题目：

思路：
该题分为三个AS区域，并且三个区别间分别使用不同的路由，EBGP,IBGP,OSFP连接等，其中AS1与AS2之间使用的是EBGP连接，这点需要EBGP的命令来进行实现，AS2中使用的OSPF，AS2，3中也E是用EBGP进行连接，要除R5外所以有的路由均可互相访问，首先配置好每个路由的网段信息，而后通过命令使路由间协议得以畅通。在过程中要宣告足够的网段命令，并且要注意特定的下一跳地址的变化，注意邻居间关系的正常建立，在过程中通过足够的验证来进行实验。

路由命令：

R1:
[r1]int lo0
[r1-LoopBack0]ip add 1.1.1.1 24
[r1-LoopBack0]int g0/0/1
[r1-GigabitEthernet0/0/1]ip add 12.1.1.1 24
[r1]bgp 1
[r1-bgp]router-id 1.1.1.1
[r1-bgp]peer 12.1.1.2 as-number 2

R2:
[r2]int g0/0/0
[r2-GigabitEthernet0/0/0]ip add 12.1.1.2 24
[r2-GigabitEthernet0/0/0]int lo0
[r2-LoopBack0]ip add 2.2.2.2 24
[r2-LoopBack0]int g0/0/1
[r2-GigabitEthernet0/0/1]ip add 23.1.1.1 24
[r2]ospf 1 router-id 2.2.2.2
[r2-ospf-1]area 0
[r2-ospf-1-area-0.0.0.0]network 23.1.1.1 0.0.0.0
[r2-ospf-1-area-0.0.0.0]network 2.2.2.2 0.0.0.0
[r2]bgp 2
[r2-bgp]router-id 2.2.2.2
[r2-bgp]peer 12.1.1.1 as-number 1
[r2-bgp]peer 3.3.3.3 as-number 2
[r2-bgp]peer 3.3.3.3 connect-interface LoopBack 0
[r2-bgp]peer 3.3.3.3 next-hop-local
[r2-bgp]peer 4.4.4.4 as-number 2
[r2-bgp]peer 4.4.4.4 connect-interface LoopBack 0
[r2-bgp]peer 4.4.4.4 next-hop-local
[r2-bgp]network 2.2.2.0 24

R3:
[r3]int g0/0/0
[r3-GigabitEthernet0/0/0]ip add 23.1.1.2 24
[r3-GigabitEthernet0/0/0]int lo0
[r3-LoopBack0]ip add 3.3.3.3 24
[r3-LoopBack0]int g0/0/1
[r3-GigabitEthernet0/0/1]ip add 34.1.1.1 24
[r3]ospf 1 router-id 3.3.3.3
[r3-ospf-1]area 0
[r3-ospf-1-area-0.0.0.0]network 23.1.1.2 0.0.0.0
[r3-ospf-1-area-0.0.0.0]network 3.3.3.3 0.0.0.0
[r3-ospf-1-area-0.0.0.0]network 34.1.1.1 0.0.0.0
[r3-bgp]router-id 3.3.3.3
[r3-bgp]peer 2.2.2.2 as-number 2
[r3-bgp]peer 2.2.2.2 connect-interface LoopBack 0
[r3-bgp]peer 4.4.4.4 as-number 2
[r3-bgp]peer 4.4.4.4 connect-interface LoopBack 0
[r3-bgp]network 3.3.3.0 24

R4:
[r4]int g0/0/0
[r4-GigabitEthernet0/0/0]ip add 34.1.1.2 24
[r4-GigabitEthernet0/0/0]int lo0
[r4-LoopBack0]ip add 4.4.4.4 24
[r4-LoopBack0]int g0/0/1
[r4-GigabitEthernet0/0/1]ip add 45.1.1.1 24
[r4-GigabitEthernet0/0/1]int g0/0/2
[r4-GigabitEthernet0/0/2]ip add 54.1.1.1 24
[r4]ospf 1 router-id 4.4.4.4
[r4-ospf-1]area 0
[r4-ospf-1-area-0.0.0.0]network 34.1.1.2 0.0.0.0
[r4-ospf-1-area-0.0.0.0]network 4.4.4.4 0.0.0.0
[r4-bgp]router-id 4.4.4.4
[r4-bgp]peer 3.3.3.3 as-number 2
[r4-bgp]peer 3.3.3.3 connect-interface LoopBack 0
[r4]ip route-static 5.5.5.0 24 45.1.1.2
[r4]ip route-static 5.5.5.0 24 54.1.1.2
[r4-bgp]peer 5.5.5.5 as-number 3
[r4-bgp]peer 5.5.5.5 connect-interface LoopBack 0
[r4-bgp]peer 5.5.5.5 ebgp-max-hop 2
[r4-bgp]peer 2.2.2.2 as-number 2
[r4-bgp]peer 2.2.2.2 connect-interface LoopBack 0
[r4-bgp]peer 2.2.2.2 next-hop-local
[r4-bgp]peer 3.3.3.3 next-hop-local
[r4]undo ip route-static 5.5.5.0 24
[r4]ip route-static 5.5.5.5 32 45.1.1.2
[r4]ip route-static 5.5.5.5 32 54.1.1.2
[r4-bgp]network 4.4.4.0 24

R5:
[r5]int g0/0/0
[r5-GigabitEthernet0/0/0]ip add 45.1.1.2 24
[r5-GigabitEthernet0/0/0]int g0/0/2
[r5-GigabitEthernet0/0/2]ip add 54.1.1.2 24
[r5-GigabitEthernet0/0/2]int lo0
[r5-LoopBack0]ip add 5.5.5.5 24
[r5]ip route-static 4.4.4.0 24 45.1.1.1
[r5]ip route-static 4.4.4.0 24 54.1.1.1
[r5-bgp]router-id 5.5.5.5
[r5-bgp]peer 4.4.4.4 as-number 2
[r5-bgp]peer 4.4.4.4 connect-interface LoopBack 0
[r5-bgp]peer 4.4.4.4 ebgp-max-hop 2
[r5-bgp]network 5.5.5.0 24
[r5]int lo1
[r5-LoopBack1]ip add 99.1.1.1 24
[r5-bgp]network 99.1.1.0 24
[r5]undo ip route-static 4.4.4.0 24
[r5]ip route-static 4.4.4.4 32 45.1.1.1
[r5]ip route-static 4.4.4.4 32 54.1.1.1

实验验证命令：