Operation Manual – MSTPH3C S7500 Series Ethernet Switches Chapter 1 MSTP Configuration1-2The switches in a network transfer BPDUs between each other to determine thetopology of the network. BPDUs carry enough information needed for switches to figureout the spanning tree.BPDUs used in STP fall into the following two categories:z Configuration BPDUs: BPDUs of this type are used to maintain the spanning treetopology.z Topology change notification BPDU (TCN BPDU): BPDUs of this type are used tonotify the switches of network changes.Similar to STP and RSTP, MSTP uses BPDUs to figure out spanning trees too. Besides,the BPDUs of MSTP carry MSTP configuration information of the switches.1.1.2 Basic MSTP TerminologiesFigure 1-1 illustrates basic MSTP terms (assuming that MSTP is enabled on eachswitch in this figure).CSTBPDUBPDU BPDUADCBRegion A0VLAN 1 mapped toVLAN 2 mapped toOther VLANs mappRegiVLANVLANOtherRegion C0VLAN 1 mapped to iVLAN 2 mapped to iOther VLANs mappedRegion D0VLAN 1 mapped to instance 1,B as regional root bridgeVLAN 2 mapped to instance 2,C as regional root bridgeOther VLANs mapped to CISTinstance 1instance 2ed to CISTon B01 mapped to instance 12 mapped to instance 2VLANs mapped to CISTnstance 1nstance 2to CISTFigure 1-1 Basic MSTP terminologiesI. MST regionAn MST region (multiple spanning tree region) comprises multiplephysically-interconnected MSTP-enabled switches and the corresponding networksegments connected to these switches. These switches have the same region name,the same VLAN-to-MSTI mapping table and the same MSTP revision level.A switched network can contain multiple MST regions. You can group multiple switchesinto one MST region by using the corresponding MSTP configuration commands. Forexample, all switches in region A0 shown in Figure 1-1 have the same MST region
