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spanning tree protocol (STP)

The Spanning Tree Protocol (STP) is a redundancy procedure for loop suppression and thus for path optimization in networks. In this procedure, physically redundant network structures are determined and mapped in a cycle-free structure. This measure reduces the active connection paths of an arbitrarily meshed network structure and leads it into a tree topology

, hence the name spanning tree. Mathematically, a tree topology is such that all networked points are connected by only one path. Moreover, all networked points are reachable from all other networked points, moreover, there are no cycles

between any two networked points.Only when the preferred connection path is broken, the network is reorganized and the optional connection paths are activated. To check the link paths, the switches or bridges communicate regularly with configuration data packets, the Bridge Protocol Data Units

(BPDU). If a link fails, the BPDU data packets no longer arrive and the SPA protocol ensures reorganization.

Spanning tree

Spanning tree

protocol
with suppression of parallel connections

with suppression of parallel connections

The spanning tree protocol was developed by Digital Equipment (DEC) and later adopted in modified form by IEEE 802.1d. The algorithm is implemented in corresponding bridge types, where each bridge computes the path towards the root of

the tree topology within certain optimality criteria. Since the conventional spanning tree procedure requires a long convergence time of approx.

30 secondsfor

the reconfiguration of the connections, the IEEE working group 802.1 has specified several spanning tree procedures, such as the Rapid Spanning Tree Protocol (RSTP) with reduced reaction time and, as a further development, the Multiple Spanning Tree Protocol (MSTP) with which the reconfiguration times are reduced even further.

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Englisch: spanning tree protocol - STP
Updated at: 18.10.2013
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Translations: DE