Spanning Tree p2p Dispute

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Sep 23rd, 2009
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We have a Datacenter solution witch Cisco 6500, 3750E and 2960 switches.

6500 distribution layer

3750E aggregation layer (connected to two distr switches)

2960 access layer (connected to 3750E stack via Etherchannel)

All switches are configured for Spanning Tree MST witch identical name, rev no and VLAN instance mapping.

On the 3750E: The etherchannel towards the 2960 goes to Spanning Tree blocking due tp "p2p dispute"

How du I fix this?


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Peter Paluch Wed, 09/23/2009 - 08:30
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  • Cisco Employee,

Hello Jorgen,

The dispute problem is caused by two ports on a single link advertising themselves as being Designated in their STP BPDUs. Check this URL for more information:

(scroll a few lines below to find the description of the Dispute Mechanism)

The problem can be caused by improper STP or EtherChannel configuration, or by an uni-directional link. Can you double-check the MST configuration and the bi-directional functionality of the link? Also, is the EtherChannel correctly bonded on both ends? I strongly recommend using a EtherChannel management protocol such as LACP to manage its creation. Your problem may well be caused by an EtherChannel forcibly bundled together on one switch only, and the second switch having the ports unbundled.

Best regards,


Hei Jørgen

We had same problem upgrading to Version 12.2(55)SE10 on the 3750E switches.

We deleted the "switchport trunk native vlan 999" on the trunks between Cisco 6500 and 3750E.
It looks like the STP need vlan 1 to handle negotiation of spanning-tree in new Version.

Adding "spanning-tree guard loop" on the link didn't help on Version 12.2(55)SE10

It did help on Version 12.2(46)SE


Per & Espen

ปลาวาฬทราย RMUT... Wed, 06/15/2016 - 23:49
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Today, I found the problem with port which connected to MSAN. I think it can't communicate with 3750 MST. My workaround is “(config-if)#spanning-tree bpdufilter enable”.


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