Check all your switches and make sure that the spanning tree mode is the same. BOS-2960PDU-SW1#show spanning-tree summary Switch is in rapid-pvst modeRoot bridge for: noneEtherChannel misconfig guard is enabledExtended system ID is enabledPortfast Default is disabledPortFast BPDU Guard Default is disabledPortfast BPDU Filter Default is disabledLoopguard Default is disabledUplinkFast is disabledBackboneFast is disabledConfigured Pathcost method used is shortName Blocking Listening Learning Forwarding STP Active---------------------- -------- --------- -------- ---------- ----------VLAN0010 0 0 0 5 5VLAN0033 0 0 0 1 1VLAN0034 0 0 0 1 1make sure that all the vlans are being properly sent out the trunk interfaces BOS-2960PDU-SW1#sh int trunkPort Mode Encapsulation Status Native vlanPo1 on 802.1q trunking 900Po48 on 802.1q trunking 900Port Vlans allowed on trunkPo1 10,64-71Po48 10,33-40,50,64-71,1001Port Vlans allowed and active in management domainPo1 10,64-71Po48 10,33-40,50,64-71,1001Port Vlans in spanning tree forwarding state and not prunedPo1 10,64-71Po48 10,33-40,50,64-71,1001BOS-2960PDU-SW1# |