VLANs and 802.1Q Trunking: Access Ports, Trunks, and the Native-VLAN Footgun
Networking from Scratch (lesson 16) — how the 4-byte 802.1Q tag splits one switch into many logical networks, what access and trunk ports actually do, why the native VLAN bites people, voice-VLAN multiplexing, why DTP is usually disabled, and the verification commands that make switch CLI output debuggable.