Cisco DHCP Snooping

just config, it's pretty easy

!enable DHCP snooping for vlan 1

ip dhcp snooping

ip dhcp snooping vlan 1

!enable DHCP option 82

ip dhcp snooping information option

!set trust port for DHCP server

int Gi0/2

ip dhcp snooping trust

!set limit per second

int range Fa0/1 - 24

ip dhcp snooping limit rate 20

!set trust trunk port:

ip dhcp snooping trust

show settings:

show ip dhcp snooping

show ip dhcp snooping binding

Cisco router as dhcp client

Sometimes ISP provide only dhcp ip for branch offices.  When you use firewall, I hope you use it , you need use rule for open dhcp traffic  in your firewall.

interface FastEthernet0/0 ip address dhcp ip access-group ISP in ip access-list extended ISP permit udp any eq bootps any eq bootpc