BGP 路由抖动惩罚实例

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BGP 路由抖动惩罚实例

Default Dampening

shows the configuration and monitoring of route dampening. Routers A and B are configured as EBGP neighbors. Router A is advertising network 172.16.2.0/24 to Router B via EBGP. This prefix is a loopback interface that we will cause to flap by administratively shutting down and reenabling the interface.

Router Ainterface loopback 0 ip address 172.16.2.1 255.255.255.0!router bgp 1 neighbor 10.1.1.2 remote-as 2 network 172.16.2.0 mask 255.255.255.0___________________________________________________________________________Router Brouter bgp 2 bgp dampening neighbor 10.1.1.1 remote-as 1

BGP dampening has been configured using the general form of the bgp dampening command. This applies route dampening to every BGP route with the following defaults:

  • half-life— 15 minutes

  • reuse— 750

  • suppress-limit— 2000

  • half-life— 15 minutes

  • max-suppress-time— 4 * half-life = 60 minutes

Router B should have an entry for prefix 172.16.2.0/24 in its BGP table:

Router B#show ip bgpBGP table version is 2, local router ID is 5.5.5.5Status codes: s suppressed, d damped, h history, * valid, > best, i – internalOrigin codes: i – IGP, e – EGP, ? – incomplete    Network           Next Hop             Metric LocPrf Weight Path

*> 172.16.2.0/24     10.1.1.1                  0              0 1 i

Shut down network 172.16.2.0 on Router A by shutting down the loopback 0 interface. Examine the BGP table on Router B:

2511#show ip bgpBGP table version is 3, local router ID is 5.5.5.5Status codes: s suppressed, d damped, h history, * valid, > best, i – internalOrigin codes: i – IGP, e – EGP, ? – incomplete    Network           Next Hop             Metric LocPrf Weight Path h 172.16.2.0/24     10.1.1.1                  0              0 1 i     ////////

The prefix 172.16.2.0/24 is still in the BGP table, but it is an invalid route. Because dampening is enabled on Router B, Router B must maintain a history for every route that has flapped. View the dampening parameters for prefix 172.16.2.0/24:

rtrB#show ip bgp 172.16.2.0/24BGP routing table entry for 172.16.2.0/24, version 3Paths: (1 available, no best path)   Not advertised to any peer   1 (history entry)     10.1.1.1 from 10.1.1.1 (172.16.88.2)       Origin IGP, metric 0, localpref 100, external, ref 2      Dampinfo: penalty 996, flapped 1 times in 00:00:08

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