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