配置DHCP服务，开启DHCP中继功能

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需求

-公司有三个部门，财务部，市场部，技术部，为了内网安全，给每个部门单独划分一个VLAN

-财务部：vlan10、市场部：vlan20、技术部：vlan30

-公司所有部门，所有VLAN内的主机都通过DHCP服务器分发IP地址

-每个部门，每个VLAN的网关地址都为，192.168.xx.254

-SW5中每个vlanif 虚接口地址都为 192.168.xx.251

-SW5通过vlanif50 与DHCP进行通信，DHCP服务器管理IP：192.168.50.1

-所有的PC都通过SW5与DHCP服务器进行通信，获取IP地址，所以SW5是DHCP中继

配置代码：

1.创建vlan，配置接口模式

[sw1]vlan batch 10 20 30 50
[sw1]int g 0/0/1
[sw1-GigabitEthernet0/0/1]port link-type access 
[sw1-GigabitEthernet0/0/1]port default vlan 20
[sw1-GigabitEthernet0/0/1]int g 0/0/2
[sw1-GigabitEthernet0/0/2]port link-type trunk    
[sw1-GigabitEthernet0/0/2]port trunk allow-pass vlan all

[sw2]vlan batch 10 20 30 50
[sw2]int g 0/0/1
[sw2-GigabitEthernet0/0/1]port link-type access 
[sw2-GigabitEthernet0/0/1]port default vlan 20
[sw2-GigabitEthernet0/0/1]int g 0/0/2
[sw2-GigabitEthernet0/0/2]port link-type trunk    
[sw2-GigabitEthernet0/0/2]port trunk allow-pass vlan all

[sw3]vlan batch 10 20 30 50
[sw3]int g 0/0/1
[sw3-GigabitEthernet0/0/1]port link-type access
[sw3-GigabitEthernet0/0/1]port default vlan 30
[sw3-GigabitEthernet0/0/1]int g 0/0/2
[sw3-GigabitEthernet0/0/2]port link-type trunk
[sw3-GigabitEthernet0/0/2]port trunk allow-pass vlan all

[sw5]vlan batch 10 20 30 50
[sw5-GigabitEthernet0/0/5]port link-type access
[sw5-GigabitEthernet0/0/5]port default vlan 50
[sw5]port-group group-member g0/0/1 g0/0/2 g0/0/3    
[sw5-port-group]port link-type trunk 
[sw5-port-group]port trunk allow-pass vlan all

2.给每个vlanif添加ip地址
[sw5-Vlanif50]ip add 192.168.50.251 24
[sw5-Vlanif10]ip address 192.168.10.251 24
[sw5-Vlanif20]ip add 192.168.20.251 24
[sw5-Vlanif30]ip add 192.168.30.251 24

3.路由器开启DHCP
[R3-GigabitEthernet0/0/1]ip add 192.168.50.1 24
[R3]ip route-static 0.0.0.0 0 192.168.50.251  //添加静态路由
[R3]ip pool vlan10-pool   //创建ip地址池
[R3-ip-pool-vlan10]network 192.168.10.0 mask 24   //配置ip地址池可分配的ip网段
[R3-ip-pool-vlan10-pool]gateway-list 192.168.10.254  //配置网关
[R3-ip-pool-vlan10-pool]dns-list 8.8.8.8   //配置dns地址，可不配
[R3-GigabitEthernet0/0/1]dhcp select global  //开启全局DHCP

[R3]ip pool vlan20-pool
[R3-ip-pool-vlan20-pool]network 192.168.20.0 mask 24
[R3-ip-pool-vlan20-pool]gateway-list 192.168.20.254
[R3-ip-pool-vlan20-pool]dns-list 8.8.8.8

[R3]ip pool vlan30-pool
[R3-ip-pool-vlan30-pool]network 192.168.30.0 mask 24
[R3-ip-pool-vlan30-pool]gateway-list 192.168.30.254
[R3-ip-pool-vlan30-pool]dns-list 8.8.8.8

4.交换机开启中继功能
[sw5]dhcp enable     //开启DHCP服务
[sw5-Vlanif10]dhcp select relay     //开启中继功能
[sw5-Vlanif10]dhcp relay server-ip 192.168.50.1  //配置DHCP服务器地址

[sw5-Vlanif20]dhcp select relay
[sw5-Vlanif20]dhcp relay server-ip 192.168.50.1

sw5-Vlanif30]dhcp select relay    
[sw5-Vlanif30]dhcp relay server-ip 192.168.50.1