Spanning Trees

Algorhyme

I think that I shall never see
a graph more lovely than a tree.

A tree whose crucial property
is loop-free connectivity.

A tree which must be sure to span
so packets can reach every LAN.

First the root must be selected.
By ID it is elected.

Least cost paths from root are traced.
In the tree these paths are placed.

A mesh is made by folks like me,
then bridges find a spanning tree.

– Radia Perlman

L2 networks were getting larger, and a common mistake was creating a loop, where frame would go around infinitely.

Spanning Tree Protocol STP disables ports to break L2 loops.