Practical TCP/IP: Designing, Using, and Troubleshooting TCP/IP Networks on Linux and Windows

I'd recommend Kurose's Computer Networking: A Top Down Approach (now in 8th edition) book if you want to learn a proper computer networks concepts because this is the definitive textbook. If you want the practical aspects of computer networks, you can try Niall Manfields' Practical TCP/IP designing, using and troubleshooting TCP/IP networks on Linux and Windows book. Granted it's a bit old (2nd edition is essentially the same 1st edition), but because you are after the essentials it should be more than fine. Here's the review of the book: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=122... (https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1220683)