At the end of almost every chapter in this book, we include lists of
resources that give further detail on relevant topics. The references
are usually either URLs or book references. Unfortunately, URLs tend
to change or disappear over time, so if you read this book some time
after it has been published and some of the URLs
aren't valid anymore, try to use a search engine
such as Google to find the updated link. If you still
can't find the listed resource, try to look it up in
the Internet archive: https://www.archive.org/.
Many chapters refer to the Request For Comments documents (RFCs),
which are mirrored by hundreds of Internet sites all around the world
and are easy to find. A good starting point is https://www.rfc-editor.org/.
