660 | Multiple Spanning Tree Protocolw w w . d e l l . c o m | s u p p o r t . d e l l . c o mDebugging and Verifying MSTP ConfigurationDisplay BPDUs using the command debug spanning-tree mstp bpdu from EXEC Privilege mode. DisplayMSTP-triggered topology change messages debug spanning-tree mstp events.Figure 29-15. Displaying BPDUs and EventsExamine your individual routers to ensure all the necessary parameters match.1. Region Name2. Region Version3. VLAN to Instance mappingThe show spanning-tree mst commands will show various portions of the MSTP configuration. To view theoverall MSTP configuration on the router, use the show running-configuration spanning-tree mstp in theEXEC Privilege mode (output sample shown in Figure 29-16).Use the debug spanning-tree mstp bpdu command to monitor and verify that the MSTP configuration isconnected and communicating as desired (output sample shown in Figure 29-17).Key items to look for in the debug report:• MSTP flags indicate communication received from the same region.• In Figure 29-17, the output shows that the MSTP routers are located in the same region.• Does the debug log indicate that packets are coming from a “Different Region” (Figure 29-18)? Ifso, one of the key parameters is not matching.• MSTP Region Name and Revision• The configured name and revisions must be identical among all the routers.• Is the Region name blank? That may mean that a name was configured on one router and but wasnot configured or was configured differently on another router (spelling and capitalization counts).• MSTP Instances.• Use the show commands to verify the VLAN to MSTP Instance mapping.• Are there “extra” MSTP Instances in the Sending or Received logs? That may mean that anadditional MSTP Instance was configured on one router but not the others.FTOS#debug spanning-tree mstp bpdu1w1d17h : MSTP: Sending BPDU on Gi 1/31 :ProtId: 0, Ver: 3, Bpdu Type: MSTP, Flags 0x68CIST Root Bridge Id: 32768:0001.e806.953e, Ext Path Cost: 20000Regional Bridge Id: 32768:0001.e809.c24a, CIST Port Id: 128:384Msg Age: 2, Max Age: 20, Hello: 2, Fwd Delay: 15, Ver1 Len: 0, Ver3 Len: 96Name: my-mstp-region, Rev: 0, Int Root Path Cost: 20000Rem Hops: 19, Bridge Id: 32768:0001.e80d.b6d6E1200#1w1d17h : INST 1: Flags: 0x28, Reg Root: 32768:0001.e809.c24a, Int Root CoBrg/Port Prio: 32768/128, Rem Hops: 19INST 2: Flags: 0x68, Reg Root: 4096:0001.e809.c24a, Int Root Cost: 20000Brg/Port Prio: 32768/128, Rem Hops: 19[output omitted]FTOS#debug spanning-tree mstp events1w1d17h : MSTP: TC flag set in the incoming BPDU on port Gi 1/31 for instance 01w1d17h : MSTP: TC flag set in the incoming BPDU on port Gi 1/31 for instance 01w1d17h : MSTP: TC flag set in the incoming BPDU on port Gi 1/31 for instance 0
