Network / Port Address Translation

Network Address Translation (NAT) is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device. 

The advantage of NAT are:

NAT allows you to incrementally increase or decrease the number of registered IP addresses without changing devices (hosts, switches, routers, and so on) in the network.

Static translations are manually configured to translate a single local IP address to a
single global IP address, and vice versa. This translation always exists in the NAT table
until it is manually removed.

NAT can be configured to allow the basic load sharing of packets among multiple servers
using the TCP load distribution feature. TCP load distribution uses a single virtual global
IP address, which is mapped to multiple real local IP addresses.

Port Address Translation (PAT) is an extension to network address translation (NAT) that permits multiple devices on a local area network (LAN) to be mapped to a single public IP address. The goal of PAT is to conserve IP addresses..

The advantage of PAT are:

PAT allows many internal hosts to share a single external IP address.

Users who do not require support for inbound connections do not consume public IP addresses.