Cisco IOS Network Address Translation (NAT) and
Port Address Translation (PAT) are mechanisms for conserving registered IPv4 addresses
in large networks and simplifying IPv4 address management tasks. NAT and PAT translate
IPv4 addresses within private internal networks to legal IPv4 addresses for transport over
public external networks, such as the Internet, without requiring a registered subnet
address. Incoming traf?¬?c is translated back for delivery within the inside network.
250 Chapter 7: Managing Address Spaces with NAT and IPv6
This translation of IPv4 addresses eliminates the need for host renumbering and allows
the same IPv4 address range to be used in multiple intranets. This section describes the
features that are offered by NAT and PAT and shows you how to con?¬?gure NAT and PAT
on Cisco routers.
Introducing NAT and PAT
NAT operates on a Cisco router and is designed for IPv4 address simpli?¬?cation and
conservation. NAT enables private IPv4 internetworks that use nonregistered IPv4
addresses to connect to the Internet. Usually, NAT connects two networks and translates the
private (inside local) addresses in the internal network into public addresses (inside global)
before packets are forwarded to another network.
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