How badly will IPv6 break your application? What do you need to consider to make your application “IPv6-ready”? What questions should you ask?

In the ideal world, your application should “just work” on IPv6, just as it does on IPv4. However, in the real world, application issues crop up. These could be as simple as having a user interface field that only allows the input of dotted-decimal IPv4 addresses, or something more fundamental, such as an application binding exclusively to an IPv4 transport interface.

While there have been many books published about IPv6, including O’Reilly’s own IPv6 Essentials and IPv6 Network Administration, almost all existing books focus on understanding the protocol itself and using it at a network layer. They contain much discussion about using network-level tools and even about creating applications that interact directly with the network. However, the concerns related to IPv6 at the upper application layers are mentioned only briefly, if at all. The Internet Engineering Task Force (IETF) has published RFC 4038, which addresses many of these concerns, but the concerns have not found their way out into mainstream books.

This short book is designed to help you understand what you need to think about to be sure that your app will work as well with IPv6 as it does with IPv4. This book is not so much about all the solutions but rather about the questions you need to be asking.

For IPv6 to truly be adopted on a large scale, ultimately the applications running on our desktop systems, laptops, and mobile devices all need to play nice with IPv6. That is the end goal of this book—to help enable individuals, companies, and organizations to migrate their apps to IPv6 so that they can transition their networks into IPv6 networks.

Given that now, in 2011, many companies are just starting to pay attention to IPv6, and given that many apps are just now moving to IPv6, this book will continue to evolve to address issues identified as more applications make the move. I’d love to receive any feedback you have on issues you encounter in migrating your apps to IPv6—and I expect that you’ll see updates to this book come out over time.