Lucas, Networking for System Administrators (2nd ed.) ch. 1 — the four layers, encapsulation, what changes at each hop, and troubleshooting commands by layer.
Updated Ch. 1
Networking for Sysadmins
Each tab is a module or chapter — the broken-down cheat sheet for this resource.
Lucas, Networking for System Administrators (2nd ed.) ch. 2 — interfaces, autonegotiation, MTU and DF ping, ARP and NDP, VLAN terms and datalink error counters.
Updated Ch. 2
Networking for Sysadmins ch. 3 — IPv4 addressing, subnets/netmasks, viewing config on Windows/Debian/FreeBSD, private addressing/NAT, and troubleshooting.
Updated Ch. 3