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Intermittent Loss of Network connectivity to One VLAN

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TitleIntermittent Loss of Network connectivity to One VLAN
Symptoms
  • Intermittently Nothing on one VLAN replies to ping
  • SNMP loss of contact
  • Enabling mac moves indicates multiple mac movements on some ports
  • set movedaddrtrap enable
  • set movedaddrtap *.*.* enable
  • show logging buffer
  • <165>Dec 16 14:46:42 203.0.113.253 AddrNtfy[2]MAC: 00-1F-5B-3A-AE-18 moved to port ge.2.2, FID 102
  • <165>Dec 16 14:46:42 203.0.113.253 AddrNtfy[2]MAC: 3C-07-54-55-FA-8A moved to port ge.2.2, FID 102
  • show neighbor shows the switch as its own LLDP neighbor 
  • Disconnecting the switch that sees itself as a neighbor resolves the outage
  • Reconnecting the N-Series that sees itself as a neighbor but disconnecting the port on which it saw itself as a neighbor resolves the outage
  • Some or all ports have higher than usual traffic volumes
  • Netsight compass shows more MAC addresses than usual on a port
Environment
  • N-Series
  • S-Series
  • K-Series
  • Securestack
Cause
A device connected to the switch reflecting traffic received back into the same port which causes the MAC to be learned on multiple ports.
Resolution
Disconnect the device reflecting the packets
Additional notes
For a methodology on the isolation process, please refer to High switch packet processing CPU use on N-Series and S-series.

Another cause for MAC moves is a potential loop on an IP phone. Some IP phones filter spanning tree BPDU's which will allow both ethernet ports to connect to the network without showing as a loop.

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