Configuring DHCP snooping

[randyclark]

I am settting up DHCP snooping for the first time on an 3750. My DHCP server resides on another switch. The 3750 is connected through a Gig SFP fiber to a 3550 with DHCP relay.

Is the following config correct? The client will not get a dhcp with the option 82 enabled.

(config)#ip dhcp snooping

(config)#ip dhcp snooping vlan 2-200

(config)#no ip dhcp snooping info option

!The client will not get an ip with

!this option enabled.

! trusted interface connected to the 3550

(config)#int gi1/0/4

(config-if)#ip dhcp trust

! untrusted interface

(config-if)#ip dhcp limit rate 100

(config)#ip dhcp snooping database flash:/database1

(config)#ip dhcp snooping database timeout 30

(config)#ip dhcp snooping database write-delay 30

[Prashanth Krishnappa]

Have you enabled option 82 on your DHCP server? Also, on your DHCP relay switch, configure the following under the VLAN interface in question and see if it makes any difference.

Example:

c3550-A(config)#int vlan 1

c3550-A(config-if)#ip dhcp relay information trusted ?

[randyclark]

I don't have DHCP snooping configured on the 3550. Does it have to be on all switches or can it be configued on a per switch basis?

I am checking with the admin of the DHCP server on option 82.

[Prashanth Krishnappa]

You will need to configure it on 3550 atleast since it is your DHCP relay.