场景：用路由器模拟PC以及DHCP_SERVER，DHCP_CLIENT与DHCP_SERVER不在同一网段。DHCP_CLIENT会广播DHCP_DISCOVER包发现DHCP_SERVER,由于不在同一网段而且路由器默认不转发广播包，所以要配置DHCP_RELAY帮忙转发广播包到DHCP_SERVER。
操作步骤：
步骤一：按照拓扑搭建实验环境
步骤二：用路由器模拟PC，关闭路由功能并将接口配置为动态获取IP
PC(config)#no iprouting //关闭路由功能
PC(config)#intf0/0
PC(config-if)#ipaddress dhcp //将接口配置为动态获取IP
步骤三：在DHCP_SERVER配置接口地址，DHCP地址池以及租期等信息
DHCP_SERVER(config)#intf1/0
DHCP_SERVER(config-if)#ipadd 172.16.10.254 255.255.255.0
DHCP_SERVER(config-if)#nosh
DHCP_SERVER(config)#ipdhcp pool dhcp_pool_1 // 配置DHCP的地址池名字
DHCP_SERVER(dhcp-config)#network192.168.10.0 255.255.255.0 // 配置DHCP地址范围
DHCP_SERVER(dhcp-config)#default-router192.168.10.254 //配置分配给主机的网关
DHCP_SERVER(dhcp-config)#lease0 8 0 //租期为0天8小时0分钟
DHCP_SERVER(dhcp-config)#ex
DHCP_SERVER(config)#ipdhcp excluded-address 192.168.10.250 192.168.10.254 //地址池中
需要排除的地址
DHCP_SERVER(config)#iproute 0.0.0.0 0.0.0.0 f1/0 //配置默认路由
步骤四：配置DHCP中继
DHCP_RELAY(config)#intf0/0
DHCP_RELAY(config-if)#ipadd 192.168.10.254 255.255.255.0
DHCP_RELAY(config-if)#nosh
DHCP_RELAY(config-if)#iphelper-address 172.16.10.254
DHCP_RELAY(config)#intf1/0
DHCP_RELAY(config-if)#ipadd 172.16.10.1 255.255.255.0
DHCP_RELAY(config-if)#nosh
步骤五：使用Wireshark，观察DHCP中继的过程
步骤六：查看接口地址获取情况
PC#sh ip int b
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.10.1 YES DHCP up up
FastEthernet1/0 unassigned YES unset administratively down down
配置文件
------------------------------------------------------------------------------
PC#sh run
!
hostname PC
!
no ip routing
!
!
……
!
!
interfaceFastEthernet0/0
ip address dhcp
no ip route-cache
duplex auto
speed auto
!
interfaceFastEthernet1/0
no ip address
no ip route-cache
shutdown
duplex auto
speed auto
!
!
……
!
line con 0
line aux 0
line vty 0 4
!
!
end
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DHCP_RELAY#sh run
Buildingconfiguration...
Currentconfiguration : 628 bytes
!
version 12.4
!
hostname DHCP_RELAY
!
!
!
interfaceFastEthernet0/0
ip address 192.168.10.254 255.255.255.0
ip helper-address 172.16.10.254
duplex auto
speed auto
!
interfaceFastEthernet1/0
ip address 172.16.10.1 255.255.255.0
duplex auto
speed auto
!
……
!
line con 0
line aux 0
line vty 0 4
!
!
end
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DHCP_SERVER#sh run
Buildingconfiguration...
!
hostname DHCP_SERVER
!
!
!
ip cef
no ip dhcp use vrfconnected
ip dhcpexcluded-address 192.168.10.250 192.168.10.254
!
ip dhcp pooldhcp_pool_1
network 192.168.10.0 255.255.255.0
default-router 192.168.10.254
lease 0 8
!
!
!
interfaceFastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interfaceFastEthernet1/0
ip address 172.16.10.254 255.255.255.0
duplex auto
speed auto
!
!
ip route 0.0.0.00.0.0.0 FastEthernet1/0
!
!
!
line con 0
line aux 0
line vty 0 4
!
!
end
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