使用的方法是采用DHCP方式为用户分配IP，然后限定这些用户只能使用动态IP的方式，如果改成静态IP的方式则不能连接上网络；也就是使用了DHCP SNOOPING功能。
例子：
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
service compress-config
!
hostname C4-2_4506
!
enable password xxxxxxx!
clock timezone GMT 8
ip subnet-zero


no ip domain-lookup
!
ip dhcp snooping vlan 180-181 // 对哪些VLAN 进行限制
ip dhcp snooping
ip arp inspection vlan 180-181
ip arp inspection validate src-mac dst-mac ip




errdisable recovery cause udld
errdisable recovery cause bpduguard
errdisable recovery cause security-violation
errdisable recovery cause channel-misconfig
errdisable recovery cause pagp-flap
errdisable recovery cause dtp-flap
errdisable recovery cause link-flap
errdisable recovery cause l2ptguard
errdisable recovery cause psecure-violation
errdisable recovery cause gbic-invalid
errdisable recovery cause dhcp-rate-limit
errdisable recovery cause unicast-flood
errdisable recovery cause vmps
errdisable recovery cause arp-inspection
errdisable recovery interval 30
spanning-tree extend system-id
!
!

interface GigabitEthernet2/1 // 对该端口接入的用户进行限制，可以下联交换机
ip arp inspection limit rate 100
arp timeout 2
ip dhcp snooping limit rate 100
!



interface GigabitEthernet2/2
ip arp inspection limit rate 100
arp timeout 2
ip dhcp snooping limit rate 100
!
interface GigabitEthernet2/3
ip arp inspection limit rate 100
arp timeout 2
ip dhcp snooping limit rate 100
!
interface GigabitEthernet2/4
ip arp inspection limit rate 100
arp timeout 2
ip dhcp snooping limit rate 100