Network address translation (NAT) is a method of remapping one IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device(wiki).
In simple word, translating IP address to another IP is called NAT. Imagine that, we have one static IP address and we want to use this IP for diffenet services in local network. For example:
FTP : 192.168.20.100
HTTP : 192.168.20. 101
Static IP: 18.104.22.168
How we can use this static IP address for different services?
NAT. By using NAT, you can map static IP address to different services, like below:
22.214.171.124: 21 –> 192.168.20.100
126.96.36.199: 80 –> 192.168.20.101
188.8.131.52: 443 –> 192.168.20.102
We can simple write in router to map IP 192.168.20.100 to 184.108.40.206 on port 21:
If we have bunch of static IP address, we can define pool and access-list and pass it to NAT:
“overload” simply translate all ports in static IP address to inside local address.