Note: This insert used when I need to clarify or explain something that I feel you need to know, but which is either not directly related to the topic under discussion, or is sufficiently “tangential” that it needs to be separated from the main text to avoid disrupting its flow. Examples include terminology explanations, “sidebar” historical discussions, anecdotes, and clarifications relating to how I am describing particular concepts.

Key Concept: I tried very hard in crafting this Guide to provide a variety of ways to present information, to better suit the learning styles of different readers. To that end, I have created hundreds of these inserts, which summarize and highlight the most important concepts and essential pieces of knowledge in The TCP/IP Guide. They can be very useful for quickly distilling the essence of a topic without reading an entire explanation, or for refreshing your memory of a topic you have already read. Obviously, however, they contain few details, so you should not assume that you fully understand a topic or concept just by reading this sort of summary.

Background Information: When you see this insert near the front of a section or a particular description, it indicates that I am recommending that you read another part of the Guide before proceeding with that section. While I have attempted to make each section able to stand alone to a certain degree, some just make more sense if read in a particular order (usually the order in which the sections are listed within their parent section).

Related Information: This insert mentions another section or topic within The TCP/IP Guide that contains information related to the section where the insert is located, but which is not background material. It may help you understand the content you are reading, or put it into better context.

On The Web: This insert is used when I need to link to a relevant document or resource on the World Wide Web. The insert contains a brief description of the linked item and its URL, highlighted in blue italics.