Remote Desktop Protocol is a proprietary protocol developed by Microsoft, which provides a user
with a graphical interface to connect to another computer over a network connection.
The user employs RDP client software for this purpose, while the other computer must run
RDP server software.
Clients exist for most versions of Microsoft Windows, Linux, Unix, OS X, iOS, Android,
and other operating systems.
RDP servers are built into Windows operating systems; an RDP server for Unix and OS X also
exists.
By default, the server listens on TCP port 3389 and UDP port 3389.
Microsoft currently refers to their official RDP server software as Remote Desktop Connection,
formerly "Terminal Services Client".
The protocol is an extension of the ITU-T T.128 application sharing protocol.
History
Every Windows version beginning with Windows XP includes an installed Remote Desktop Connection
client whose version is determined by that of the operating system or last applied Windows
Service Pack.
The Terminal Services server is supported as an official feature on Windows NT 4.0 Terminal
Server Edition, Windows 2000 Server, all editions of Windows XP except Windows XP Home Edition,
Windows Server 2003, Windows Home Server, on Windows Fundamentals for Legacy PCs, in
Windows Vista Ultimate, Enterprise and Business editions, Windows Server 2008 and Windows
Server 2008 R2 and on Windows 7 Professional and above.
Microsoft provides the client required for connecting to newer RDP versions for downlevel
operating systems.
Since the server improvements are not available downlevel, the features introduced with each
newer RDP version only work on downlevel operating systems when connecting to a higher version
RDP server from these older operating systems, and not when using the RDP server in the older
operating system.
Version 4.0 Based on the ITU-T T.128 application sharing
protocol from the T.120 recommendation series, the first version of RDP was introduced by
Microsoft with "Terminal Services", as a part of their product Windows NT 4.0 Server, Terminal
Server Edition.
The Terminal Services Edition of NT 4.0 relied on Citrix's MultiWin technology, previously
provided as a part of Citrix WinFrame atop Windows NT 3.51, in order to support multiple
users and login sessions simultaneously.
Microsoft required Citrix to license their MultiWin technology to Microsoft in order
to be allowed to continue offering their own terminal services product, then named Citrix
MetaFrame, atop Windows NT 4.0.
The Citrix-provided DLLs included in Windows NT 4.0 Terminal Services Edition still carry
a Citrix copyright rather than a Microsoft copyright.
Later versions of Windows integrated the necessary support directly.
The T.128 application sharing technology was acquired by Microsoft from UK software developer
Data Connection Limited.
Version 5.0 This version was introduced with Windows 2000
Server, added support for a number of features, including printing to local printers, and
aimed to improve network bandwidth usage.
Version 5.1 This version was introduced with Windows XP
Professional, included support for 24-bit color and sound.
The client is available for Windows 2000, Windows 9x, Windows NT 4.0.
With this version, the name of the client was changed from Terminal Services Client
to Remote Desktop Connection.
Version 5.2 This version was introduced with Windows Server
2003, included support for console mode connections, a session directory, and local resource mapping.
It also introduces Transport Layer Security 1.0 for server authentication, and to encrypt
terminal server communications.
This version is built into Windows XP Professional x64 Edition and Windows Server 2003 x64 & x86
Editions.
Version 6.0 This version was introduced with Windows Vista
and incorporated support for Windows Presentation Foundation applications, Network Level Authentication,
multi-monitor spanning and large desktop support, and TLS 1.0 connections.
Version 6.0 client is available for Windows XP SP2, Windows Server 2003 SP1/SP2 and Windows
XP Professional x64 Edition.
Microsoft Remote Desktop Connection Client for Macintosh OS X is also available with
support for Intel and PowerPC Mac OS versions 10.4.9 and greater.
Server 2012 can support RDC 6.0 or later.
Version 6.1 This version was released in February 2008
and is included with Windows Server 2008, as well as with Windows Vista Service Pack
1.
The client is included with Windows XP SP 3.
In addition to changes related to how a remote administrator connects to the "console", this
version hasnew functionality introduced in Windows Server 2008, such as connecting remotely
to individual programs and a new client-side printer redirection system that makes the
client's print capabilities available to applications running on the server, without having to install
print drivers on the server.
Version 7.0 This version was released to manufacturing
in July 2009 and is included with Windows Server 2008 R2, as well as with Windows 7.
