Contents

Loop detection commands· 1

display loopback-detection· 1

loopback-detection action· 2

loopback-detection delay-timer 3

loopback-detection enable· 3

loopback-detection global action· 4

loopback-detection delay-timer 5

loopback-detection global enable· 6

loopback-detection interval-time· 6

 

Loop detection commands

display loopback-detection

Use display loopback-detection to display the loop detection configuration and status.

Syntax

display loopback-detection

Views

Any view

Predefined user roles

network-admin

network-operator

Usage guidelines

In the command output, a port shut down by loop detection stays in looped state until it comes up.

Example

# Display the loop detection configuration and status.

<Sysname> display loopback-detection

Loop detection is enabled.

Global loop detection interval is 30 second(s).

Loop is detected on following interfaces:

  Interface                      Action mode     VLANs/VSI

  GigabitEthernet1/0/3           None            10

Table 1 Command output

Field	Description
Action mode	Loop protection action: ·     Block—When a loop is detected on an interface, the device performs the following operations: ¡     Generates a log. ¡     Disables the interface from learning MAC addresses. ¡     Blocks the interface. ·     None—When a loop is detected on an interface, the device generates a log but performs no action on the interface. ·     No-learning—When a loop is detected on an interface, the device generates a log and disables the interface from learning MAC addresses. ·     Shutdown—When a loop is detected on an interface, the device performs the following operations: ¡     Generates a log. ¡     Shuts down the interface to disable the interface from receiving or sending frames. The device automatically sets the interface to the forwarding state after a time interval. Set the time interval by using the shutdown-interval command (see Fundamentals Command Reference).
VLANs/VSI	VSI-based loop detection is not supported in the current software version. VLANs or VSI to which the interface belongs and where loops are detected.

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loopback-detection action

Use loopback-detection action to set the loop protection action on an interface.

Use undo loopback-detection action to restore the default.

Syntax

loopback-detection action { block | no-learning | shutdown }

undo loopback-detection action

Default

When the device detects a loop on an interface, it generates a log but performs no action on the interface.

Views

Layer 2 Ethernet interface view

Layer 2 aggregate interface view

Predefined user roles

network-admin

Parameters

block: Enables the block mode. If a loop is detected, the device performs the following operations:

·     Generates a log.

·     Disables MAC address learning.

·     Blocks the interface.

no-learning: Enables the no-learning mode. If a loop is detected, the device generates a log and disables MAC address learning on the interface. Layer 2 aggregate interfaces do not support this keyword.

shutdown: Enables the shutdown mode. If a loop is detected, the device generates a log and shuts down the interface. The device automatically sets the interface to the forwarding state after the time interval set by using the shutdown-interval command (see Fundamentals Command Reference).

Usage guidelines

To set the loop protection action globally, use the loopback-detection global action command.

The global action applies to all interfaces. An interface-specific action applies only to the interface on which the action is configured. On an interface, the interface-specific action takes precedence over the global action.

Example

# Set the loop protection action to shutdown on GigabitEthernet 1/0/1.

<Sysname> system-view

[Sysname] interface gigabitethernet 1/0/1

[System-GigabitEthernet1/0/1] loopback-detection action shutdown

Related commands

display loopback-detection

loopback-detection global action

loopback-detection delay-timer

Use loopback-detection delay-timer to set the loop protection delay timer on an interface.

Use undo loopback-detection delay-timer to disable loop protection delay on an interface.

Syntax

loopback-detection delay-timer time

undo loopback-detection delay-timer

Default

Loop protection delay is disabled on an interface.

Views

Layer 2 Ethernet interface view

Layer 2 aggregate interface view

Predefined user roles

network-admin

Parameters

time: Sets the loop protection delay timer, in seconds. The value range for this argument is 1 to 1000.

Usage guidelines

On a network protected by loop detection, the shutdown or block action taken on a looped interface of an upstream device might cause traffic interruption to its downstream devices. To minimize the impacts of loop detection on downstream traffic, set the loop protection delay timer on upstream devices. This delay allows the downstream devices to remove loops before the upstream devices take an action.

The global delay timer applies to all interfaces enabled with loop detection. An interface-specific delay timer applies only to the interface on which it is configured. On an interface, the interface-specific delay timer takes precedence over the global delay timer.

Example

# Set the loop protection delay timer to 100 seconds on GigabitEthernet 1/0/1.

<Sysname> system-view

[Sysname] interface gigabitethernet 1/0/1

[System-GigabitEthernet1/0/1] loopback-detection delay-timer 100

Related commands

loopback-detection global delay-timer

loopback-detection enable

Use loopback-detection enable to enable loop detection on an interface.

Use undo loopback-detection enable to disable loop detection on an interface.

Syntax

loopback-detection enable vlan { vlan-id-list | all }

undo loopback-detection enable vlan { vlan-id-list | all }

Default

Loop detection is disabled on interfaces.

