Stage 2 · Lesson 3 of 8
Trunks, 802.1Q and the native VLAN
When must cross between , one link carries all of them as a . The 802.1Q standard inserts a small tag with the VLAN number into each frame, so the far switch knows where it belongs. Frames in the native VLAN cross the trunk untagged.
Set trunks explicitly with switchport mode trunk, list the allowed VLANs so only the needed ones cross, and set the native VLAN to an unused one on both ends. Trunks also connect switches to , to wireless access points and to virtualisation hosts. Check with trunk, which lists what is allowed and actually forwarding.
Common trapa native VLAN mismatch between the two ends: traffic quietly leaks from one VLAN into another, and the only clue is a log message.
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Resources for this stage
Start with· follow one of these
- VideoFreeJeremy's IT Lab: CCNA 200-301 Complete Course
Jeremy's IT Lab · Beginner
The VLAN, spanning tree and EtherChannel days, each with a Packet Tracer lab to do straight after
- PlatformFreeCisco Networking Academy
Cisco · Beginner
The switching and VLAN modules of the CCNA courses, if your university or institute runs them