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PVST Spanning-Tree: Port stuck in LIS state [Debugs/Topology Included]

Hello,

I've run into what seems to be a strange STP issue while doing some labbing.     

Capture.PNG

PVST enabled, VLANs 100 and 200 on all switches, SW06 configured as the root bridge.

Naturally Fa0/9 on SW05 is a root port but about 90% of the time never leaves the "listening" state.

It seems to be related to how quickly the link is reconnected. For instance, if I unplug or shutdown Fa0/9 on SW05 and either plug it back in or no shut the interface before Fa0/7 has gotten past the listening state then Fa0/7 returns to blocking and Fa0/9 never moves past the listening state. However, if I wait until Fa0/7 reaches atleast the learning state to no shut or reconnect Fa0/9 then Fa0/7 transitions to the blocking state and Fa0/9 successfully transitions to the forwarding state.

Is there a reason for this? I realize R-PVST or MST is probably the preferred method but am curious as to why this happens.

Below is the output of "debug spanning-tree events" and "debug spanning-tree general" after shutting and no shutting both Fa0/7 and Fa0/9.

SW05(config-if-range)#no shut
SW05(config-if-range)#
1d05h: %LINK-3-UPDOWN: Interface FastEthernet0/7, changed state to up
1d05h: %LINK-3-UPDOWN: Interface FastEthernet0/9, changed state to up
SW05(config-if-range)#
1d05h: Created spanning tree: VLAN0100 (80DC1970)
1d05h: Setting spanning tree MAC address: VLAN0100 (80DC1970) to 0008.20f8.ca80
1d05h: setting bridge id (which=3) prio 32868 prio cfg 32768 sysid 100 (on) id

8064.0008.20f8.ca80
1d05h: STP PVST: Assigned bridge address of 0008.20f8.ca80 for VLAN0100 [64] @ 80DC1970.
1d05h: Starting spanning tree: VLAN0100 (80DC1970)
1d05h: set portid: VLAN0100 Fa0/7: new port id 8007
1d05h: Created spanning tree port Fa0/7 (80E204D8) for tree VLAN0100 (80DC1970)

SW05(config-if-range)#1d05h: Enabling spanning tree port: FastEthernet0/7 (80E204D8)
1d05h: STP: VLAN0100 Fa0/7 -> listening
1d05h: Created spanning tree: VLAN0200 (80E10DB8)
1d05h: Setting spanning tree MAC address: VLAN0200 (80E10DB8) to 0008.20f8.ca80
1d05h: setting bridge id (which=3) prio 32968 prio cfg 32768 sysid 200 (on) id

80C8.0008.20f8.ca80
1d05h: STP PVST: Assigned bridge address of 0008.20f8.ca80 for VLAN0200 [C8] @ 80E10DB8.
1d05h: Starting spanning tree: VLAN0200 (80E10DB8)
1d05h: set portid: VLAN0200 Fa0/
SW05(config-if-range)#7: new port id 8007
1d05h: Created spanning tree port Fa0/7 (80E19504) for tree VLAN0200 (80E10DB8)
1d05h: Enabling spanning tree port: FastEthernet0/7 (80E19504)
1d05h: STP: VLAN0200 Fa0/7 -> listening
1d05h: set portid: VLAN0100 Fa0/9: new port id 8009
1d05h: Created spanning tree port Fa0/9 (80E16A44) for tree VLAN0100 (80DC1970)
1d05h: Enabling spanning tree port: FastEthernet0/9 (80E16A44)
1d05h: STP: VLAN0100 Fa0/9 -> listening
1d05h: set portid: VLAN0200 Fa0/9: new port id 8009
1d05h: Cre
SW05(config-if-range)#ated spanning tree port Fa0/9 (80EAB0D0) for tree VLAN0200 (80E10DB8)
1d05h: Enabling spanning tree port: FastEthernet0/9 (80EAB0D0)
1d05h: STP: VLAN0200 Fa0/9 -> listening
1d05h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/7, changed state to up
1d05h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/9, changed state to up
1d05h: STP: VLAN0200 heard root 24776-000b.5f42.3e00 on Fa0/9
1d05h:     supersedes 32968-0008.20f8.ca80
1d05h: STP: VLAN0200 new root is 24776, 0
SW05(config-if-range)#00b.5f42.3e00 on port Fa0/9, cost 19
1d05h: STP: VLAN0200 Fa0/7 -> blocking
1d05h: STP: VLAN0100 heard root 24676-000b.5f42.3e00 on Fa0/9
1d05h:     supersedes 32868-0008.20f8.ca80
1d05h: STP: VLAN0100 new root is 24676, 000b.5f42.3e00 on port Fa0/9, cost 19
1d05h: STP: VLAN0100 Fa0/7 -> blocking
SW05(config-if-range)#

*** No further output for several minutes ***

Any input is appreciated.

Thanks in advance,

Mitch

Everyone's tags (2)
3 REPLIES
Cisco Employee

PVST Spanning-Tree: Port stuck in LIS state [Debugs/Topology Inc

Hello Mitch,

Personally, I am almost certain that this is a bug. The STP is a perfectly deterministic algorithm and regardless of the sequence and speed of topological changes, it should always arrive at the same active topology after the network stabilizes.

What switches and IOS versions are you running?

Best regards,

Peter

New Member

PVST Spanning-Tree: Port stuck in LIS state [Debugs/Topology Inc

Thanks for the response Peter.

SW06 and SW07 are 3550's running 12.2.44.SE6, SW04 and SW05 are 2950's running 12.1.22.EA14.

Cisco Employee

PVST Spanning-Tree: Port stuck in LIS state [Debugs/Topology Inc

Mitch,

Hmmm, you seem to be running the latest IOS software. Not that it does not contain bugs But I would not expect such a silly issue to be present in these IOSes.

Anyway, does the behavior change when you change to RSTP? Also, do you happen to have any special STP features configured on the switch or on the port (UplinkFast, BackboneFast, PortFast, different Guards or Filters)?

Best regards,

Peter

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