3Com Switch 8800 Configuration Guide Chapter 38 MSTP Region-configuration38-16If the primary root is down or powered off, the secondary root will take its place, unlessyou configure a new primary root. Of two or more configured secondary root bridges,MSTP selects the one with the smallest MAC address to take the place of the failedprimary root.When configuring the primary and secondary switches, you can also configure thenetwork diameter and hello time of the specified switching network. For detailedinformation, refer to the configuration tasks “Configure switching network diameter” and“Configure the Hello Time of the switch”.Note:You can configure the current switch as the root of several STIs. However, it is notnecessary to specify two or more roots for an STI. In other words, do not specify theroot for an STI on two or more switches.You can configure more than one secondary root for a spanning tree through specifyingthe secondary STI root on two or more switches.Generally, you are recommended to designate one primary root and more than onesecondary root for a spanning tree.By default, a switch is neither the primary root nor the secondary root of the spanningtree.38.2.3 Configuring the MSTP Running ModeMSTP and RSTP are compatible and they can recognize the packets of each other.However, STP cannot recognize MSTP packets. To implement the compatibility, MSTPprovides two operation modes, STP-compatible mode and MSTP mode. InSTP-compatible mode, the switch sends STP packets via every port. In MSTP mode,the switch ports send MSTP or STP packets (when connected to the STP switch) andthe switch provides multiple spanning tree function.You can use the following command to configure MSTP running mode. MSTP canintercommunicate with STP. If there is a STP switch in the switching network, you mayuse the command to configure the current MSTP to run in STP-compatible mode.Otherwise, configure it to run in MSTP mode.Perform the following configuration in system view.Table 38-5 Configure the MSTP running modeOperation CommandConfigure MSTP to run in STP-compatible mode stp mode stpConfigure MSTP to run in MSTP mode stp mode mstp
