关于cisco交换机端口自己down的解决办法

关于cisco交换机端口自己down的解决办法 公司一个楼层交换机cisco2960的F0/21端口自己down了，一片怨声载道，人生鼎沸， 妈了个B的。 通过命令:sh int f0/21 看到如下结果: cisco12#sh int f0/21 FastEthernet0/21 is down, line protocol is down (err-disabled) Hardware is Fast Ethernet, address is 0024.1351.2e95 (bia 0024.1351.2e95) MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Auto-duplex, Auto-speed, media type is 10/100BaseTX input flow-control is off, output flow-control is unsupported ARP type: ARPA, ARP Timeout 04:00:00 Last input 19:29:25, output 19:29:20, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 130997686 packets input, 111565127662 bytes, 0 no buffer Received 3733082 broadcasts (0 multicasts) 0 runts, 0 giants, 0 throttles 38 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 watchdog, 3191174 multicast, 0 pause input 0 input packets with dribble condition detected 121355446 packets output, 78684231708 bytes, 0 underruns 0 output errors, 0 collisions, 1 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier, 0 PAUSE output 0 output buffer failures, 0 output buffers swapped out 通过红色部分了解端口处于故障状态，然后通过命令sh logging看看日志，结果如下: cisco12#sh logging Syslog logging: enabled (0 messages dropped, 1 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled) Console logging: level debugging, 219 messages logged, xml disabled, filtering disabled Monitor logging: level debugging, 0 messages logged, xml disabled, filtering disabled Buffer logging: level debugging, 219 messages logged, xml disabled, filtering disabled Exception Logging: size (4096 bytes) Count and timestamp logging messages: disabled File logging: disabled Trap logging: level informational, 222 message lines logged Log Buffer (4096 bytes): hernet0/5, changed state to down 7w5d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 7w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 7w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 7w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 7w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 7w5d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 7w5d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 7w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 7w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 7w5d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 7w6d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 7w6d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 7w6d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 7w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 8w1d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 8w1d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 8w1d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 8w1d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 8w1d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 8w1d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 8w4d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 8w4d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 8w4d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 8w4d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 8w5d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 8w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 9w1d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 9w1d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 9w3d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 9w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 9w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down 9w3d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down 9w4d: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up 9w4d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up 9w5d: %ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on FastEthernet0/21. 9w5d: %PM-4-ERR_DISABLE: loopback error detected on Fa0/21, putting Fa0/21 in err-disable state 9w5d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/21, changed state to down 9w5d: %LINK-3-UPDOWN: Interface FastEthernet0/21, changed state to down 9w6d: %LINK-3-UPDOWN: Interface FastEthernet0/19, changed state to up 9w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/19, changed state to up 9w6d: %SYS-5-CONFIG_I: Configured from console by vty0 (192.168.200.254) 9w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/19, changed state to down 9w6d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/19, changed state to up 红色部分知道了网络有loopback error detected，日吧。 找到问题了，解决吧。进入config模式下通过命令:errdisable recovery cause loopback， 心急了用show errdisable recovery命令看看还有多少秒完成，日，修复个错误还要几分 钟。 至此，完成。我发誓再出现loopback error，我一定断他们的网，谁说都没用。