The Internet Protocol Journal - Volume 7, Number 3

From The Editor

Network Address Translators (NATs) were designed to allow multiple devices in a private address realm to dynamically share a single public IP address. NATs are widely deployed in today's Internet. They provide an effective way of IPv4 address conservation while simultaneously offering some level of security because individual IP addresses on the "inside" are hidden from the "outside," or global Internet. But NATs also present a challenge to existing Internet applications that may depend on globally unique IP addressing for proper operation. To further complicate matters, not all NATs are created equal, leading to unpredictable behavior. This edition of IPJ is almost entirely devoted to an indepth look at NATs. Geoff Huston looks inside the NAT, and explains the complexities behind each variation of NAT implementation. It seemed only natural that he would name such an exposé "Anatomy."

Many IPJ subscriptions had an official expiration date of September 30, 2004, but I am pleased to report that all these subscriptions have been extended for another year. You should still make sure your delivery address and e-mail is up-to-date in our database by sending e-mail to with your updated information.

If you're hungry for even more networking-related reading material, look at the Internet Society's publication page at Here you will find The ISP Column, Member Briefings, Articles of Interest, and links to other material.

We didn't have room for a book review in this issue, but we have several in store for future editions. If you'd like to contribute a book reviewfor publication in IPJ, please contact me.

—Ole J. Jacobsen, Editor and Publisher