BGP路由抖动惩罚

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　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.