Explanation for the animation

The root node here is A. Initially, each node selects itself as the root node. This is shown by the green boxes. The nodes send configuration messages, to its neighbors and finally all of them decide on A as the root node. The election process is shown explicitly and in the final phase, note that all the loops have been eliminated and that all the nodes have decided on A as the root node. The links that have been selected are marked by bold lines.

Go run it again....