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本案例介绍环路检测的配置方法。

如图1所示，

·     三台设备Device A、Device B和Device C组成一个物理上的环形网络。

·     通过在Device A上配置环路检测功能，使系统能够自动关闭Device A上出现环路的端口，并通过打印日志信息来通知用户检查网络。

图1 环路检测基本功能配置组网图

# 创建VLAN 100，并全局开启该VLAN内的环路检测功能。

system-view

[DeviceA] vlan 100

[DeviceA–vlan100] quit

[DeviceA] loopback-detection global enable vlan 100

# 配置端口GigabitEthernet1/0/1和GigabitEthernet1/0/2为Trunk类型，并允许VLAN 100通过。

[DeviceA] interface gigabitethernet 1/0/1

[DeviceA-GigabitEthernet1/0/1] port link-type trunk

[DeviceA-GigabitEthernet1/0/1] port trunk permit vlan 100

[DeviceA-GigabitEthernet1/0/1] quit

[DeviceA] interface gigabitethernet 1/0/2

[DeviceA-GigabitEthernet1/0/2] port link-type trunk

[DeviceA-GigabitEthernet1/0/2] port trunk permit vlan 100

[DeviceA-GigabitEthernet1/0/2] quit

# 全局配置环路检测的处理模式为Shutdown模式。

[DeviceA] loopback-detection global action shutdown

# 配置环路检测的时间间隔为35秒。

[DeviceA] loopback-detection interval-time 35

# 保存配置。

[DeviceA] save force

# 创建VLAN 100。

system-view

[DeviceB] vlan 100

[DeviceB–vlan100] quit

# 配置端口GigabitEthernet1/0/1和GigabitEthernet1/0/2为Trunk类型，并允许VLAN 100通过。

[DeviceB] interface gigabitethernet 1/0/1

[DeviceB-GigabitEthernet1/0/1] port link-type trunk

[DeviceB-GigabitEthernet1/0/1] port trunk permit vlan 100

[DeviceB-GigabitEthernet1/0/1] quit

[DeviceB] interface gigabitethernet 1/0/2

[DeviceB-GigabitEthernet1/0/2] port link-type trunk

[DeviceB-GigabitEthernet1/0/2] port trunk permit vlan 100

[DeviceB-GigabitEthernet1/0/2] quit

# 保存配置。

[DeviceB] save force

# 创建VLAN 100。

system-view

[DeviceC] vlan 100

[DeviceC–vlan100] quit

# 配置端口GigabitEthernet1/0/1和GigabitEthernet1/0/2为Trunk类型，并允许VLAN 100通过。

[DeviceC] interface gigabitethernet 1/0/1

[DeviceC-GigabitEthernet1/0/1] port link-type trunk

[DeviceC-GigabitEthernet1/0/1] port trunk permit vlan 100

[DeviceC-GigabitEthernet1/0/1] quit

[DeviceC] interface gigabitethernet 1/0/2

[DeviceC-GigabitEthernet1/0/2] port link-type trunk

[DeviceC-GigabitEthernet1/0/2] port trunk permit vlan 100

[DeviceC-GigabitEthernet1/0/2] quit

# 保存配置。

[DeviceC] save force

当配置完成后，系统在一个环路检测时间间隔内在Device A的端口GigabitEthernet1/0/1和GigabitEthernet1/0/2上都检测到了环路，于是将这两个端口自动关闭，并打印了如下日志信息：

%Aug 26 19:17:29:760 2021 DeviceA IFNET/3/PHY_UPDOWN: -MDC=1; Physical state on the interface GigabitEthernet1/0/2 changed to up.

%Aug 26 19:17:29:760 2021 DeviceA IFNET/5/LINK_UPDOWN: -MDC=1; Line protocol state on the interface GigabitEthernet1/0/2 changed to up.

%Aug 26 19:17:30:356 2021 DeviceA IFNET/3/PHY_UPDOWN: -MDC=1; Physical state on the interface GigabitEthernet1/0/1 changed to up.

%Aug 26 19:17:30:356 2021 DeviceA IFNET/5/LINK_UPDOWN: -MDC=1; Line protocol state on the interface GigabitEthernet1/0/1 changed to up.

%Aug 26 19:17:33:985 2021 DeviceA LPDT/4/LPDT_LOOPED: -MDC=1; A loop was detected on GigabitEthernet1/0/1.

%Aug 26 19:17:34:005 2021 DeviceA IFNET/3/PHY_UPDOWN: -MDC=1; Physical state on the interface GigabitEthernet1/0/1 changed to down.

