Table of Contents

Chapter 1 Port Loopback Detection Commands. 1-1

1.1 Port Detection Configuration Commands. 1-1

1.1.1 display loopback-detection. 1-1

1.1.2 loopback-detection control 1-2

1.1.3 loopback-detection disable. 1-2

1.1.4 loopback-detection enable. 1-3

1.1.5 loopback-detection enable vlan. 1-4

1.1.6 loopback-detection interval-time. 1-4

 

Chapter 1  Port Loopback Detection Commands

1.1  Port Detection Configuration Commands

1.1.1  display loopback-detection

Syntax

display loopback-detection

View

Ethernet port view

Parameters

None

Description

Use the display loopback-detection command to display whether the port loopback detection function is enabled or not. If the function is enabled, the command will display the interval for detection, the VLANs enabled with detection function, the existing loops, and the ports which are shutdown for loop.

Examples

# Display whether the port loopback detection function is enabled or not.

<H3C> display loopback-detection

Loopback-detection is running on!

Detection interval time is 60 seconds!

Following vlans enable loopback-detection: 1

Following ports are detected for loop: GigabitEthernet2/1/1

Following ports are shutdown for loop: NULL

Table 1-1 Description on the fields of the display loopback-detection command

Field	Description
Loopback-detection is running on!	Port loopback detection function is enabled.
Detection interval time is 60 seconds	Detection interval is 60 seconds.
Following ports are detected for loop:	Ports on which loop exists
Following ports are shutdown for loop:	Ports which are shutdown for loop

 

1.1.2  loopback-detection control

Syntax

loopback-detection control

undo loopback-detection control

View

Ethernet port view

Parameters

None

Description

Use the loopback-detection control command to configure the system to shut down the current port once the port is found in a loop in addition to sending a trap message.

Use the undo loopback-detection control command to disable the system from shutting down the current port when the port is found in a loop. Still, trap information will be reported.

By default, the system does not shut down the ports that are found in loop.

Examples

# Enable the system to shut down the current port once it is found in a loop.

<H3C> system-view

[H3C] interface GigabitEthernet 2/1/1

[H3C-GigabitEthernet2/1/1] loopback-detection control

1.1.3  loopback-detection disable

Syntax

loopback-detection disable

undo loopback-detection disable

View

Ethernet port view

Parameters

None

Description

Use the loopback-detection disable command to disable a port from sending loopback detection packets.

Use the undo loopback-detection disable command to re-enable a port to send loopback detection packets.

 

 

Examples

# Disable GigabitEthernet 2/1/1 from sending loopback detection packets.

<H3C> system-view

[H3C] interface GigabitEthernet 2/1/1

[H3C-GigabitEthernet2/1/1] loopback-detection disable

1.1.4  loopback-detection enable

Syntax

loopback-detection enable

undo loopback-detection enable

View

System view

Parameters

None

Description

Use the loopback-detection enable command to enable the global port loopback detection function, so that the system can detect whether there is an external loop on each port in a VLAN which is enabled with the loopback detection function. If a loop is found on a port, the switch will give out an alarm or give out an alarm and shutdown the port according to your configuration.

Use the undo loopback-detection enable command to disable the global port loopback function.

By default, the global port loopback detection function is disabled.

Related commands: display loopback-detection.

Examples

# Enable the global port loopback detection function.

<H3C> system-view

[H3C] loopback-detection enable

1.1.5  loopback-detection enable vlan

Syntax

loopback-detection enable vlan { vlanlist | all }

undo loopback-detection  enable vlan { vlanlist | all }

View

System view

Parameters

vlanlist: Defines one or multiple VLANs. You can provide up to 10 VLAN lists, by each of which you can specify an individual VLAN in the form of vlan-id, or a VLAN range in the form of start-vlan-id to end-vlan-id, where the end VLAN ID must be greater than the start VLAN ID.

all: Enables loopback detection for all existing VLANs.

Description

Use the loopback-detection enable vlan command to enable loopback detection on the specified VLAN(s) to check for loop on all ports in the VLAN(s).

Use the undo loopback-detection enable vlan command to disable loopback detection on the specified VLAN(s).

By default, loopback detection is disabled on all VLANs.

Examples

# Enable loopback detection for all ports in VLAN 2.

<H3C> system-view

[H3C] loopback-detection enable vlan 2

1.1.6  loopback-detection interval-time

Syntax

loopback-detection interval-time time

undo loopback-detection interval-time

View

System view

Parameters

time: Interval in seconds at which external loopback detection is performed on ports, in the range of 10 to 7200. The default value is 60 seconds.

Description

Use the loopback-detection interval-time command to set the interval at which the external loopback detection is performed on ports.

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

Related commands: display loopback-detection.

Examples

# Set the interval for external loopback detection on ports to 120 seconds.

<H3C> system-view

[H3C] loopback-detection interval-time 120#