配置好各个路由器的IP地址，测试连通性，配好EIGRP 50，查看两路由器的路由表：

R1#show ip route
Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.8/30 is directly connected, Serial0/0
D       172.16.0.0/16 is a summary, 00:00:35, Null0
     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.1.1.0/24 is directly connected, Loopback0
D       10.0.0.0/8 is a summary, 00:00:35, Null0
D    192.168.1.0/24 [90/2297856] via 172.16.1.10, 00:00:22, Serial0/0

R2#show ip route 
Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.8/30 is directly connected, Serial0/0
D       172.16.0.0/16 is a summary, 00:01:35, Null0
D    10.0.0.0/8 [90/2297856] via 172.16.1.9, 00:01:35, Serial0/0
C    192.168.1.0/24 is directly connected, Loopback0

结果说明学习路由正常。

配置R1的EIGRP认证：

R1#conf t
R1(config)#key chain xiaoyang（创建名为xiaoyang的密钥链）
R1(config-keychain)#key  1（创建密钥链1）
R1(config-keychain-key)#key-string xiaoyang（配置密文为xiaoyang）

R1(config-keychain-key)#exit
R1(config-keychain)#exit
R1(config)#int s0/0
R1(config-if)#ip authentication key-chain eigrp 50 xiaoyang（在s0/0接口下为EIGRP 50启用路由认证。使用xiaoyang密钥链。）
R1(config-if)#ip authentication mode eigrp 50 md5（设置认证模式为md5加密方式，即传输过程以密文传输。）
R1(config-if)#end

查看两路由器的路由表变化：

R1#show ip route
Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.8/30 is directly connected, Serial0/0
D       172.16.0.0/16 is a summary, 00:12:30, Null0
     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.1.1.0/24 is directly connected, Loopback0
D       10.0.0.0/8 is a summary, 00:12:30, Null0

R2#show ip route
Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.8/30 is directly connected, Serial0/0
D       172.16.0.0/16 is a summary, 00:12:40, Null0
C    192.168.1.0/24 is directly connected, Loopback0

此时双方都不能学习到对方的路由信息，同时R2上有如下反馈信息：

R2#
*Mar  1 00:16:10.975: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 50: Neighbor 172.16.1.9 (Serial0/0) is down: Auth failure

说明认证失败，不能建立邻居关系。

配置R2的EIGRP认证：

R2#conf t
R2(config)#key chain xiaoyang
R2(config-keychain)#key 1
R2(config-keychain-key)#key-string xiaoyang
R2(config-keychain-key)#exit
R2(config-keychain)#exit
R2(config)#int s0/0
R2(config-if)#ip authentication key-chain eigrp 50 xiaoyang
R2(config-if)#ip authentication mode eigrp 50 md5
R2(config-if)#exit
*Mar  1 00:26:31.007: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 50: Neighbor 172.16.1.9 (Serial0/0) is up: new adjacency

配置完成，最后一条日志信息说明邻居重新建立，认证成功。

查看R2上邻居信息：

R2(config)#do show ip eigrp 50 nei
IP-EIGRP neighbors for process 50
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
0   172.16.1.9              Se0/0             12 00:03:35   65   390  0  12

正常！

再查看双方路由表：

R1#show ip route
Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.8/30 is directly connected, Serial0/0
D       172.16.0.0/16 is a summary, 00:23:03, Null0
     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       10.1.1.0/24 is directly connected, Loopback0
D       10.0.0.0/8 is a summary, 00:23:03, Null0
D    192.168.1.0/24 [90/2297856] via 172.16.1.10, 00:05:04, Serial0/0

R2(config)#do show ip route 
Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.8/30 is directly connected, Serial0/0
D       172.16.0.0/16 is a summary, 00:23:23, Null0
D    10.0.0.0/8 [90/2297856] via 172.16.1.9, 00:05:38, Serial0/0
C    192.168.1.0/24 is directly connected, Loopback0

一切正常。