A network technician is investigating several common Layer 2 switching and trunking issues on a campus network. Match each observed diagnostic symptom or console log message on the left with its corresponding underlying root cause on the right.
- Console logs repeatedly display: %CDP-4-NATIVE_VLAN_MISMATCH discovered on interface GigabitEthernet0/1.The untagged VLAN configured on one end of the 802.1Q trunk does not match the untagged VLAN on the opposite end.
- Interface statistics show an increasing count of late collisions and alignment errors on a full-duplex link.One end of the Ethernet connection is operating in half-duplex mode while the connected device operates in full-duplex mode.
- An unexpected switch becomes the STP Root Bridge following a power outage due to default priority settings.All switches share the default Spanning Tree Protocol priority of 32768, causing election based solely on the lowest MAC address.
- A workstation cannot reach its default gateway after being plugged into a newly provisioned switch port.The access port is assigned to the default VLAN (VLAN 1) instead of the target operational VLAN.
Answer
CDP Native VLAN mismatch log maps to mismatched untagged VLAN IDs across trunk ends; Late collisions and alignment errors map to a duplex mismatch between connected interfaces; Unintended STP root bridge election maps to default STP priority tie-breaking via MAC address; Workstation gateway unreachability maps to incorrect switch port VLAN assignment.
Each symptom directly corresponds to a fundamental Layer 2 switching error: CDP Native VLAN logs indicate mismatched untagged trunk VLANs; late collision counters indicate a duplex negotiation mismatch; default STP priority causes root elections based on MAC address; and lack of gateway access on a new port typically indicates incorrect access VLAN assignment.
Step-by-Step Solution
Key Concept
Troubleshooting VLAN, Trunking, and Switching Issues