Today, network address translators, or NATs, are everywhere. Their ubiquitous adoption was not promoted by design or planning but by the continued growth of the Internet, which places an ever-increasing demand not only on IP address space but also on other functional requirements that network address translation is perceived to facilitate. This article presents a personal perspective on the history of NATs, their pros and cons in a retrospective light, and the lessons we can learn from the NAT experience. A Retrospective View of Network Address Translation Authorized licensed use limited to: IEEE Xplore. Downloaded on February 9, 2009 at 17:52 from IEEE Xplore. Restrictions apply.