"I'm still a fan of TCP/IP illustrated (book 1) [1] for understanding the fundamentals."
Agreed.
I find it difficult to gratuitously study a broad topic and instead prefer to learn by building and doing.
However, that book was one of the most readable, well paced and well presented books and it really did give me a good broad understanding that I rely on even now, 25 years later.
Even if you think a book just about TCP/IP is pigeonholing you and you'd like a broader picture of "computer networking" I would still start with this - the design decisions and solutions described can be applied very broadly.
A good example of this is the discussion of exponential backoff algorithms ... that's useful everywhere.