网络工程 - Cisco：由于环路而导致错误禁用 - 但没有冗余物理路径/电线/连接 - 吾爱随笔录

大约两年内，我们第三次或第四次（痛苦地）注意到我们的数据中心出现了一些非常奇怪（至少对我们而言）的行为：

由于检测到环回，只有一个 (!) 物理上行链路（层次结构的较低端点）的接入交换机上的上行链路接口将进入err-disable状态。

没有物理（有线）环路。怎么会这样？

RZ2-AS18#展示版

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    1 28    WS-C3560G-24TS     12.2(55)SE1           C3560-IPSERVICESK9-M

RZ2-AS18# show int des

Gi0/24  up  up  *** Uplink to rz2-cs4 Gi0/24 ***

RZ2-AS18# 显示日志

Jul 26 11:35:55.328: %ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on GigabitEthernet0/24.
Jul 26 11:35:55.328: %PM-4-ERR_DISABLE: loopback error detected on Gi0/24, putting Gi0/24 in err-disable state
Jul 26 11:35:56.611: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/24, changed state to down
Jul 26 11:35:57.651: %LINK-3-UPDOWN: Interface GigabitEthernet0/24, changed state to down
.Jul 26 12:12:04.173: %LINK-5-CHANGED: Interface GigabitEthernet0/24, changed state to administratively down
.Jul 26 12:12:06.295: %LINK-3-UPDOWN: Interface GigabitEthernet0/24, changed state to down
.Jul 26 12:12:09.131: %LINK-3-UPDOWN: Interface GigabitEthernet0/24, changed state to up
.Jul 26 12:12:10.137: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/24, changed state to up
.Jul 26 12:13:05.117: %SYS-5-CONFIG_I: Configured from console by console

rz2-as18# 显示运行 int gi 0/24

interface GigabitEthernet0/24
 description *** rz2-cs4 Gi0/24 ***
 switchport trunk encapsulation dot1q
 switchport mode trunk
 switchport nonegotiate
end

一般网络结构：

核心交换机 (CS) 之间的环
接入交换机连接到星形拓扑中的核心交换机

有任何想法吗？想法？提前致谢！