.

NAT definitions--This section covers the four NAT address classes: Inside Local,
Inside Global, Outside Local, and Outside Global. All are used throughout the
discussion and should be well understood by the successful CCNP candidate.

NAT configurations--This section explores the four configurations of NAT: simple,
overload, overlap, and TCP load distribution.

Verfication of NAT translation--The administrator must verify the translations that
occur using NAT. For this purpose, the show ip nat translation command is available.

Port address translation--This section covers port address translation (PAT), which
is a form of NAT that translates the port address as well as the network layer address.