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Issue forming lag connection between S-Series / Securestack and Cisco switch with PVST+or Rapid-PVST

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Information

 
TitleIssue forming lag connection between S-Series / Securestack and Cisco switch with PVST+or Rapid-PVST
Symptoms
Issue forming lag connection between S-Series / Securestack and Cisco switch with PVST+ or Rapid-PVST
Environment
  • C5-Series
  • Securestack
  • Cisco PVST
Cause
  • When multiple Cisco switches are running PVST+ the Spanning Tree multicast packets are flooded through network ports and Cisco determines a loop is present
  • PVST+ being a proprietary protocol, we do not acknowledge the packets as standard BPDU
Resolution
Options to resolve:

1) Change all Cisco switches to Multiple Spanning Tree mode instead of proprietary Per-VLAN Spanning Tree mode (PVST+ or Rapid-PVST) such as:
configure
spanning-tree mode mst
Additional PVST+ cleanup:
Distribution1(config)#no spanning-tree backbonefast
Distribution2(config)#no spanning-tree backbonefast
Distribution2(config)#interface FastEthernet1/0/24
Distribution2(config-if)#no spanning-tree vlan 20,40,200 port-priority 64
 
2) Block PVST+ multicast MAC 01:00:0c:cc:cc:cd on the ports in question (ensuring there will not be any Layer-2 loops when doing this) - See: How to Block PVST on a port using Policy
Additional notes
  • On S-Series or Securestack, review show logging buffer command output for any possible issues
  • On Cisco, review show logging command output to see if port is going into down state usually due to err-disable feature

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