I ran into an odd behaviour on a 3560-E, WS-C3560E-24TD with IOS 12.2(55)SE.
I'm running Rapid PVST:
spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree logging
spanning-tree extend system-id
spanning-tree pathcost method long
I have an interface in trunk mode, connected to another switch; only 1 VLAN is extended on this trunk, and I configured a specific STP port cost for it:
interface GigabitEthernet0/8
description To-Switch-1
switchport trunk encapsulation dot1q
switchport trunk native vlan 123
switchport trunk allowed vlan 123
switchport mode trunk
switchport nonegotiate
spanning-tree vlan 123 cost 100000
If I unplug the cable, the spanning-tree vlan 123 cost 100000 line disappears from the interface configuration. Even if the port comes up the configuration line does not appear again.
In order to avoid this issue I had to use the spanning-tree cost 100000 command, but it just has sense because at this time I only have 1 VLAN on the trunk.
Anyone can help me? What am I missing?
