The following shows the route after four flaps. The penalty is now 2851, which has exceeded the 2500 limit. The route is now suppressed (dampened) and will not be passed on to RTH. The route will be usable in 31 minutes and 40 seconds. At that time, the penalty would have decayed to the reuse limit of 950.

    RTC#show ip bgp 172.16.220.0
    BGP routing table entry for 172.16.220.0/24, version 329
    Paths: (1 available, no best path, advertised over IBGP)
    3, (suppressed due to dampening)
     172.16.20.2 from 172.16.20.2 (172.16.220.1)
      Origin IGP, metric 0, valid, external
      Dampinfo: penalty 2851, flapped 4 times in 00:03:05, reuse
        in 00:31:40

The following output shows the same route after six flaps. The differences are that the half-life-time has been set to 5 minutes instead of 20 minutes, and the maximum suppress-time is 20 minutes instead of 80. With a shorter half-life-time, the penalty will be decayed much faster, and the route will be used a lot sooner. Note the reuse time of 8 minutes and 10 secs.

    RTC#show ip bgp 172.16.220.0
    BGP routing table entry for 172.16.220.0/24, version 336
    Paths: (1 available, no best path, advertised over IBGP)
    3, (suppressed due to dampening)
     172.16.20.2 from 172.16.20.2 (172.16.220.1)
      Origin IGP, metric 0, valid, external
      Dampinfo: penalty 2939, flapped 6 times in 00:08:21, reuse
       in 00:08:10

Adjusting the dampening timers becomes essential when administators cannot afford to have a long outage for a specific route. BGP dampening with route maps is a powerful tool to selectively penalize ill-behaved routes in a user-configurable and controlled manner.

Looking Ahead

The Internet has come a long way from the NSFNET backbone to the information highway of the 21st century—and there are no signs of its slowing down. And how could the Internet slow down when hundreds and thousands of users come online every day, attracted by the most advanced applications technology affords?

Routing protocols have struggled to keep up with the demand, from the early days of EGP to the latest in BGP. BGP started as a simple exterior routing protocol and has evolved into a de facto standard, gluing the Internet together. Indeed, every hook and tweak that BGP can offer has been used, and still it seems that more capabilities are requested every day. As a result, new protocols and new techniques will emerge. Whether they will make routing easier or more complicated, more robust or more shaky is yet to be seen. One thing is certain: common sense will never go away, and as long as it is the basis of all your designs, you will be the master of your domain.