交换机端口err-disable、配置速率和双工模式

实例：

和客户IDC机房拉了一条MSTP线路，接入到Cisco 3750x后端口灯不亮，更换了端口也是不亮，查看端口信息发现因为客户端有环路导致我们接口出现err-disable错误。
故障现象：
线路不通，物理指示灯不亮，有的会显示为橙色(不同平台指示灯状态不同)
解决思路：
取消环路，将端口重启
排错过程：
1、查看接口状态
GigabitEthernet1/0/8 is down, line protocol is down (err-disabled)

C3750X-5F-I02-2-252#SHOw INTERfaces GIgabitEthernet 1/0/8
GigabitEthernet1/0/8 is down, line protocol is down (err-disabled)
Hardware is Gigabit Ethernet, address is 00af.1fe0.63d0 (bia 00af.1fe0.63d0)
Description: "HTZQ Network"
Internet address is 165.16.241.174/30
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 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 16:07:19, output 16:07:19, 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
42 packets input, 10117 bytes, 0 no buffer
Received 33 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 19 multicast, 0 pause input
0 input packets with dribble condition detected
77 packets output, 21350 bytes, 0 underruns
0 output errors, 0 collisions, 9 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
C3750X-5F-I02-2-252#SHOw INTERfaces GIgabitEthernet 1/0/8 STATUS

Port      Name               Status       Vlan       Duplex  Speed Type
Gi1/0/8   "HTZQ Network"     err-disabled routed       auto   auto 10/100/1000BaseTX
C3750X-5F-I02-2-252#

2、查看导致接口err-disable的原因

C3750X-5F-I02-2-252#show interfaces status err-disabled

Port      Name               Status       Reason               Err-disabled Vlans
Gi1/0/8   "HTZQ Network"     err-disabled loopback
Gi1/0/9                      err-disabled loopback
Gi1/0/10                     err-disabled loopback
Gi1/0/20                     err-disabled loopback
C3750X-5F-I02-2-252#

从图中可以看出导致接口err-disable的原因是loopback，因为期间我更换过接口，因为环路导致了所有更换过的接口都是err-disable
看到哪些原因会导致接口处于err-disable

C3750X-5F-I02-2-252#show errdisable detect
ErrDisable Reason            Detection    Mode
-----------------            ---------    ----
arp-inspection               Enabled      port
bpduguard                    Enabled      port
channel-misconfig (STP)      Enabled      port
community-limit              Enabled      port
dhcp-rate-limit              Enabled      port
dtp-flap                     Enabled      port
gbic-invalid                 Enabled      port
inline-power                 Enabled      port
invalid-policy               Enabled      port
l2ptguard                    Enabled      port
link-flap                    Enabled      port
loopback                     Enabled      port
lsgroup                      Enabled      port
mac-limit                    Enabled      port
pagp-flap                    Enabled      port
port-mode-failure            Enabled      port
pppoe-ia-rate-limit          Enabled      port
psecure-violation            Enabled      port/vlan
security-violation           Enabled      port
sfp-config-mismatch          Enabled      port
small-frame                  Enabled      port
storm-control                Enabled      port
udld                         Enabled      port
vmps                         Enabled      port
C3750X-5F-I02-2-252#

从列表中，我们可以看出常见的原因有udld，bpduguard，link-flap以及loopback等。 具体由什么原因导致当前接口err-disable可以由show interface status err-disable来查看。

3、恢复

在接口模式下采用shutdown，no shutdown进行手动的激活即可恢复，前提是环路要接触，不然接口会再次被置于err-disable。

在缺省配置下，一旦接口被置为err-disable，IOS将不会试图恢复接口。 这个可以由show errdisable recovery来查看，timer status下面所有的值都是disable。

C3750X-5F-I02-2-252#show errdisable recovery
ErrDisable Reason            Timer Status
-----------------            --------------
arp-inspection               Disabled
bpduguard                    Disabled
channel-misconfig (STP)      Disabled
dhcp-rate-limit              Disabled
dtp-flap                     Disabled
gbic-invalid                 Disabled
inline-power                 Disabled
l2ptguard                    Disabled
link-flap                    Disabled
mac-limit                    Disabled
loopback                     Disabled
pagp-flap                    Disabled
port-mode-failure            Disabled
pppoe-ia-rate-limit          Disabled
psecure-violation            Disabled
security-violation           Disabled
sfp-config-mismatch          Disabled
small-frame                  Disabled
storm-control                Disabled
udld                         Disabled
vmps                         Disabled

Timer interval: 300 seconds

Interfaces that will be enabled at the next timeout:

C3750X-5F-I02-2-252#

配置IOS自动重新激活errdisable的接口

C3750X-5F-I02-2-252(config)#errdisable recovery cause ?
all                      Enable timer to recover from all error causes
arp-inspection           Enable timer to recover from arp inspection error disable state
bpduguard                Enable timer to recover from BPDU Guard error
channel-misconfig (STP)  Enable timer to recover from channel misconfig error
dhcp-rate-limit          Enable timer to recover from dhcp-rate-limit error
dtp-flap                 Enable timer to recover from dtp-flap error
gbic-invalid             Enable timer to recover from invalid GBIC error
inline-power             Enable timer to recover from inline-power error
l2ptguard                Enable timer to recover from l2protocol-tunnel error
link-flap                Enable timer to recover from link-flap error
loopback                 Enable timer to recover from loopback error
mac-limit                Enable timer to recover from mac limit disable state
pagp-flap                Enable timer to recover from pagp-flap error
port-mode-failure        Enable timer to recover from port mode change failure
pppoe-ia-rate-limit      Enable timer to recover from PPPoE IA rate-limit error
psecure-violation        Enable timer to recover from psecure violation error
security-violation       Enable timer to recover from 802.1x violation error
sfp-config-mismatch      Enable timer to recover from SFP config mismatch error
small-frame              Enable timer to recover from small frame error
storm-control            Enable timer to recover from storm-control error
udld                     Enable timer to recover from udld error
vmps                     Enable timer to recover from vmps shutdown error

