BGP Query on Flaps

Unanswered Question
Apr 21st, 2009

Hi,



One of the circuit was reported down,When checked in PE/CE router did not find physical interface logs.But BGP got flapped,Below mentioned is the logs captured.Would be helpfull if someone can explain why BGP Flaps did not get reflected in PE/CE interfaces.In what all cases this can happen (Interface will not go down/but BGP flapps)




=================CE Router logs =============


Apr 20 12:58:14.602: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx Down BGP Notification sent

Apr 20 12:58:14.602: %BGP-3-NOTIFICATION: sent to neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 12:58:26.898: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx Up

Apr 20 13:10:16.120: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx Down BGP Notification sent

Apr 20 13:10:16.120: %BGP-3-NOTIFICATION: sent to neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 13:11:05.701: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx Up

Apr 20 13:34:11.043: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx Down Peer closed the session

Apr 20 13:41:24.769: %BGP-3-NOTIFICATION: received from neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 13:41:32.510: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx Up





======================PE Router logs ==========




xx.xx.xx.xx


Apr 20 12:01:18.778: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx vpn vrf Extranet_VRF1 Down BGP Notification sent

Apr 20 12:01:18.778: %BGP-3-NOTIFICATION: sent to neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 12:02:03.945: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx vpn vrf Extranet_VRF1 Up

Apr 20 12:11:04.146: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx vpn vrf Extranet_VRF1 Down BGP Notification sent

Apr 20 12:11:04.146: %BGP-3-NOTIFICATION: sent to neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 12:14:42.765: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx vpn vrf Extranet_VRF1 Up

Apr 20 12:37:43.131: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx vpn vrf Extranet_VRF1 Down BGP Notification sent

Apr 20 12:37:43.131: %BGP-3-NOTIFICATION: sent to neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 12:41:26.531: %BGP-3-NOTIFICATION: sent to neighbor xx.xx.xx.xx 4/0 (hold time expired) 0 bytes

Apr 20 12:45:09.566: %BGP-5-ADJCHANGE: neighbor xx.xx.xx.xx vpn vrf Extranet_VRF1 Up




Thanks in advance

Lijesh.N.C


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Overall Rating: 4.5 (2 ratings)
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Giuseppe Larosa Tue, 04/21/2009 - 04:45

Hello Lijesh,


depending on routing platform an implicit system queue can exist or not fo routing protocol traffic.


if BGP messages are not protected by QoS by either an implicit or explicit traffic class in a QoS policy-map if 3 BGP keepalives are missed the session fails.


other possible reasons are :

at least another device is in the middle or a L2 transport service interconnects the two routers so a failure of communication is not reflected on the state of the router interfaces that are still kept up/up by device(s) in the middle.


What kind of link is this ?

What is the link usage over time ?



Hope to help

Giuseppe


Lijesh NC Tue, 04/21/2009 - 05:20

Hi Giuseppe,


Thanks for the quick reply,this is P to P link (MPLS),2Meg E1 circuit, the link utilization was very much normal during the flapping Ocrd...still small confusion why interface did not go down...this had happend to some other customer also...


Thanks

Lijesh.N.C

Giuseppe Larosa Tue, 04/21/2009 - 05:29

Hello Lijesh,

your service provider may use some L2 transport service this could make the interface happy up/up even during out of service.



Hope to help

Giuseppe


Lijesh NC Tue, 04/21/2009 - 06:36

Hai Giuseppe,


Since we are the service provider Its end to end Our Media and i am not sure wheather L2 Transport service can be enabled in SDH level for E1 circuits???!!!,I guess its is possible for Ethernet links,Correct me if i am wrong.


Thanks alot once again it was informative.


Regards

Lijesh.N.C

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