In order to integrate a driver for a network interface, the TCP/IP stack exposes an interface to its lowest layers, sending and receiving buffers containing frames or packets. If the device supports the link-layer Ethernet address, TCP/IP stacks must connect an additional component to deal with Ethernet frames, and activate the neighbor discovery protocols to learn the MAC address of the receiving device before initiating any IP communication.
lwIP provides a netif structure, describing a network interface, which must be allocated by the driver code, but is then initialized automatically by the stack using the netif_add function:
struct *netif netif_add(struct netif *mynetif, struct ip_addr *ipaddr, struct ip_addr *netmask, ...
