在上图中，我们配置相应接口以及配置EIGRP，详细配置如下
R1:
interface Serial0/0
ip address 10.0.0.1 255.0.0.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.0.0.4 104 broadcast
frame-relay map ip 10.0.0.5 105 broadcast
interface Loopback0
ip address 1.0.0.1 255.0.0.0
router eigrp 1
network 0.0.0.0
auto-summary
R4:
interface Serial0/0
ip address 10.0.0.4 255.0.0.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.0.0.1 401 broadcast
frame-relay map ip 10.0.0.5 401
no frame-relay inverse-arp
interface Loopback0
ip address 4.0.0.1 255.0.0.0
router eigrp 1
network 0.0.0.0
auto-summary
R5:
interface Serial0/0
ip address 10.0.0.5 255.0.0.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.0.0.4 501
frame-relay map ip 10.0.0.1 501 broadcast
no frame-relay inverse-arp
interface Loopback0
ip address 5.0.0.1 255.0.0.0
router eigrp 1
network 0.0.0.0
auto-summary
问题出现了：在配置完成后我们发现R4与R5直接互相学习不到对方的loopback0的地址，
原因是：水平分割引起的，水平分割法的规则和原理是：路由器从某个接口接收到的更新信息不允许再从这个接口发回去。
我们会发现R1是从s0/0接口学习到R4的4.0.0.0/8的路由，它要想从S0/0传递给R5，这违背了水平分割协议，因此如果想让R4与R5互相学习对方的loopback地址，需要在R1上关闭水平分割协议
R1配置水平分割：
int s0/0
no ip split-horizon eigrp 1
配置水平分割之前R5中的路由表
R5#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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 1.0.0.0/8 [90/2297856] via 10.0.0.1, 00:00:29, Serial0/0
C 5.0.0.0/8 is directly connected, Loopback0
C 10.0.0.0/8 is directly connected, Serial0/0
配置水平分割之后R5中的路由表
R5#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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 1.0.0.0/8 [90/2297856] via 10.0.0.1, 00:28:15, Serial0/0
D 4.0.0.0/8 [90/2809856] via 10.0.0.1, 00:01:44, Serial0/0
C 5.0.0.0/8 is directly connected, Loopback0
C 10.0.0.0/8 is directly connected, Serial0/0
本文转自zcm8483 51CTO博客，原文链接:http://blog.51cto.com/haolun/993153