实验拓扑

实验要求

1. 实现通过修改AS-Path属性来影响路径选择
2. 实现通过修改Local_Preference属性来影响路径选择
3. 实现通过修改MED属性来影响路径选择
4. 实现通过修改preferred-value属性来影响路径选择

实验配置与效果

1.改名与IP配置

2.as300配置OSPF

R3已经学到R2和R4的路由

3.配置BGP

查看R4和R2确保全部peer成功建立，值得注意的是，由于ospf没有宣告AS300和其他两个区域间的信息，在R2和R4上搭建10.0.3.3的peer时，需要将下一跳修改为本地

上述操作省略，仅贴出配置图

4.发布路由

[R1]bgp 100
[R1-bgp]net 172.16.1.0 24
[R1-bgp]net 172.16.2.0 24
[R1-bgp]net 172.16.3.0 24
[R1-bgp]net 172.16.4.0 24
[R5]bgp 200
[R5-bgp]net 172.16.1.0 24
[R5-bgp]net 172.16.2.0 24
[R5-bgp]net 172.16.3.0 24
[R5-bgp]net 172.16.4.0 24

修改AS_Path

创建前缀列表匹配相关流量，用路由策略修改172.16.1.0的as-path，最后在R1的出口方向调用路由策略，实现修改，这里我 选择添加as-path400 500，值得注意的是，路由策略需要写一条空语句以放行其他路由信息

打入refresh bgp all export 刷新下R1bgp路由的出方向，在R3路由器上查看相关路由可见其as-path加上了500 和 400

还是R3，可以看到其优选R4的路径

 修改Local_Preference属性

同上创建路由策略修改指定参数，同样的，bgp调用将要发送给R3的172.16.2.0的路由local_preference修改为200

同样查看表项，来自R4的路由被优选

修改MED属性

修改MED由于其继承上个区域的cost，因此只要在边界设备修改cost即可

值得注意的是这里要使用import刷新的时候也是一样，同时还需要在R3上开启med比较

使用此条命令打开compare-different-as-med 

打开R3查看信息，ok的老弟，也是选上了R4

修改preferred-value属性

同理，在R3上修改preferred-value值，在R3的bgp上对来自R4的import方向调用相关策略

刷新路由表，查看R3路由信息

可见路由优选R4，值也被改为300

相关配置

R1

interface LoopBack0ip address 10.0.1.1 255.255.255.255 
#
interface LoopBack1ip address 172.16.1.1 255.255.255.0 
#
interface LoopBack2ip address 172.16.2.1 255.255.255.0 
#
interface LoopBack3ip address 172.16.3.1 255.255.255.0 
#
interface LoopBack4ip address 172.16.4.1 255.255.255.0 
#
bgp 100router-id 10.0.1.1peer 10.0.12.2 as-number 300 #ipv4-family unicastundo synchronizationnetwork 172.16.1.0 255.255.255.0 network 172.16.2.0 255.255.255.0 network 172.16.3.0 255.255.255.0 network 172.16.4.0 255.255.255.0 peer 10.0.12.2 enablepeer 10.0.12.2 route-policy as export
#
route-policy as permit node 10 if-match ip-prefix 1 apply as-path 500 400 additive
#
route-policy as permit node 20 
#
ip ip-prefix 1 index 10 permit 172.16.1.0 24 greater-equal 24 less-equal 24

R2

interface GigabitEthernet0/0/0ip address 10.0.12.2 255.255.255.0 
#
interface GigabitEthernet0/0/1ip address 10.0.23.2 255.255.255.0 
#
interface GigabitEthernet0/0/2
#
interface NULL0
#
interface LoopBack0ip address 10.0.2.2 255.255.255.255 
#
bgp 300router-id 10.0.2.2peer 10.0.3.3 as-number 300 peer 10.0.3.3 connect-interface LoopBack0peer 10.0.12.1 as-number 100 #ipv4-family unicastundo synchronizationpeer 10.0.3.3 enablepeer 10.0.3.3 next-hop-local peer 10.0.12.1 enablepeer 10.0.12.1 route-policy med import
#
ospf 1 router-id 10.0.2.2 area 0.0.0.0 network 10.0.2.2 0.0.0.0 network 10.0.23.2 0.0.0.0 
#
route-policy med permit node 10 if-match ip-prefix 1 apply cost 200 
#
route-policy med permit node 20 
#
ip ip-prefix 1 index 10 permit 172.16.3.0 24 greater-equal 24 less-equal 24
#

