Spanning Tree Protocol: Loop Prevention

Real switched networks are wired with redundant links for resilience — but two switches connected by more than one active path create a broadcast loop that can melt a LAN in seconds. This simulator builds a random 3D switch topology with deliberate redundant links, runs the real IEEE 802.1D Spanning Tree algorithm — root bridge election by Bridge ID, root path cost using standard per-speed port costs, and root/designated/blocking port assignment — and renders the result live: green and cyan links are forwarding, dimmed red links are blocked to break every loop, and animated pulses trace BPDUs flowing outward from the root along the resulting spanning tree. Pick any switch as the root bridge or add more redundant links and watch the whole tree recompute.