Netboot cannot get DHCP IP address

- Testing netboot on a Macbook Pro 9,2 with Yosemite installed. - Infoblox DHCP/DNS (Linux style) giving out IP address. - Reservation for this Mac is set - Logging into OSX provides correct IP etc. - I have a OSX Server with Netinstall running. If I try a netboot (press N at power on), this results in the globe flashing but eventually just reverts to disk boot. Checking the Netinstall server logs, there is no activity - the client didn't attempt to conact. If I try to boot to menu (press Option key), I get an option of booting from the disk, or selecting a WiFi network. There is no ethernet network option. If I press N at this point, nothing happens. It *appears* that the ethernet port is not working at this stage in the process, even though it works when booting to OSX. Can anyone advise? How can I check this? Using the latest available: - BOOTROM: MBP91.00D3.B08 (EFI 2.9) - SMC: 2.2f44 (SMC 1.8)