Views

Layer 2 Ethernet interface view

Layer 2 aggregate interface view

Predefined user roles

network-admin

Parameters

vlan-id-list: Specifies a space-separated list of up to 10 VLAN items. Each item specifies a VLAN ID or a range of VLAN IDs in the form of vlan-id1 to vlan-id2. The value range for VLAN IDs is 1 to 4094. The ID for vlan-id2 must be no less than the ID for vlan-id1.

all: Specifies all existing VLANs.

Usage guidelines

You can enable loop detection globally or on a per-interface basis. When an interface receives a detection frame in any VLAN, the loop protection action is triggered on that interface, regardless of whether loop detection is enabled on it.

Example

# Enable loop detection on GigabitEthernet 1/0/1 for VLAN 10 through VLAN 20.

<Sysname> system-view

[Sysname] interface gigabitethernet 1/0/1

[System-GigabitEthernet1/0/1] loopback-detection enable vlan 10 to 20

Related commands

display loopback-detection

loopback-detection global enable

loopback-detection global action

Use loopback-detection global action to set the global loop protection action.

Use undo loopback-detection global action to restore the default.

Syntax

loopback-detection global action shutdown

undo loopback-detection global action

Default

When the device detects a loop on an interface, it generates a log but performs no action on the interface.

Views

System view

Predefined user roles

network-admin

Parameters

shutdown: Enables the shutdown mode. If a loop is detected, the device generates a log and shuts down the interface. The device automatically sets the interface to the forwarding state after you set the time interval by using the shutdown-interval command (see Fundamentals Command Reference).

Usage guidelines

To set the loop protection action on a per-interface basis, use the loopback-detection action command in interface view.

The global action applies to all interfaces. An interface-specific action applies only to the interface on which it is configured. On an interface, the interface-specific action takes precedence over the global action.

Example

# Set the global loop protection action to shutdown.

<Sysname> system-view

[System] loopback-detection global action shutdown

Related commands

display loopback-detection

loopback-detection action

loopback-detection delay-timer

Use loopback-detection delay-timer to set the global loop protection delay timer.

Use undo loopback-detection delay-timer to disable loop protection delay globally.

Syntax

loopback-detection delay-timer time

undo loopback-detection delay-timer

Default

Loop protection delay is disabled on globally.

Views

System view

Predefined user roles

network-admin

Parameters

time: Sets the loop protection delay timer, in seconds. The value range for this argument is 1 to 1000.

Usage guidelines

On a network protected by loop detection, the shutdown or block action taken on a looped interface of an upstream device might cause traffic interruption to its downstream devices. To minimize the impacts of loop detection on downstream traffic, set the loop protection delay timer on upstream devices. This delay allows the downstream devices to remove loops before the upstream devices take an action.

The global delay timer applies to all interfaces enabled with loop detection. An interface-specific delay timer applies only to the interface on which it is configured. On an interface, the interface-specific delay timer takes precedence over the global delay timer.

Example

# Set the global loop protection delay timer to 100 seconds.

<Sysname> system-view

[Sysname] loopback-detection global delay-timer 100

Related commands

loopback-detection delay-timer

loopback-detection global enable

Use loopback-detection global enable to enable loop detection globally.

Use undo loopback-detection global enable to disable loop detection globally.

Syntax

loopback-detection global enable vlan { vlan-id-list | all }

undo loopback-detection global enable vlan { vlan-id-list | all }

Default

Loop detection is globally disabled.

Views

System view

Predefined user roles

network-admin

Parameters

vlan-id-list: Specifies a space-separated list of up to 10 VLAN items. Each item specifies a VLAN ID or a range of VLAN IDs in the form of vlan-id1 to vlan-id2. The value range for VLAN IDs is 1 to 4094. The ID for vlan-id2 must be equal to or greater than the ID for vlan-id1.

all: Specifies all existing VLANs.

Usage guidelines

You can enable loop detection globally or on a per-interface basis. When an interface receives a detection frame in any VLAN, the loop protection action is triggered on that interface, regardless of whether loop detection is enabled on it.

Example

# Globally enable loop detection for VLAN 10 through VLAN 20.

<Sysname> system-view

[System] loopback-detection global enable vlan 10 to 20

Related commands

display loopback-detection

loopback-detection enable

loopback-detection interval-time

Use loopback-detection interval-time to set the loop detection interval.

Use undo loopback-detection interval-time to restore the default.

Syntax

loopback-detection interval-time interval

undo loopback-detection interval-time

Default

The loop detection interval is 30 seconds.

Views

System view

Predefined user roles

network-admin

Parameters

interval: Sets the loop detection interval in the range of 1 to 300 seconds.

Usage guidelines

With loop detection enabled, the device sends loop detection frames at the specified interval. A shorter interval offers more sensitive detection but consumes more resources. Consider the system performance and loop detection speed when you set the loop detection interval.

Example

# Set the loop detection interval to 10 seconds.

<Sysname> system-view

[Sysname] loopback-detection interval-time 10

Related commands

display loopback-detection