.. _net_if_interface:

Network Interface
#################

Overview
********

The network interface is a nexus that ties the network device drivers
and the upper part of the network stack together. All the sent and received
data is transferred via a network interface. The network interfaces cannot be
created at runtime. A special linker section will contain information about them
and that section is populated at linking time.

Network interfaces are created by ``NET_DEVICE_INIT()`` macro.
For Ethernet network, a macro called ``ETH_NET_DEVICE_INIT()`` should be used
instead as it will create VLAN interfaces automatically if
:option:`CONFIG_NET_VLAN` is enabled. These macros are typically used in
network device driver source code.

The network interface can be turned ON by calling ``net_if_up()`` and OFF
by calling ``net_if_down()``. When the device is powered ON, the network
interface is also turned ON by default.

The network interfaces can be referenced either by a ``struct net_if *``
pointer or by a network interface index. The network interface can be
resolved from its index by calling ``net_if_get_by_index()`` and from interface
pointer by calling ``net_if_get_by_iface()``.

The IP address for network devices must be set for them to be connectable.
In a typical dynamic network environment, IP addresses are set automatically
by DHCPv4, for example. If needed though, the application can set a device's
IP address manually.  See the API documentation below for functions such as
``net_if_ipv4_addr_add()`` that do that.

The ``net_if_get_default()`` returns a *default* network interface. What
this default interface means can be configured via options like
:option:`CONFIG_NET_DEFAULT_IF_FIRST` and
:option:`CONFIG_NET_DEFAULT_IF_ETHERNET`.
See Kconfig file :file:`subsys/net/ip/Kconfig` what options are available for
selecting the default network interface.

The transmitted and received network packets can be classified via a network
packet priority. This is typically done in Ethernet networks when virtual LANs
(VLANs) are used. Higher priority packets can be sent or received earlier than
lower priority packets. The traffic class setup can be configured by
:option:`CONFIG_NET_TC_TX_COUNT` and :option:`CONFIG_NET_TC_RX_COUNT` options.

If the :option:`CONFIG_NET_PROMISCUOUS_MODE` is enabled and if the underlaying
network technology supports promiscuous mode, then it is possible to receive
all the network packets that the network device driver is able to receive.
See :ref:`promiscuous_interface` API for more details.

API Reference
*************

.. doxygengroup:: net_if
   :project: Zephyr