I'm also seconding this, but from microcontroller perspective.
I want to try developing a simple tcp echo server for a microcontroller, but most examples just use the vendor's own tcp library and put no effort explaining how to manually setup and establish connection to the router.
Because implementing TCP not just as a toy is incredibly difficult with tripwires that even subject matter experts struggle to get it right without decades of in field testing.
There lots on networking in general, but I've had a hard time finding some on Linux specific implementation