I refer to drafts often throughout this book. Drafts always have version numbers in their names, and this number often increases frequently during the process. So let us have a closer look at the draft process:
During the standardization process, the drafts are published on the Internet. Drafts may eventually become RFCs. At the IETF web site at http://www.ietf.org, click on Internet Drafts to find all documents. To use the search engine and find the most updated status of any document, refer to https://datatracker.ietf.org/public/pidtracker.cgi. You can also click on "IETF Working Group" to find all groups sorted by areas (application, operation, routing, security, etc). Within the groups, you find all relevant RFCs and drafts. This is the best place to find out what is in the queue and what groups are working on. The goal of this process is to make a specification under development accessible to a large audience in order to get reviews and comments. Another good link to get an overview of RFCs and active drafts with regard to specific working groups is http://tools.ietf.org.
So let us understand the draft version numbers. As you have noted, it can change frequently. When you enter a draft name in the search engine, it will always show you the latest version. The rules for draft numbers are as follows:
Every time a draft is updated, it receives a new version number. At some point, a draft may be published as an RFC and then be removed from the draft directory. A draft with a specific version number has a lifetime of 6 months at a maximum. After this, if it has not been updated or become an RFC, it is removed from the draft directory. As this book is going to be on the market for some time, some drafts mentioned in here might not be active when you try to find them. They may have been removed or published as RFCs.
Drafts are not standards and should not be implemented in commercial products, because they are going to change for sure in the case they ever become an RFC. This can also lead to incompatibility issues, such as when vendors implement drafts at different maturity levels of development or if one implementation is based on draft and another on RFC. In practice, you will find draft implementations in commercial products, but now you know to be careful when using them.