按照上图所示配置好所有基本配置,配置如下:
R1:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#int s 1/1
R1(config-if)#ip add 10.10.10 .1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#clo ra 64000
R1(config-if)#router eigrp 1
R1(config-router)#net 10.10.10 .0 0.0.0.255
R1(config-router)#no auto
R1(config-router)#exi
R1(config)#
R2:
R2(config)#int s 1/1
R2(config-if)#ip add 10.10.10 .2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#int s 1/0
R2(config-if)#ip add 20.20.20 .1 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#clo ra 64000
R2(config-if)#exi
R2(config)#router eigrp 1
R2(config-router)#net 10.10.10 .0 0.0.0.255
R2(config-router)#net 20.20.20 .0 0.0.0.255
R2(config-router)#no auto
R2(config-router)#exi
R2(config)#
R3:
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#int s 1/1
R3(config-if)#ip add 20.20.20 .2 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#exi
R3(config)#router eigrp 1
R3(config-router)#net 40.40.40.0 0.0.0 .255
R3(config-router)#net 20.20.20 .0 0.0.0.255
R3(config-router)#no auto
R3(config-router)#exi
注意,上图为本实验原图的截图,按照刚才上一页的配置,我们已经完成了除R2-R3以太网连接配置的所有其他配置,现在我们去看一下从R1访问R3的LOOP 0接口的开销为多少?见以下。
R1#show ip route
*Jun 2 21:51:34.123: %SYS-5-CONFIG_I: Configured from console by console
R1#show ip route 40.40.40.0
Routing entry for 40.40.40.0/24
Known via "eigrp 1", distance 90, metric 2809856, type internal
Redistributing via eigrp 1
Last update from 10.10.10 .2 on Serial1/1, 00:12:22 ago
Routing Descriptor Blocks:
* 10.10.10 .2, from 10.10.10.2, 00:12:22 ago, via Serial1/1
Route metric is 2809856, traffic share count is 1
Total delay is 45000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
R1#
从以上配置可以看出从R1到达目的地40.40.40.0的Metric为metric 2809856,从R1上通过查看TOP表可以看到如下内容。
R1#show ip eigrp topo
IP-EIGRP Topology Table for AS(1)/ID( 10.10.10 .1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.10.10
.0/24, 1 successors, FD is 2169856
via Connected, Serial1/1
P 20.20.20
.0/24, 1 successors, FD is 2681856
vi a 10.10.10 .2 (2681856/2169856), Serial1/1
P 30.30.30.0/24, 1 successors, FD is 2684416
vi a 10.10.10 .2 (2684416/2172416), Serial1/1
P 40.40.40.0/24, 1 successors, FD is 2809856
vi a 10.10.10 .2 (2809856/2297856), Serial1/1
R1#
从以上可见从R1到达40.40.40.0的后继为如上配置加粗部分,其FD=2809856。
现在我们去配置以上截图部分R2的以太网口和R3的以太网口地址分别设置为30.30.30.2和30.30.30.3并把相应地址通告入EIGRP,见如下配置。
R2:
R2(config)#int fa 0/0
R2(config-if)#ip add 30.30.30.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exi
R2(config)#router eigrp 1
R2(config-router)#net 30.30.30.0 0.0.0 .255
R2(config-router)#exi
R2(config)#
R3:
R3(config)#int fa 0/0
R3(config-if)#ip add 30.30.30.3 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#exi
R3(config)#router eigrp 1
R3(config-router)#net 30.30.30.0 0.0.0 .255
R3(config-router)#exi
R3(config)#
在配置好以上设置,并提示正确邻接后回到R1,查看TOP表中到达40.40.40.0的后继是否被度量值更优的新的后继代替,见如下显示。
R1#show ip eigrp topo
IP-EIGRP Topology Table for AS(1)/ID( 10.10.10 .1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.10.10
.0/24, 1 successors, FD is 2169856
via Connected, Serial1/1
P 20.20.20
.0/24, 1 successors, FD is 2681856
vi a 10.10.10 .2 (2681856/2169856), Serial1/1
P 30.30.30.0/24, 1 successors, FD is 2172416
vi a 10.10.10 .2 (2172416/28160), Serial1/1
P 40.40.40.0/24, 1 successors, FD is 2300416
vi a 10.10.10 .2 (2300416/156160), Serial1/1
R1#
由以上查看显示,Metric更小的后继已经顶替了劣质的后继,成为了新的后继,因此从此实验可以看出,EIGRP的后继抢夺具有实时性!
那么为什么以前的后继被抢夺了呢,是因为通过以太网的默认链路带宽远大于通过Serial的链路带宽,并且延迟也更加小,只有100 usec,所以通过以太链路到达目的地具有更小的度量值。