配置地址，AS123使用ospf保证通讯，修改接口类型保证ospf学习环回20.0,30.0,100.0 地址时，是以24位掩码学习，R1，R2，R3都处于BGP边界，各自都需要宣告三者的私网环回
1，
R4\]ip ip-prefix aa permit 192.168.10.0 24 \[R4\]route-policy aa permit node 10 \[R4-route-policy\]if-match ip-prefix aa \[R4-route-policy\]apply preferred-value 100 \[R4\]route-policy aa permit node 20 \[R4\]bgp 400 \[R4-bgp\]peer 42.1.1.2 route-policy aa import \[R4-bgp
2，
R4\]ip ip-prefix bb permit 192.168.11.0 24 \[R4\]route-policy aa permit node 15 \[R4-route-policy\]if-match ip-prefix bb \[R4-route-policy\]apply as-path 123 123 500 overwrite ---使用已出现的AS号 Warning: The AS-Path lists of routes to which this route-policy is applied will be overwritten. Continue? \[Y/N\]y
3，R2
Huawei\]ip ip-prefix aa permit 192.168.12.0 24 \[Huawei\]route-policy aa permit node 10 \[Huawei-route-policy\]if-match ip-prefix aa \[Huawei-route-policy\]apply cost 200 \[Huawei\]route-policy aa permit node 20 \[Huawei\]bgp 123 \[Huawei-bgp\]peer 42.1.1.4 route-policy aa export
R3：
Huawei\]ip ip-prefix aa permit 192.168.12.0 24 \[Huawei\]route-policy aa permit node 10 \[Huawei-route-policy\]if-match ip-prefix aa \[Huawei-route-policy\]apply cost 20 \[Huawei\]route-policy aa permit node 20 \[Huawei\]bgp 123 \[Huawei-bgp\]peer 43.1.1.4 route-policy aa export
4，5
Huawei\]ip ip-prefix aa permit 192.168.1.0 24 \[Huawei\]ip ip-prefix bb permit 192.168.2.0 24 \[Huawei\]route-policy aa permit node 10 \[Huawei-route-policy\]if-match ip-prefix aa \[Huawei-route-policy\]apply local-preference 200 \[Huawei\]route-policy aa permit node 20 \[Huawei\]route-policy bb permit node 10 \[Huawei-route-policy\]if-match ip-prefix bb \[Huawei-route-policy\]apply local-preference 200 \[Huawei\]route-policy bb permit node 20 \[Huawei\]bgp \[Huawei\]bgp 123 \[Huawei-bgp\]peer 2.2.2.2 route-policy aa import \[Huawei-bgp\]peer 3.3.3.3 route-policy bb import \[Huawei-bgp
6，
Huawei\]bgp 123 \[Huawei-bgp\]maximum load-balancing 2
7，
Huawei\]ip as-path-filter 1 deny \^123$ \[Huawei\]ip as-path-filter 1 permit .\* \[Huawei\]bgp 500 \[Huawei-bgp\]peer 15.1.1.1 as-path-filter 1 import
8，
Huawei\]ip ip-prefix cc permit 192.168.3.0 24 \[Huawei\]route-policy aa permit node 15 \[Huawei-route-policy\]if-match ip-prefix cc \[Huawei-route-policy\]apply community no-export \[Huawei\]route-policy bb permit node 15 \[Huawei-route-policy\]if-match ip-prefix cc \[Huawei-route-policy\]apply community no-export