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How to identify and quickly fix switching loops


What is a network loop? 

network loop

A switching loop occurs in a computer network when there is more than one layer 2 path between two endpoint devices, i.e. multiple connection between 2 network switches or two ports on the same switch connected together. For more information, visit: https://en.wikipedia.org/wiki/Switching_loop


WHAT IS THE EFFECT OF A NETWORK LOOP?

When this happens on your network, the destination will be unreachable until the loop disappears because to join the next hope you have to pass by the previous one.
Depending to the routing protocol (OSPF, RIPv2, etc. …) this can take several minutes.

Loops generate broadcast storms, as the broadcast packets are forwarded to every port on the switch; the switch will repeatedly rebroadcast the broadcast messages flooding the network.

When this happens on your network, everyone will lose the ability to communicate on the network, you break the loop, your network will return to normal in a few minutes.


To learn how to troubleshoot network and application performance degradations in 4 easy steps, you can download our Performance Troubleshooting Guide: 

Performance Troubleshooting Guide

DO YOU HAVE ANY LOOP ON YOUR NETWORKS?

All recent network devices provide loop detection and remove them to avoid any issue on your network. But it doesn't mean your users are not impacted, this is just not visible to you.

With PerformanceVision, you can see these loops in a single screen (you can even create a shortcut on your desktop).

You simply have to connect to PerformanceVision’s UI and select the view protocols/non IP/ ICMP errors and enter the filter icmp.type=11.

identifying a network loop in one click

 

Topics: NPM, Network troubleshooting

Posted by Boris Rogier on 19 mai 2016
Boris Rogier
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