Who invented the Spanning Tree Algorithm, and what is the core idea behind it?

Radia Perlman invented the STA (Spanning Tree Algorithm) while at Digital Equipment Corporation, published in 1985.

* A graph and all of its spanning trees. — Andreschulz, CC BY-SA 3.0, via Wikimedia Commons. *

The paper was titled "An Algorithm for Distributed Computation of a Spanning Tree in an Extended LAN (Local Area Network)."

Core idea of the STA:

1. Select a single root bridge as the reference point for the entire network
2. All other switches determine the single least-cost path to the root bridge
3. Redundant paths are placed in blocking state

How STP (Spanning Tree Protocol) uses this:

• Configures a loop-free path using strategically placed blocking-state ports
• Blocked ports are not permanently disabled — they can be dynamically unblocked if a failure occurs
• This gives you both loop prevention and failover capability

Tip: Radia Perlman is sometimes called "the Mother of the Internet" for this and other foundational networking contributions. The STA essentially turns a messy mesh of switches into a clean tree structure.

Go deeper:

• Radia Perlman (Wikipedia) — the inventor's page, with the full "Algorhyme" poem that encodes the algorithm.
• Spanning tree (graph theory) (Wikipedia) — the underlying math: a loop-free subgraph touching every node, which is the idea STP applies to switches.