测试拓扑：
先进行IP地址的配置，保证连通性：
R1#sho ip int brief Interface IP-Address OK? Method Status Protocol Ethernet0/0 12.1.1.1 YES manual up up Ethernet0/1 13.1.1.1 YES manual up up Ethernet0/2 unassigned YES unset administratively down down Ethernet0/3 unassigned YES unset administratively down down
R2#show ip int brief Interface IP-Address OK? Method Status Protocol Ethernet0/0 12.1.1.2 YES manual up up Ethernet0/1 unassigned YES unset administratively down down Ethernet0/2 unassigned YES unset administratively down down Ethernet0/3 unassigned YES unset administratively down down
R3#show ip int brief Interface IP-Address OK? Method Status Protocol Ethernet0/0 13.1.1.3 YES manual up up Ethernet0/1 unassigned YES unset administratively down down Ethernet0/2 unassigned YES unset administratively down down Ethernet0/3 unassigned YES unset administratively down down
R1#ping 12.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 12.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 16/23/32 ms R1#ping 13.1.1.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 13.1.1.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 16/22/28 ms
配置R1
R1#conf t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#ip domain lookup
R1(config)#ip name-server 12.1.1.2
配置R2
R2#conf t Enter configuration commands, one per line. End with CNTL/Z. R2(config)#ip domain-lookup R2(config)#ip host R3 13.1.1.3
R2(config)#ip dns server
测试：R1 ping R3
R1#ping R3 Translating "R3"...domain server (12.1.1.2) [OK] Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 13.1.1.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 16/21/28 ms
测试：R1登陆R3
R1#sho run | in ip name ip name-server 12.1.1.2 R1#R3 Translating "R3"...domain server (12.1.1.2) (12.1.1.2) Translating "R3"...domain server (12.1.1.2) [OK] Trying R3 (13.1.1.3)... Open User Access Verification Username: cisco Password: R3#