交换机端口呈现err-disable的原因

导致交换机端口呈现err-disable状态的原因有很多，为方便大家查询，特归纳如下：

1. duplex mismatch (A is correct)

2. port-channel misconfiguration

3. Bridge Protocol Data Unit (BPDU) Guard violation

4. UniDirectional Link Detection (UDLD) condition (B is correct)

5. late-collision detection

6. link-flap detection

7. security violation

8. Port Aggregation Protocol (PAgP) flap

9. Layer 2 Tunneling Protocol (L2TP) Guard

10. DHCP snooping rate-limiting

11. EtherChannel guard detects a misconfigured EtherChannel