1、原理

2、实验拓扑

3、实验配置

R3配置

interface FastEthernet1/0

 ip address 13.1.1.3 255.255.255.0

ip route 0.0.0.0 0.0.0.0 13.1.1.1

ip dhcp excluded-address 12.1.1.1 12.1.1.200      

ip dhcp pool dhcp

   network 12.1.1.0 255.255.255.0

   dns-server 114.114.114.114 

   default-router 12.1.1.1 

   lease 3

R1配置

interface FastEthernet0/0

 ip address 12.1.1.1 255.255.255.0

 ip helper-address 13.1.1.3         

interface FastEthernet1/0

 ip address 13.1.1.1 255.255.255.0

R2配置

interface FastEthernet0/0

 ip address dhcp

4、过程分析