Configuring Loopback Detection; How Lbd Works - Cisco Small Business 200 Series Administration Manual

Port Management
Loopback Detection
• Direct multi-ports loop—Switch is connected to another switch with more than one port and STP is
disabled.
• LAN segment loop—Switch is connected with one or more ports to a LAN segment that has loops.

How LBD Works

LBD protocol periodically broadcast loopback detection packets. A switch detects a loop when it
receives its own LBD packets.
The following conditions must be true for a port to be LBD active:
• LBD is globally enabled.
• LBD is enabled on the port.
• Port operational status is up.
• Port is in STP forwarding/disable state (MSTP instance forwarding state, instance 0).
LBD frames are transmitted on the highest priority queue on LBD active ports (in case of LAGs, the LBD is
transmitted on every active port member in LAG).
When a loop is detected, the switch performs the following actions:
• Sets the receiving ports or LAGs to Error Disable state.
• Issues an appropriate SNMP trap.
• Generates an appropriate SYLOG message.

Configuring Loopback Detection

Default Settings and Configuration
Loopback detection is not enabled by default.
Interactions with Other Features
If STP is enabled on a port on which Loopback Detection is enabled, the port must be in STP forwarding
state.
Configuring LBD Workflow
To enable and configure LBD:
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