We currently have 3 VLANs setup in our network. On our DHCP server (Windows 2008) we have 3 scopes created for the 3 separate subnets. Our clients can't seem to pull addresses on the subnets, except for the one the server is attached to. DHCP forwarding is enabled on our procurve switches (ip-helper)
If we make the scopes part of the same superscope in windows DHCP, then addresses are handed out fine, but if a client roams from one VLAN to another, they will always pull the same address from their existing lease, even if it's from another subnet. If the scopes are not part of the same superscope, the DHCP server responds with a NAK to the client's DHCP request if they're not on the same subnet as the server.