DHCP For Several Vlans

[jcleary]

Whats my best way for providing DHCP for a company having 1 server and several VLANS

[scottosan]

Put "ip helper-address x.x.x.x" statement under the vlan interface of your switch. x.x.x.x being the ip address of your DHCP server.

[jcleary]

But I want a different subnet for the different vlans. how will the dhcp server knowwhich scope to assign the address from

[scottosan]

Because the DHCP server will see that the request is coming from a different subnet. Once you set up the scope for a new subnet on your DHCP server and apply the ip helper command to the vlan interface on the switch(if using a MLS) or subinterface on the router(if your doing router on a stick) it will work.

Command Description:

To have the Cisco IOS software forward User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface, use the ip helper-address interface configuration command. To disable the forwarding of broadcast packets to specific addresses, use the no form of this command.

Example:

Router(config-if)#ip helper-address 121.24.43.2

[paddyxdoyle]

Assuming you will be using a layer three switch to provide your inter VLAN routing

Each VLAN will have its own interface

e.g.

int vlan 1

ip address 1.1.1.254

int vlan 2

ip address 2.2.2.254

or similar

As mentioned in previous post, you would add the ip helper address to each of these VLAN interfaces and the request to the DHCP server will use the VLAN interface as its source address.

e.g.

int vlan 1

ip address 1.1.1.254

ip helper-address 3.3.3.1

int vlan 2

ip address 2.2.2.254

ip helper-address 3.3.3.1

The IP address of the interface on which the router received the DHCP request is also added to the DHCP request and sent to the helper address, which in our case is the VLAN interface, this will allow the DHCP server to allocate an address from the correct scope to the client

Rgds

Paddy