A bridge whose role in radio network setting is root device does not necessarily become the root device in the spanning tree. Note In discussions about STP, the term root is used to describe two concepts: the bridge on the network that serves as a central point in the spanning tree is called the root device, and the port on each device that provides the most efficient path to the device is called the root port. STP defines a tree with a root device and a loop-free path from the root to all infrastructure devices in the Layer 2 network. These conditions result in an insecure network. Infrastructure devices might also learn end-station MAC addresses on multiple Layer 2 interfaces. If a loop exists in the network, end stations might receive duplicate messages. Multiple active paths among end stations cause loops in the network. The devices do not forward these frames but use them to construct a loop-free path. Infrastructure devices such as wireless bridges and switches send and receive spanning-tree frames, called bridge protocol data units (BPDUs), at regular intervals. The spanning-tree algorithm calculates the best loop-free path throughout a Layer 2 network. When you create fault-tolerant internetworks, you must have a loop-free path between all nodes in a network. Spanning-tree operation is transparent to end stations, which cannot detect whether they are connected to a single LAN segment or to a LAN of multiple segments. For a Layer 2 network to function properly, only one active path can exist between any two stations. STP is a Layer 2 link management protocol that provides path redundancy while preventing loops in the network. This section describes how spanning-tree features work. This document descibes Spanning Tree Protocol (STP) in a wireless environment.
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