So basically ive been configuring a ton of site-to-site VPN's previously, but i have never got the theory behind it 100% straight.. Youtube is filled with videos on how to configure a site-to-site connection, that is obviously no issue but i'm looking for a video or text that describes the different phases and possibilities.. Like what is Phase 1 and Phase 2, and what kind of encryptions and algorithm are available and why exactly do we prefer to use one over another? All the configuration videoes out there basically just tells you to use this and this because its the best, it never compares the different possibilites and goes further in depth.
Does anyone know a video or tutorial on this without having to read or view additional 3 hours footage of stuff i already know before getting to the point?