Dell S4048T Configuration Manual page 258

• is withdrawn
• is readvertised after being withdrawn
• has an attribute change
The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process.
To minimize this instability, you may configure penalties (a numeric value) for routes that flap. When that
penalty value reaches a configured limit, the route is not advertised, even if the route is up. In Dell Networking
OS, that penalty value is 1024. As time passes and the route does not flap, the penalty value decrements or is
decayed. However, if the route flaps again, it is assigned another penalty.
The penalty value is cumulative and penalty is added under following cases:
• Withdraw
• Readvertise
• Attribute change
When dampening is applied to a route, its path is described by one of the following terms:
• history entry — an entry that stores information on a downed route
• dampened path — a path that is no longer advertised
• penalized path — a path that is assigned a penalty
To configure route flap dampening parameters, set dampening parameters using a route map, clear
information on route dampening and return suppressed routes to active state, view statistics on route
flapping, or change the path selection from the default mode (deterministic) to non-deterministic, use the
following commands.
• Enable route dampening.
CONFIG-ROUTER-BGP mode
bgp dampening [half-life | reuse | suppress max-suppress-time] [route-map map-
name]
Enter the following optional parameters to configure route dampening parameters:
• half-life: the range is from 1 to 45. Number of minutes after which the Penalty is decreased. After
the router assigns a Penalty of 1024 to a route, the Penalty is decreased by half after the half-life
period expires. The default is 15 minutes.
• reuse: the range is from 1 to 20000. This number is compared to the flapping route's Penalty value.
If the Penalty value is less than the reuse value, the flapping route is once again advertised (or no
longer suppressed). Withdrawn routes are removed from history state. The default is 750.
• suppress: the range is from 1 to 20000. This number is compared to the flapping route's Penalty
value. If the Penalty value is greater than the suppress value, the flapping route is no longer
advertised (that is, it is suppressed). The default is 2000.)
• max-suppress-time: the range is from 1 to 255. The maximum number of minutes a route can be
suppressed. The default is four times the half-life value. The default is 60 minutes.
• route-map map-name: name of a configured route map. Only match commands in the configured
route map are supported. Use this parameter to apply route dampening to selective routes.
• Enter the following optional parameters to configure route dampening.
CONFIG-ROUTE-MAP mode
set dampening half-life reuse suppress max-suppress-time
Border Gateway Protocol IPv4 (BGPv4) 258