Napt (Network Address And Port Translation) Or Pat (Port Address Translation) - Asus iPBX30 User Manual

Chapter 9
9.2.1 NAPT (Network Address and Port Translation)
or PAT (Port Address Translation)
Also called IP Masquerading, this feature maps many internal
hosts to one globally valid Internet address. The mapping contains
a pool of network ports to be used for translation. Every packet
is translated with the globally valid Internet address and the port
number is translated with an un-used port from the pool of network
ports. The figure below shows that all the hosts on the local network
gain access to the Internet by mapping to only one globally valid
IP address and different port numbers from a free pool of network
ports.
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iPBX30 User Manual