I finished 'An Introduction to Computer Networks', Peter L Dordal. A bit more than I probably needed to know about metrics for routing traffic in ISP's and so forth, but interesting. I took some networking classes a while back, and little has changed fundamentally.
On one of the potential big changes: 'conversion [to IPv6] has been slow. Many ISPs still provide limited (to nonexistent) support, and inexpensive IPv6 firewalls to replace the ubiquitous consumer-grade NAT routers are just beginning to appear. Time will tell how all this evolves. However, while IPv6 has now been around for twenty years, top-level IPv4 address blocks disappeared much more recently. It is quite possible that this will prove to be just the catalyst IPv6 needs.'