.. _echo-server-sample:

Echo Server
###########

Overview
********

The echo-server sample application for Zephyr implements a UDP/TCP server
that complements the echo-client sample application: the echo-server listens
for incoming IPv4 or IPv6 packets (sent by the echo client) and simply sends
them back.

The source code for this sample application can be found at:
:file:`samples/net/echo_server`.

Requirements
************

- :ref:`networking_with_qemu`

Building and Running
********************

There are multiple ways to use this application. One of the most common
usage scenario is to run echo-server application inside QEMU. This is
described in :ref:`networking_with_qemu`.

There are configuration files for different boards and setups in the
echo-server directory:

- :file:`prj.conf`
  Generic config file, normally you should use this.

- :file:`overlay-frdm_k64f_cc2520.conf`
  This overlay config enables support for IEEE 802.15.4 CC2520 and frdm_k64f

- :file:`overlay-frdm_k64f_mcr20a.conf`
  This overlay config enables support for IEEE 802.15.4 mcr20a and frdm_k64f

- :file:`overlay-ot.conf`
  This overlay config enables support for OpenThread

- :file:`overlay-enc28j60.conf`
  This overlay config enables support for enc28j60 ethernet board. This
  add-on board can be used for example with Arduino 101 board.

- :file:`overlay-cc2520.conf`
  This overlay config enables support for IEEE 802.15.4 cc2520 chip.

- :file:`overlay-bt.conf`
  This overlay config enables support for Bluetooth IPSP connectivity.

- :file:`overlay-qemu_802154.conf`
  This overlay config enables support for two QEMU's when simulating
  IEEE 802.15.4 network that are connected together.

- :file:`overlay-tls.conf`
  This overlay config enables support for TLS.

- :file:`overlay-netusb.conf`
  This overlay config enables support for Ethernet over USB setup with
  supported boards. The setup is described in :ref:`usb_device_networking_setup`

Build echo-server sample application like this:

.. zephyr-app-commands::
   :zephyr-app: samples/net/echo_server
   :board: <board to use>
   :conf: <config file to use>
   :goals: build
   :compact:

Example building for the FRDM-K64F with TI CC2520 support:

.. zephyr-app-commands::
   :zephyr-app: samples/net/echo_server
   :host-os: unix
   :board: frdm_k64f
   :conf: "prj.conf overlay-frdm_k64f_cc2520.conf"
   :goals: run
   :compact:

Make can select the default configuration file based on the BOARD you've
specified automatically so you might not always need to mention it.

Running echo-client in Linux Host
=================================

There is one useful testing scenario that can be used with Linux host.
Here echo-server is run in QEMU and echo-client is run in Linux host.

To use QEMU for testing, follow the :ref:`networking_with_qemu` guide.

Run echo-server application in QEMU:

.. zephyr-app-commands::
   :zephyr-app: samples/net/echo_server
   :host-os: unix
   :board: qemu_x86
   :goals: run
   :compact:

In a terminal window:

.. code-block:: console

    $ sudo ./echo-client -i tap0 2001:db8::1

Note that echo-server must be running in QEMU before you start the
echo-client application in host terminal window.