Operation Manual – MSTPH3C S3610&S5510 Series Ethernet Switches Chapter 1 MSTP Configuration1-12Note:z In RSTP, a newly elected root port can enter the forwarding state rapidly if thiscondition is met: The old root port on the device has stopped forwarding data andthe upstream designated port has started forwarding data.z In RSTP, a newly elected designated port can enter the forwarding state rapidly ifthis condition is met: The designated port is an edge port or a port connected with apoint-to-point link. If the designated port is an edge port, it can enter the forwardingstate directly; if the designated port is connected with a point-to-point link, it canenter the forwarding state immediately after the device undergoes handshake withthe downstream device and gets a response.Although RSTP support rapid network convergence, it has the same drawback as STPdoes: All bridges within a LAN share the same spanning tree, so redundant links cannotbe blocked based on VLANs, and the packets of all VLANs are forwarded along thesame spanning tree.2) Features of MSTPThe multiple spanning tree protocol (MSTP) overcomes the shortcomings of STP andRSTP. In addition to support for rapid network convergence, it also allows data flows ofdifferent VLANs to be forwarded along their own paths, thus providing a better loadsharing mechanism for redundant links. For description about VLANs, refer to VLANConfiguration in the Access Volume.MSTP features the following:z MSTP supports mapping VLANs to MST instances by means of aVLAN-to-instance mapping table. MSTP can save communication overheads andresource usage by mapping multiple VLANs to one MST instance.z MSTP divides a switched network into multiple regions, each containing multiplespanning trees that are independent of one another.z MSTP prunes loop networks into a loop-free tree, thus avoiding proliferation andendless recycling of packets in a loop network. In addition, it provides multipleredundant paths for data forwarding, thus supporting load balancing of VLAN datain the data forwarding process.z MSTP is compatible with STP and RSTP.II. Basic concepts in MSTPAssume that all the four switches in Figure 1-4 are running MSTP. In light with thediagram, the following paragraphs will present some basic concepts of MSTP.
