DHCP Snooping is used to block untheorized DHCP server.

Step 1) Enable DHCP snooping Globally

Switch(config)#ip dhcp snooping

Switch(config)#ip dhcp snooping vlan 30

Step 2) Apply to the interface that need to be trusted  (By default all other ports will be untrusted)

Switch(config)#interface gigabitethernet1/0/1

Switch(config-if)#ip dhcp snooping trust

 —————————————————————————

To Become Cretified For Cisco CCNP Please Visit This Link