I want to clarify something regarding this Ethernet PHY development:
The Ethernet API and EMAC sample I am working with, it has emerged from the simplest of three SAM3X-EK Ethernet examples contained in Atmel Studio 6 and it is called "EMAC_EMAC_EXAMPLE1". This example only demonstrates how to configure and use the EMAC peripheral and does not uses Adam Dunkels' lwIP stack.
The other two examples are more elaborated: "LWIP_EXAMPLE1" which is a basic web server and basic TFTP server application with DHCP enabled through the lwIP TCP/IP stack and FreeRTOS of Sam port and finally "THIRDPARTY_FREERTOS_SAM_LWIP_DHCP_EXAMPLE1" which is a basic HTTP web server using also the lwIP TCP/IP stack standalone SAM port (i.e. no OS).