For BGP there’s [1] which is quite new and I wanted to check out, haven’t had the time yet. There are some older guides e.g. by Cisco as well.

I think in general more of the documentation and information is in blog posts and RFCs, so I’d start there, e.g. [2] is quite nice.

1: BGP (Border Gateway Protocol): from theory to practice - https://amzn.eu/d/i6EUYGj

2: https://labs.ripe.net/author/samir_jafferali/build-your-own-...