bgp dampening

bgp dampening 使用来抑制一些频繁浮动路由的，每当某条路由浮动一次，它的惩罚值就会加1000，当超过抑制阀值时就被抑制，从而防止bgp表的抖动。
half-time 是指半衰期，单位min，每经过half-time的时间，抑制值就会减半，默认15min。
reuse 当一条被抑制路由的惩罚值低于该值后，该路由重新被标记为可用。默认750
suppress 该值就是抑制阀值，超过该值路由被抑制。默认2000
max-suppress 最大抑制时间，被抑制路由的抑制时间超过该值后，不管惩罚值为多少，都会重新标记为可用，默认60min。
bgp dampening 只对EBGP学习过来的路由起作用.对IBGP不起作用.

bgp dampening

To enable BGP route dampening or change various BGP route dampening factors, use the bgp dampening command in address family or router configuration mode. To disable the function or restore the default values, use the no form of this command.

bgp dampening [half-life reuse suppress max-suppress-time] [route-map map-name]

no bgp dampening [half-life reuse suppress max-suppress-time] [route-map map-name]

Syntax Description

half-life

(Optional) Time (in minutes) after which a penalty is decreased. Once the route has been assigned a penalty, the penalty is decreased by half after the half-life period (which is 15 minutes by default). The process of reducing the penalty happens every 5 seconds. The range of the half-life period is 1 to 45 minutes. The default is 15 minutes.

reuse

(Optional) If the penalty for a flapping route decreases enough to fall below this value, the route is unsuppressed. The process of unsuppressing routes occurs at 10-second increments. The range of the reuse value is from 1 to 20000; the default is 750.

suppress

(Optional) A route is suppressed when its penalty exceeds this limit. The range is from 1 to 20000; the default is 2000.

max-suppress-time

(Optional) Maximum time (in minutes) a route can be suppressed. The range is from 1 to 20000; the default is 4 times the half-life. If the half-life value is allowed to default, the maximum suppress time defaults to 60 minutes. When the max-suppress-time is configured, the maximum penalty will never be exceeded, regardless of the number of times that the prefix dampens. The maximum penalty is computed with the following formula:

Max penalty = reuse-limit *2^(maximum suppress time/half time)

route-map map-name

(Optional) Name of route map that controls where BGP route dampening is enabled.

Defaults

Disabled by default.

half-life: 15 minutes.

reuse: 750.

suppress: 2000.

max-suppress-time: 4 times half-life.

Command Modes

Address family configuration

Router configuration

Command History

Release Modification

11.0

This command was introduced.

12.0(7)T

Address family configuration mode was added.

Usage Guidelines

If this command is used with no arguments, it enables BGP route dampening. The half-life, reuse, suppress, and max-suppress-time arguments are position-dependent. Therefore, if any of these arguments are issued, they must all be specified.

When BGP dampening is configured and a prefix is withdrawn, BGP considers the withdrawn prefix as a flap and increases the penalty by a 1000. If BGP receives an attribute change, BGP increases the penalty by 500. If then the prefix has been withdrawn, BGP keeps the prefix in the BGP table as a history entry. If the prefix has not been withdrawn by the neighbor and BGP is not using this prefix, the prefix is marked as dampened. Dampened prefixes are not used in the BGP decision process and not installed to the routing table.

Examples

The following router configuration mode example sets the half life to 30 minutes, the reuse value to 1500, the suppress value to 10000; and the maximum suppress time to 120 minutes:

router bgp 5

bgp dampening 30 1500 10000 120

The following address family configuration mode example sets the half life to 30 minutes, the reuse value to 1500, the suppress value to 10000; and the maximum suppress time to 120 minutes:

router bgp 5

address-family ipv4 multicast

bgp dampening 30 1500 10000 120

Related Commands

Command Description

address-family ipv4

Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard IPv4 address prefixes.

address-family vpnv4

Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard VPNv4 address prefixes.

clear ip bgp dampening

Clears BGP route dampening information and unsuppresses the suppressed routes.

clear ip bgp flap-statistics

Clears BGP flap statistics.

show ip bgp dampened-paths

Displays BGP dampened routes.

show ip bgp flap-statistics

Displays BGP flap statistics.