Tuning BGP Performance - BGP Design and Implementation - page 90

• Damp state —When a route is in the Damp state, the router does not consider this path
for best-path selection and therefore does not advertise this prefix to its peers.
• Half life —The penalty for a route is decreased based on the half-life period, which by
default is 15 minutes. The penalty on the route is reduced every 5 seconds. The half
life can be configured.
• Reuse limit —The penalty on a route decreases over time. When the penalty falls
below the reuse limit, the route is unsuppressed. The default reuse limit is 750. The
router checks for prefixes to unsuppress every 10 seconds. The reuse limit can be
configured. When the penalty reaches one-half of the reuse limit, the history is cleared
for that prefix to make more efficient use of memory.
• Maximum suppress limit —This is an upper bound for prefix suppression. If a route
exhibits extreme instability for a short period of time and then stabilizes, the penalty
accrued might result in the route's being dampened for an excessive period of time.
This is essentially an upper bound on the penalty. If the route exhibits continuous
instability, the penalty remains at its upper bound, which keeps the route dampened.
The default maximum suppress limit is 60 minutes. The maximum suppress limit can
be configured.
When a route flaps, a penalty is assigned to the route, and the route is marked as having a
history of instability. Successive route flaps increase the penalty. When the penalty
increases above the suppress limit, the route is suppressed, or dampened.

Figure 3-6 shows route dampening for a prefix.

Figure 3-6 BGP Route Dampening

5000

4000

3000

Suppress Limit

2000

Reuse Limit

1000

0

Time

Prefix
Announced

Prefix
Not Announced

Prefix
Re-Announced