Weighted Route Dampening Statement

Currently only routes learned via BGP are subject to weighted route dampening. Although, no protocols will announce suppressed routes. Note that the weighted route dampening configuration statement is not within the BGP statement but, a separate and distinct configuration; conceptually, much like interface or kernel statements.

The syntax for weighted route damping in GateD is :

dampen-flap {
[suppress-above metric ;
reuse-below metric ;
max-flap metric;
unreach-decay time ;
reach-decay time ;
keep-history time ; ]
};

suppress-above metric
is the value of the instability metric at which route suppression will take place (a route will not be installed in the FIB or announced even if it is reachable during the period that it is suppressed).

reuse-below metric
is the value of the instability metric at which a suppressed route will become unsuppressed, if it is reachable but currently suppressed. The value assigned to reuse-below must be less than suppress-above.

max-flap metric
is the upper limit of the instability metric. This value must be greater than the larger of 1 and suppress_above.

Assigned to the above three parameters is a floating point number in units of flaps. Each time a route becomes unreachable, 1 is added to the current instability metric.

reach-decay time
specifies the time desired for the instability metric value to reach one half of its current value when the route is reachable. This half-life value determines the rate at which the metric value is decayed. A smaller half-life value will make a suppressed route reusable sooner than a larger value.

unreach-decay time
acts the same as reach-decay except that it specifies the rate at which the instability metric is decayed when a route is unreachable. It should have a value greater than or equal to reach-decay.

keep-history time
specifies the period over which the route flapping history is to maintained for a given route. The size of the configuration arrays described below is directly affected by this value.

If only dampen-flap {}; is specified in the configuration file then the following default values are (currently) used:

suppress-above = 3.0;

reuse-below = 2.0;

max-flap = 16.0;

unreach-decay = 900;

reach-decay = 300;

keep-history 1800;

Last updated April 27, 1997