Configuring BFD Session Flapping Suppression

Context

If link quality is poor, BFD results in frequent service switchover. You can configure link flapping suppression times to prevent frequent service switchover, protecting link resources and reducing link resource consumption.

Do not configure both the dampening timer-interval and wtr commands. Otherwise, the BFD session recovery period becomes long.

Procedure

Run system-view
The system view is displayed.
Run bfd
The BFD view is displayed.
Run dampening timer-interval maximum maximum-milliseconds initial initial-milliseconds secondary secondary-milliseconds
BFD session flapping suppression timers are configured.

BFD session flapping suppression timers start by default. The default initial, secondary, and maximum BFD session flapping suppression timer values are 2000 ms, 5000 ms, and 12000 ms, respectively.

After the dampening timer-interval command is run:
1. When a BFD session flaps for the first time, the initial BFD session flapping suppression timer starts. If the BFD session flaps again before the initial BFD session flapping suppression timer expires, BFD session renegotiation is triggered after the initial BFD session flapping suppression timer expires.
2. After the initial BFD session flapping suppression timer ends, the secondary BFD session flapping suppression timer starts. If the BFD session flaps before the secondary BFD session flapping suppression timer expires, BFD session renegotiation is triggered after the secondary BFD session flapping suppression timer expires. After that, the timer value is secondary-milliseconds x 2^(n-1), where n is the number of times that the secondary BFD session flapping suppression timer starts.
3. After the timer value of secondary-milliseconds x 2^(n-1) is greater than or equal to the value specified by maximum-milliseconds, the BFD session uses the value specified by maximum-milliseconds as a flapping suppression three consecutive times. Then, the BFD session flapping suppression is recalculated based on Step a.
BFD session flapping suppression is enabled by default. The device can adjust the flapping suppression time based on the penalty value in addition to the value of the intelligent timer. The penalty value is adjusted as follows:
1. When a BFD session goes Down each time, the penalty value of the BFD session increases by 20. The initial value is 0 and the maximum penalty value is 240.
2. When a BFD session keeps Up for 1s each time, the penalty value decreases by 1. The minimum penalty value is 0.
3. If the penalty value of a BFD session exceeds 45, the flapping suppression time is twice (that is, 2¹) the value of maximum-milliseconds. If the penalty value of a BFD session exceeds 90, the flapping suppression time is four times (that is, 2²) the value of maximum-milliseconds, and so on. maximum-milliseconds is configured using the dampening timer-interval command.
4. If a BFD session is suppressed by the intelligent timer, the penalty value is adjusted based on rules a and b and the BFD session does not enter the penalty suppression state. That is, rule c does not take effect. Rule c takes effect only when suppression by the intelligent timer ends.
When multiple BFD sessions exist on the device, the penalty value is adjusted considering Down events of all BFD sessions in a period of time.
The configured maximum BFD session flapping suppression timer value must be greater than the configured initial or secondary BFD session flapping suppression timer value. Otherwise, the configuration fails.

By default, BFD session flapping suppression is enabled. To allow the system to immediately start the next negotiation after a BFD session goes Down (excluding AdminDown), run the session-damping disable command to disable BFD session flapping suppression.