24、BGP配置之选路，优选MED属性值最小的

一、实验拓扑

二、实验需求

1、配置基本BGP，在R4和R5上采用network的方式注入互联的网段

2、在R2上修改10.0.45.0传给R1的MED值为20

3、在R1上开启来自不同AS的MED值比较

三、实验过程

1、R1的配置

sys
un in en
sys R1
int g0/0/0
ip add 10.0.12.1 24
int g0/0/1
ip add 10.0.13.1 24
int loo0
ip add 1.1.1.1 32

ospf 1 router-id 1.1.1.1
area 0
net 10.0.12.0 0.0.0.255
net 10.0.13.0 0.0.0.255
net 1.1.1.1 0.0.0.0

bgp 200
router-id 1.1.1.1
pe 2.2.2.2 as 200
pe 2.2.2.2 con loo0
pe 3.3.3.3 as 200
pe 3.3.3.3 con loo0
compare-different-as-med

2、R2的配置

sys
un in en
sys R2
int g0/0/0
ip add 10.0.12.2 24
int g0/0/1
ip add 10.0.24.2 24
int loo0
ip add 2.2.2.2 32

ospf 1 router-id 2.2.2.2
area 0
net 2.2.2.2 0.0.0.0
net 10.0.12.0 0.0.0.255

ip ip-prefix 45 index 10 permit 10.0.45.0 24

route-policy 45-med permit node 1
if-match ip-prefix 45
apply cost 20
route-policy 45-med permit node 2

bgp 200
router-id 2.2.2.2
pe 1.1.1.1 as 200
pe 1.1.1.1 con loo0
pe 1.1.1.1 next-hop-local
pe 3.3.3.3 as 200
pe 3.3.3.3 con loo0
pe 3.3.3.3 next-hop-local
pe 10.0.24.4 as 100
 peer 1.1.1.1 route-policy 45-med export

3、R3的配置

sys
un in en
sys R3
int g0/0/1
ip add 10.0.13.3 24
int g0/0/0
ip add 10.0.35.3 24
int loo0
ip add 3.3.3.3  32

ospf 1 router-id 3.3.3.3
area 0
net 10.0.13.0 0.0.0.255
net 3.3.3.3 0.0.0.0

bgp 200
router-id 3.3.3.3
pe 1.1.1.1 as 200
pe 1.1.1.1 con loo0
pe 1.1.1.1 next-hop-local
pe 2.2.2.2 as 200
pe 2.2.2.2 con loo0
pe 2.2.2.2 next-hop-local
pe 10.0.35.5 as 300

4、R4的配置

sys
un in en
sys R4
int g0/0/1
ip add 10.0.24.4 24
int g0/0/2
ip add 10.0.45.4 24
int g0/0/3
ip add 10.0.54.4 24
int loo0
ip add 4.4.4.4 32
bgp 100
router-id 4.4.4.4
pe 10.0.24.2 as 200
pe 10.0.45.5 as 300
pe 10.0.54.5 as 300
pe 10.0.35.3 as 200
net 10.0.45.0 24
net 10.0.54.0 24

5、R5的配置

sys
un in en
sys R5
int g0/0/0
ip add 10.0.35.5 24
int g0/0/2
ip add 10.0.45.5 24
int g0/0/3
ip add 10.0.54.5 24
int loo0
ip add 5.5.5.5 32

bgp 300
router-id 5.5.5.5
pe 10.0.45.4 as 100
pe 10.0.54.4 as 100
pe 10.0.35.3 as 200
net 10.0.45.0 24
net 10.0.54.0 24

四、实验结果

1、在R1上查看BGP路由表信息

• R4发布的BGP路由的MED值为20，R5发布的BGP路由不携带MED值（默认为0），R5发布的BGP路由拥有更小的MED值，R1优选R5发布BGP的路由