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