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Webcast-Catalyst9k
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Switch doesn't give up STP root for VLAN 1?

I have four switches connected into a full mesh with dual, non-aggregated trunks (yes, I know...). Two 3560v2 running 15.0(2)SE6 IPServices and two 2960 running 15.0(2)SE6 LANBase.

 

One of the switches is running VTP version 2, the others are running VTP version 3.

 

All of the VLAN operations are happening as expected.

 

Spanning Tree works on all VLANs that are created except on VLAN 1. By that I mean that I configured a root-primary switch for vlans 1-4094, and all VLANs EXCEPT VLAN 1 follow this; each switch is retaining it's root status for VLAN 1

 

No matter what I do - lowering or raising priorities - VLAN 1 stays as root on each switch.

 

Can anyone help me understand why this is?

Thanks!

 

TopLeft3560>sho span root

                                        Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001         32769 e840.406f.8b80         0    2   20  15                  
VLAN0021         28693 e840.406f.7380        19    2   20  15  Fa0/11          
VLAN0022         28694 e840.406f.7380        19    2   20  15  Fa0/11                 
TopLeft3560>

 

BottomRight2960>sho span root

                                        Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001         61441 0017.95cf.1680         0    2   20  15                  
VLAN0021         28693 e840.406f.7380        19    2   20  15  Fa0/7           
VLAN0022         28694 e840.406f.7380        19    2   20  15  Fa0/7           
BottomRight2960>

 

 

Everyone's tags (4)
1 REPLY
Cisco Employee

Hi Riedmuller, This behavior

Hi Riedmuller, 

This behavior can be seen if the switches are not able to hear the BPDUs of the other switches for that specific VLAN.

What is the configuration of your trunk links and switches?

 

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