Hi all,
I've been trying to configure 4 new switches to improve the core of the network.
We already had two C3650-48TS in stack as network core (nwcore2). Now I am expanding the core with two C3560-CX (nwcore3 and nwcore4). Those switches are not stackable so I am using a gigabit cable to connect them and two fibre 1Gb links to nwcore2. Finally I connected a stack (2 x C2960-X) to nwcore3 and nwcore4 using two gigabit links.
The spanning tree configuration I am using is:
nwcore2
spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree logging
spanning-tree extend system-id
spanning-tree vlan 1-10,12,14-17 priority 4096
nwcore3 and nwcore4
spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree logging
spanning-tree extend system-id
spanning-tree vlan 1-10,12,14-17 priority 16384
nwswitch32
spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree logging
spanning-tree portfast edge default
spanning-tree portfast edge bpduguard default
spanning-tree extend system-id
All "user" ports are configured as portfast and bpduguard enabled.
Spanning tree blocks the link between nwcore3 and nwcore4 and one of the links to nwswitch32 stack as you can see in the diagram.
Everything works fine until about 5 hours and 50 minutes later. Then I see a huge amount of traffic, and all the network freezes until nwcore 3 reboots itself. Then another 5 hours and 50 minutes later the problem begins again.
Seems to be a loop, but I don't know why as rstp seems to be correctly configured, isn't it? I see no spanning tree messages in logs, only mac addresses flapping between the links.
What happens every 5 hours and 50 minutes? Why that concrete amount of time?
Can anyone help me, please?
