I still can't get some clients to receive my dhcp packets. After some more testing i figured out packet size differences. In other dhcp server responses it's 342 bytes ... on radius dhcp server i've 618 bytes. Is it possible to make send back messages as short as possbile ? :) Also found some references that dhcp clients can refuse messages if thay are larger that expected. Haralds from rfc: The client SHOULD include the 'maximum DHCP message size' option to let the server know how large the server may make its DHCP messages. The parameters returned to a client may still exceed the space allocated to options in a DHCP message. In this case, two additional options flags (which must appear in the 'options' field of the message) indicate that the 'file' and 'sname' fields are to be used for options.