Diagnosing a Broken Router-on-a-Stick

Bundle lab · $29.99

Advanced CCNA troubleshooting lab on a router-on-a-stick design. VLAN 10 users can reach their gateway and other hosts, but VLAN 20 users cannot reach their gateway or any resources in VLAN 10. Methodically trace L2/L3 intent end-to-end - from the access ports through the trunks up to the router subinterfaces - to isolate the first-hop failure and implement fixes that restore inter-VLAN routing while maintaining enterprise trunk hardening and clean configurations.

Learning objectives

• Correlate endpoint symptoms to L2/L3 design intent in a router-on-a-stick topology
• Identify and correct a dot1Q tag mismatch on a router subinterface
• Identify and correct a trunk allowed VLAN list that omits a required VLAN
• Verify inter-VLAN reachability using Linux hosts and IOS show commands
• Develop a systematic troubleshooting flow from endpoint failure back to infrastructure

Troubleshooting focus

• 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.