5560交换机端口设置环路检测后，action 是shutdown,产生环路后端口没能shutdown，网络仍然处于拥塞状态，这是什么原因？

设备有没有开STP？

参考下案例，看看配置有没有问题：

1.10.1  环路检测基本功能配置举例

1. 组网需求

·     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。

2. 组网图

图1-3 环路检测基本功能配置组网图

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3. 配置步骤

(1)     配置Device A

# 创建VLAN 100，并全局开启该VLAN内的环路检测功能。

<DeviceA> 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

(2)     配置Device B

# 创建VLAN 100。

<DeviceB> 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

(3)     配置Device C

# 创建VLAN 100。

<DeviceC> 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

4. 验证配置

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：

[DeviceA]

%Feb 24 15:04:29:663 2019 DeviceA LPDT/4/LPDT_LOOPED:  A loop was detected on GigabitEthernet1/0/1.

%Feb 24 15:04:29:664 2019 DeviceA LPDT/4/LPDT_VLAN_LOOPED: A loop was detected on GigabitEthernet1/0/1 in VLAN 100.

%Feb 24 15:04:29:667 2019 DeviceA LPDT/4/LPDT_LOOPED: A loop was detected on GigabitEthernet1/0/2.

%Feb 24 15:04:29:668 2019 DeviceA LPDT/4/LPDT_VLAN_LOOPED: A loop was detected on GigabitEthernet1/0/2 in VLAN 100.

%Feb 24 15:04:44:243 2019 DeviceA LPDT/5/LPDT_VLAN_RECOVERED: A loop was removed on GigabitEthernet1/0/1 in VLAN 100.

%Feb 24 15:04:44:243 2019 DeviceA LPDT/5/LPDT_RECOVERED: All loops were removed on GigabitEthernet1/0/1.

%Feb 24 15:04:44:248 2019 DeviceA LPDT/5/LPDT_VLAN_RECOVERED: A loop was removed on GigabitEthernet1/0/2 in VLAN 100.

%Feb 24 15:04:44:248 2019 DeviceA LPDT/5/LPDT_RECOVERED: 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。

[DeviceA] 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：

# 显示Device A上端口GigabitEthernet1/0/1的状态信息。

[DeviceA] display interface gigabitethernet 1/0/1

GigabitEthernet1/0/1 current state: DOWN (Loopback detection down)

...

# 显示Device A上端口GigabitEthernet1/0/2的状态信息。

[DeviceA] 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。