Network Address Translation (NAT) is a way of reassigning one address space to another by changing the network address information in IP (Internet Protocol). That is, the packet headers change while they are in transit through the traffic routing device. This method was originally used to easily redirect traffic on IP networks without renumbering each host. It has become a popular and important tool for maintaining and distributing global address space in the face of a lack of IPv4 addresses.
What is NAT?
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Port Address Translation (PAT)
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PAT (Port AddressTranslation) resolves conflicts that can arise between two different hosts using the same source port number to establish unique connections at the same time.