BGP-route flap经典案例

2007-08-02 17:07:25

　标签：BGP route flap　　　[推送到技术圈]

R1s2/1－>s2/1R2s2/2－>s2/1R3s2/2－>s2/1R4s2/2－>s2/2R5f0/0－>f0/0R1

AS234内跑eigrp

R1#sh run | b r b

router bgp 100

no synchronization

bgp router-id 1.1.1.1

network 1.1.1.1 mask 255.255.255.255

network 12.0.0.0 mask 255.255.255.0

neighbor 12.0.0.2 remote-as 234

neighbor 15.0.0.5 remote-as 500

no auto-summary

R2#sh run | b r e

router eigrp 90

network 2.2.2.0 0.0.0.255

network 23.0.0.0 0.0.0.255

no auto-summary

router bgp 234

no synchronization

bgp router-id 2.2.2.2

neighbor 3.3.3.3 remote-as 234

neighbor 3.3.3.3 update-source Loopback0

neighbor 12.0.0.1 remote-as 100

no auto-summary

R3#sh run | b r e

router eigrp 90

network 3.3.3.0 0.0.0.255

network 23.0.0.0 0.0.0.255

network 34.0.0.0 0.0.0.255

no auto-summary

router bgp 234

no synchronization

bgp router-id 3.3.3.3

neighbor 2.2.2.2 remote-as 234

neighbor 2.2.2.2 update-source Loopback0

neighbor 4.4.4.4 remote-as 234

neighbor 4.4.4.4 update-source Loopback0

no auto-summary

R4#sh run | b r e

router eigrp 90

network 4.4.4.0 0.0.0.255

network 34.0.0.0 0.0.0.255

no auto-summary

router bgp 234

no synchronization

bgp router-id 4.4.4.4

neighbor 3.3.3.3 remote-as 234

neighbor 3.3.3.3 update-source Loopback0

neighbor 3.3.3.3 next-hop-self

neighbor 45.0.0.5 remote-as 500

no auto-summary

R5#sh run | b r b

router bgp 500

no synchronization

bgp router-id 5.5.5.5

neighbor 15.0.0.1 remote-as 100

neighbor 45.0.0.4 remote-as 234

no auto-summary

观察R3上的bgp路由变化

Network Next Hop Metric LocPrf Weight Path

*>i1.1.1.1/32 4.4.4.4 0 100 0 500 100 i

* i 12.0.0.1 0 100 0 100 i

Network Next Hop Metric LocPrf Weight Path

* i1.1.1.1/32 4.4.4.4 0 100 0 500 100 i

*>i 12.0.0.1 0 100 0 100 i

* i12.0.0.0/24 4.4.4.4 0 100 0 500 100 i

*>i 12.0.0.1 0 100 0 100 i

Network Next Hop Metric LocPrf Weight Path

*>i1.1.1.1/32 4.4.4.4 0 100 0 500 100 i

* i 12.0.0.1 0 100 0 100 i

*>i12.0.0.0/24 4.4.4.4 0 100 0 500 100 i

* i 12.0.0.1 0 100 0 100 i

Network Next Hop Metric LocPrf Weight Path

* i1.1.1.1/32 4.4.4.4 0 100 0 500 100 i

*>i 12.0.0.1 0 100 0 100 i

* i12.0.0.0/24 4.4.4.4 0 100 0 500 100 i

*>i 12.0.0.1 0 100 0 100 i

R3(config-router)#do sh ip cef 1.1.1.1

1.1.1.1/32, version 34, epoch 0

0 packets, 0 bytes

via 12.0.0.1, 0 dependencies, recursive

unresolved

Network Next Hop Metric LocPrf Weight Path

*>i1.1.1.1/32 4.4.4.4 0 100 0 500 100 i

* i 12.0.0.1 0 100 0 100 i

*>i12.0.0.0/24 4.4.4.4 0 100 0 500 100 i

* i 12.0.0.1 0 100 0 100 i

R3(config-router)#do sh ip cef 1.1.1.1

1.1.1.1/32, version 36, epoch 0, cached adjacency to Serial2/2

0 packets, 0 bytes

via 4.4.4.4, 0 dependencies, recursive

next hop 34.0.0.4, Serial2/2 via 4.4.4.0/24

valid cached adjacency

注：

先宣告bgp路由1.1.1.1到R1，R3学到的bgp路由1.1.1.1是从R4学来的，因为下一跳可达，R4上做了nei 3.3.3.3 next－hop－self。

再宣告12.0.0.0bgp路由到R1，观察R3学到的bgp路由，bgp路由翻动，下一跳是12.0.0.1，这个路由是从5->4->3这个方向学到的，R3扫描发现12.0.0.1下一跳不可达，因为R2上没有做nei 3.3.3.3 next－hop－self，bgp路由又翻动了，走下一跳4.4.4.4了。

最后还有一个问题：r> 12.0.0.0/24 12.0.0.1 0 0 100 i

R2#sh ip bgp

BGP table version is 4, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 1.1.1.1/32 12.0.0.1 0 0 100 i

r> 12.0.0.0/24 12.0.0.1 0 0 100 i

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BGP-route flap经典案例