:вЂЉ393ДЄfter STP enabled switches in a LAN have elected the root bridge, all non-root bridges assign one of their ports as root port. STP will enable this preferred link as the only path to be used for Ethernet frames between the two switches, and disable all other possible links by designating the switch ports that connect the preferred path as root port. STP will select the path with the lowest cost, that is the highest bandwidth, as the preferred link. Provided there is more than one link between two switches, the STP root bridge calculates the cost of each path based on bandwidth. All switches constantly communicate with their neighbors in the LAN using bridge protocol data units (BPDUs). All switches then select their best connection towards the root bridge for forwarding and block other redundant links. When implemented in a network, STP designates one layer-2 switch as root bridge. This preferred link is used for all Ethernet frames unless it fails, in which case a non-preferred redundant link is enabled. The spanning-tree algorithm then blocks forwarding on redundant links by setting up one preferred link between switches in the LAN. Every link between switches, and in particular redundant links, are catalogued. To avoid the problems associated with redundant links in a switched LAN, STP is implemented on switches to monitor the network topology. :вЂЉ388 If redundant links are used to connect switches, then switching loops need to be avoided.

:вЂЉ386 However, this connection configuration creates a switching loop resulting in broadcast radiations and MAC table instability. The need for the Spanning Tree Protocol (STP) arose because switches in local area networks (LANs) are often interconnected using redundant links to improve resilience should one connection fail. Switches with Spanning Tree Protocol implementation in a local area network (LAN) STP was originally standardized as IEEE 802.1D but the functionality of spanning tree (802.1D), rapid spanning tree (802.1w), and multiple spanning tree (802.1s) has since been incorporated into IEEE 802.1Q-2014. RSTP was designed to be backwards-compatible with standard STP. RSTP provides significantly faster recovery in response to network changes or failures, introducing new convergence behaviors and bridge port roles to do this. In 2001, the IEEE introduced Rapid Spanning Tree Protocol ( RSTP) as 802.1w. STP is based on an algorithm that was invented by Radia Perlman while she was working for Digital Equipment Corporation. Spanning tree also allows a network design to include backup links providing fault tolerance if an active link fails.ДЄs the name suggests, STP creates a spanning tree that characterizes the relationship of nodes within a network of connected layer-2 bridges, and disables those links that are not part of the spanning tree, leaving a single active path between any two network nodes. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. The Spanning Tree Protocol ( STP) is a network protocol that builds a loop-free logical topology for Ethernet networks.

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