In college we used the Kurose textbook: https://www.amazon.com/Computer-Networking-Top-Down-Approach...

It explains just about every networking concept in grueling detail. However I don't remember anything I learned in that class, and now as a working developer don't have the time to work through a 900 page textbook.

These Youtube playlists covered the important networking parts. Search Wikipedia for the topics you don't understand.

1) Stanford Networking: https://www.youtube.com/playlist?list=PLx_Dnlrnkd6f3mtJgmoBk...

2) New Boston: https://www.youtube.com/playlist?list=PL6gx4Cwl9DGBpuvPW0aHa...

3) Gate Lectures by Ravindrababu Ravula: https://www.youtube.com/playlist?list=PLEbnTDJUr_IegfoqO4iPn...