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Uplink btw Core & Access switches not coming backup


I have a customer, who is facing a strange problem. His current scenario has a couple of Cisco 4500-X core switches (running in VSS) that are connected to some SG-200, old 3com (manageable) and unmanageable access switches. He is running PVST with only vlan-1 configured in his network and his Core-switch ports towards access switches are configured in trunk mode. So, all the production traffic is spanning on vlan1. The problem is that whenever one access switch goes down (e.g. because of power-cuts) the link between core and access switch doesn't come back up. He has to either physically change the port on core switch or restart the core switch to bring up the connection. Every access switch has only one uplink towards the Core, so their is no need of STP actually but in any case I'm curious to know the cause.

3 Replies 3

VIP Mentor VIP Mentor
VIP Mentor


 - Start by examining logs on the involved equipment; preferably during and also after the issue has been resolved (show logging).


paul driver
VIP Expert VIP Expert
VIP Expert


What is the are interconnects between the access switches and core ( access or trunk) as you only have one vlan they don't need to be trunks.


Do you have any Port-security, bpduguard applied on the ports, ?
What dos the interface status log when the switch goes come back up from the power outage?


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Kind Regards

They currently have configured all ports as trunks and also their is no Port-security or bpduguard applied on any of the ports.




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