The switch can be configured to detect general loopback conditions caused by hardware problems or faulty protocol settings. When enabled, a control frame is transmitted on the participating ports, and the switch monitors inbound traffic to see if the frame is looped back.
Usage Guidelines
The default settings for the control frame transmit interval and recover time may be adjusted to improve performance for your specific environment. The shutdown mode may also need to be changed once you determine what kind of packets are being looped back.
General loopback detection provided by the commands described in this section and loopback detection provided by the spanning tree protocol cannot both be enabled at the same time. If loopback detection is enabled for the spanning tree protocol, general loopback detection cannot be enabled on the same interface.
When a loopback event is detected on an interface or when a interface is released from a shutdown state caused by a loopback event, a trap message is sent and the event recorded in the system log.
Loopback detection must be enabled both globally and on an interface for loopback detection to take effect.
Use the Administration > LBD (Configure Global) page to enable loopback detection globally, specify the interval at which to transmit control frames, the interval to wait before releasing an interface from shutdown state, the response to detectd loopback, and traps to send.
Enables loopback detection globally on the switch. (Default: Enabled)
Specifies the interval at which to transmit loopback detection control frames. (Range: 1-32767 seconds; Default: 10 seconds)
Specifies the interval to wait before the switch automatically releases an interface from shutdown state. (Range: 60-1,000,000 seconds; Default: 60 seconds)
When the loopback detection mode is changed (enabled or disabled), any ports placed in shutdown state by the loopback detection process will be immediately restored to operation regardless of the remaining recover time.
If the recover time is not enabled (checkbox unmarked), all ports placed in shutdown state can be restored to operation using the Release button. To restore a specific port, re-enable Admin status on the Configure Interface page.
The recover-time is the maximum time when recovery is triggered after a loop is detected. The actual interval between recovery and detection will be less than or equal to the recover-time.
None - No action is taken.
Shutdown - When the response to a detected loopback condition is set to shut down a port, and a port receives a control frame sent by itself, this means that the port is in looped state, and the VLAN in the frame payload is also in looped state with the wrong VLAN tag. The looped port is therefore shut down.
When the loopback detection response is changed, any ports placed in shutdown state by the loopback detection process will be immediately restored to operation regardless of the remaining recover time.
Sends a trap when a loopback condition is detected, or when the switch recovers from a loopback condition. (Options: Both, Detect, None, Recover; Default: None)
Both - Sends an SNMP trap message when a loopback condition is detected, or when the switch recovers from a loopback condition.
Detect - No action is takenSends an SNMP trap message when a loopback condition is detected.
None - Does not send an SNMP trap for loopback detection or recovery.
Recover - Sends an SNMP trap message when the switch recovers from a loopback condition.
Releases all interfaces currently shut down by the loopback detection feature.
Use the Administration > LBD (Configure Interface) page to enable loopback detection on an interface, to display the loopback operational state, and the VLANs which are looped back.
Port identifier.
Trunk identifier.
Manually enables or disables an interface. (Default: Enabled)
Valid states include Normal or Looped.
Shows the VLANs which are in looped state.