Network/Port Address Translation

We will now talk about Network and Port Address Translation(also known as NAT and PAT respectively). NAT is the process of modifying(or translating) an IP address information in an IP packet header when it is travels through a traffic routing device such as a router.

"An example of NAT diagram"

This is how a NAT translation simply works. Imagine I am uploading a file to a server through the Internet from my own private network. My IP address and other relevant information such as MAC address will be stored in the packet header. However, when my packet pass through the router to access the server outside of my network, the IP address information in the packet header changes! Because as a private network user, my computer IP address is considered to be 'unregistered'. When the packet is sent to the router and directed to the my network ISP, it will map my 'unregistered' address to a registered address which is publicly known to the Internet world. There are 3 types of NAT translation. Static NAT, Dynamic NAT and Nat Overloading(also known as PAT). What I have shown in the example can be considered as an example of static NAT translation.

Static NAT

In static NAT, an unregistered IP address is mapped to a registered IP address so that it can be accessed by people outside the network.

Dynamic NAT

In this type of NAT translation, instead of mapping just one registered IP address to an unregistered address, a pool of IP addresses will be available for mapping to the unregistered address.

PAT(or also known as NAT overloading)

This type of NAT translation is used when addresses from the inside network overlaps with IP addresses that are registered on another network in the outside network. To solve the overlapping issues, the router must maintain a table containing overlapping addresses so that it could intercept the packets and replace the overlapping addresses in the header with acceptable and uniquely registered addresses.