1-10For this reason, the protocol uses a state transition mechanism. Namely, a newly elected root port andthe designated ports must go through a period, which is twice the forward delay time, before they transitto the forwarding state. The period allows the new configuration BPDUs to be propagated throughoutthe entire network.z Hello time, the interval for sending hello packets. Hello packets are used to check link state.A switch sends hello packets to its neighboring devices at a regular interval (the hello time) to checkwhether the links are faulty.z Max time, lifetime of the configuration BPDUs stored in a switch. A configuration BPDU that has“expired” is discarded by the switch.Rapid Spanning Tree Protocol OverviewRapid spanning tree protocol (RSTP) is an optimized version of STP. RSTP allows a newly elected rootport or designated port to enter the forwarding state much quicker under certain conditions than in STP.As a result, it takes a shorter time for the network to reach the final topology stability.z In RSTP, the state of a root port can transit fast under the following conditions: the old root port onthe device has stopped forwarding data and the upstream designated port has started forwardingdata.z In RSTP, the state of a designated port can transit fast under the following conditions: thedesignated port is an edge port or a port connected with a point-to-point link. If the designated portis an edge port, it can enter the forwarding state directly; if the designated port is connected with apoint-to-point link, it can enter the forwarding state immediately after the device undergoeshandshake with the downstream device and gets a response.Multiple Spanning Tree Protocol OverviewWhy MSTP1) Disadvantages 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 it is an edge port (an edge port refers to a port that directly connects to a userterminal rather than to another device or a shared LAN segment.)RSTP supports rapid convergence. Like STP, it is of the following disadvantages: all bridges in a LANare on the same spanning tree; redundant links cannot be blocked by VLAN; the packets of all VLANsare forwarded along the same spanning tree.2) Features of MSTPThe multiple spanning tree protocol (MSTP) overcomes the shortcomings of STP and RSTP. In additionto support for rapid network convergence, it also allows data flows of different VLANs to be forwardedalong their own paths, thus providing a better load sharing mechanism for redundant links.MSTP features the following:
