I've got a strange behavior on a c3850. We use VLAN 381 as transfer vlan. After the changing the core switches, this vlan doesn't work any more.
The output of "sh int trunk":
Port Mode Encapsulation Status Native vlan Gi1/0/1 on 802.1q trunking 1 Gi1/0/2 on 802.1q trunking 1 Po16 on 802.1q trunking 1 Port Vlans allowed on trunk Gi1/0/1 381,401-499 Gi1/0/2 381,401-499 Po16 1-4094 Port Vlans allowed and active in management domain Gi1/0/1 381,401,444 Gi1/0/2 381,401,444 Po16 1,33-37,41-42,100,381,401,444,500 Port Vlans in spanning tree forwarding state and not pruned Gi1/0/1 381,401,444 Gi1/0/2 381,401,444 Po16 1,33-37,41,100
So i take a look at the "sh spanning-tree vlan 381"
VLAN0381 Spanning tree enabled protocol rstp Root ID Priority 8573 Address 0008.e3xx.xxxx Cost 1 Port 2392 (Port-channel16) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 33149 (priority 32768 sys-id-ext 381) Address a4b2.39yy.yyyy Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- Gi1/0/1 Desg FWD 4 128.1 P2p Gi1/0/2 Desg FWD 4 128.2 P2p Po16 Root FWD 1 128.2392 P2p
Here is the state on forwarding and he know the Po is his root-port. But there no connection possible to the devices that are connected on Gi1/0/1 and Gi1/0/2.
Here the (simple) portconfig:
interface Port-channel16 switchport mode trunk interface TenGigabitEthernet1/1/4 switchport mode trunk channel-group 16 mode active interface TenGigabitEthernet3/1/4 switchport mode trunk channel-group 16 mode active
I connected a third fiber, to fix the problem quick and dirty, and configured this connection as switchport (vlan 381). Then it worked. The devices on the Gi-Ports worked again.
Now I want to get rid of this third fiber and get the trunk working properly. Does anyone an idea whats happend on this trunk? Why doens't came this vlan in the forwarding state? The Portchannel and trunk worked fine before the Core-Switch-Change.
The core switch was already connected to the edge switch. its working fine for 2 weeks, until I moved die Router IP from the old Core to the new core. the other recent change was the shut down of the old core switches -> spanning-tree change.
Before the faulty trunk topology:
old core* <-> new core <-> edge switch
Faulty trunk topology:
new core* <-> edge switch
*Default Gateway and Root Bridge
Did you actually create that vlan at l2 prior to enabling on a access port - I would say now if you shutdown that third fibre it would work just make sure the vlan is propagated to all switches in the vtp domain
The vlan was created before I created the thrid fibre connection. We used the connection 2 weeks (with all vlans) before the change at the core without any problems. There was no configuration change at the edge or the core side of the trunk. I just moved the IP addresses from the old core to the new one. Then I shut down the old core.
VTP is not configured in this network.