Scaling to Three VLANs: Adding a Department

Bundle lab · $29.99

Extend a working two-VLAN router-on-a-stick design to a third VLAN (Guest) without breaking Sales and Engineering. Add one router subinterface, one switch VLAN + access port, and update the switch trunk’s allowed-VLAN list safely using 'add' so existing VLANs remain transported.

Learning objectives

• Extend an existing router-on-a-stick configuration to support an additional VLAN
• Create VLANs on a Layer-2 switch and place host access ports into the correct VLANs
• Safely extend an 802.1Q trunk's allowed-VLAN list by appending the new VLAN rather than replacing the entire list
• Validate end-to-end inter-VLAN connectivity from hosts and with IOS show commands
• Recognize and correct common change-related faults: missing VLAN, trunk allow-list omissions

Troubleshooting focus

• Diagnose and resolve the introduced fault: Trunk allow-lists, native VLAN alignment, and host VLAN assignment.
• Verify every link's interface status and IP addressing (`show ip interface brief`) and correct any interface that is down or misaddressed.
• Confirm each device's running configuration matches the lab objective, and bring any interface, route, or service that is not in its expected state back to health.
• Trace end-to-end reachability with ping/traceroute and isolate the first hop where forwarding fails.