802.1Q Trunk Fundamentals: Static Trunk and VLANs

Bundle lab · $29.99

Build a static 802.1Q trunk between two Layer-2 switches to carry VLANs 10 and 20. Map hosts to access ports, verify trunk encapsulation and allowed VLANs, demonstrate same-VLAN reachability across the trunk, and confirm inter-VLAN isolation. Then simulate an allow-list drift fault, diagnose with show commands, and restore service.

Learning objectives

• Create VLANs and assign correct access ports on Layer-2 switches.
• Configure a static 802.1Q trunk that explicitly forces 802.1Q tagging, hardens the native VLAN, and restricts the allowed VLAN list precisely.
• Verify trunks and transported VLANs using show interfaces trunk and show vlan brief.
• Validate same-VLAN reachability across the trunk and confirm isolation between different VLANs.
• Diagnose and fix trunk allow-list drift and native VLAN mismatches.

Troubleshooting focus

• Trunk forms but does not carry a required VLAN due to an incomplete allowed list.
• Native VLAN mismatch detected; traffic may be misclassified/untagged inconsistently.
• Endpoint plugged into an access port assigned to the wrong VLAN.
• Trunk left dependent on DTP negotiation instead of forced static trunking, so it may not form deterministically on both ends.
• VLAN missing from the local VLAN database on one switch.