20、BGP配置之选路，本地始发BGP路由优于从其他对等体学习到的

一、实验拓扑

二、实验需求

1、在R3上配置，两条静态路由，下一跳指向null，分别是：10.0.45.0/25、10.0.45.128/25。

2、在R5上注入路由10.0.45.0/24和10.0.0.0/8，

3、在R3上分别配置自动聚合（过滤掉明细）和手动聚合，引入静态。

4、其他设备配置基本BGP即可，不需要注入路由。

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

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

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

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

ip route-static 10.0.45.0 255.255.255.128 NULL0
ip route-static 10.0.45.128 255.255.255.128 NULL0

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
summary automatic   //自动聚合
aggregate 10.0.0.0 255.0.0.0 detail-suppressed    //手动聚合
import-route static   //引入静态

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

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
int loo1
ip add 10.0.0.1 8

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 10.0.0.0 8

四、实验结果

1、在R3上查看BGP路由表信息

• 观察发现去往10.0.0.0条目有三个下一跳，根据BGP选路规则，本地始发的（手工汇总>自动汇总>network>import-route>从对等体学到的）BGP路由优于从其他对等体学习到的。很明显条目127.0.0.1就是本地始发的。我们在观察10.0.0.0的详细信息，发现第一个127.0.0.1带有标志Atomic-Aggregate原子聚合说明是手动聚合路由。第二条没有则是自动聚合路由。所以本地始发的BGP路由优于从其他对等体学习到的。