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Challenge: Spanning Tree Control Between 2 links from Switch DELL M6220 to 2 links towards 2 switches CISCO 3750 connected with an stack (behavior like one switch for redundancy)

Hello,

I have an Spanning tree problem when i conect  2 links from Switch DELL M6220 (there are blades to virtual machines too) to 2 links towards 2 switches CISCO 3750 connected with an stack (behavior  like one switch  for redundancy, with one IP of management)

In dell virtual machine is Spanning tree rapid stp, and in 3750 is Spanning tree mode pvst, cisco says that this is not important, only is longer time to create the tree.


 I dont know but do you like this solutions i want to try on sunday?:

  •  Could Spanning tree needs to work to send one native vlan to negociate the bdpus? switchport trunk native vlan 250
  • Is it better to put spanning-tree guard root in both 3750 in the ports to mitigate DELL to be root in Spanning Tree?
  • Is it better to put spanning- tree port-priority in the ports of Swicht Dell?

¿could you help me to control the root? ¿Do you think its better another solution? thanks!

 CONFIG WITH PROBLEM

======================

3750: (the 2 ports are of 2 switches 3750s conected with a stack cable, in a show run you can see this)

interface GigabitEthernet2/0/28
 description VIRTUAL SNMP2
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 4,13,88,250
 switchport mode trunk
 switchport nonegotiate
 logging event trunk-status
 shutdown


interface GigabitEthernet1/0/43
 description VIRTUAL SNMP1
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 4,13,88,250
 switchport mode trunk
 switchport nonegotiate
 shutdown

DELL M6220: (its only one swith)


interface Gi3/0/19
switchport mode trunk
switchport trunk allowed vlan 4,13,88,250
exit
!


!
interface Gi4/0/19
switchport mode trunk
switchport trunk allowed vlan 4,13,88,250
exit

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