Troubleshooting an RPVST+ configuration

This section describes the show spanning tree commands you can use to monitor, troubleshoot, and debug the operation of a per-VLAN spanning tree configuration in your network.


	NOTE: The `show spanning-tree` commands described in this section, allow you to troubleshoot RPVST+ activity in your network by focusing on increasingly specific levels of operation. For example, you can display debug information for: All VLANs All ports of one VLAN A specific port or several ports used in one VLAN

Displaying the change history of root bridges

Syntax:

show spanning-tree root-history vlan <vlan-id>

Displays the last 10 root bridge changes on a specified VLAN configured with RPVST+. Included are the timestamp and Root Bridge ID recorded at each root bridge change.

Use the show spanning-tree root-history command to view the number and dates of changes in the assignment of a root bridge. Possible intrusion into your VLAN network may occur if an unauthorized external device gains access to a spanning tree by posing as the root device in a topology. To prevent a port connected to the device from being selected as the root port in a topology, use the spanning-tree root-guardcommand.

Displaying the change history of root bridges

switch#: show spanning-tree root-history vlan 20

 Status and Counters - RPVST Root Changes History

  VLAN ID                : 20
  Root Changes Counter   : 53
  Current Root Bridge ID : 32768:0024a8-d13a40

 Root Bridge ID      Date       Time
 ------------------- ---------- --------
 32768:0024a8-d13a40 05/04/2012 21:54:11
     0:001185-c6e500 05/04/2012 21:54:07
 32768:0024a8-d13a40 05/04/2012 16:41:11
     0:001185-c6e500 05/04/2012 16:41:11

Enabling traps and displaying trap configuration

Syntax:

[no]spanning-tree trap [ errant-bpdu | loop-guard | new-root topology-change [vlan < vid-list | instance [instance-ID] {cstt} | root-guard ]

Enables or disables SNMP traps for errant-BPDU, loop guard, new root, and root guard event notifications.

errant-bpdu
Enables SNMP notification when an errant BPDU is received. Designed for use with BPDU filtering (seeConfiguring BPDU filtering).

loop-guard
Enables SNMP notification when a loop guard inconsistency is detected. Designed for use with the Loop Guard option (see Configuring STP loop guard).

new-root
Enables SNMP notification when a new root is elected on any VLAN configured for RPVST+ on the switch.

root-guard
Enables SNMP notifications when a root-guard inconsistency is detected.

topology-change
Enables notifications sent when a topology change occurs.

topology-change-history
Shows the spanning tree topology history changes.

Default for all of the above options: Disabled

The no form of the command disables traps on the switch.

Syntax:

show spanning-tree traps

Displays the current spanning tree trap configuration on the switch.

Displaying spanning tree traps in the default configuration

switch#: show spanning-tree traps

 Status and Counters - STP Traps Information

 Trap Name              | Status
 ---------------------- + --------
 errant-bpdu            | Disabled
 new-root               | Disabled
 root-guard             | Disabled
 loop-guard             | Disabled

Displaying debug counters for all VLAN instances

Syntax:

show spanning-tree debug-counters

Displays the aggregate values of all RPVST+ debug counters that are maintained on a switch. These aggregate values are a summary of the information collected from all ports and from all spanning tree instances for all switch ports. Use the displayed diagnostic information to globally monitor RPVST+ operation on a per-switch basis.

Displaying debug counters for all VLANs

switch#: show spanning-tree debug-counters

 Status and Counters - RPVST Debug Counters Information

                                 Aggregated Value
  Counter Name                   Collected from VLANs
  ------------------------------ -------------------------
  Invalid BPDUs                  0
  Errant BPDUs                   0
  Looped-back BPDUs              0
  Starved BPDUs                  18
  Exceeded Max Age BPDUs         3
  Topology Changes Detected      9
  Topology Changes Tx            9
  Topology Changes Rx            4
  Topology Change ACKs Tx        0
  Topology Change ACKs Rx        6
  TCN BPDUs Tx                   4
  TCN BPDUs Rx                   0
  CFG BPDUs Tx                   0
  CFG BPDUs Rx                   0
  RST BPDUs Tx                   0
  RST BPDUs Rx                   0
  RPVST BPDUs Tx                 1881
  RPVST BPDUs Rx                 2617

See Field descriptions for RPVST+ debug command output.

