EIGRP水平分割
1.1.1.所需设备
下面是做这个实验练习所需的设备：
1) 三台具有一个串行端口的Cisco路由器；
2) Cisco IOS 10.0版或更高；
3) 一台运行了终端仿真程序的PC；
4) 三根Cisco DTE/DCE交叉电缆；
5) 一根Cisco扁平电缆供路由器的控制台端口访问使用。
配置概述
验证EIGRP在Hub-Spoke拓扑结构下水平分割对其影响及解决方式，具体实验要求：R1、R2、R3三台路由器通过帧中继网络连接，拓扑类型为 Hub-Spok模型。R1为Hub，R2、R3为Spoke路由器，三台路由器之间运行EIGRP协议，通过配置EIGRP水平分割特性，始三台路由器路由表学习完整，即三台路由器均通过EIGRP学习到2条路由
3.路由器配置
1. 帧交换机
FrameSwitch# show running-config
!
hostname FrameSwitch
!
frame-relay switching
!
interface Serial0/1
encapsulation frame-relay
frame-relayintf-type dce
frame-relayroute 102 interface Serial0/2 201
!
interface Serial0/2
encapsulation frame-relay
frame-relayintf-type dce
frame-relayroute 201 interface Serial0/1 102
frame-relayroute 203 interface Serial0/3 302
!
interface Serial0/3
encapsulation frame-relay
frame-relay intf-type dce
frame-relayroute 302 interface Serial0/2 203
!
end
2. 路由器R1
R1#show running-config
interface Loopback0
ip address 1.1.1.1255.255.255.0
!
interface Serial0/1
ip address 123.123.123.1255.255.255.0
encapsulation frame-relay
frame-relaymap ip 123.123.123.3 102 broadcast
frame-relaymap ip 123.123.123.2 102 broadcast
!
router EIGRP 90
network 1.0.0.0
network 123.123.123.0
auto-summary
!
!
end
3. 路由器R2
R2#show running-config
!
interface Loopback0
ip address 2.2.2.2255.255.255.0
!
interface Serial0/2
ip address 123.123.123.2255.255.255.0
encapsulation frame-relay
frame-relaymap ip 123.123.123.3 203 broadcast
frame-relaymap ip 123.123.123.1 201 broadcast
!
router EIGRP 90
network 2.0.0.0
network 123.123.123.0
auto-summary
!
!
end
4. 路由器R3
R3#showrunning-config
!
interface Loopback0
ip address 3.3.3.3255.255.255.0
!
interface Serial0/3
ip address 123.123.123.3255.255.255.0
encapsulation frame-relay
frame-relaymap ip 123.123.123.2 301 broadcast
frame-relaymap ip 123.123.123.1 301 broadcast
!
router EIGRP 90
network 3.0.0.0
network 123.123.123.0
auto-summary
!
!
end
4.监测配置
查看EIGRP邻居
R1
R1#show ip eigrp neighbors
IP-EIGRP neighbors for process 90
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 123.123.123.2 Se0/1 178 00:03:40 1311 5000 0 7
R2
R2#show ip eigrp neighbors
IP-EIGRP neighbors for process 90
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 123.123.123.1 Se0/2 158 00:05:45 176 1584 0 3
0 123.123.123.3 Se0/2 154 00:06:00 158 948 0 3
R3
R3#show ip eigrp neighbors
IP-EIGRP neighbors for process 90
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 123.123.123.2 Se0/3 158 00:06:58 170 1020 0 7
查看路由表
R1
Gateway of last resort is not set
Gateway of last resort is not set
1.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 1.1.1.0/24is directly connected, Loopback0
D 1.0.0.0/8is a summary, 00:07:05, Null0
D 2.0.0.0/8[90/2297856] via 123.123.123.2, 00:07:03, Serial0/1
123.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 123.123.123.0/24 is directly connected, Serial0/1
D 123.0.0.0/8 is a summary, 00:07:05, Null0
R1 路由表不正常，不能够正常学习到R3 环回接口的路由条目
R2
R2#show ip route
Gateway of last resort is not set
D 1.0.0.0/8[90/2297856] via 123.123.123.1, 00:08:55, Serial0/2
2.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24is directly connected, Loopback0
D 2.0.0.0/8is a summary, 00:09:12, Null0
D 3.0.0.0/8[90/2297856] via 123.123.123.3, 00:09:12, Serial0/2
123.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 123.123.123.0/24 is directly connected, Serial0/2
D 123.0.0.0/8 is a summary, 00:09:12, Null0
R2的路由表正常，学到R1、R3的环回接口路由
R3
R3#show ip route
Gateway of last resort is not set
D 2.0.0.0/8[90/2297856] via 123.123.123.2, 00:09:38, Serial0/3
3.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 3.3.3.0/24is directly connected, Loopback0
D 3.0.0.0/8is a summary, 00:09:54, Null0
123.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 123.123.123.0/24 is directly connected, Serial0/3
D 123.0.0.0/8 is a summary, 00:09:54, Null0
同样，R3无法学到R1的路由
在这里，因为帧中继网络是一个NBMA网络，R2通过相同的物理接口s0/2接口与R1、R３通信，由于EIGRP 是一个距离矢量型协议，具有水平分割特性，所以水平分割抑制了R1、R3 之间的路由学习（R1、R3 之间的路由学习需要通过R2转发，但由于水平分割特性，R2从s0/1接口学习到的路由不会再从相同接口转发出去）。
