1-22To do... Use the command... RemarksConfigure the max age timer stp timer max-age timeOptional2,000 centiseconds (20seconds) by defaultz The length of the forward delay time is related to the network diameter of the switched network.Typically, the larger the network diameter is, the longer the forward delay time should be. Note thatif the forward delay setting is too small, temporary redundant paths may be introduced; if theforward delay setting is too big, it may take a long time for the network to converge. We recommendthat you use the default setting.z An appropriate hello time setting enables the device to timely detect link failures on the networkwithout using excessive network resources. If the hello time is set too long, the device will takepacket loss as a link failure and trigger a new spanning tree calculation process; if the hello time isset too short, the device will send repeated configuration BPDUs frequently, which adds to thedevice burden and causes waste of network resources. We recommend that you use the defaultsetting.z If the max age time setting is too small, the network devices will frequently launch spanning treecalculations and may take network congestion as a link failure; if the max age setting is too large,the network may fail to timely detect link failures and fail to timely launch spanning tree calculations,thus reducing the auto-sensing capability of the network. We recommend that you use the defaultsetting.The settings of hello time, forward delay and max age must meet the following formulae; otherwise,network instability will frequently occur.z 2 × (forward delay – 1 second) ú max agez Max age ú 2 × (hello time + 1 second)We recommend that you specify the network diameter with the stp bridge-diameter command and letMSTP automatically calculate optimal settings of these three timers based on the network diameter.Configuring the Timeout FactorThe timeout factor is a parameter used to decide the timeout time, as shown in the following formula:Timeout time = timeout factor × 3 × hello time.After the network topology is stabilized, each non-root-bridge device forwards configuration BPDUs tothe downstream devices at the interval of hello time to check whether any link is faulty. Typically, if adevice does not receive a BPDU from the upstream device within nine times the hello time, it assumesthat the upstream device has failed and starts a new spanning tree calculation process.Sometimes a device may fail to receive a BPDU from the upstream device because the upstreamdevice is busy. A spanning tree calculation that occurs in this case not only is unnecessary, but alsowastes the network resources. In a very stable network, you can avoid such unwanted spanning treecalculations by setting the timeout factor to 5, 6, or 7.Follow these steps to configure the timeout factor:
