实验拓扑：
实验目的：
1. 熟悉BGP的基本配置
2. 控制BGP邻居的下一跳指向
3. EBGP和IBGP的基本配置
实验步骤：
1. 各路由器接口的IP地址的配置：
a) R1的配置：
Router#configure terminal
R1(config)#interface s1/2
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config)#interface loopback 0
R1(config-if)#ip address 1.1.1 .1 255.255.255.0
R1(config)#interface loopback 10
R1(config-if)#ip address 10.1.1 .1 255.255.255.0
b) R2的配置：
R2(config)#interface s1/3
R2(config-if)#ip address 192.168.1.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#interface s1/2
R2(config-if)#ip address 192.168.2.1 255.255.255.0
R2(config-if)#no shutdown
R2(config)#interface loopback 0
R2(config-if)#ip address 2.2.2 .2 255.255.255.0
c) R3的配置：
R3(config)#interface s1/3
R3(config-if)#ip address 192.168.2.2 255.255.255.0
R3(config-if)#no shutdown
R3(config)#interface loopback 0
R3(config-if)#ip address 3.3.3 .3 255.255.255.0
2. IGP路由配置为EIGRP，做到全网全通：
a) R1的配置：
R1(config)#router eigrp 100
R1(config-router)#no auto-summary
R1(config-router)#network 192.168.1.0 0.0.0 .255
R1(config-router)#network 1.1.1 .0 0.0.0.255
R1(config-router)#network 10.1.1 .0 0.0.0.255
b) R2的配置：
R2(config)#router eigrp 100
R2config-router)#no auto-summary
R2(config-router)#network 192.168.1.0 0.0.0 .255
R2(config-router)#network 192.168.2.0 0.0.0 .255
R2(config-router)#network 2.2.2 .0 0.0.0 .255
c) R3的配置：
R3(config)#router eigrp 100
R3(config-router)#no auto-summary
R3(config-router)#network 192.168.2.0 0.0.0 .255
R3(config-router)#network 3.3.3 .0 0.0.0 .255
配置完成后在R3上分别ping 10.1.1 .1和1.1.1.1测试连通性。
3. R1和R3配置为AS1，R2配置为AS 2：
a) R1的配置：
R1(config)#router bgp 1
R1(config-router)#bgp router-id 1.1.1 .1
R1(config-router)#no auto-summary
R1(config-router)#no synchronization
R1(config-router)#neighbor 3.3.3 .3 remote-as 1
R1(config-router)#neighbor 3.3.3 .3 update-source loopback 0
R1(config-router)#network 10.1.1 .0 mask 255.255.255.0
b) R3的配置：
R3(config)#router bgp 1
R3(config-router)#bgp router-id 3.3.3 .3
R3(config-router)#no auto-summary
R3(config-router)#no synchronization
R3(config-router)#neighbor 1.1.1 .1 remote-as 1
R3(config-router)#neighbor 1.1.1 .1 update-source loopback 0
R3(config-router)#neighbor 2.2.2 .2 remote-as 2
R3(config-router)#neighbor 2.2.2 .2 ebgp-multihop
R3(config-router)#neighbor 2.2.2 .2 update-source loopback 0
c) R2的配置：
R2(config)#router bgp 2
R2(config-router)#bgp router-id 2.2.2 .2
R2(config-router)#no auto-summary
R2(config-router)#no synchronization
R2(config-router)#neighbor 3.3.3 .3 remote-as 1
R2(config-router)#neighbor 3.3.3 .3 update-source loopback 0
R2(config-router)#neighbor 3.3.3 .3 ebgp-multihop
4. 这样配置完成后在R3上ping 10.1.1 .1是不通的，如下：
R3#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF , IA
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
D 1.1.1 .0 [90/2809856] via 192.168.2.1, 00:16:01, Serial1/3
D 2.2.2 .0 [90/2297856] via 192.168.2.1, 00:18:06, Serial1/3
C 3.3.3 .0/24 is directly connected, Loopback0
D 3.0.0 .0/8 is a summary, 00:16:01, Null0
B 10.1.1 .0 [200/0] via 1.1.1.1, 00:04:10
D 192.168.1.0/24 [90/2681856] via 192.168.2.1, 00:18:06, Serial1/3
C 192.168.2.0/24 is directly connected, Serial1/3
R3#ping 10.1.1 .1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1 .1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R3#traceroute 10.1.1 .1
Type escape sequence to abort.
Tracing the route to 10.1.1 .1
1 192.168.2.1 80 msec 192 msec 72 msec
2 192.168.2.2 240 msec 168 msec 488 msec
3 192.168.2.1 216 msec 192 msec 168 msec
4 192.168.2.2 312 msec 264 msec 288 msec
5 192.168.2.1 496 msec 264 msec 360 msec
6 192.168.2.2 432 msec 368 msec 504 msec
7 192.168.2.1 360 msec 312 msec 424 msec
8 192.168.2.2 404 msec 592 msec 312 msec
9 192.168.2.1 308 msec 576 msec 552 msec
10 192.168.2.2 712 msec 528 msec 536 msec
11 192.168.2.1 452 msec 380 msec 480 msec
12 192.168.2.2 528 msec 648 msec 456 msec
13 192.168.2.1 816 msec 736 msec 456 msec
14 192.168.2.2 552 msec 816 msec 768 msec
15 192.168.2.1 784 msec 604 msec 672 msec
16 192.168.2.2 912 msec 744 msec 864 msec
17 192.168.2.1 800 msec 704 msec 748 msec
18 192.168.2.2 972 msec 840 msec 648 msec
19 192.168.2.1 936 msec 736 msec 720 msec
20 192.168.2.2 792 msec 768 msec 992 msec
21 192.168.2.1 824 msec 864 msec 936 msec
22 192.168.2.2 1072 msec 1224 msec 1120 msec
23 192.168.2.1 1000 msec 1048 msec 1104 msec
24 192.168.2.2 1368 msec 1104 msec 1560 msec
25 192.168.2.1 1080 msec 1200 msec 1248 msec
26 192.168.2.2 1912 msec 1296 msec 944 msec
27 192.168.2.1 1260 msec 1280 msec 1144 msec
28 192.168.2.2 1288 msec 1220 msec 1232 msec
29 192.168.2.1 1336 msec 1144 msec 1568 msec
30 192.168.2.2 1296 msec 1368 msec 1416 msec
在R3上做设置：R3(config-router)#neighbor 2.2.2 .2 next-hop-unchanged
然后再测试：
R3#ping 10.1.1 .1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1 .1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 96/170/216 ms
R3#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF , IA
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
D 1.1.1 .0 [90/2809856] via 192.168.2.1, 00:23:46, Serial1/3
D 2.2.2 .0 [90/2297856] via 192.168.2.1, 00:25:51, Serial1/3
C 3.3.3 .0/24 is directly connected, Loopback0
D 3.0.0 .0/8 is a summary, 00:23:46, Null0
B 10.1.1 .0 [200/0] via 1.1.1.1, 00:11:55
D 192.168.1.0/24 [90/2681856] via 192.168.2.1, 00:25:51, Serial1/3
C 192.168.2.0/24 is directly connected, Serial1/3
R2#show ip bgp
BGP table version is 3, local router ID is 2.2.2 .2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.1.1 .0/24 1.1.1 .1 0 1 i
实验总结：当R3在设置BGP邻居R2的时候要设点R2的next-hop指向保持不变，即指向1.1.1 .1，不然ping 10.1.1.1的时候包会在R3和R2之间循环。
