实验目的：
1、掌握EIGRP的不等价均衡的条件。
2、掌握EIGRP的metric值修改方法。
3、掌握EIGRP的AD、FD、FC、Successor、FS概念。
实验拓扑：
实验步骤：
1、 配置各路由器的名称、相连接口IP地址，并且使用Ping命令确认各路由器的直连口的互通性。
R1：
R1(config)#int s1/0
R1(config-if)#ip add 172.16.1.1 255.255.255.252
R1(config-if)#no shut
R1(config)#int s1/2
R1(config-if)#ip add 172.16.1.9 255.255.255.252
R1(config-if)#no shut
R2、R3类似配置好接口的IP地址，并能够ping通直连的接口。
2、 配置EIGRP协议，自治系统号80.
R1(config)#router eigrp 80
R1(config-router)#network 172.16.0.0
R1(config-router)#exit
R2、R3类似配置好。
3、 在R1仔细观察R1去R3的路由，即如拓扑图上的L1链路。
R1#sh 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
172.16.0.0/30 is subnetted, 3 subnets
C 172.16.1.8 is directly connected, Serial1/2
D 172.16.1.4 [90/2681856] via 172.16.1.2, 00:05:20, Serial1/1
[90/2681856] via 172.16.1.10, 00:05:20, Serial1/2
C 172.16.1.0 is directly connected, Serial1/1
D 10.0.0.0/8 [90/2297856] via 172.16.1.10, 00:00:20, Serial1/2
可以看到只有一条路径172.16.1.10，即L1.
4、 通常为了提高网络的传输性能，将经过R2到达R3的路由L2与上面的直达路由L1做均衡负载，尽管两条路由的metric不同，但可以通过人工设置改变。
5、 如何设置才能将L1、L2这两条路由变为均衡负载呢？答案就是让L2成为L1的可行后继（FS），成为FS前提是满足可行条件FC。先查看R1上的EIGRP的路由表
R1#sh ip eigrp 80 topology
IP-EIGRP Topology Table for AS(80)/ID(172.16.1.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2297856
via 172.16.1.10 (2297856/128256), Serial1/2
P 172.16.1.8/30, 1 successors, FD is 2169856
via Connected, Serial1/2
P 172.16.1.4/30, 2 successors, FD is 2681856
via 172.16.1.10 (2681856/2169856), Serial1/2
via 172.16.1.2 (2681856/2169856), Serial1/1
P 172.16.1.0/30, 1 successors, FD is 2169856
via Connected, Serial1/1
可以看到并没有发现R2的有关IP地址 ，即不存在L2的链路。再查看R1的完整拓扑图
R1#sh ip eigrp 80 topology all-links
IP-EIGRP Topology Table for AS(80)/ID(172.16.1.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2297856, serno 5
via 172.16.1.10 (2297856/128256), Serial1/2
via 172.16.1.2 (2809856/2297856), Serial1/1
P 172.16.1.8/30, 1 successors, FD is 2169856, serno 2
via Connected, Serial1/2
P 172.16.1.4/30, 2 successors, FD is 2681856, serno 4
via 172.16.1.10 (2681856/2169856), Serial1/2
via 172.16.1.2 (2681856/2169856), Serial1/1
P 172.16.1.0/30, 1 successors, FD is 2169856, serno 1
via Connected, Serial1/1
根据可行条件FC的公式：
AD of secondary-best route < FD of best route(Successor) = Feasible Successor
根据本例可得出：
R2到达192.168.1.0网络的Distance(2297856) =2297856
要改变R2到达的AD，须改变R2到达R3的度量值。
6、 改变R2到达R3的度量值，就要修改R2到达R3的串口的带宽和延迟，确保R2到达192.168.1.0/24的网络的FD变小。让L2成为FS。
R2(config)#int s1/2
R2(config-if)#bandwidth 100000
R2(config-if)#delay 10
R2(config-if)#exit
R2(config)#int s1/2
R2(config-if)#band
R2(config-if)#bandwidth 1000000
R2(config-if)#exit
完成后再次查看一下R1的拓扑表
R1#sh ip eigrp 80 topology
IP-EIGRP Topology Table for AS(80)/ID(172.16.1.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2297856
via 172.16.1.10 (2297856/128256), Serial1/2
via 172.16.1.2 (2300416/156160), Serial1/1
P 172.16.1.8/30, 1 successors, FD is 2169856
via Connected, Serial1/2
P 172.16.1.4/30, 1 successors, FD is 2172416
via 172.16.1.2 (2172416/28160), Serial1/1
via 172.16.1.10 (2681856/2169856), Serial1/2
P 172.16.1.0/30, 1 successors, FD is 2169856
via Connected, Serial1/1
可以看到R1已经将L2当成了FS。下面还要进一步配置以使得L1、L2均衡负载。
7、 Varince缺省为1。AC<FD：备份路径（无环路的次佳路径）Varince（容忍度）：表示容忍哪些满足条件的次佳路径，强行进入路由表，与度量值成反比负载均衡Variance=想要进入路径的metric/最佳路径的metric（取整）（1-128）根据如下公式配置R1的EIGRP的variance值。
FD of FS route < FD of best route(Successor) * Varince
根据公式可得出：
2297856 < 2297856 * x
x≈1
8、 为了测试能否成功，先将R1上variance值配置为1，观察路由表。
R1(config)#router eigrp 80
R1(config-router)#var
R1(config-router)#variance 1
R1(config-router)#exit
R1#clear ip route *
R1#sh 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
172.16.0.0/30 is subnetted, 3 subnets
C 172.16.1.8 is directly connected, Serial1/2
D 172.16.1.4 [90/2172416] via 172.16.1.2, 00:00:13, Serial1/1
C 172.16.1.0 is directly connected, Serial1/1
D 10.0.0.0/8 [90/2297856] via 172.16.1.10, 00:00:13, Serial1/2
可以看到设置R1上variance值为1时并不能实现L1、L2均衡负载。下面将variance值设置为2，
R1(config)#router eigrp 80
R1(config-router)#var
R1(config-router)#variance 2
R1(config-router)#exit
再查看R1路由表，
R1#sh ip r
*Oct 10 23:38:43.395: %SYS-5-CONFIG_I: Configured from console by consoleoute
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
172.16.0.0/30 is subnetted, 3 subnets
C 172.16.1.8 is directly connected, Serial1/2
D 172.16.1.4 [90/2172416] via 172.16.1.2, 00:00:07, Serial1/1
[90/2681856] via 172.16.1.10, 00:00:07, Serial1/2
C 172.16.1.0 is directly connected, Serial1/1
D 10.0.0.0/8 [90/2297856] via 172.16.1.10, 00:00:07, Serial1/2
[90/2300416] via 172.16.1.2, 00:00:07, Serial1/1
可以看到，设置正确的variance值后，此处显示为正确的不等价均衡负载的路由。
本文转自 独钩寒江雪 51CTO博客，原文链接：http://blog.51cto.com/bennie/404387，如需转载请自行联系原作者
