Why Switching Loops Are Dangerous

Redundant links make networks more reliable, but on a switched network they can create a deadly problem: a switching loop. A loop forms when there are two or more paths between switches and frames circle endlessly. Unlike a slow connection, a loop can take an entire network down in seconds. This lesson explains how loops form and why they are so destructive.

To understand loops, recall how switches handle unknown or broadcast traffic. When a switch receives a broadcast frame, or a frame for a destination it has not yet learned, it floods the frame out every port except the one it came in on. This flooding is normal and useful. But with a loop in the topology, flooding becomes a runaway disaster.