TO 6.6.4: STP Facts.pdf - TestOut LabSim 6.6.4STPFacts To...

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10/26/2017 TestOut LabSim https://cdn.testout.com/client-v5-1-10-464/startlabsim.html 1/3 6.6.4 STP Facts To provide for fault tolerance, many networks implement redundant paths between multiple switches. However, providing redundant paths between segments could cause frames to be endlessly passed between the redundant paths. This condition is known as a switching loop . To prevent switching loops, the IEEE 802.1d committee defined the Spanning Tree Protocol (STP). With STP, one switch for each route is assigned as the designated bridge. Only the designated bridge can forward packets. Redundant switches are assigned as backups. The spanning tree protocol: Eliminates loops. Provides redundant paths between devices. Enables dynamic role configuration. Recovers automatically from a topology change or device failure. Identifies the optimal path between any two network devices. The spanning tree protocol uses a spanning tree algorithm (STA) to calculate the best loop-free path through a network by assigning a role to each bridge or switch. The bridge role determines how the device functions in relation to other devices and whether the device forwards traffic to other segments. The following table describes the three types of bridge roles: Role Characteristics Root bridge The root bridge is the master, or controlling, bridge. There is only one root bridge in the network. The root bridge is the logical center of the spanning tree topology in a switched network. The root bridge is determined by the switch with the lowest bridge ID (BID): The bridge ID is composed of two parts—a bridge priority number and the MAC address assigned to the switch. The default priority number for all switches is 32,768. This means the switch with the lowest MAC address becomes the root bridge unless you customize the priority values. You can manually configure the priority number to force a specific switch to become the root switch. The root bridge periodically broadcasts configuration messages. These messages are used to select routes and reconfigure the roles of other bridges, if necessary. All ports on a root bridge forward messages to the network. Designated bridge A designated bridge is any other device that participates in forwarding packets through the network. They are selected automatically by exchanging bridge configuration packets. To prevent bridge loops, there is only one designated bridge per segment. Backup bridge All redundant devices are classified as backup bridges .
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