%Aug 26 19:17:34:006 2021 DeviceA IFNET/5/LINK_UPDOWN: -MDC=1; Line protocol state on the interface GigabitEthernet1/0/1 changed to down.

%Aug 26 19:17:34:018 2021 DeviceA LPDT/4/LPDT_VLAN_LOOPED: -MDC=1; A loop was detected on GigabitEthernet1/0/1 in VLAN 100.

%Aug 26 19:17:34:019 2021 DeviceA LPDT/4/LPDT_LOOPED: -MDC=1; A loop was detected on GigabitEthernet1/0/2.

%Aug 26 19:17:34:040 2021 DeviceA IFNET/3/PHY_UPDOWN: -MDC=1; Physical state on the interface GigabitEthernet1/0/2 changed to down.

%Aug 26 19:17:34:041 2021 DeviceA IFNET/5/LINK_UPDOWN: -MDC=1; Line protocol state on the interface GigabitEthernet1/0/2 changed to down.

%Aug 26 19:17:34:055 2021 DeviceA LPDT/4/LPDT_VLAN_LOOPED: -MDC=1; A loop was detected on GigabitEthernet1/0/2 in VLAN 100.

%Aug 26 19:17:34:055 2021 DeviceA LPDT/5/LPDT_VLAN_RECOVERED: -MDC=1; A loop was removed on GigabitEthernet1/0/1 in VLAN 100.

%Aug 26 19:17:34:055 2021 DeviceA LPDT/5/LPDT_RECOVERED: -MDC=1; All loops were removed on GigabitEthernet1/0/1.

%Aug 26 19:17:34:056 2021 DeviceA LPDT/5/LPDT_VLAN_RECOVERED: -MDC=1; A loop was removed on GigabitEthernet1/0/2 in VLAN 100.

%Aug 26 19:17:34:056 2021 DeviceA LPDT/5/LPDT_RECOVERED: -MDC=1; All loops were removed on GigabitEthernet1/0/2.

使用display loopback-detection命令可以查看Device A上环路检测的配置和运行情况：

# 显示Device A上环路检测的配置和运行情况。

display loopback-detection

Loop detection is enabled.

Global loop detection interval is 35 second(s).

Loop is detected on following interfaces:

  Interface                         Action mode     VLANs/VSI

  GigabitEthernet1/0/1              Shutdown        100

  GigabitEthernet1/0/2              Shutdown        100

由此可见，Device A上显示在端口GigabitEthernet1/0/1和GigabitEthernet1/0/2上检测到环路，由于环路检测功能运行在Shutdown模式下，端口GigabitEthernet1/0/1和GigabitEthernet1/0/2上出现环路后均已被自动关闭，因此设备打印的日志信息显示这两个端口上的环路已消除。此时，使用display interface命令分别查看Device A上端口GigabitEthernet1/0/1和GigabitEthernet1/0/2的状态信息：

display interface gigabitEthernet 1/0/1

GigabitEthernet1/0/1

Current state: DOWN (Loopback detection down)

display interface gigabitEthernet 1/0/2

GigabitEthernet1/0/2

Current state: DOWN (Loopback detection down)

由此可见，端口GigabitEthernet1/0/1和GigabitEthernet1/0/2均已被环路检测模块自动关闭。

·     Device A：

#

 loopback-detection global enable vlan 100

 loopback-detection global action shutdown

 loopback-detection interval-time 35

#

vlan 100

#

interface GigabitEthernet1/0/1

 port link-mode bridge

 port link-type trunk

 port trunk permit vlan 1 100

#

interface GigabitEthernet1/0/2

 port link-mode bridge

 port link-type trunk

 port trunk permit vlan 1 100

#

·     Device B ：

#

vlan 100

#

interface GigabitEthernet1/0/1

 port link-mode bridge

 port link-type trunk

 port trunk permit vlan 1 100

#

interface GigabitEthernet1/0/2

 port link-mode bridge

 port link-type trunk

 port trunk permit vlan 1 100

#

·     Device C ：

#

vlan 100

#

interface GigabitEthernet1/0/1

 port link-mode bridge

 port link-type trunk

 port trunk permit vlan 1 100

#

interface GigabitEthernet1/0/2

 port link-mode bridge

 port link-type trunk

 port trunk permit vlan 1 100

#

·     产品配套“二层技术-以太网交换配置指导”中的“环路检测”。

·     产品配套“二层技术-以太网交换命令参考”中的“环路检测”。