doc: networking: document native_sim with offloaded sockets

Document how offloaded sockets can be used with 'native_sim' for networking
capability.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>

doc/connectivity/networking/native_sim_setup.rst

@@ -7,7 +7,10 @@ Networking with native_sim board
     :local:
     :depth: 2
 
-This page describes how to set up a virtual network between a (Linux) host
+Using virtual/TAP Ethernet driver
+*********************************
+
+This paragraph describes how to set up a virtual network between a (Linux) host
 and a Zephyr application running in a :ref:`native_sim <native_sim>` board.
 
 In this example, the :zephyr:code-sample:`sockets-echo-server` sample application from
@@ -16,7 +19,7 @@ native_sim board instance is connected to a Linux host using a tuntap device
 which is modeled in Linux as an Ethernet network interface.
 
 Prerequisites
-*************
+=============
 
 On the Linux Host, fetch the Zephyr ``net-tools`` project, which is located
 in a separate Git repository:
@@ -27,7 +30,7 @@ in a separate Git repository:
 
 
 Basic Setup
-***********
+===========
 
 For the steps below, you will need three terminal windows:
 
@@ -39,7 +42,7 @@ For the steps below, you will need three terminal windows:
   instance (optional).
 
 Step 1 - Create Ethernet interface
-==================================
+----------------------------------
 
 Before starting native_sim with network emulation, a network interface
 should be created.
@@ -59,7 +62,7 @@ by running ``net-setup.sh`` like this:
 
 
 Step 2 - Start app in native_sim board
-======================================
+--------------------------------------
 
 Build and start the ``echo_server`` sample application.
 
@@ -74,7 +77,7 @@ In terminal #2, type:
 
 
 Step 3 - Connect to console (optional)
-======================================
+--------------------------------------
 
 The console window should be launched automatically when the Zephyr instance is
 started but if it does not show up, you can manually connect to the console.
@@ -89,3 +92,53 @@ You can manually connect to it like this:
 .. code-block:: console
 
    screen /dev/pts/5
+
+Using offloaded sockets
+***********************
+
+The main advantage over `Using virtual/TAP Ethernet driver`_ is not needing to
+setup a virtual network interface on the host machine. This means that no
+leveraged (root) privileges are needed.
+
+Step 1 - Start app in native_sim board
+======================================
+
+Build and start the ``echo_server`` sample application:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/net/sockets/echo_server
+   :host-os: unix
+   :board: native_sim
+   :gen-args: -DEXTRA_CONF_FILE=overlay-nsos.conf
+   :goals: run
+   :compact:
+
+Step 2 - run echo-client from net-tools
+=======================================
+
+On the Linux Host, fetch the Zephyr ``net-tools`` project, which is located
+in a separate Git repository:
+
+.. code-block:: console
+
+   git clone https://github.com/zephyrproject-rtos/net-tools
+
+.. note::
+
+   Native Simulator with the offloaded sockets network driver is using the same
+   network interface/namespace as any other (Linux) application that uses BSD
+   sockets API. This means that :zephyr:code-sample:`sockets-echo-server` and
+   ``echo-client`` applications will communicate over localhost/loopback
+   interface (address ``127.0.0.1``).
+
+To run UDP test, type:
+
+.. code-block:: console
+
+   ./echo-client 127.0.0.1
+
+For TCP test, type:
+
+.. code-block:: console
+
+   ./echo-client -t 127.0.0.1

doc/connectivity/networking/networking_with_host.rst

@@ -59,7 +59,8 @@ possible:
     system. This is the most convenient way to debug the Zephyr system as one
     can attach host debugger directly to the running Zephyr instance. This
     requires that there is an adaptation driver in Zephyr for interfacing
-    with the host system. An Ethernet driver exists in Zephyr for this purpose.
+    with the host system. Two possible network drivers can be used for this
+    purpose, a TAP virtual Ethernet driver and an offloaded sockets driver.
     See :ref:`networking_with_native_sim` for details.
 
 * USB device networking.