Spanning Tree Protocol (STP) was created to prevent problems that develop in a redundant switched network. It executes a spanning-tree algorithm that works by choosing one reference point in the network. Then, each switch selects one path back to the root and puts all others in a standby, or blocked, state. Spanning tree is enabled by default on all Cisco switches and has a default configuration. You might want to make some changes, however, to optimize spanning-tree operation for your particular network.