Configuring MSTP 139Too short a Max Age may cause the network device frequently calculate thespanning tree and mistake the congestion as a link fault. However, if the Max Ageis too long, the network device may not be able to discover the link fault andrecalculate the spanning tree in time, which will weaken the auto-adaptationcapacity of the network. The default value is recommended.To avoid frequent network flapping, the values of Hello Time, Forward Delay andMax Age should guarantee the following formulas.2 x (Forward-Delay - 1 second) >= Max AgeMax Age >= 2 x (Hello Time + 1 second)You are recommended to use the stp bridge-diameter command to specify thenetwork diameter and Hello Time of the switching network, and then MSTP willautomatically calculate and give the rather desirable values.By default, Forward Delay is 15 seconds, Hello Time is 2 seconds, and Max Age is20 seconds.Setting the TimeoutFactor of a SpecificBridgeA switch transmits hello packet regularly to the adjacent bridges to check if thereis link failure. Generally, if the switch does not receive the STP packets from theupstream switch for 3 times of hello time, the switch will decide the upstreamswitch is dead and will recalculate the topology of the network. Then, in a steadynetwork, the recalculation may be caused when the upstream is busy. In this case,user can redefine the timeout interval to a longer time to avoid this kind ofmeaningless recalculation.You can use the following command to set the multiple value of hello time of aspecified bridge.Perform the following configurations in system view.It is recommended to set 5, 6 or 7 as the timeout factor in the steady network.By default, the timeout factor of the switch is 3.Configuring the MaxTransmission Speed on aPortThe max transmission speed on a port specifies how many MSTP packets will betransmitted via the port every Hello Time.The max transmission speed on a port is limited by the physical state of the portand the network structure. You can configure it according to the networkconditions.You can configure the max transmission speed on a port in the following ways.Table 114 Setting the timeout factor of a specific switchOperation CommandSet the timeout factor of a specified switch stp timer-factor numberRestore the default timeout factor undo stp timer-factor
