flap-control

Allows you to set values that control route flapping.

flap-control <half-life> <reuse> <suppress>
 
no flap-control
 

• half-life--integer in the range 1 through 45
• reuse--integer in the range 1 through 20,000
• suppress--integer in the range 1 through 20,000

Must be in engine or policy configuration mode (config-engine or config-engine-policy), which requires privileged-level access.

Use once.

• half-life--15
• reuse--750
• suppress--2,000

The flap-control command is used to achieve an acceptable interval between successive updates from CNA to an edge router for a single prefix, thereby avoiding flapping.

CNA measures flapping by use of an index derived from the elapsed time between updates and the user-configurable value of half-life.

The half-life value should represent the time (in minutes) that you want it to take for the index to decay by half.

The index is increased by 1,000 every time the prefix is updated. The suppress and reuse values serve as upper and lower update thresholds--if the index exceeds the value of suppress, CNA will not send updates to the router until the index has fallen below reuse.

If you find your CNA device to be flapping--sending updates for the same prefix too frequently--you should increase the value of half-life. Conversely, if your CNA device stops sending updates, or the sustainable rate of updates is too low, you should decrease the value of half-life.

The suppress and reuse values can also be adjusted, but you should do so cautiously.

Increasing the suppress value introduces more burstiness into the system.

If you adjust the rate of updates simply by increasing the suppress value, you may find the increase in frequency to be a temporary phenomenon.

If you do increase the suppress value, you should also increase the reuse value by a proportional amount. That is, the distances between 0 and reuse and between reuse and suppress should remain proportional to the distances between the comparable default values.

If the command is entered while in engine configuration mode, the parameters will be applied to all prefixes globally.

If the command is entered while in policy configuration mode, the parameters will be applied only to those prefixes associated with the policy.

For more information about policies, see the decision-policy command and Chapter 6: Decision Policies and Application Models of the CNA Basic Monitoring Guide.