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660 | Multiple Spanning Tree Protocol
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Debugging and Verifying MSTP Configuration
Display BPDUs using the command debug spanning-tree mstp bpdu from EXEC Privilege mode. Display
MSTP-triggered topology change messages
debug spanning-tree mstp events.
Figure 29-15. Displaying BPDUs and Events
Examine your individual routers to ensure all the necessary parameters match.
1. Region Name
2. Region Version
3. VLAN to Instance mapping
The
show spanning-tree mst commands will show various portions of the MSTP configuration. To view the
overall MSTP configuration on the router, use the
show running-configuration spanning-tree mstp in the
EXEC 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 is
connected 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)? If
so, 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 was
not 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 an
additional MSTP Instance was configured on one router but not the others.
FTOS#debug spanning-tree mstp bpdu
1w1d17h : MSTP: Sending BPDU on Gi 1/31 :
ProtId: 0, Ver: 3, Bpdu Type: MSTP, Flags 0x68
CIST Root Bridge Id: 32768:0001.e806.953e, Ext Path Cost: 20000
Regional Bridge Id: 32768:0001.e809.c24a, CIST Port Id: 128:384
Msg Age: 2, Max Age: 20, Hello: 2, Fwd Delay: 15, Ver1 Len: 0, Ver3 Len: 96
Name: my-mstp-region, Rev: 0, Int Root Path Cost: 20000
Rem Hops: 19, Bridge Id: 32768:0001.e80d.b6d6
E1200#1w1d17h : INST 1: Flags: 0x28, Reg Root: 32768:0001.e809.c24a, Int Root Co
Brg/Port Prio: 32768/128, Rem Hops: 19
INST 2: Flags: 0x68, Reg Root: 4096:0001.e809.c24a, Int Root Cost: 20000
Brg/Port Prio: 32768/128, Rem Hops: 19
[output omitted]
FTOS#debug spanning-tree mstp events
1w1d17h : MSTP: TC flag set in the incoming BPDU on port Gi 1/31 for instance 0
1w1d17h : MSTP: TC flag set in the incoming BPDU on port Gi 1/31 for instance 0
1w1d17h : MSTP: TC flag set in the incoming BPDU on port Gi 1/31 for instance 0