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| 3.1 |  | Spanning-Tree Protocol Operation |
| 3.1.1 |  | STP concepts |

Spanning-Tree Protocol (STP) is a Layer 2 protocol that utilizes a special-purpose algorithm to discover physical loops in a network and effect a logical loop-free topology. STP creates a loop-free tree structure consisting of leaves and branches that span the entire Layer 2 network. The actual mechanics of how bridges communicate and how the STP algorithm works will be discussed at length in the following topics. Note that the terms bridge and switch are used interchangeably when discussing STP. In addition, unless otherwise indicated, connections between switches are assumed to be trunks.

The greater discussion of STP concerns its behavior on trunk connections, which form the spanning tree. Loops can occur in a network for a variety of reasons. Usually, loops in a network are the result of a deliberate attempt to provide redundancy. However, loops can also result from configuration errors. Figure shows a typical switched network and how loops can be intentionally used to provide redundancy.

Physical loops without proper STP design can be disastrous. Two problems that can result are broadcast loops and bridge table corruption. These phenomena are discussed in the next two topics.