解决方法
方法一：关闭R2路由器s0/2接口的水平分割
配置如下：
R2(config)#int s0/2
R2(config-if)#no ip split-horizon eigrp 90
//注意，这里跟RIP下关闭水平分割不同，命令后面必须跟上eigrp及AS号。
再查看R1、R3的路由表
R1#show ip route
Gateway of last resort is not set
1.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 1.1.1.0/24is directly connected, Loopback0
D 1.0.0.0/8is a summary, 00:00:09, Null0
D 2.0.0.0/8[90/2297856] via 123.123.123.2, 00:12:17, Serial0/1
D 3.0.0.0/8[90/2809856] via 123.123.123.2, 00:00:09, Serial0/1
123.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 123.123.123.0/24 is directly connected, Serial0/1
D 123.0.0.0/8 is a summary, 00:12:19, Null0
R3#show ip route
Gateway of last resort is not set
D 1.0.0.0/8[90/2809856] via 123.123.123.2, 00:00:41, Serial0/3
D 2.0.0.0/8[90/2297856] via 123.123.123.2, 00:13:06, Serial0/3
3.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 3.3.3.0/24is directly connected, Loopback0
D 3.0.0.0/8is a summary, 00:00:41, Null0
123.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 123.123.123.0/24 is directly connected, Serial0/3
D 123.0.0.0/8 is a summary, 00:13:22, Null0
可以看到R1、R3 已经正常学习到对方的路由信息了
方法二：将单一物理接口划分为两个子接口
使用帧中继子接口，将原本的单一物理接口划分为两个子接口，水平分割便不会影响路由器间的路由转发了，但是启用子接口之后会需要另一个子网（帧中继每个子接口都是一个独立子网）：
图-- 帧中继子接口
R2需要将s0/2接口配置为帧中继子接口，分为两个网段。
R2：
interface Serial0/2
no ipaddress
encapsulation frame-relay
serialrestart-delay 0
!
interface Serial0/2.1 point-to-point
ip address123.1.1.2 255.255.255.0
frame-relayinterface-dlci 201
!
interface Serial0/2.2 point-to-point
ip address123.1.2.2 255.255.255.0
frame-relayinterface-dlci 203
!
R1：
interface Serial0/1
ip address123.1.1.1 255.255.255.0
encapsulation frame-relay
serialrestart-delay 0
frame-relay map ip 123.1.1.2 102 broadcast
noframe-relay inverse-arp
!
R3：
interface Serial0/3
ip address123.1.2.3 255.255.255.0 //与前例不同，这里R3在另一个子网内，对应R2子接口s0/2.2。
encapsulation frame-relay
serialrestart-delay 0
frame-relaymap ip 123.1.2.2 302 broadcast
配置EIGRP：
R1：
router eigrp 90
network 1.1.1.00.0.0.255
network 123.1.1.0 0.0.0.255
noauto-summary
R2：
router eigrp 90
network 2.2.2.0 0.0.0.255
network 123.1.1.0 0.0.0.255
network 123.1.2.0 0.0.0.255
no auto-summary
R3：
routereigrp 90
network 3.3.3.00.0.0.255
network 123.1.2.0 0.0.0.255
no auto-summary
现在查看路由表
R1
R1#show ip rou
Gateway of last resort is not set
1.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 1.1.1.0/24is directly connected, Loopback0
D 1.0.0.0/8is a summary, 00:31:52, Null0
D 2.0.0.0/8[90/2297856] via 123.1.1.2, 00:09:28, Serial0/1
D 3.0.0.0/8[90/2809856] via 123.1.1.2, 00:03:33, Serial0/1
123.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
D 123.1.2.0/24 [90/2681856] via 123.1.1.2, 00:09:28, Serial0/1
C 123.1.1.0/24 is directly connected, Serial0/1
D 123.0.0.0/8 is a summary, 00:31:52, Null0
R2
R2#show ip rou
Gateway of last resort is not set
D 1.0.0.0/8[90/2297856] via 123.1.1.1, 00:10:10, Serial0/2.1
2.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24is directly connected, Loopback0
D 2.0.0.0/8is a summary, 00:33:07, Null0
D 3.0.0.0/8[90/2297856] via 123.1.2.3, 00:04:16, Serial0/2.2
123.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C 123.1.2.0/24 is directly connected, Serial0/2.2
C 123.1.1.0/24 is directly connected,Serial0/2.1
D 123.0.0.0/8 is a summary, 00:33:06, Null0
R3
R3#show ip rou
Gateway of last resort is not set
D 1.0.0.0/8[90/2809856] via 123.1.2.2, 00:04:39, Serial0/3
D 2.0.0.0/8[90/2297856] via 123.1.2.2, 00:04:39, Serial0/3
3.0.0.0/8is variably subnetted, 2 subnets, 2 masks
C 3.3.3.0/24is directly connected, Loopback0
D 3.0.0.0/8is a summary, 00:54:07, Null0
123.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C 123.1.2.0/24 is directly connected, Serial0/3
D 123.1.1.0/24 [90/2681856] via 123.1.2.2, 00:04:39, Serial0/3
D 123.0.0.0/8 is a summary, 00:06:34, Null0
在帧中继Hub-and-Spoken 拓扑结构中，默认水平分割开启的情况下，只有Hub路由器能够学习到完整的路由，由于水平分割作用，两个Spoke路由器均不能学习到对方的路由信息，解决方法是将Hub路由器接口的水平分割关闭，或者使用帧中继子接口来解决这个问题。