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/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single TCP/UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2010-2018 Fox Crypto B.V. <openvpn@fox-it.com>
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/**
* @file
* Main page documentation file.
*/
/**
* @mainpage OpenVPN source code documentation
*
* This documentation describes the internal structure of OpenVPN. It was
* automatically generated from specially formatted comment blocks in
* OpenVPN's source code using Doxygen. (See
* http://www.stack.nl/~dimitri/doxygen/ for more information on Doxygen)
*
* The \ref mainpage_modules "Modules section" below gives an introduction
* into the high-level module concepts used throughout this documentation.
* The \ref mainpage_relatedpages "Related Pages section" below describes
* various special subjects related to OpenVPN's implementation which are
* discussed in the related pages section.
*
* @section mainpage_modules Modules
*
* For the purpose of describing the internal structure of OpenVPN, this
* documentation and the underlying source code has been broken up into a
* number of conceptually well-defined parts, known as modules. Each
* module plays a specific role within the OpenVPN process, and in most
* cases each module has a clear interfacing strategy for interacting with
* other modules.
*
* The following modules have been defined:
* - Driver module:
* - The \link eventloop Main Event Loop\endlink: this module drives the
* event handling of OpenVPN. It implements various types of
* select-loop which wait until an event happens, and then delegate
* the handling of that event to the appropriate module.
* - Network interface modules:
* - The \link external_multiplexer External Multiplexer\endlink: this
* module sends and receives packets to and from remote OpenVPN peers
* over the external network interface. It also takes care of
* demultiplexing received packets to their appropriate VPN tunnel and
* splitting control channel and data channel packets.
* - The \link internal_multiplexer Internal Multiplexer\endlink: this
* module sends and receives packets to and from locally reachable
* posts over the virtual tun/tap network interface. It also takes
* care of determining through which VPN tunnel a received packet must
* be sent to reach its destination.
* - Control channel modules:
* - The \link reliable Reliability Layer\endlink: this module offers a
* %reliable and sequential transport layer for control channel
* messages.
* - The \link control_tls Control Channel TLS module\endlink: this
* module offers a secure encapsulation of control channel messages
* using the TLS protocol.
* - The \link control_processor Control Channel Processor\endlink: his
* module manages the setup, maintenance, and shut down of VPN
* tunnels.
* - Data channel modules:
* - The \link data_control Data Channel Control module\endlink: this
* module controls the processing of data channel packets and,
* depending on the settings of the packet's VPN tunnel, passes the
* packet to the three modules below for handling.
* - The \link data_crypto Data Channel Crypto module\endlink: this
* module performs security operations on data channel packets.
* - The \link fragmentation Data Channel Fragmentation module\endlink:
* this module offers fragmentation of data channel packets larger
* than the VPN tunnel's MTU.
* - The \link compression Data Channel Compression module\endlink: this
* module offers compression of data channel packets.
*
* @subsection mainpage_modules_example Example event: receiving a packet
*
* OpenVPN handles many types of events during operation. These include
* external events, such as network traffic being received, and internal
* events, such as a %key session timing out causing renegotiation. An
* example event, receiving a packet over the network, is described here
* together with which modules play what roles:
* -# The \link eventloop Main Event Loop\endlink detects that a packet
* can be read from the external or the virtual tun/tap network
* interface.
* -# The \link eventloop Main Event Loop\endlink calls the \link
* external_multiplexer External Multiplexer\endlink or \link
* internal_multiplexer Internal Multiplexer\endlink to read and
* process the packet.
* -# The multiplexer module determines the type of packet and its
* destination, and passes the packet on to the appropriate handling
* module:
* - A control channel packet received by the \link
* external_multiplexer External Multiplexer\endlink is passed on
* through the \link reliable Reliability Layer\endlink and the \link
* control_tls Control Channel TLS module\endlink to the \link
* control_processor Control Channel Processor\endlink.
* - A data channel packet received by either multiplexer module is
* passed on to the \link data_control Data Channel Control
* module\endlink.
* -# The packet is processed by the appropriate control channel or data
* channel modules.
* -# If, after processing the packet, a resulting packet is generated
* that needs to be sent to a local or remote destination, it is given
* to the \link external_multiplexer External Multiplexer\endlink or
* \link internal_multiplexer Internal Multiplexer\endlink for sending.
* -# If a packet is waiting to be sent by either multiplexer module and
* the \link eventloop Main Event Loop\endlink detects that data can be
* written to the associated network interface, it calls the
* multiplexer module to send the packet.
*
* @section mainpage_relatedpages Related pages
*
* This documentation includes a number of descriptions of various aspects
* of OpenVPN and its implementation. These are not directly related to
* one module, function, or data structure, and are therefore listed
* separately under "Related Pages".
*
* @subsection mainpage_relatedpages_key_generation Data channel key generation
*
* The @ref key_generation "Data channel key generation" related page
* describes how, during VPN tunnel setup and renegotiation, OpenVPN peers
* generate and exchange the %key material required for the symmetric
* encryption/decryption and HMAC signing/verifying security operations
* performed on data channel packets.
*
* @subsection mainpage_relatedpages_tunnel_state VPN tunnel state
*
* The @ref tunnel_state "Structure of VPN tunnel state storage" related
* page describes how an OpenVPN process manages the state information
* associated with its active VPN tunnels.
*
* @subsection mainpage_relatedpages_network_protocol Network protocol
*
* The @ref network_protocol "Network protocol" related page describes the
* format and content of VPN tunnel packets exchanged between OpenVPN
* peers.
*
* @subsection mainpage_relatedpages_memory_management Memory management
*
* The @ref memory_management "Memory management strategies" related page
* gives a brief introduction into OpenVPN's memory %buffer library and
* garbage collection facilities.
*/
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