An interactive introduction to the spanning tree protocol

Warning This post contains interactive examples. To visualize and interact with them, you need to leave your RSS reader. Imagine you rent office space for a three-day event. You quickly set up a few Ethernet switches and tape some cables on the floor to get everyone online. Unfortunately, Stan, your clumsiest coworker, kicks out a cable every time he gets up for coffee. You could add extra cables, but then you’d get a broadcast storm: Ethernet packets that loop and multiply until nothing else gets through. That’s where the spanning tree protocol (STP) comes in. STP blocks just enough of your spare cables to leave a loop-free tree. When Stan strikes again, it rebuilds the tree in a second, leaving some time for Blobby, your one-person support crew, to reconnect the cable. See for yourself: the diagram below runs a real STP implementation in your browser! :demo A1 @0,0 prio=4096 A2 @0,1 A3 @0,2 A4 @0,3 B1 @1,0 prio=8192 B2 @1,1 B3 @1,2 B4 @1,3 C1 @2,0 prio=8192 C2 @2,1 C3 @2,2 C4 @2,3…