VLANs: One Switch, Many Networks
7:38Coming soon
An office floor: forty computers, one switch, one network. Every broadcast reaches all forty, and the visitor's laptop in the lobby sits on the same network as the finance server. You could buy a second switch. Or you could do what every office does: build walls inside the one you already have. That is a VLAN. This lesson shows what the walls do, what the tags on a trunk are for, and how traffic gets from one VLAN to another.
You'll learn
- What a VLAN is: one switch divided into separate Layer 2 networks, each its own broadcast domain and its own subnet
- Why a switch never forwards a frame from one VLAN to another, and why the MAC address table has a VLAN column
- Access ports and trunk ports: one VLAN and no tags, or many VLANs and a tag on every frame
- 802.1Q tagging: the four-byte tag that goes on at one end of a trunk and comes off at the other
- The default VLAN and the native VLAN, and what a native VLAN mismatch does
- Inter-VLAN routing: router on a stick, and the Layer 3 switch that replaces it on a busy floor
- Three reasons to use VLANs: security, smaller broadcast domains, and moving a host without moving a cable
- The voice VLAN
- The real thing: show vlan brief, show interfaces trunk, the MAC address table, and ipconfig on the host
- Exam corner: two VLANs on one switch and a host that cannot reach the server
Chapters
- 0:00Forty houses, one street
- 0:48Walls inside the switch-depot
- 1:19One room's bells: the broadcast
- 1:50The corridor between two depots: tags
- 2:33Access and trunk, and the native room
- 3:03Crossing rooms: through the gate
- 3:50Router on a stick, and the Layer 3 switch
- 4:12Three reasons the walls are worth it
- 5:02The real names
- 5:53The real thing: show vlan brief
- 6:32Exam corner
- 6:56Recap and next time
Exam objectives: CompTIA Network+ N10-009: 2.2 (VLANs, native VLAN, voice VLAN, 802.1Q tagging), 2.1 (subinterfaces: router on a stick), 5.3 (incorrect VLAN assignment), 5.5 (show vlan, show mac-address-table, ipconfig).
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