Middleboxes: NATs
In this lesson, we'll study Network Address Translation!
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 ...