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BFD Session Flapping Occurred Due to Poor Transmission Quality

Publication Date:  2013-09-27 Views:  144 Downloads:  0
Issue Description

A customer deployed BFD on its network that comprised a large amount of transmission devices between NE40Es. After the BFD-session status change upon interface status change function is enabled, BFD session frequently occurred on the interface. Services were affected.

Handling Process

Huawei completed the following steps to diagnose the problem:

1. Checked the BFD session flap log BFD/4/STACHG_TODWN on the NE40Es.

According to the Diagnostic parameter, the flap type was DetectDown, meaning that BFD packets were not received as expected (BFD down) during the BFD session detection period.

2. Checked whether BFD configurations were correct on the NE40Es. The configurations were correct, using the default packet sending interval.

3. Suspected that intermediate transmission equipment was faulty.

4. Set the BFD-packet sending and detection intervals to larger values. BFD session flapping did not occur.
Root Cause
Transmission quality was poor. The timer for the peer end to receive BFD packets expired, so the BFD session was down.
Increase the BFD-packet detection period.
Check whether BFD session status is normal when configuring BFD. To be specific, after enabling BFD and configuring the packet detection interval, check whether BFD flapping occurs. If yes, increase the detection interval. After verifying that the BFD session is normal over time period, enable the BFD-session status change upon interface status change function.