Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 219

To view the configuration, use the show config command in CONFIGURATION ROUTER BGP mode. Enabling Route Flap Dampening When EBGP routes become unavailable, they "flap" and the router issues both WITHDRAWN and UPDATE notices. A flap is when a route: • is withdrawn • is readvertised after being withdrawn • has an attribute change The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process.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 EMC 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 Withdrawn routes are removed from history state.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 - 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. Border Gateway Protocol version 4 (BGPv4) 219