Displaying debug counters per-VLAN

Syntax:

show spanning-tree debug vlan <vlan-id>

Displays the aggregate values of all RPVST+ debug counters maintained on a switch for a specified VLAN.

Displaying debug counters for a specific VLAN

switch(config)#: show spanning-tree debug vlan 20

 Status and Counters - RPVST Debug Counters Information

  VLAN ID : 20

                                 Aggregated Value
  Counter Name                   Collected from Ports
  ------------------------------ --------------------
  Invalid BPDUs                  5
  Errant BPDUs                   10
  Looped-back BPDUs              0
  Starved BPDUs                  9
  Exceeded Max Age BPDUs         2
  Topology Changes Detected      9
  Topology Changes Tx            4
  Topology Changes Rx            181
  Topology Change ACKs Tx        0
  Topology Change ACKs Rx        0
  TCN BPDUs Tx                   0
  TCN BPDUs Rx                   0
  CFG BPDUs Tx                   0
  CFG BPDUs Rx                   0
  RST BPDUs Tx                   0
  RST BPDUs Rx                   0
  RPVST BPDUs Tx                 1531
  RPVST BPDUs Rx                 1428

See Field descriptions for RPVST+ debug command output.

Displaying debug counters per-port per-VLAN

Syntax:

show spanning-tree debug ports <port-list> vlan <vlan-id>

Displays the aggregate values of all RPVST+ debug counters maintained on one or more ports used by a specified VLAN.

Displaying debug counters for a specific port on a VLAN

Switch_A(config)#: show spanning-tree debug ports 9 vlan 20

 Status and Counters - RPVST Debug Counters Information

  VLAN ID : 20
  Port : 9

  Counter Name                   Value           Last Updated
  ------------------------------ --------------- --------------------
  Invalid BPDUs                  0               04/16/2012 22:27:15
  Errant BPDUs                   0               04/16/2012 22:27:15
  Looped-back BPDUs              0               04/16/2012 22:27:15
  Starved BPDUs                  5               05/01/2012 21:48:11
  Exceeded Max Age BPDUs         0               04/16/2012 22:27:15
  Topology Changes Detected      9               05/04/2012 21:54:05
  Topology Changes Tx            5               05/05/2012 22:04:49
  Topology Changes Rx            2               05/07/2012 18:08:34
  Topology Change ACKs Tx        0               04/16/2012 22:27:15
  Topology Change ACKs Rx        0               04/16/2012 22:27:15
  TCN BPDUs Tx                   0               04/16/2012 22:27:15
  TCN BPDUs Rx                   0               04/16/2012 22:27:15
  CFG BPDUs Tx                   0               04/16/2012 22:27:15
  CFG BPDUs Rx                   0               04/16/2012 22:27:15
  RST BPDUs Tx                   0               04/16/2012 22:27:15
  RST BPDUs Rx                   0               04/16/2012 22:27:15
  RPVST BPDUs Tx                 7812            05/05/2012 22:04:49
  RPVST BPDUs Rx                 1065            05/08/2012 19:43:11

