How to configure DHCP to assign devices to subnets?

Question

I have Windows 2008 R2. There are three classes of devices on our network- IP phones, Handheld (WM5 & 6) devices, and everything else (Computer, printers, servers). I use 2 Cisco Catalyst switches and have everything on a single VLAN. Our IP phones are Cisco also. I would like to create three subnets to handle these three different classes of equipment. I have a remote site with a Windows 2008 DHCP server that I would like to configure. What is the best way to set this up? Thanks for your help!

Answer 1

You need to have a separate vlan for each subnet, and that means a switch that supports layer 3 to route between the vlans. Then you set an ip-helper in the switch for each vlan that allows the switch to pass dhcp traffic through to your server.

Now you can set up the separate subnets (scopes) in your dhcp server. The dhcp server will know which scope to use for which request because of which virtual interface the switch used to forward the request. If your phones are sharing ports with the PCs (connection passes through the phone to reach the PC), you can set LLDP information in the phones and configure the switch to use that information to know to assign the proper vlan to them.

Answer 2

You can have everything on a single VLAN, but YOU have to define how to separate them. I wouldn't recommend using Windows 2008 as the DHCP server, isc-dhcp-server is much more powerful. Here's how I would do it:

# MODIFY TO MATCH YOUR ENVIRONMENT
class "phones"    { match if substring (hardware,1,3) = 00:11:22; }
class "handhelds" { match if substring (hardware,1,3) = 00:33:44; }

# Common configuration
option domain-name "your.domain.name.here";
option domain-name-servers 192.168.2.2;

shared-network lan {
        # phones
        subnet 192.168.0.0 netmask 255.255.255.0 {
                pool {
                        range 192.168.0.10 192.168.0.254;
                        allow members of "phones";
                }
                option routers 192.168.0.1;
                option subnet-mask 255.255.255.0;
        }

        # handheld devices
        subnet 192.168.1.0 netmask 255.255.255.0 {
                pool {
                        range 192.168.1.10 192.168.1.254;
                        allow members of "handhelds";
                }
                option routers 192.168.1.1;
                option subnet-mask 255.255.255.0;
        }

        # Everything else
        subnet 192.168.2.0 netmask 255.255.255.0 {
                pool {
                        range 192.168.2.10 192.168.2.254;
                        allow unknown-clients;
                }
                option routers 192.168.1.1;
                option subnet-mask 255.255.255.0;
        }
}