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

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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)
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)
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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