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Spanning Tree Root Port Always Changing (Vlan 20)

PolyCaleb
Beginner
Beginner

‎09-29-2014 01:01 PM - edited ‎03-07-2019 08:55 PM

I'm trying to figure out what would cause Spanning Tree to keep changing over to a new port for forwarding on Vlan 20 (but no other Vlans) and then immediately change back to the old port.

This just started happening 3 days ago and it flickered over to the "backup port" and then back to the "primary port" over 70 times.  There is no record/log of any ports going down and none of the other Vlans went through the change over and back in spanning-tree.

The Root port is supposed to be G1/2 but will go to G1/1 and then back to G1/2 right away.

 

The switch in question is 3560X-24T running 12.2(55)SE5 IPServices using the UniversalK9.

The switch attached to G1/2 is a 3750X-12S and a second switch attached to G1/1 is also a 3750X-12S.  There is a fourth switch attached to each of those that also uses Vlan 20, 22, 26-27, 900-906, 920

 

The changes have triggered broadcast storms as well as HSRP failovers.

 

If you have commands that I might use to help diagnose what is going one I would appreciate it.

 

Included are "sh trunk int", "sh span sum", "sh span vlan 20 det", "sh span vlan 22 det", and "debug spanning-tree uplinkfast" during one of these flips.

Results from "sh trunk int"

Port        Mode             Encapsulation  Status        Native vlan
Gi0/10      on               802.1q         trunking      1
Gi1/1       on               802.1q         trunking      66
Gi1/2       on               802.1q         trunking      67
Gi1/4       on               802.1q         trunking      920

Port        Vlans allowed on trunk
Gi0/10      20,22
Gi1/1       20,22,26-27,66,900-906,920
Gi1/2       20,22,26-27,67,900-906,920
Gi1/4       900-906,920

Port        Vlans allowed and active in management domain
Gi0/10      20,22
Gi1/1       20,22,26-27,66,900-906,920
Gi1/2       20,22,26-27,67,900-906,920
Gi1/4       900-906,920

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/10      20,22
Gi1/1       66
Gi1/2       20,22,26-27,67,900-906,920
Gi1/4       900-906,920

 

Results from "sh span sum"

Switch is in pvst mode
Root bridge for: VLAN1001
EtherChannel misconfig guard is enabled
Extended system ID           is enabled
Portfast Default             is disabled
PortFast BPDU Guard Default  is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default            is disabled
UplinkFast                   is enabled
BackboneFast                 is disabled
Configured Pathcost method used is short

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0020                     1         0        0          2          3
VLAN0022                     1         0        0          3          4
VLAN0026                     1         0        0          1          2

VLAN0027                     1         0        0          2          3
VLAN0066                     0         0        0          1          1
VLAN0067                     0         0        0          1          1
VLAN0900                     1         0        0          2          3
VLAN0901                     1         0        0          2          3
VLAN0902                     1         0        0          2          3

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0903                     1         0        0          2          3
VLAN0904                     1         0        0          2          3
VLAN0905                     1         0        0          2          3
VLAN0906                     1         0        0          2          3
VLAN0920                     1         0        0          2          3
VLAN1001                     0         0        0          1          1
---------------------- -------- --------- -------- ---------- ----------
15 vlans                    12         0        0         27         39

Station update rate set to 150 packets/sec.

UplinkFast statistics
-----------------------
Number of transitions via uplinkFast (all VLANs)            : 906
Number of proxy multicast addresses transmitted (all VLANs) : 7072

 

Results from "sh span vlan 20 det":

 VLAN0020 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 49152, sysid 20, address 4c00.82a6.7700
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 49172, address 10f3.11a0.1280
  Root port is 26 (GigabitEthernet1/2), cost of root path is 3004
  Topology change flag not set, detected flag not set
  Number of topology changes 1458 last change occurred 00:08:48 ago
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300
  Uplinkfast enabled

 Port 10 (GigabitEthernet0/10) of VLAN0020 is designated forwarding
   Port path cost 3004, Port priority 128, Port Identifier 128.10.
   Designated root has priority 49172, address 10f3.11a0.1280
   Designated bridge has priority 49172, address 4c00.82a6.7700

   Designated port id is 128.10, designated path cost 3004
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 6949896, received 0

 Port 25 (GigabitEthernet1/1) of VLAN0020 is alternate blocking
   Port path cost 3004, Port priority 128, Port Identifier 128.25.
   Designated root has priority 49172, address 10f3.11a0.1280
   Designated bridge has priority 49172, address 10f3.11af.d480
   Designated port id is 128.11, designated path cost 3004
   Timers: message age 3, forward delay 0, hold 0
   Number of transitions to forwarding state: 0
   Link type is point-to-point by default
   BPDU: sent 1720, received 2888276

 Port 26 (GigabitEthernet1/2) of VLAN0020 is root forwarding
   Port path cost 3004, Port priority 128, Port Identifier 128.26.
   Designated root has priority 49172, address 10f3.11a0.1280
   Designated bridge has priority 49172, address 10f3.11a0.1280
   Designated port id is 128.11, designated path cost 0
   Timers: message age 1, forward delay 0, hold 0
   Number of transitions to forwarding state: 75

   Link type is point-to-point by default
   BPDU: sent 1745, received 2714716

 

Results from "sh span vlan 22 det":  (This is a vlan that is not acting crazy)

 VLAN0022 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 49152, sysid 22, address 4c00.82a6.7700
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 49174, address 10f3.11a0.1280
  Root port is 26 (GigabitEthernet1/2), cost of root path is 3004
  Topology change flag not set, detected flag not set
  Number of topology changes 33 last change occurred 8w6d ago
          from GigabitEthernet1/2
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300
  Uplinkfast enabled

