An interactive introduction to the spanning tree protocol

The spanning tree protocol (STP) prevents network loops when adding extra Ethernet cables to a three-day office event. It blocks just enough spare cables to create a loop-free tree, allowing Stan's clumsiness and Blobby's cable connections to coexist. This protocol was designed in the 1980s and has evolved into rapid (RSTP) and VLAN-aware (MSTP) versions. STP uses a complex state machine, timers, link state changes, and control frames (BPDUs) to eliminate network loops.

RSTP converges to a tree from the root to each bridge, displaying the time taken to reach this state. By cutting links, you can see how the protocol finds alternate paths. The protocol runs in a browser using an open-source MSTPD implementation. Radia Perlman, who invented STP, described it as a "graph more lovely than a tree" with loop-free connectivity that spans all LANs.