The Spanning Tree Protocol

Consider the following network toplogy:

The loops in here create a broadcast storm (due to the loops, so it keeps getting sent over and over and never dies) which takes down the whole network. With switches instead:

you'll also get the same problem. Ethernet in general doesn't do well with loops, but we like loops for redundancy. That's where the spanning tree comes into play.

Here it's an active algorithm. It essentially take out loops and reconfigures when the traffic requires it to take a faster path. The steps are:

1. Pick a root node
2. Determine shortest path based on time from each switch back to the root node.
3. Administratively, take down any link that is not on that shortest path.