How to prevent loop for Zyxel Switch in standalone mode?

Zyxel_Melen

Scenario

Loop occurs as a result of human error. It happens when two ports on a switch are connected with the same cable. When a switch in loop state sends out broadcast messages the messages loop back to the switch and are re-broadcast again and again causing a broadcast storm. 

If a switch (not in loop state) connects to a switch in loop state, then it will be affected by the switch in loop state.

We can use Loop Guard to handle this issue on the edge of your network. Loop guard allows your Switch to shut down a port if it detects that packets sent out on that port loop back to the Switch. While you can use Spanning Tree Protocol (STP) to prevent loops in the core of your network, STP cannot prevent loops that occur on the edge of your network.

Topology

This topic will introduce how to configure loop guard and it’s result.

Configuration

1 Configure loop guard

1.1 Go to “Menu > Advanced Application > Loop Guard” to setup loop guard.

1.2 Enable loop guard and the port you want to enable loop guard.

Verification

If the switch which connects to port 1 has loop, loop guard will automatically disable this port when it detects that packets sent out on that port loops back to the Switch. We can check port status (Menu > Management > Port Status) to check the status of this port. 

Note

1 The loop guard feature cannot be enabled on the ports that have Spanning Tree Protocol (RSTP, MRSTP or MSTP) enabled.

2 After resolving the loop problem on your network, you can manually re-activate the disabled ports or setup err-disable recovery to automatically recover disabled ports. Please go to “Menu > Advanced Application > Errdisable > Errdisable Recovery” to active err-disable recovery and enable the timer status for loop guard. The interval can be set from 30 to 2592000.