cisco交换机端口从errdisable状态恢复

故障描述

经用户反馈，一台cisco2960x接入交换机的一个端口插网线不通，ip电话也没有poe供电。

排查过程

查看交换机端口状态，发现变成了errdisable：

ZH_HQN_SW2960X_04#show int g1/0/14
GigabitEthernet1/0/14 is down, line protocol is down (err-disabled)

从官方文档找到恢复的方法：

errdisable recovery cause all

接下来就可以查看errdisable的详细信息了：

ZH_HQN_SW2960X_04#show errdisable recovery
ErrDisable Reason            Timer Status
-----------------            --------------
arp-inspection               Enabled
bpduguard                    Enabled
channel-misconfig (STP)      Enabled
dhcp-rate-limit              Enabled
dtp-flap                     Enabled
gbic-invalid                 Enabled
inline-power                 Enabled
link-flap                    Enabled
mac-limit                    Enabled
loopback                     Enabled
pagp-flap                    Enabled
port-mode-failure            Enabled
pppoe-ia-rate-limit          Enabled
psecure-violation            Enabled
security-violation           Enabled
sfp-config-mismatch          Enabled
small-frame                  Enabled
storm-control                Enabled
udld                         Enabled
vmps                         Enabled
psp                          Enabled
dual-active-recovery         Disabled
evc-lite input mapping fa    Disabled
Recovery command: "clear     Disabled

Timer interval: 300 seconds

Interfaces that will be enabled at the next timeout:

Interface       Errdisable reason       Time left(sec)
---------       -----------------       --------------
Gi1/0/14                loopback          293

可以看到，所有的errdisable恢复类别都被激活，并且底部显示了处于errdisable状态的端口，报错的原因，以及还剩多久自动恢复(time left)。

继续查找报错原因loopback，官方给的解释如下：

Loopback error：A loopback error occurs when the keepalive packet is looped back to the port
that sent the keepalive. The switch sends keepalives out all the interfaces by default. A device
can loop the packets back to the source interface, which usually occurs because there is a
logical loop in the network that the spanning tree has not blocked. The source interface
receives the keepalive packet that it sent out, and the switch disables the interface
(errdisable).

意思是交换机默认会从所有端口发出keepalive报文，如果发出keepalive的源端口接收到自己发送的keepalive报文，那么交换机就会认为产生了环路(这个环路没有被生成树阻塞)。

交换机会把这个端口设置为errdisable状态。

确认端口恢复后，记得关闭errdisable recovery恢复功能：

no errdisable recovery cause all