I’ve started going through a free course offered by Stanford

https://lagunita.stanford.edu/courses/Engineering/Networking-SP

Seems pretty good.  A difficulty I’m having is that I’m familiar-ish enough to get bored sometimes but not so familiar that there aren’t a lot of jewels i didn’t have down.

So,, I’ve gotten through the first section and here is a summary of some of the choicest bits:

network ports are part of TCP. Guess I didn’t know that.

Home routers are doing NAT (Network address translation). To the outside world you have an IP address and a port that maps to internal IP and ports in your internal network. The router stores a table .

There is a rhyme and reason to the assignments of IP, both logical and geographical. Routing happens by sort of a wild card matching inside an internal table inside the router. It finds the best match according to the highest level of the address.

ARP lets ethernet or find out IPs for devices on the local physical link.