A method is disclosed for policy-based determination of a network address for a client in a network. A request for a network address is received from a client. A policy response is received that identifies a scope of network addresses for the client. A request source address value in the client request is modified, based on the policy response. The modified client request is sent to a server that can assign network addresses within the identified scope. A network address for the client is received, which has been assigned by the server within the identified scope. The network address is provided to the client. A specific embodiment modifies a "giaddr" field value in a DHCP request, before relaying the request to a DHCP server, based on a policy decision that specifies a scope to be used for the network address of the client.