Discussion

Using the default reuse threshold of 750, a maximum suppression time of 60 minutes,
and a half-life of 30 minutes, the calculation looks like this:
ε c ≤ 750 * e (60/30) (ln 2)
ε c ≤ 3000
In this case, a route’s figure-of-merit value will stop increasing when it reaches 3,000.
If you change the default damping parameter values, use this formula to make sure
that the suppression threshold is not greater than the merit ceiling. If it is, routes will
never be suppressed and route flap damping will never occur.
After setting the damping parameters, you are ready to create the routing policy for
route flap damping. In this recipe, the policy named damping-policy applies to a particular
peer, 10.0.31.1.
In larger networks, it is common to set up different degrees of damping policy to
apply to different types of routes. In addition to the normal damping parameters set
in this recipe, you can also set up parameters to suppress routes for longer periods of
time:
[edit policy-options damping damping-medium]
aviva@Router3# show
half-life 15;
reuse 1500;
suppress 6000;
max-suppress 45;
[edit policy-options damping damping-high]
aviva@Router3# show
half-life 30;
reuse 1640;
suppress 6000;
max-suppress 60;
The damping-medium parameters increase the decay half-life from 10 to 15 minutes
and the maximum suppression time from 30 to 45 minutes, and the damping-high
parameters increase the half-life to 30 minutes and maximum suppression to 60 minutes.
You apply these two damping parameters to routes that flap a bit more than
normal or severely more than normal. Then, instead of applying the policy to specific
BGP peers, you can apply it to a range of prefixes:
[edit policy-options policy-statement flap-damping]
aviva@Router3# show
from {
route-filter 0.0.0.0/0 upto /21 damping damping-normal;
route-filter 0.0.0.0/0 upto /23 damping damping-medium;
route-filter 0.0.0.0/0 orlonger damping damping-high;
}
then accept;
460 | Chapter 13: BGP
This is the Title of the Book, eMatter Edition
Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.