Multiple Instance Spanning-Tree Operation

 

Troubleshooting an MSTP Configuration

 

 

Field

Description

 

 

MST Config Error BPDUs

Number of BPDUs received from a neighbor bridge with inconsistent MST configuration

 

information. For example, BPDUs from a transmitting bridge may contain the same MST

 

configuration identifiers (region name and revision number) and format selector as the

 

receiving bridge, but the value of the Configuration Digest field (VLAN ID assignments to

 

regional IST and MST instances) is different. This difference indicates a probable

 

configuration error in MST region settings on the communicating bridges. The received

 

BPDU is still processed by MSTP.

 

This counter is maintained by the CIST (default MST instance 0) on a per-port basis.

 

 

Looped-back BPDUs

Number of times a port has received self-sent BPDU packets as the result of an external

 

loop condition in which the BPDUs were looped back to the originating transmission port.

 

The received BPDU is still processed by MSTP and the port changes to a blocked state.

 

This counter is maintained by the CIST (default MST instance 0) on a per-port basis.

 

 

Starved BPDUs

Number of times that no BPDUs are received within the scheduled interval (three times the

 

Hello Time value configured with the spanning-treehello-timecommand) from a

 

downstream CIST-designated peer port on the CIST root, alternate, or backup port. As a

 

result, the “starved” port triggers a spanning-tree topology regeneration.

 

This counter is maintained by the CIST (default MST instance 0) on a per-port basis.

 

 

Starved MSTI MSGs

Number of times that no BPDUs are received within the scheduled interval (three times the

 

Hello Time value configured with the spanning-treehello-timecommand) from a

 

downstream MSTI-designated peer port on the MSTI root, alternate, or backup port. As a

 

result, the “starved” port triggers a spanning-tree topology regeneration.

 

This counter is maintained by the CIST (default MST instance 0) on a per-port basis.

 

 

Exceeded Max Age

Number of times that a BPDU packet is received from a bridge external to the MST region

BPDUs

with a Message Age value greater than the configured value of the Max Age parameter

 

(spanning-tree maximum age command). This may occur if the receiving bridge is located

 

too far from the root bridge (beyond the configured size of the spanning-tree domain on the

 

root bridge) or if a BPDU packet with invalid root information is continuously circulating

 

between bridges in a spanning-tree domain and needs to be aged out.

 

This counter is maintained by the CIST (default MST instance 0) on a per-port basis.

 

 

Exceeded Max Hops

Number of times that a BPDU packet is received from a bridge internal to the MST region

BPDUs

with a CIST Remaining Hops value less than or equal to 1. This may occur if the receiving

 

bridge is located too far from the CIST regional root bridge (beyond the configured size of

 

the MST region on the CIST regional root bridge) or if a PDU packet with invalid CIST regional

 

root bridge information is continuously circulating between bridges in the MST Region and

 

needs to be aged out.

 

This counter is maintained by the CIST (default MST instance 0 in the region) on a per-port

 

basis.

 

 

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