Network Driver Interface Specification (NDIS)
TCP/IP, along with other Microsoft networking protocols, uses the Network Driver Interface Specification (NDIS) interface to communicate with network card drivers. Much of the Open Systems Interconnection (OSI) model link layer functionality is implemented in the NDIS interface. This makes development of network card drivers much simpler.
Link layer functionality is divided between the network interface card/driver combination and the low-level protocol stack driver. The link layer is responsible for discovering the Maximum Transmission Unit (MTU) and reporting it to the protocols above the link layer.