1.实验目的
通过本实验可以掌握通过DHCP中继实现跨网络的DHCP服务。
2.拓扑结构
实验拓扑图如图10-3所示。
图10-3 DHCP中继配置
在本实验中，R1仍然担任DHCP服务器的角色，负责向PC所在网络和PC2所在网络的主机动态分配IP地址，所以，R1上需要定义两个地址池。整个网络运行RIPv2协议，确保网络IP连通性。
3.实验步骤
（1）步骤1：配置路由器R1提供DHCP服务
R1(config)#interface gigabitEhternet0/0
R1(config-if)# no switchport
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config)#ip routing
R1(config)#router rip
R1(config-router)#version 2
R1(config-router)#no auto-summary
R1(config-router)#network 192.168.1.0
R1(config-router)# network 192.168.12.0
R1(config)#service dhcp
R1(config)#no ip dhcp conflict logging //取消地址冲突记录
R1(config)#ip dhcp pool ccie //定义第一个地址池
R1(dhcp-config)#network 192.168.1.0 /24
R1(dhcp-config)#default-router 192.168.1.1
R1(dhcp-config)#domain-name cisco.com
R1(dhcp-config)#netbios-name-server 192.168.1.2
R1(dhcp-config)#dns-server 192.168.1.4
R1(dhcp-config)#option 150 ip 192.168.1.3
R1(dhcp-config)#lease infinite
R1(dhcp-config)#ip dhcp excluded-address 192.168.1.1 192.168.1.5
R1(config)#ip dhcp pool ccnp //定义第二个地址池
R1(dhcp-config)#network 172.16.1.0 255.255.255.0
R1(dhcp-config)#domain-name szpt.net
R1(dhcp-config)#default-router 172.16.1.2
R1(dhcp-config)#netbios-name-server 192.168.1.2
R1(dhcp-config)#dns-server 192.168.1.4
R1(dhcp-config)#option 150 ip 192.168.1.3
R1(dhcp-config)#lease infinite
R1(dhcp-config)#ip dhcp excluded-address 172.16.1.1 172.16.1.2
（2）步骤2：配置路由器R2
R2(config)#interface gigabitEhternet0/0
R2(config-if)# no switchport
R2(config-if)#ip address 172.16.1.2 255.255.255.0
R2(config-if)#ip helper-address 192.168.12.1 //配置帮助地址
R2(config-if)#no shutdown
R2(config)#router rip
R2(config-router)#version 2
R2(config-router)#no auto-summary
R2(config-router)# network 192.168.12.0
R2(config-router)# network 172.16.0.0
【技术要点】路由器是不能转发”255.255.255.255”广播的，但是很多服务（如DHCP和TFTP等）的客户请求都是以泛洪广播的方式发起的，我们不可能将每个网段都旋转这样的服务器，因此使用Cisco IOS帮助地址特性是很好的选择。通过使用帮助地址，路由器可以被配置为接受对UDP服务的广播请求，然后将之以单点传送的方式发给某个具体的IP地址，或者以定向广播形式向某个网段转发这些请求，这就是中继。
4.实验调试
（1）show ip dhcp binding
在PC1和PC2上自动获取IP地址后，在R1上执行：
R1#show ip dhcp binding
Bindings from all pools not associated with VRF;
IP address Client-ID/ Lease expiration Type
Hardware address/
Username
172.16.1.3 0100.6067.00dd.5b
192.168.1.6 0063.6973.636f.2d Infinite Automatic
192.168.1.7 0100.6067.00ef.31 Infinite Automatic
以上输出表明两个地址池都为相应的网络上的主机分配了IP地址
（2）show ip dhcp pool
R1#show ip dhcp pool
Pool ccie;
Utilization mark(high/low) ;100/0
Subnet size(first/next) ;0/0
Total addresses ;254
Leased addresses ;2
Pending event ;none
1 subnet is currently in the pool;
Current index IP address range Leased addresses
192.168.1.8 192.168.1.1 -192.168.1.254 2
Pool ccnp;
Utilization mark(high/low) ;100/0
Subnet size(first/next) ;0/0
Total addresses ;254
Leased addresses ;1
Pending event ;none
1 subnet is currently in the pool;
Current index IP address range Leased addresses
172.16.1.4 172.16.1.1 -192.168.1.254 1
（3）debug ip dhcp server events
在PC2上先执行”ipconfig/release”，再执行”ipconfig/renew”，显示如下：
R1#debug ip dhcp server
R1#clear ip dhcp binding *
*Feb 2 05;50;24.475;DHCPD;Sending notification of DISCOVER;
*Feb 2 05;50;24.475;DHCPD;htype 1 chaddr 0060.6700.dd5b
*Feb 2 05;50;24.475;DHCPD;circuit id 00000000
*Feb 2 05;50;24.475;DHCPD;Seeing if there is an internally specified pool class;
*Feb 2 05;50;24.475;DHCPD;htype 1 chaddr 0060.6700.dd5b
*Feb 2 05;50;24.475;DHCPD;circuit id 00000000
*Feb 2 05;50;26.475;DHCPD;client requests 172.16.1.4.
*Feb 2 05;50;26.475;DHCPD;Adding binding to radix tree (172.16.1.4)
*Feb 2 05;50;26.475;DHCPD;Adding binding to hash tree
*Feb 2 05;50;26.475;DHCPD;assigned IP address 172.16.1.4 to client 0100.6067.00dd.5b
*Feb 2 05;50;26.519;DHCPD;Sending notification of ASSIGNMENT;
*Feb 2 05;50;26.519;DHCPD;address 172.16.1.4 mask 255.255.255.0
*Feb 2 05;50;26.519;DHCPD;htype 1 chaddr 0060.6700.dd5b
*Feb 2 05;50;26.519;DHCPD;lease time remaining(secs)=4294967295
（4）show ip interface
R2#show ip interface gigabitEthernet0/0
GigabitEthernet0/0 is up ，line protocol is up
Internet address is 172.16.1.2/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is 192.168.12.1
......
从以上输出看到gigabitEthernet0/0 
