loopback-detection enable

Syntax

loopback-detection enable

undo loopback-detection enable

View

System view, Ethernet interface view, port group view

Default level

2: System level

Parameters

None

Description

Use loopback-detection enable to enable loopback detection globally in system view or on interfaces in Ethernet interface or port group view. To use loopback detection on an Ethernet interface, you must enable the function both globally and on the port.

Use undo loopback-detection enable to disable loopback detection globally or on Ethernet interfaces.

The undo loopback-detection enable command in system view disables loopback detection on all interfaces.

By default, loopback detection is disabled on all Ethernet interfaces.

If an interface receives a packet that it sent out, a loop has occurred. Loops may cause broadcast storms, which degrade network performance. You can enable loopback detection to detect loops on an interface and, if the interface supports the loopback-detection action command, configure the protective action (shut down the port, for example) to take on the interface when a loop is detected.

In addition to the configured protective action, the switch also performs other actions to alleviate the impact of the loop condition. For more information, see Table 9.

Table 9: Actions to take upon detection of a loop condition

Port type	Actions
	No protective action is configured	A protective action is configured
Access port	Place the interface in controlled mode. The interface does not receive or send packets. Generate traps. Delete all MAC address entries of the interface.	Perform the configured protective action. Generate traps and log messages. Delete all MAC address entries of the interface.
Hybrid or trunk port	Generate traps. If loopback detection control is enabled, set the interface in controlled mode. The interface does not receive or send packets. Delete all MAC address entries of the interface.	Create traps and log messages. If loopback detection control is enabled, take the configured protective action on the interface. Delete all MAC address entries of the interface.

Related commands: loopback-detection control enable.

Examples

# Enable loopback detection on Ethernet 1/0/1.

<Sysname> system-view
[Sysname] loopback-detection enable
[Sysname] interface ethernet 1/0/1
[Sysname-Ethernet1/0/1] loopback-detection enable

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