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sporadic VRRP transitions or OSPF timeouts

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Titlesporadic VRRP transitions or OSPF timeouts
Symptoms
  • VRRP sometimes flaps from Backup to Master and back
  • OSPF could show sporadic neighbor timeouts
  • EAPS possibly shows failed seg-timers which clear again shortly afterwards
  • other protocols with CPU handled packets could show flapping behavior as well
  • CPU congestion can also be seen around this time
Environment
  • EXOS
  • CPU congestion can be seen
  • OSPF
  • VRRP
  • EAPS
  • other protocols have short flaps
Cause
Take a packet capture of the CPU bound traffic at the time the congestion is seen to investigate what packets are going to the CPU.
If you see what seems an excessive amount of LS updates or similar OSPF messages, then check the OSPF configuration.
If many VLANs are added to OSPF on multiple switches, and not configured as "passive", then neighbor relationships will be formed on each VLAN which often is not wanted, as then all overhead, such as LS updates, need to be sent for each session on each VLAN which can quickly cause thousands of update messages. This can cause congestion and then regular hello messages might be dropped, making other protocol sessions instable.
Resolution
Configure OSPF properly to have only one active session with each OSPF switch and add the other participating VLANs as passive, so they are propagated within OSPF .
Additional notes

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