几天前，使用一台cisco 2950交换机和tp-link 24口的100mb端口的交换机级联。导致cisco 2950设备上的级联端口在使用一天后，第二天早上上班时发现端口显示err-disabled.网络不通。如何处理？
查看接口状况：
GX-SW-2950-01#sh interfaces f0/2
FastEthernet0/2 is down, line protocol is down (err-disabled)
Hardware is Fast Ethernet, address is 0011.bb48.d4c2 (bia 0011.bb48.d4c2)
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 254/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Auto-duplex, Auto-speed, media type is 100BaseTX
input flow-control is unsupported output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 12:08:35, output 12:08:35, 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
7828496 packets input, 3836732423 bytes, 0 no buffer
Received 153627 broadcasts (0 multicast)
0 runts, 0 giants, 0 throttles
2 input errors, 1 CRC, 1 frame, 0 overrun, 0 ignored
0 watchdog, 89124 multicast, 0 pause input
0 input packets with dribble condition detected
7809493 packets output, 2721732114 bytes, 0 underruns
0 output errors, 0 collisions, 2 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
只有2 input errors, 1 CRC, 1 frame,2 interface resets。按道理不足以导致接口进入err-disabled状态。
没有办法，只能配置err-disabled。启用recovery功能。命令如下：
GX-SW-2950-01(config)#errdisable recovery interval 30
GX-SW-2950-01(config)#errdisable recovery cause all
经过几天测试，可以正常使用。可惜的事情，没有搞清楚为何进入err-disabled状态。原因有很多种可能。但不知道是哪个。下面是cisco默认提供的几种可能原因：
GX-SW-2950-01#show errdisable detect
ErrDisable Reason Detection status
----------------- ----------------
udld Enabled
bpduguard Enabled
security-violatio Enabled
channel-misconfig Enabled
psecure-violation Enabled
dhcp-rate-limit Enabled
unicast-flood Enabled
vmps Enabled
pagp-flap Enabled
dtp-flap Enabled
link-flap Enabled
gbic-invalid Enabled
loopback Enabled
dhcp-rate-limit Enabled
unicast-flood Enabled
其实可以单独测试每一条。以找出真正的原因，但有15种可能。想想还是算了。