Hello Muhammad
I understand your confusion. It is true that the penalty is decreased by 50% every 15 minutes. This however does not occur “all at once” when 15 minutes have elapsed. It takes place gradually over time.
From the output you have in your post, you see that after 60 seconds the penalty has been reduced by 24. It is later reduced by 23 in the next 60 seconds. The rate of reduction every 60 seconds is such that by the time 15 minutes have elapsed, the value will reach 50% of what it was 15 minutes ago.
I will ask Rene to add this detail to the lesson.
BGP dampening introduces some unwanted phenomena in BGP. RIPE NCC, or Réseaux IP Européens Network Coordination Centre is the regional internet registry for Europe, the Middle East, and parts of Asia. They’ve issued the following Working Group Recommendation concerning dampening:
In it, they mention that impeded convergence and incompatible minimum route advertisement interval on networks managed by different ISPs are problems that are induced by dampening.
Like Rene mentioned in the lesson, the CPU power of today’s network devices is more than enough to deal with BGP flapping routes. In the past, overwhelming the CPU resources of a BGP router due to flapping BGP routes was worse than the network problems introduced by the feature.
Today, it is preferable to just let BGP routes flap, rather than dampen them.
I hope this has been helpful!
Laz