Field descriptions for RPVST+ debug command output

Field	Shows the number of —
`Invalid BPDUs`	Received BPDUs that failed standard RPVST+ (802.1Q-REV/D5.0 14.4) validation checks and were dropped. This counter is maintained on a per-port per-VLAN basis.
`Errant BPDUs`	Received BPDUs that were dropped on a port that is configured to not expect BPDU packets. This counter is maintained on a per-port basis and is incremented each time a BPDU is received on a port configured with the BPDU filter to ignore incoming BPDU packets (`spanning-tree bpdu-filter` command) or the BPDU protection feature to disable the port when BPDU packets are received (`spanning-tree bpdu-protection` command).
`Looped-back BPDUs`	Times that 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 RPVST+ and the port changes to a blocked state. This counter is maintained on a per-port per-VLAN basis.
`Starved BPDUs`	Times that no BPDUs are received within the scheduled interval (three times the Hello Time value configured with the `spanning-tree vlan hello-time` command) from a VLAN-designated peer port on the VLAN root, alternate, or backup port. As a result, the “starved” port triggers a spanning tree topology regeneration. This counter is maintained on a per-port per-VLAN basis.
`Exceeded Max Age BPDUs`	Times that a BPDU packet is received from a bridge 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.
`Topology Changes Detected`	Times that a Topology Change event is detected by the port on a given VLAN and the port triggers a topology change propagation throughout the network. A Topology Change event occurs when a non-edge port enters forwarding state. This counter is maintained on a per-VLAN per-port basis.
`Topology Changes Tx`	Times that Topology Change information is propagated (sent out) through the port to the rest of the network. For a VLAN port running PVST (non-rapid), the counter is the number of times that a CFG or RST BPDU with the TC flag set is transmitted out of the port. This counter is maintained on a per-VLAN per-port basis.
`Topology Changes Rx`	Times that Topology Change information is received from the peer port. For a VLAN port running PVST (non-rapid), the counter is the number of times that a CFG or RST BPDU with the TC flag set is received. This counter is maintained on a per-port per-VLAN basis.
`Topology Change ACKs Tx`	Times that the Topology Change acknowledgement is transmitted through the port (number of CFG or RST BPDUs transmitted with the Topology Change Acknowledge flag set). This counter is maintained on a per-port per-VLAN basis.
`Topology Change ACKs Rx`	Times that the Topology Change acknowledgement is received on the port (number of CFG or RST BPDUs received with the Topology Change Acknowledge flag set). This counter is maintained on a per-VLAN basis.
`TCN BPDUs Tx`	Topology Change Notification BPDUs that are transmitted through the port. This counter is maintained on a per-port basis.
`TCN BPDUs Rx`	Topology Change Notification BPDUs that are received on the port. This counter is maintained on a per-port per-VLAN basis.
`CFG BPDUs Tx`	802.1D configuration BPDUs that are transmitted through the port. This counter is maintained on a per-port per-VLAN basis.
`CFG BPDUs Rx`	802.1D configuration BPDUs that are received on the port. This counter maintained on a per-port per-VLAN basis.
`RST BPDUs Tx`	802.1w RST BPDUs that are transmitted through the port. This counter is maintained on a per-port per-VLAN basis.
`RST BPDUs Rx`	802.1w RST BPDUs that are received on the port. This counter is maintained on a per-port per-VLAN basis.

RPVST+ event log messages

Event	Log message
STP enabled/disabled on a VLAN	`Spanning tree Protocol enabled/disabled on vlan <vlan-id>`
Switch does not receive BPDUs from peer on a particular VLAN and port	`VLAN <vlan-id> starved for a BPDU on port <port number> from <bridge name>`
Switch received BPDU with inconsistent VLAN	`Blocking port-name on vlan <vlan-id>.`
Inconsistency is restored	`Unblocking port-name on vlan <vlan-id>Port consistency restored.`.
Root port is changed on a VLAN	`VLAN <vlan-id>root changed from <bridgepriorty:mac> to <bridge priority:mac>`
Switch received a BPDU with invalid TLV	`Received SSTP BPDU with bad TLV on <port-number> <vlan-id>`
The number of `vlan-port` instances exceeds the recommended limit	`The number of vlan-port instances exceeded the recommended limit of <num>`
RADIUS subsystem tries to dynamically change port VLAN assignments when mode is RPVST	`RADIUS unable to assign port to VLAN <vlan-id> because spanning-tree is running in RPVST+ mode`
LLDP subsystem tries to dynamically change port VLAN assignments when mode is RPVST	`LLDP unable to assign port <port-number> to VLAN <vlan-id> because spanning-tree is running in RPVST+ mode`
VPORT counts exceed 200	`The number of vPorts on slot <slot-number> exceeds the recommended limit of <vport-count>. PVST BPDUs may be dropped.`

