BGP-route flap经典案例
R1s2/1
－
>s2/1R2s2/2
－
>s2/1R3s2/2
－
>s2/1R4s2/2
－
>s2/2R 5f 0/0
－
>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
*>i 1.1.1 .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
* i 1.1.1 .1/32 4.4.4 .4 0 100 0 500 100 i
*>i 12.0.0 .1 0 100 0 100 i
* i 12.0.0 .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
*>i 1.1.1 .1/32 4.4.4 .4 0 100 0 500 100 i
* i 12.0.0 .1 0 100 0 100 i
*>i 12.0.0 .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
* i 1.1.1 .1/32 4.4.4 .4 0 100 0 500 100 i
*>i 12.0.0 .1 0 100 0 100 i
* i 12.0.0 .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
vi a 12.0.0 .1, 0 dependencies, recursive
unresolved
Network Next Hop Metric LocPrf Weight Path
*>i 1.1.1 .1/32 4.4.4 .4 0 100 0 500 100 i
* i 12.0.0 .1 0 100 0 100 i
*>i 12.0.0 .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
vi a 4.4.4 .4, 0 dependencies, recursive
next hop 34.0.0.4, Serial2/2 vi a 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