Match each Layer 2 switching diagnostic symptom or log output on the left with its primary underlying root cause on the right.
- Switch console continuously outputs `%CDP-4-NATIVE_VLAN_MISMATCH` log messages while untagged control traffic is dropped across the interconnect link.The interconnected trunk interfaces are configured with mismatched native VLAN ID settings.
- Interface counter metrics display a rapidly incrementing count of late collisions and frame check sequence (FCS) errors on a 100 Mbps Ethernet link.One interface is manually set to full-duplex while the connecting interface falls back to half-duplex via failed auto-negotiation.
- Hosts on VLAN 20 cannot communicate across the switch interconnect, and running `show interfaces trunk` reveals VLAN 20 is missing from the active allowed list.An explicit trunk interface allowed VLAN list filter configuration excludes VLAN 20 from traversing the link.
- The switching domain experiences persistent MAC address table instability and periodic frame unicast flooding driven by continuous topology change notifications (TCNs).An unstable or conflicting Spanning Tree Protocol (STP) priority assignment triggers perpetual root bridge elections.
Cevap
1. CDP native VLAN mismatch logs match mismatched native VLAN ID settings across trunk interfaces. 2. Incrementing late collisions and FCS errors match a duplex mismatch between full-duplex and half-duplex auto-negotiation. 3. Absence of VLAN 20 from allowed VLAN output matches explicit trunk allowed list filter exclusion. 4. Persistent MAC table instability and TCN flooding match an unstable Spanning Tree Protocol priority triggering perpetual root bridge elections.
Each diagnostic indicator corresponds to a standard Layer 2 troubleshooting signature: native VLAN mismatches produce CDP console errors; duplex mismatches trigger late collisions and FCS frame drops; missing allowed VLAN entries prune trunk traffic; and STP root bridge priority conflicts cause continuous topology changes and MAC table instability.
Adım Adım Çözüm
Anahtar Kavram
Layer 2 Switching, Trunking, Duplex, and STP Troubleshooting