1.概述
EIGRP能够被配置来负载平衡最多四条不等成本的路径。这个性能被称为不等成本负载平衡,使用variance命令实现，缺省时，路由器将会负载平衡四条等成本道路。variance命令让你设置更差的可选道路（以度量值为依据），还能被用来进行负载平衡。
例如，路由器R2有两条到达网络3.3.3.0的路径，一条的成本是4，另一条的成本是8，缺省时只会使成本为4的路径来发送包到3.3.3.3。如果被设置了variance命令，路由器将会在道路间进行负载平衡。之所以发生这种情况是因为费用为8的路径在variance内，它是最优路径的两倍（4（最优路径）×2 = 8）。
2.配置概述
这个配置将会验证variance命令的使用，这允许EIGRP启动的路由器在不等成本道路间进行负载平衡。variance命令被设置到路由器R2上，所以到达网络3.3.3.3的两条道路都被使用。
路由器R2、R6、R3用一个交叉电缆串行的接在一起，路由器R2和R6还经过一个以太网交换机连在一起。
路由器R6作为DCE，向路由器R2和提供时钟，各自的IP地址如图7 - 8所示。所有路由器都配置了EIGRP，路由器R2将被用来进行负载平衡交通，通过到达3.3.3.3的两条不等成本道路。
图 EIGRP不等成本负载平衡
3.路由器配置
这个例子中的三个路由器的配置如下所示：
（1. ）路由器R2
R2#showrunn
interface Loopback0
ip address 2.2.2.2255.255.255.0
!
interface Ethernet1/1
ip address62.62.62.2 255.255.255.0
half-duplex
!
interface Serial0/2
ip address26.26.26.2 255.255.255.0
serialrestart-delay 0
clock rate64000
!
router EIGRP 90
variance 2
network 2.0.0.0
network26.0.0.0
network62.0.0.0
auto-summary
!
（2.） 路由器R6
R6#show runn
!
interface Loopback0
ip address 6.6.6.6255.255.255.0
!
interface Ethernet1/1
ip address62.62.62.6 255.255.255.0
half-duplex
!
interface Serial0/2
ip address26.26.26.6 255.255.255.0
serialrestart-delay 0
clock rate64000
!
interface Serial0/3
ip address36.36.36.6 255.255.255.0
serialrestart-delay 0
clock rate64000
!
router EIGRP 90
network 6.0.0.0
network26.0.0.0
network36.0.0.0
network62.0.0.0
auto-summary
!
（3. ）路由器R3
R3#showrunn
!
interface Loopback0
ip address 3.3.3.3255.255.255.0
!
interface Serial0/3
ip address36.36.36.3 255.255.255.0
serial restart-delay0
clock rate64000
!
router EIGRP 90
network 3.0.0.0
network36.0.0.0
auto-summary
!
!
4.监测配置
使用命令show ip route显示在路由器R2上的路由表。
注意有两条到网络3.0.0.0的路径：一条经过以太网接口，另一条经过串行接口。通过这两条道路到达网络的成本是不同的；
但是因为variance设为2，既然第二条道路的成本不比最优道路的两倍多，那么就使用这条道路。
让我们仔细看一下这种情况，到达网络3.0.0.0的最优路径是经过以太网接口的，它的成本是2 323 456。因为两者都有variance，而其它任何到达网络3.0.0.0的路径的成本都比4 646 912 （2 323 456×2）少，那么就使用这条路径。因为通过串行接口的费用是2 809 856，它比4 646 912少，所以使用这条路径。
R2#show ip route
Gateway of last resort is not set
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, 00:00:45, Null0
D 3.0.0.0/8[90/2323456] via 62.62.62.6, 00:00:46, Ethernet1/1
[90/2809856] via 26.26.26.6, 00:00:46, Serial0/2
D 36.0.0.0/8 [90/2195456] via 62.62.62.6, 00:00:46, Ethernet1/1
[90/2681856] via 26.26.26.6, 00:00:46, Serial0/2
6.0.0.0/8is variably subnetted, 2 subnets, 2 masks
D 6.6.6.0/24[90/2297856] via 26.26.26.6, 00:05:50, Serial0/2
D 6.0.0.0/8[90/409600] via 62.62.62.6, 00:00:46, Ethernet1/1
26.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 26.26.26.0/24 is directly connected, Serial0/2
D 26.0.0.0/8 is a summary, 00:00:46, Null0
62.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 62.62.62.0/24 is directly connected, Ethernet1/1
D 62.0.0.0/8 is a summary, 00:00:49, Null0
使用命令show ip route 3.3.3.3在路由器R2上显示到达3.3.3.3的路径。注意两条路径都被使用，在第二条路径旁有一个星号“*”。这个“*”表示下一个离开路由器R2的包目标是3.3.3.3要使用这条路径。
R2#show ip route 3.3.3.3
Routing entry for 3.0.0.0/8
Known via"eigrp 90", distance 90, metric 2323456, type internal
Redistributing via eigrp 90
Lastupdate from 62.62.62.6 on Ethernet1/1, 00:11:30 ago
RoutingDescriptor Blocks:
62.62.62.6, from 62.62.62.6, 00:11:30 ago, via Ethernet1/1
Routemetric is 2323456, traffic share count is 40
Totaldelay is 26000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
*26.26.26.6, from 26.26.26.6, 00:11:30 ago, via Serial0/2
Routemetric is 2809856, traffic share count is 33
Totaldelay is 45000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
在路由器R2上，测试主机3.3.3.3是否连通。
R2#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3,timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-tripmin/avg/max = 8/59/164 ms
现在在路由器R2上运行命令show ip route 3.3.3.3显示到达主机3.3.3.3的路径。注意现在“*” 在第二条路径旁，因为路由器现在正在两条链路上负载平衡。这两条链路都是到网络3.0.0.0的。
R2#show ip route 3.3.3.3
Routing entry for 3.0.0.0/8
Known via"EIGRP 90", distance 90, metric 2323456, type internal
Redistributing via EIGRP 90
Lastupdate from 62.62.62.6 on Ethernet0/0, 00:18:30 ago
RoutingDescriptor Blocks:
*62.62.62.6, from 62.62.62.6, 00:18:30 ago, via Ethernet0/0
Routemetric is 2323456, traffic share count is 40
Totaldelay is 26000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
26.26.26.6, from 26.26.26.6, 00:18:30 ago,via Serial1/0
Routemetric is 2809856, traffic share count is 33
Totaldelay is 45000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
使用路由器配置命令novariance取消路由器R2上的variance命令。
R2(config)#router ei90
R2(config-router)#novariance
在路由器R2上，使用命令show ip route 3.3.3.3显示到达主机3.3.3.3的路径，注意只使用了一条路径。这条路径有最低的度量值，也没有运行负载平衡。
R2#show ip route 3.3.3.3
Routing entry for 3.0.0.0/8
Known via"eigrp 90", distance 90, metric 2323456, type internal
Redistributing via eigrp 90
Lastupdate from 62.62.62.6 on Ethernet1/1, 00:00:09 ago
RoutingDescriptor Blocks:
*62.62.62.6, from 62.62.62.6, 00:00:09 ago, via Ethernet1/1
Routemetric is 2323456, traffic share count is 1
Totaldelay is 26000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
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