.. _net_capture_interface:

Network Packet Capture
######################

.. contents::
    :local:
    :depth: 2

Overview
********

The ``net_capture`` API allows user to monitor the network
traffic in one of the Zephyr network interfaces and send that traffic to
external system for analysis. The monitoring can be setup either manually
using ``net-shell`` or automatically by using the ``net_capture`` API.

Cooked Mode Capture
*******************

If capturing is enabled and configured, the system will automatically capture
network traffic for a given network interface. If you would like to capture
network data when there is no network interface involved, then you need to use
the cooked mode capture API.

In cooked mode capture, arbitrary network packets can be captured and there
does not need to be network interface involved. For example low level HDLC
packets in PPP can be captured, as the HDLC L2 layer data is stripped away when
using the normal network interface based capture. Also CANBUS or Bluetooth
network data could be captured although currently there is no support in the
network stack to capture those.

The cooked mode capture works like this:

* An ``any`` network interface is created. It acts as a sink where the cooked
  mode captured packets are written by the cooked mode capture API.
* A ``cooked`` virtual network interface is attached on top of this ``any``
  interface.
* The ``cooked`` interface must be configured to capture certain L2 packet types
  using the network interface configuration API.
* When cooked mode capture API is used, the caller must specify what is the
  layer 2 protocol type of the captured data. The cooked mode capture API is then
  able to determine what to capture when receiving such a L2 packet.
* The network packet capturing infrastructure is then setup so that the ``cooked``
  interface is marked as captured network interface.
  The packets received by the ``cooked`` interface via the ``any`` interface are
  then automatically placed to the capture IP tunnel and sent to remote host
  for analysis.

For example, in the sample capture application, these network interfaces
are created:

.. code-block:: c

	Interface any (0x808ab3c) (Dummy) [1]
	================================
	Virtual interfaces attached to this : 2
	Device    : NET_ANY (0x80849a4)

	Interface cooked (0x808ac94) (Virtual) [2]
	==================================
	Virtual name : Cooked mode capture
	Attached  : 1 (Dummy / 0x808ab3c)
	Device    : NET_COOKED (0x808497c)

	Interface eth0 (0x808adec) (Ethernet) [3]
	===================================
	Virtual interfaces attached to this : 4
	Device    : zeth0 (0x80849b8)
	IPv6 unicast addresses (max 4):
	     fe80::5eff:fe00:53e6 autoconf preferred infinite
	     2001:db8::1 manual preferred infinite
	IPv4 unicast addresses (max 2):
	     192.0.2.1/255.255.255.0 overridable preferred infinite

	Interface net0 (0x808af44) (Virtual) [4]
	==================================
	Virtual name : Capture tunnel
	Attached  : 3 (Ethernet / 0x808adec)
	Device    : IP_TUNNEL0 (0x8084990)
	IPv6 unicast addresses (max 4):
	     2001:db8:200::1 manual preferred infinite
	     fe80::efed:6dff:fef2:b1df autoconf preferred infinite
	     fe80::56da:1eff:fe5e:bc02 autoconf preferred infinite

In this example, the ``192.0.2.2`` is the address of the outer end point of the
host that terminates the tunnel. Zephyr uses this address to select the
internal interface to use for the tunnel. In this example it is interface 3.

The interface 2 is a virtual interface that runs on top of interface 1. The
cooked capture packets are written by the capture API to sink interface 1.
The packets propagate to interface 2 because it is linked to the first interface.
The ``net capture enable 2`` net-shell command will cause the packets sent to
interface 2 to be written to capture interface 4, which in turn then capsulates
the packets and tunnels them to peer via the Ethernet interface 3.

The above IP addresses might change if you change the addresses in the
sample :zephyr_file:`samples/net/capture/overlay-tunnel.conf` file.

Sample usage
************

See :zephyr:code-sample:`net-capture` sample application and
:ref:`network_monitoring` for details.


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

.. doxygengroup:: net_capture