What Is a Broadcast Storm?
a Broadcast Storm — a network meltdown where broadcast traffic multiplies uncontrollably — usually from a Layer 2 loop — consuming all available bandwidth and effectively taking the network down.
How it works
Without loop prevention, a single broadcast frame entering a looped topology gets endlessly duplicated and re-flooded by switches, exponentially multiplying traffic within seconds until the network saturates and stops functioning for everyone. This is precisely why Spanning Tree Protocol exists — it prevents the loops that cause broadcast storms in the first place.
Why it matters
A broadcast storm is one of the most severe and fast-moving network failures — recognising the symptoms (sudden total slowdown, spiking CPU on switches, MAC address flapping) and knowing STP/loop prevention is core CCNA knowledge and a classic troubleshooting interview scenario.
Frequently asked questions
What causes a broadcast storm?
Almost always a Layer 2 loop — redundant switch links without proper loop prevention (Spanning Tree) causing broadcast frames to circulate and multiply endlessly.
How do you prevent broadcast storms?
Spanning Tree Protocol (STP/RSTP) detects and blocks redundant paths that would create loops, which is the primary defence.
What are the symptoms of a broadcast storm?
Sudden severe network slowdown or total outage, spiking switch CPU utilisation, and rapidly flapping MAC address table entries.
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