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
　　--More--

　　编者注：对不需要明确地址的所有人的时候是一个很好的解决办法。另外，可以查看www.cisco.com的
　　IP Source Guard
　　Similar to DHCP snooping, this feature is enabled on a DHCP snooping untrusted Layer 2 port. Initially, all IP traffic on the port is blocked except for DHCP packets that are captured by the DHCP snooping process. When a client receives a valid IP address from the DHCP server, or when a static IP source binding is configured by the user, a per-port and VLAN Access Control List (PACL) is installed on the port. This process restricts the client IP traffic to those source IP addresses configured in the binding; any IP traffic with a source IP address other than that in the IP source binding will be filtered out. This filtering limits a host's ability to attack the network by claiming neighbor host's IP address.