1-10Introduction to MSTPWhy MSTP1) Weaknesses of STP and RSTPSTP does not support rapid state transition of ports. A newly elected root port or designated port mustwait twice the forward delay time before transiting to the forwarding state, even if it is a port on apoint-to-point link or an edge port, which directly connects to a user terminal rather than to anotherdevice or a shared LAN segment.Although RSTP supports rapid network convergence, it has the same drawback as STP does: Allbridges within a LAN share the same spanning tree, so redundant links cannot be blocked based onVLAN, and the packets of all VLANs are forwarded along the same spanning tree.2) Features of MSTPThe Multiple Spanning Tree Protocol (MSTP) overcomes the shortcomings of STP and RSTP. Inaddition to the support for rapid network convergence, it also allows data flows of different VLANs to beforwarded along separate paths, thus providing a better load sharing mechanism for redundant links.For description about VLANs, refer to VLAN Configuration in the Access Volume.MSTP features the following:z MSTP supports mapping VLANs to MST instances (MSTIs) by means of a VLAN-to-MSTI mappingtable. MSTP can reduce communication overheads and resource usage by mapping multipleVLANs to one MSTI.z MSTP divides a switched network into multiple regions, each containing multiple spanning treesthat are independent of one another.z MSTP prunes a loop network into a loop-free tree, thus avoiding proliferation and endless cycling ofpackets in a loop network. In addition, it provides multiple redundant paths for data forwarding, thussupporting load balancing of VLAN data.z MSTP is compatible with STP and RSTP.
