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CCIE Security Exam Certification Guide by Henry Benjamin

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Network Address Translation and Port Address Translation

NAT is a router function, which allows it to translate the addresses of hosts behind a firewall. This also helps to overcome IP address shortage. It also provides security by hiding the entire network and their real IP addresses.

NAT is typically used for internal IP networks that have unregistered (not globally unique) IP addresses. NAT translates these unregistered addresses into legal addresses on the outside (public) network.

PAT provides additional address expansion but is less flexible than NAT. With PAT, one IP address can be used for up to 64,000 hosts by mapping several IP port numbers to one IP address. PAT is secure because the inside hosts' source IP addresses are hidden from ...

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