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EBGP Peers Frequently Oscillated at the Gateway Office of Country S

Publication Date:  2012-07-27 Views:  43 Downloads:  0
Issue Description
A device in the international gateway office of Country S had four EBGP peers, one of which frequently oscillated between Idle and Established. On this peer, about 100,000 routes were learned and then re-learned after resetting. The other three peers worked normally. On them, about 250,000 routes were learned.
Because the international links pass through the transmission device, the function of responding to the alarms sent from the transmission device is configured on the POS interface so that the router can rapidly perceive the failures of the corresponding interfaces when the optical paths work normally between the router and the transmission device. Thus, the fast switchover is enabled.
interface Pos3/0/3
link-protocol ppp
description to-Turktelecom
ip address xx.175.16.14 255.255.255.252
traffic-policy Anti-Spoofing-ACL inbound
undo scramble
crc 16
flag c2 207
flag j0 peer
flag j1 peer
alarm lrdi sensitive
alarm prdi sensitive
alarm pais sensitive 

 
Alarm Information
Checking the debug information of the peer, the engineer found the link flash alarm on the POS interface. 

 
Handling Process
After the alarm prdi sensitive command was deleted, the problem was solved. Since then, the BGP peers have worked normally and the routes could be learned normally. 

 
Root Cause
Normally, the alarm { prdi | pais | lrdi } sensitive command is configured when the two routers are far from each other and connected to each other with a transmission device in between. If the link with the transmission device fails, the optical transmission device can perceive such failure, but the router cannot immediately perceive the failures of the corresponding interfaces (when the optical path linking the router with the transmission device works normally). In this case, the fast switchover function cannot be implemented.
On the site, the engineer found the problem with the transmission quality. The outbound link failed and then could resume to the normal state in a second. After the alarm { prdi | pais | lrdi } sensitive command was deleted, the LPU at the POS interface did not respond to the alarms, thus avoiding the oscillation of the EBGP peer and repeated learning of the BGP routes.
Before the failure of the international transmission link is thoroughly cleared, preventing the EBGP peers from oscillating in the preceding way proves to be effective. 

 
Suggestions
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END