 Port 9 (GigabitEthernet0/9) of VLAN0022 is designated forwarding
   Port path cost 3004, Port priority 128, Port Identifier 128.9.
   Designated root has priority 49174, address 10f3.11a0.1280
   Designated bridge has priority 49174, address 4c00.82a6.7700
   Designated port id is 128.9, designated path cost 3004
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   The port is in the portfast mode
   Link type is point-to-point by default
   BPDU: sent 6934433, received 0

 Port 10 (GigabitEthernet0/10) of VLAN0022 is designated forwarding
   Port path cost 3004, Port priority 128, Port Identifier 128.10.
   Designated root has priority 49174, address 10f3.11a0.1280
   Designated bridge has priority 49174, address 4c00.82a6.7700
   Designated port id is 128.10, designated path cost 3004
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 6934437, received 0

 Port 25 (GigabitEthernet1/1) of VLAN0022 is alternate blocking
   Port path cost 3004, Port priority 128, Port Identifier 128.25.
   Designated root has priority 49174, address 10f3.11a0.1280
   Designated bridge has priority 49174, address 10f3.11af.d480
   Designated port id is 128.11, designated path cost 3004
   Timers: message age 3, forward delay 0, hold 0
   Number of transitions to forwarding state: 0
   Link type is point-to-point by default
   BPDU: sent 13, received 2882504

 Port 26 (GigabitEthernet1/2) of VLAN0022 is root forwarding
   Port path cost 3004, Port priority 128, Port Identifier 128.26.
   Designated root has priority 49174, address 10f3.11a0.1280
   Designated bridge has priority 49174, address 10f3.11a0.1280
   Designated port id is 128.11, designated path cost 0
   Timers: message age 2, forward delay 0, hold 0
   Number of transitions to forwarding state: 0
   Link type is point-to-point by default
   BPDU: sent 4, received 2710134

 

Results from "debug spanning-tree uplinkfast":

Sep 29 14:53:21.321 CDT: STP FAST: UPLINKFAST: make_forwarding on VLAN0020 GigabitEthernet1/1 root port id new: 128.25 prev: 128.26

Sep 29 14:53:21.321 CDT: %SPANTREE_FAST-7-PORT_FWD_UPLINK: VLAN0020 GigabitEthernet1/1 moved to Forwarding (UplinkFast).
Sep 29 14:53:21.321 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet0/10 VLAN0020 is: uplink enabled new root GigabitEthernet1/1 (not me)prev root exists(801A/GigabitEthernet1/2) cur state forwarding role uplink
Sep 29 14:53:21.321 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/2 VLAN0020 is: uplink enabled new root GigabitEthernet1/1 (not me)prev root exists(801A/GigabitEthernet1/2) cur state blocking role looped
Sep 29 14:53:21.321 CDT: STP FAST: UPLINKFAST: make_forwarding on VLAN0020 GigabitEthernet1/2 root port id new: 128.26 prev: 128.25

Sep 29 14:53:21.321 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet0/10 VLAN0020 is: uplink enabled new root GigabitEthernet1/2 (not me)prev root exists(8019/GigabitEthernet1/1) cur state forwarding role uplink
Sep 29 14:53:39.331 CDT: STP FAST: UPLINKFAST: make_forwarding on VLAN0020 GigabitEthernet1/1 root port id new: 128.25 prev: 128.26

Sep 29 14:53:39.331 CDT: %SPANTREE_FAST-7-PORT_FWD_UPLINK: VLAN0020 GigabitEthernet1/1 moved to Forwarding (UplinkFast).
Sep 29 14:53:39.331 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet0/10 VLAN0020 is: uplink enabled new root GigabitEthernet1/1 (not me)prev root exists(801A/GigabitEthernet1/2) cur state forwarding role uplink
Sep 29 14:53:39.331 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/2 VLAN0020 is: uplink enabled new root GigabitEthernet1/1 (not me)prev root exists(801A/GigabitEthernet1/2) cur state blocking role looped
Sep 29 14:53:39.331 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet0/10 VLAN0020 is: uplink enabled new root <none> (not me)prev root not set(0000/<none>) cur state forwarding role uplink
Sep 29 14:53:39.331 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/1 VLAN0020 is: uplink enabled new root <none> (not me)prev root not set(0000/<none>) cur state forwarding role uplink
Sep 29 14:53:39.331 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/2 VLAN0020 is: uplink enabled new root <none> (not me)prev root not set(0000/<none>) cur state listening role uplink
Sep 29 14:53:40.329 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/2 VLAN0020 is: uplink enabled new root GigabitEthernet1/2 (me)prev root not set(0000/<none>) cur state listening role uplink
Sep 29 14:53:40.329 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet0/10 VLAN0020 is: uplink enabled new root GigabitEthernet1/2 (not me)prev root not set(0000/<none>) cur state forwarding role uplink
Sep 29 14:53:40.329 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/1 VLAN0020 is: uplink enabled new root GigabitEthernet1/2 (not me)prev root not set(0000/<none>) cur state forwarding role uplink
Sep 29 14:53:41.344 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet1/2 VLAN0020 is: uplink enabled new root GigabitEthernet1/2 (me)prev root not set(0000/<none>) cur state listening role uplink
Sep 29 14:53:41.344 CDT: STP FAST: make_forwarding: via UPLINKFAST: NOT: port GigabitEthernet0/10 VLAN0020 is: uplink enabled new root GigabitEthernet1/2 (not me)prev root not set(0000/<none>) cur state forwarding role uplink

 

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