Middleboxes: NATs
Learn how Network Address Translation (NAT) functions as a middlebox connecting private and public IPv4 address spaces. Understand NAT's role in broadband and enterprise networks, how it translates IP addresses for outgoing and incoming traffic, and its impact on network transparency and connection initiation. This lesson helps you grasp NAT's advantages and its limitations affecting end-to-end communication.
Introduction
Network Address Translation (NAT) was proposed as a short term solution to deal with the expected shortage of IPv4 addresses in the late 1980s to early 1990s. Combined with CIDR, NAT helped to significantly slow down the consumption of IPv4 addresses. A NAT is a middlebox that interconnects two networks that are using IPv4 addresses from different addressing spaces. Usually, one of these addressing spaces is the public Internet while the other is using a private IPv4 address. Unlike a router, when a NAT box forwards traffic, it modifies the IP addresses in the IP header, as will be described shortly.
Broadband Access Routers
A very common deployment of NAT is in broadband access routers as shown in the figure below. The broadband access router interconnects a home network, either WiFi ...