一、網絡拓撲
需求：AR1默認選擇路線是AR1 > AR2 > AR4到200.1.1.1（AR2 route-id小），但是鏈路帶寬低。現在希望在AS65008內僅改變AR3的local-pre值，實現選擇高帶寬鏈路，路線訪問：AR1 > AR3 > AR4 到200.1.1.1
- Local_Pref屬性僅在IBGP鄰居之間有效，不通告給其他AS。它表明路由器的BGP優先級，值越大越優。
- Local_Pref屬性用於判斷流量離開AS時的最佳路由。當BGP路由器通過不同的IBGP鄰居獲得目的地址相同但下一跳不同的多條路由時，將優先選擇Local_Pref屬性值較高的路由，其默認值爲100。
- 在AR3上做Local_Pref配置，將策略應用在對AR1發佈路由的export方向，從而影響AR1的選路。（因爲有Preference_Value方法，可以直接在AR1上做配置，從而影響AR1的選路，在另外一篇文章介紹）
二、基本配置
1、AR1
1、配置接口
<Huawei>system-view
[Huawei]sysname AR1
[AR1]interface GigabitEthernet 0/0/0
[AR1-GigabitEthernet0/0/0]ip address 10.1.12.1 24
[AR1-GigabitEthernet0/0/0]quit
[AR1]interface GigabitEthernet 0/0/1
[AR1-GigabitEthernet0/0/1]ip address 10.1.13.1 24
[AR1-GigabitEthernet0/0/1]quit
[AR1]interface LoopBack 0
[AR1-LoopBack0]ip address 1.1.1.1 32
[AR1-LoopBack0]quit
2、配置OSPF
[AR1]ospf 1 router-id 1.1.1.1
[AR1-ospf-1]area 0
[AR1-ospf-1-area-0.0.0.0]network 10.1.12.0 0.0.0.255
[AR1-ospf-1-area-0.0.0.0]network 10.1.13.0 0.0.0.255
[AR1-ospf-1-area-0.0.0.0]quit
[AR1-ospf-1]import-route direct
[AR1-ospf-1]quit
3、配置IBGP
[AR1]bgp 65008
[AR1-bgp]router-id 1.1.1.1
[AR1-bgp]peer 10.1.12.2 as-number 65008
[AR1-bgp]peer 10.1.13.3 as-number 65008
[AR1-bgp]import-route ospf 1
[AR1-bgp]quit
2、AR2
1、配置接口
<Huawei>system-view
[Huawei]sysname AR2
[AR2]interface LoopBack 0
[AR2-LoopBack0]ip address 2.2.2.2 32
[AR2-LoopBack0]quit
[AR2]interface GigabitEthernet 0/0/0
[AR2-GigabitEthernet0/0/0]ip address 10.1.12.2 24
[AR2-GigabitEthernet0/0/0]quit
[AR2]interface GigabitEthernet 0/0/2
[AR2-GigabitEthernet0/0/2]ip address 10.1.24.2 24
[AR2-GigabitEthernet0/0/2]quit
2、配置OSPF
[AR2]ospf 1 router-id 2.2.2.2
[AR2-ospf-1]area 0
[AR2-ospf-1-area-0.0.0.0]network 10.1.12.0 0.0.0.255
[AR2-ospf-1]import-route direct
[AR2-ospf-1]quit
3、配置BGP
[AR2]bgp 65008
[AR2-bgp]router-id 2.2.2.2
[AR2-bgp]peer 10.1.12.1 as-number 65008 #IBGP
[AR2-bgp]peer 10.1.24.4 as-number 65009 #EBGP
[AR2-bgp]import-route ospf 1
[AR2-bgp]quit
3、AR3
1、配置接口
<Huawei>system-view
[Huawei]sysname AR3
[AR3]interface GigabitEthernet 0/0/1
[AR3-GigabitEthernet0/0/1]ip address 10.1.13.3 24
[AR3-GigabitEthernet0/0/1]quit
[AR3]interface GigabitEthernet 0/0/0
[AR3-GigabitEthernet0/0/0]ip address 10.1.34.3 24
[AR3-GigabitEthernet0/0/0]quit
[AR3]interface LoopBack 0
[AR3-LoopBack0]ip address 3.3.3.3 32
[AR3-LoopBack0]quit
2、配置OSPF
[AR3]ospf 1 router-id 3.3.3.3
[AR3-ospf-1]area 0
