Skip to content
Any configuration changes made locally on the switch won't be synchronized with Sophos Central. We recommend making changes from the Sophos Central control panel instead.

Page permalink

Always use the following permalink when referencing this page. It will remain unchanged in future help versions.

https://docs.sophos.com/nsg/switch/help/en-us/index.html?contextId=user-guide-features-configure-LDB

Loopback detection

Loopback detection (LBD) protects against network loops by sending out loop protocol packets and shutting down ports that receive the packets. You can use LBD in environments where connected devices don't support Spanning Tree Protocol (STP) since it functions independently from STP and provides the same service.

When the switch detects a loop, for example, if two ports on the same switch are mistakenly connected, it sets the port that received the loop protocol packet to Disabled. It also logs the event in its flash logs, which you can see in the local UI and Sophos Central. Here's an example log entry:

Example

LDB: Loop protocol packet received on port 2.

In addition to logging the LBD event, the red Fault light on the switch hardware will turn on to indicate a port is disabled due to a loop.

Global settings

Select Turned on or Turned off to turn Loopback detection status on or off.

Port status

The Port status tab shows whether ports are blocked by LBD.