04-Layer 2 - LAN Switching

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04-Loop detection commands
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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

Example

# Display the loop detection configuration and status.

<Sysname> display loopback-detection

Loopback detection is enabled.

Loopback detection interval is 30 second(s).

Loopback is detected on following interfaces:

 Interface                Action mode

 GigabitEthernet1/0/1     Block

 GigabitEthernet1/0/2     Shutdown

 GigabitEthernet1/0/3     None

 GigabitEthernet1/0/4     No-learning

Table 1 Command output

Field

Description

Action mode

Loop protection action:

·     BlockWhen a loop is detected on a port, the device performs the following operations:

¡     Generates a log.

¡     Disables the port from learning MAC addresses.

¡     Blocks inbound traffic on the port.

·     NoneWhen a loop is detected on a port, the device generates a log but performs no action on the port.

·     No-learningWhen a loop is detected on a port, the device generates a log and disables the port from learning MAC addresses.

·     ShutdownWhen a loop is detected on a port, the device performs the following operations:

¡     Generates a log.

¡     Shuts down the port to disable the port from receiving or sending frames. The device automatically sets the port to the forwarding state after a time interval. Set the time interval by using the shutdown-interval command (see Fundamentals Command Reference).

 

loopback-detection action

Use loopback-detection action to set the loop protection action on a per-port basis.

Use undo loopback-detection action to restore the default.

Syntax

In Layer 2 Ethernet interface view:

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

undo loopback-detection action

In Layer 2 aggregate interface view:

loopback-detection action shutdown

undo loopback-detection action

Default

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

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 port.

Layer 2 aggregate interfaces do not support this keyword.

no-learning: Enables the no-learning mode. If a loop is detected, the device generates a log and disables MAC address learning on the port. 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 port. The device automatically sets the port 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 configuration applies to all ports. The per-port configuration applies to the individual ports. The per-port configuration takes precedence over the global configuration.

Example

# Set the loop protection action to shutdown on port 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 enable

Use loopback-detection enable to enable loop detection on a per-port basis.

Use undo loopback-detection enable to disable loop detection on a port.

Syntax

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

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

Default

The loop detection feature is disabled on ports.

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

The per-port loop detection configuration takes effect only after you enable loop detection globally. To enable loop detection globally, use the loopback-detection global enable command.

The global configuration applies to all ports in the specified VLAN. The per-port configuration applies to the individual port only when the port belongs to the specified VLAN. The per-port configuration takes precedence over the global configuration.

Example

# Enable loop detection on port 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 a port, it generates a log but performs no action on the port.

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 port. The device automatically sets the port 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 on a per-port basis, use the loopback-detection action command in interface view.

The global configuration applies to all ports. The per-port configuration applies to the individual ports. The per-port configuration takes precedence over the global configuration.

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 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

The loop detection feature 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

To enable loop detection on a per-port basis, use the loopback-detection enable command in interface view.

The global configuration applies to all ports in the specified VLAN. The per-port configuration applies to the individual port only when the port belongs to the specified VLAN. The per-port configuration takes precedence over the global configuration.

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