R3

interface GigabitEthernet0/0/0ip address 10.0.23.3 255.255.255.0 
#
interface GigabitEthernet0/0/1ip address 10.0.34.3 255.255.255.0 
#
interface GigabitEthernet0/0/2
#
interface NULL0
#
interface LoopBack0ip address 10.0.3.3 255.255.255.255 
#
bgp 300router-id 10.0.3.3peer 10.0.2.2 as-number 300 peer 10.0.2.2 connect-interface LoopBack0peer 10.0.4.4 as-number 300 peer 10.0.4.4 connect-interface LoopBack0#ipv4-family unicastundo synchronizationcompare-different-as-medpeer 10.0.2.2 enablepeer 10.0.4.4 enablepeer 10.0.4.4 route-policy pv import
#
ospf 1 router-id 10.0.3.3 area 0.0.0.0 network 10.0.3.3 0.0.0.0 network 10.0.23.3 0.0.0.0 network 10.0.34.3 0.0.0.0 
#
route-policy pv permit node 10 if-match ip-prefix 1 apply preferred-value 300
#
route-policy pv permit node 20 
#
ip ip-prefix 1 index 10 permit 172.16.4.0 24 greater-equal 24 less-equal 24
#

R4

#
interface GigabitEthernet0/0/0ip address 10.0.34.4 255.255.255.0 
#
interface GigabitEthernet0/0/1ip address 10.0.45.4 255.255.255.0 
#
interface GigabitEthernet0/0/2
#
interface NULL0
#
interface LoopBack0ip address 10.0.4.4 255.255.255.255 
#
bgp 300router-id 10.0.4.4peer 10.0.3.3 as-number 300 peer 10.0.3.3 connect-interface LoopBack0peer 10.0.45.5 as-number 200 #ipv4-family unicastundo synchronizationpeer 10.0.3.3 enablepeer 10.0.3.3 route-policy lp exportpeer 10.0.3.3 next-hop-local peer 10.0.45.5 enable
#
ospf 1 router-id 10.0.4.4 area 0.0.0.0 network 10.0.4.4 0.0.0.0 network 10.0.34.4 0.0.0.0 
#
route-policy lp permit node 10 if-match ip-prefix 1 apply local-preference 200 
#
route-policy lp permit node 20 
#
ip ip-prefix 1 index 10 permit 172.16.2.0 24 greater-equal 24 less-equal 24
#

R5 

interface GigabitEthernet0/0/0ip address 10.0.45.5 255.255.255.0 
#
interface GigabitEthernet0/0/1
#
interface GigabitEthernet0/0/2
#
interface NULL0
#
interface LoopBack0ip address 10.0.5.5 255.255.255.255 
#
interface LoopBack1ip address 172.16.1.1 255.255.255.0 
#
interface LoopBack2ip address 172.16.2.1 255.255.255.0 
#
interface LoopBack3ip address 172.16.3.1 255.255.255.0 
#
interface LoopBack4ip address 172.16.4.1 255.255.255.0 
#
bgp 200router-id 10.0.5.5peer 10.0.45.4 as-number 300 #ipv4-family unicastundo synchronizationnetwork 172.16.1.0 255.255.255.0 network 172.16.2.0 255.255.255.0 network 172.16.3.0 255.255.255.0 network 172.16.4.0 255.255.255.0 peer 10.0.45.4 enable
#