[AR3-ospf-1-area-0.0.0.0]network 10.1.13.0 0.0.0.255
[AR3-ospf-1-area-0.0.0.0]quit
[AR3-ospf-1]import-route direct
[AR3-ospf-1]quit
3、配置BGP
[AR3]bgp 65008
[AR3-bgp]router-id 3.3.3.3
[AR3-bgp]peer 10.1.13.1 as-number 65008
[AR3-bgp]peer 10.1.34.4 as-number 65009
[AR3-bgp]import-route ospf 1
[AR3-bgp]quit
4、AR4
1、配置接口
<Huawei>system-view
[Huawei]sysname AR4
[AR4]interface GigabitEthernet 0/0/2
[AR4-GigabitEthernet0/0/2]ip address 10.1.24.4 24
[AR4-GigabitEthernet0/0/2]quit
[AR4]interface GigabitEthernet 0/0/0
[AR4-GigabitEthernet0/0/0]ip address 10.1.34.4 24
[AR4-GigabitEthernet0/0/0]quit
[AR4]interface LoopBack 0
[AR4-LoopBack0]ip address 4.4.4.4 32
[AR4-LoopBack0]quit
[AR4]interface LoopBack 1
[AR4-LoopBack1]ip address 200.1.1.1 24
[AR4-LoopBack1]quit
[AR4]interface LoopBack 2
[AR4-LoopBack2]ip address 200.1.2.1 24
[AR4-LoopBack2]quit
2、配置BGP
[AR4]bgp 65009
[AR4-bgp]peer 10.1.24.2 as-number 65008
[AR4-bgp]peer 10.1.34.3 as-number 65008
[AR4-bgp]import-route direct
[AR4-bgp]quit
5、查看BGP路由表
<AR1>tracert 200.1.1.1
traceroute to 200.1.1.1(200.1.1.1), max hops: 30 ,packet length: 40,press CTRL_C to break
1 10.1.12.2 30 ms 30 ms 10 ms
2 10.1.24.4 20 ms 20 ms 20 ms
<AR1>tracert 200.1.2.1
traceroute to 200.1.2.1(200.1.2.1), max hops: 30 ,packet length: 40,press CTRL_C to break
1 10.1.12.2 30 ms 30 ms 20 ms
2 10.1.24.4 20 ms 20 ms 30 ms
三、全部目的地址改變線路
1、修改local-preference值，默認爲100（越大越優先）
[AR3]bgp 65008
[AR3-bgp]ipv4-family unicast
[AR3-bgp-af-ipv4]default local-preference 200
[AR3-bgp-af-ipv4]return
2、查看BGP路由表，線路已經被改變
3、跟蹤路由確認
<AR1>tracert 200.1.1.1
traceroute to 200.1.1.1(200.1.1.1), max hops: 30 ,packet length: 40,press CTRL_C to break
1 10.1.13.3 30 ms 20 ms 20 ms
2 10.1.34.4 20 ms 20 ms 30 ms
<AR1>tracert 200.1.2.1
traceroute to 200.1.2.1(200.1.2.1), max hops: 30 ,packet length: 40,press CTRL_C to break
1 10.1.13.3 30 ms 20 ms 10 ms
2 10.1.34.4 30 ms 20 ms 20 ms
四、部分目的地址改變線路
1、修改BGP的Local_Preference，將策略應用在對AR1發佈路由的export方向
[AR3]bgp 65008
[AR3-bgp]undo default local-preference
[AR3-bgp]ipv4-family unicast
[AR3-bgp-af-ipv4]peer 10.1.13.1 route-policy local-pre export
[AR3-bgp-af-ipv4]return
2、定義路由策略
[AR3]route-policy local-pre permit node 10
[AR3-route-policy]if-match ip-prefix local-pre
[AR3-route-policy]apply local-preference 200
[AR3-route-policy]quit
3、創建IPv4地址前綴列表
[AR3]ip ip-prefix local-pre index 10 permit 200.1.1.0 24
4、查看BGP路由表
5、跟蹤路由測試（200.1.1.1線路已經被改變，200.1.2.1使用默認線路）
