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Cisco AP and BPDU-guard setting on the switch port


Hi everyone,

I have looked on different forums and it's quite confusing. So if someone could clarify, then thanks in advance.


Cisco AP connected to switch, port in trunk mode.

Config of port on switch:

interface FastEthernet0/37
 description AP1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 303
 switchport trunk allowed vlan 1,303,313,353
 switchport mode trunk
 switchport nonegotiate
 storm-control broadcast level 60.00
 storm-control multicast level 60.00
 storm-control action shutdown
 storm-control action trap
 spanning-tree bpduguard enable

This is a config not set by myself and what is bothering me most is the last line. "spanning-tree bpduguard enable". This setting puts another AP in "err-disable" mode (not this one).

Logfile switch:

286229: Nov  6 10:59:39.288 CET: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 1
286233: Nov  6 11:01:45.872 CET: %SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on port Fa0/3 with BPDU Guard enabled. Disabling port.

286234: Nov  6 11:01:45.872 CET: %PM-4-ERR_DISABLE: bpduguard error detected on Fa0/3, putting Fa0/3 in err-disable state
286235: Nov  6 11:01:46.896 CET: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to down
286236: Nov  6 11:01:47.894 CET: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to down

So I disabled "spanning-tree bpduguard". Problem solved. BUT, didn't I disabled an important anti-loop rule here? Although the network is still running fine. And the other AP's have this enabled, but aren't going into "err disable".

This is a trunk port, maybe this rule is more applied on access ports?




2 Replies 2

John Blakley

I never enable bpdu guard on AP switchports. Primarily because our business relies heavily on APs and I don't want something accidentally connecting to it that could start sending bpdus in some way. That being said, is there another AP that's in bridge mode or is this AP in bridge that could be receiving a bpdu from the other switchport? That's the only thing off the top of my head that could cause this.

Yes, I also avoid putting bpdu guard on trunks unless I know it's a port for a host and a phone.



HTH, John *** Please rate all useful posts ***

Thank you for your reply John.

The AP's are connected to a controller. In that particular environment they are in Flexconnect.

I understand the way you configured it in your network. It's obvious if your business relies on the AP's.

I intend to get rid of that config line on all trunk ports connected to an AP. For pc's and phones I keep:

 spanning-tree portfast
 spanning-tree bpduguard enable



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