NAT and PAT

Network and Port Address Translation

Before beginning these notes, you need to have a full understanding of IPv4 Addressing, CIDR and VLSM and you need to know what a router is.

The version of IP we use most commonly is called IPv4; there is an IPv6, let’s not worry about that for now. IP addresses are allocated by the Internet Assigned Numbers Authority (IANA) and the world has run out of IPv4 addresses.

The standards body which regulates the technical side of the Internet is called the Internet Engineering Task Force or IETF. The standards by which the Internet is regulated are called Request for Comment or RFCs. These standards are open and easily accessed through any web browser/search engine.

A kludge was developed to mitigate the problem, this is called Network Address Translation or NAT. In this document, we will explain the basis of NAT in a simplified way. NAT can be immensely complicated and confusing and there are many similar permutations to implement it.