You might be thinking: "But, what's the concept guide supposed to be?"
This concept guide is a quick reference for default parameters and differences between the core protocols and commands tested on ICND2. It covers things such as the difference between IPv4 and IPv6 versions of some of the routing protocols, side-by-side comparisons of the different VTP types, and similar concepts to these.
The reason why it's so important to understand some of these differences and comparisons in reference to the test is that Cisco has a noted history of loving to test examgoers' knowledge of minute differences in the tested protocols. As such, it's really handy to give this concept guide a quick review prior to going in to sit for the test as it can help with the small handful of questions Cisco will use to break down your understanding of why to use a given protocol in a certain situation and forego using another.