C3750X-5F-I02-2-252(config)#errdisable recovery cause loopback

可以指定什么情况下导致接口err-disable后自动激活，也可以选择所有导致接口err-disable后自动接口。
配置完上述命令后，IOS在一段时间后试图恢复被置为err-disable的接口，这段时间缺省为300秒，这个时间通过show errdisable recovery的Timer interval: 300 seconds值。
调整err-disable的超时时间，可以使用以下命令：

C3750X-5F-I02-2-252(config)#errdisable recovery interval ?
<30-86400>  timer-interval(sec)

C3750X-5F-I02-2-252(config)#errdisable recovery interval 600

可以调整在30－86400秒，缺省是300秒

查看所有接口的状态

C3750X-5F-I02-2-252#show interfaces status

Port      Name               Status       Vlan       Duplex  Speed Type
Gi1/0/1   "AA Network"  connected    routed     a-half  a-100 10/100/1000BaseTX
Gi1/0/2   "BB Network   connected    routed     a-full  a-100 10/100/1000BaseTX
Gi1/0/3   "CC Network"  connected    routed     a-half  a-100 10/100/1000BaseTX
Gi1/0/4   "DD Network"  connected    routed     a-half  a-100 10/100/1000BaseTX
Gi1/0/5   "EE Network"  connected    routed     a-half  a-100 10/100/1000BaseTX
Gi1/0/6   "FF Network"  connected    routed     a-half  a-100 10/100/1000BaseTX
Gi1/0/7   "GG Network   connected    routed     a-half  a-100 10/100/1000BaseTX
Gi1/0/8   "HH Network"  connected    routed     a-full  a-100 10/100/1000BaseTX
Gi1/0/9                      err-disabled 1            auto   auto 10/100/1000BaseTX
Gi1/0/10                     err-disabled 1            auto   auto 10/100/1000BaseTX
Gi1/0/11                     notconnect   515          auto   auto 10/100/1000BaseTX
Gi1/0/12                     connected    515        a-full a-1000 10/100/1000BaseTX
Gi1/0/13                     connected    514        a-full  a-100 10/100/1000BaseTX
Gi1/0/14                     connected    514        a-full  a-100 10/100/1000BaseTX
Gi1/0/15                     notconnect   513          auto   auto 10/100/1000BaseTX
Gi1/0/16                     notconnect   513          auto   auto 10/100/1000BaseTX
Gi1/0/17                     connected    502        a-full a-1000 10/100/1000BaseTX
Gi1/0/18                     connected    502        a-full a-1000 10/100/1000BaseTX
Gi1/0/19                     connected    502        a-full a-1000 10/100/1000BaseTX
Gi1/0/20                     err-disabled 502          auto   auto 10/100/1000BaseTX
Gi1/0/21                     connected    515        a-full a-1000 10/100/1000BaseTX
Gi1/0/22                     connected    515        a-full a-1000 10/100/1000BaseTX
Gi1/0/23                     notconnect   1            auto   auto 10/100/1000BaseTX
Gi1/0/24                     connected    trunk      a-full a-1000 10/100/1000BaseTX
Fa0                          notconnect   routed       auto   auto 10/100BaseTX
C3750X-5F-I02-2-252#

配置接口速率和双工模式接口双工模式分为全双工和半双工，指的是数据的传输方式：
1.半双工（Half Duplex）是指接口任意时刻只能接收数据或者发送数据，并存在最大传输距离的限制。
2.全双工（Full Duplex）是指在发送数据的同时也能够接收数据，两者同步进行，最大吞吐量可达到双倍速率，且消除了半双工的物理距离限制。目前的网卡一般都支持全双工。

配置接口双工模式
接口双工模式可以是自协商模式（auto）、半双工模式（half）、全双工模式（full）
自协商的内容包括两端接口的双工模式和接口速率。一旦协商通过，链路两端的设备就锁定在同样的双工模式和接口速率。自协商功能只有在链路两端设备均支持才可以生效。如果对端设备不支持自协商功能，或者对端设备自协商机制和本端设备不一致，则接口可能会处于Down状态
如果数据流量较大，则链路两端的自协商结果只能为全双工模式，不能为半双工模式，否则会出现丢包现象。如果数据流量较小，链路两端的自协商结果为半双工模式即可以满足数据传输需求。
链路两端的双工模式必须保持一致。电接口对接时有可能因为两端接口自协商模式不一致等原因，造成接口被协商成半双工模式，此时可能会出现报文交互异常现象

C3750X-5F-I02-2-252#SHOw INTERfaces GigabitEthernet1/0/8
GigabitEthernet1/0/8 is down, line protocol is down (err-disabled)
Hardware is Gigabit Ethernet, address is 00af.1fe0.63d0 (bia 00af.1fe0.63d0)
Description: "HTZQ Network"
Internet address is 165.16.241.174/30
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 10/100/1000BaseTX  # auto | full | half设置端口为-自动/全双工/半双工
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 01:41:48, output 01:41:48, 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
C3750X-5F-I02-2-252(config)#INTErface GigabitEthernet1/0/8
C3750X-5F-I02-2-252(config-if)# DUplex full
C3750X-5F-I02-2-252(config-if)# Speed 100
C3750X-5F-I02-2-252(config-if)#speed ?
10    Force 10 Mbps operation
100   Force 100 Mbps operation
1000  Force 1000 Mbps operation
auto  Enable AUTO speed configuration
C3750X-5F-I02-2-252(config-if)#