ospf flapping

Unanswered Question
Jul 21st, 2008
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we find some ospf notification log on our core-switch like below:

Jul 21 07:15:56.167: %OSPF-5-ADJCHG: Process 1, Nbr 202.165.96.216 on Port-channel3 from FULL to DOWN, Neighbor Down: Dead timer expired

Jul 21 07:16:03.227: %OSPF-5-ADJCHG: Process 1, Nbr 202.165.96.216 on Port-channel3 from LOADING to FULL, Loading Done


anyone had seen it before ??

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Ryan Carretta Mon, 07/21/2008 - 02:12
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Dead timer expired suggests that there were lost hello packets between the two switches. Check to see if the link(s) between these OSPF neighbors is congested and/or if there is (or was) a high-cpu condition on either device.

shiva_ial Mon, 07/21/2008 - 02:26
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hi,

from the output what i could see


is preobelm occured in ospf relationship,

which makes the portchannel down at 15:56


means this neighbor is not reachable from

the router you have taken log.


it was again reachable only by 16:03


in simple, 7 mins no ospf relationship between the router you have taken log and its

neighbor 202.165.96.216


rgds/shiva

Ryan Carretta Mon, 07/21/2008 - 03:06
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Please upload the output of 'show process cpu history' from both devices.

Giuseppe Larosa Tue, 07/22/2008 - 03:38
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Hello shiva,

are only 7 seconds just the time to rebuild the OSPF adjacency.


Down doesn't mean that the portchannel went down, but refers to ospf neighbor state machine from Full -> down because DEAD timer expired means router was not able to receive ospf hello during last 40 seconds. (with default timer values)




Jul 21 07:15:56.167: %OSPF-5-ADJCHG: Proces(s 1, Nbr 202.165.96.216 on Port-channel3 from FULL to DOWN, Neighbor Down: Dead timer expired

Jul 21 07:16:03.227: %OSPF-5-ADJCHG: Process 1, Nbr 202.165.96.216 on Port-channel3 from LOADING to FULL, Loading Done


The trouble comes if the event happens many times.

Try to investigate on how much the port-channel is used. A QoS scheduler to protect ospf traffic could be needed if the link is very busy.




hope to help

Giuseppe

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