Network protocol stuff on Wikipedia has been top notch and my go-to since at least 2010. It really is highly underrated for that. I had to implement a layer 7 protocol on top of UDP back in the day, and it required a lot of understanding/fiddling with UDP and IP packet details to get it working right, and even required some router config (IP fragmentation became a huge problem, gotta love protocols designed by committee D-:)