If you walk into a wiring closet and every switch is blinking at a consistent, rapid rate — all ports simultaneously — you're looking at a broadcast storm caused by a network loop.
What happened: Someone patched a cable from one switch port back into another port on the same switch (or between two switches that were already connected on another path). Without loop prevention, Ethernet frames multiply exponentially — every broadcast is re-broadcast infinitely.
The fix: Physically trace and remove the redundant cable. The network will stabilize within seconds once the loop is broken.
Prevention (the real solution):
- Spanning Tree Protocol (STP): Should be enabled on every managed switch — it detects loops and blocks redundant paths automatically
- BPDU Guard: Shuts down access ports that receive STP frames (prevents rogue switches)
- Storm Control: Rate-limits broadcast/multicast traffic to contain damage
- Port Security: Limits what can be connected to each port
A single mispatched cable shouldn't be able to take down an entire floor. If it can, your switching infrastructure needs hardening.