Using RPVST+ debug

While the Event Log records switch-level progress, status, and warning messages on the switch, the Debug/System Logging (Syslog) feature provides a way to record Event Log and debug messages on a remote device. For example, you can send messages about routing misconfigurations and other network protocol details to an external device, and later use them to debug network-level problems. The Debug/Syslog feature allows you to specify the types of Event Log and debug messages that you want to send to an external device. The two commands described next affect debug operation for RPVST+.

Syntax:

spanning-tree clear-debug-counters [ports <port-list>][vlan <vid-list>]

Clears all spanning tree debug counters unless specific ports and/or VLANs are specified.

ports <port-list>
Clears spanning tree debug counters on the specified ports.

[ethernet]<port-list>
Clears spanning tree debug counters on an entered list of posts or all for the ports command parameter.

vlan
Clears spanning tree debug counters for the VLAN.

vlan <vlan-id-list>
One or more identifiers for the VLAN command parameter.

Using the vlan and ports options together clears the spanning tree debug counters on the specified ports for the specified VLANs. Counters maintained on the same ports for other VLANs are not cleared.

Syntax:

[no] debug rpvst [event [filter vlan <vid-list>]]

[no] debug rpvst [packet [filter port <port-list> [vlan <vid-list>]]]

Displays RPVST+ debug messages on the destination device specified with the debug destination logging | session | buffercommand.

event
Displays RPVST+ Event Log messages.

filter vlan <vid-list>
Limits log messages to those generated on the specified VLANs.

packet
Displays RPVST+ packets sent and received.

filter port <port-list> [vlan <vid-list>]
Limits packets displayed to those generated on the specified ports. If the vlan option is used, then packets displayed are further limited to the ports on the specified VLANs.

The no form of the command disables display of RPVST+ debug messages on the destination device.

`errant-bpdu`	Enables SNMP notification when an errant BPDU is received. Designed for use with BPDU filtering (seeConfiguring BPDU filtering).
`loop-guard`	Enables SNMP notification when a loop guard inconsistency is detected. Designed for use with the Loop Guard option (see Configuring STP loop guard).
`new-root`	Enables SNMP notification when a new root is elected on any VLAN configured for RPVST+ on the switch.
`root-guard`	Enables SNMP notifications when a root-guard inconsistency is detected.

`ports <port-list>`	Clears spanning tree debug counters on the specified ports.
`[ethernet]<port-list>`	Clears spanning tree debug counters on an entered list of posts or `all` for the `ports` command parameter.
`vlan`	Clears spanning tree debug counters for the VLAN.
`vlan <vlan-id-list>`	One or more identifiers for the `VLAN` command parameter.

`event`	Displays RPVST+ Event Log messages.
`filter vlan <vid-list>`	Limits log messages to those generated on the specified VLANs.
`packet`	Displays RPVST+ packets sent and received.
`filter port <port-list> [vlan <vid-list>]`	Limits packets displayed to those generated on the specified ports. If the `vlan` option is used, then packets displayed are further limited to the ports on the specified VLANs.

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Displaying RPVST+ statistics and configuration	home	About RPVST+

Troubleshooting an RPVST+ configuration

Displaying the change history of root bridges

​Syntax:

Enabling traps and displaying trap configuration

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Displaying debug counters for all VLAN instances

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Displaying debug counters per-VLAN

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Displaying debug counters per-port per-VLAN

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Field descriptions for RPVST+ debug command output

RPVST+ event log messages

Using RPVST+ debug

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