multiple spanning tree protocol (802.1s) (MSTP)

Multiple Spanning Tree Protocol (MSTP) is a spanning tree protocol standardized by the IEEE working group802.1s, later 802.1Q, with not only one spanning tree spanning the entire network, but with several smaller spanning trees that can be built over a larger physical network.

For large networks, a single spanning tree has the disadvantage that reconfiguration times are relatively long. This can be avoided by using multiple spanning trees with shorter STP instances. In the MSTP method, each individual root bridge has its own Multiple Spanning Tree Instance (MSTI), which is completely independent of others. The MSTP discussed in 802.1s can be seen as a further development of the Rapid Spanning Tree Protocol( RSTP), it supports up to 64 MSTIs, with some effort even up to 4,000.

In the MSTP method, a root bridge is determined and the lowest path cost between the root bridge and the offered root ports of the individual bridges. The root bridge sends Bridge Protocol Data Units( BPDU) to all bridges and uses the configuration data contained in the BPDU data packets to determine the network configuration.