With this release, the server name was also changed from Terminal Services to Remote Desktop
Services.
This version has new functions such as Windows Media Player redirection, bidirectional audio,
multi-monitor support, Aero glass support, enhanced bitmap acceleration, Easy Print redirection,
Language Bar docking.
The RDP 7.0 client is available on Windows XP SP3 and Windows Vista SP1/SP2 through KB969084.
RDP 6.1 client and RDP 7.0 client are not supported on Windows Server 2003 x86 and Windows
Server 2003 / Windows XP Professional x64 editions.
RDP 7.0 is also not supported on Windows Server 2008.
RDP 7.0 clients also do not support connecting to terminal servers running Windows 2000 Server.
Most RDP 7.0 features like Aero glass remote use, bidirectional audio, Windows Media Player
redirection, multiple monitor support and Remote Desktop Easy Print are only available
in Windows 7 Enterprise or Ultimate editions.
Version 7.1 This version appeared in Windows 7 SP1 and
Server 2008 R2 SP1.
It adds RemoteFX functionality.
Version 8.0 This version appeared in Windows 8 and Windows
Server 2012.
This version has new functions such as Adaptive Graphics, automatic selection of TCP or UDP
as transport protocol, multi touch support, DirectX 11 support for vGPU, USB redirection
supported independently of vGPU support, etc.
A "connection quality" button is displayed in the RDP client connection bar for RDP 8.0
connections; clicking on it provides a bit of further information about connection, including
whether UDP is in use or not.
The RDP 8.0 client and server components are also available as an add-on for Windows 7
SP1.
The RDP 8.0 client is also available for Windows Server 2008 R2 SP1, but the server components
are not.
The add-on requires the DTLS protocol to be installed as prerequisite.
Even after installing the updates, for the RDP 8.0 protocol to be usable between Windows
7 machines, an extra configuration step is needed using the Group Policy editor.
A new feature in RDP 8.0 is limited support for RDP session nesting; it only works for
Windows 8 and Server 2012 though, Windows 7 and Server 2008 R2 do not support this feature.
The "shadow" feature from RDP 7, which allowed an administrator to monitor on a RDP connection
has been removed in RDP 8.
The Aero Glass remoting feature has also been removed in RDP 8.
Version 8.1 This version appeared in Windows 8.1 and Windows
Server 2012 R2.
A RDP 8.1 client update exists for Windows 7 SP1 as well, but unlike the RDP 8.0 update
for Windows 7, it does not add a RDP 8.1 server component to Windows 7.
Furthermore, if RDP 8.0 server function is desired on Windows 7, the KB 2592687 update
must be installed before installing the RDP 8.1 update.
Support for session shadowing was added back in RDP version 8.1.
This version also fixes some visual glitches with Microsoft Office 2013 when running as
a RemoteApp.
Version 8.1 of the RDP protocol also enables a "restricted admin" mode.
Logging into this mode only requires knowledge of the hashed password, rather than of its
plaintext, therefore making a pass the hash attack possible.
Microsoft has released an 82-page document explaining how to mitigate against this type
of attack.
Features 32-bit color support.
8-, 15-, 16-, and 24-bit color are also supported.
128-bit encryption, using the RC4 encryption algorithm, as of Version 6.
Audio Redirection allows users to process audio on a remote desktop and have the sound
redirected to their local computer.
File System Redirection allows users to use their local files on a remote desktop within
the terminal session.
Printer Redirection allows users to use their local printer within the terminal session
as they would with a locally- or network-shared printer.
Port Redirection allows applications running within the terminal session to access local
serial and parallel ports directly.
The remote computer and the local computer can share the clipboard.
Microsoft introduced the following features with the release of RDP 6.0 in 2006:
Seamless Windows: remote applications can run on a client machine that is served by
a Remote Desktop connection.
It is available since RDP 6.
Remote Programs: application publishing with client-side file-type associations.
Terminal Services Gateway: enables the ability to use a front-end IIS server to accept connections
for back-end Terminal Services servers via an https connection, similar to how RPC over
https allows Outlook clients to connect to a back-end Exchange 2003 server.
Requires Windows Server 2008.
Network Level Authentication Support for remoting the Aero Glass Theme,
including ClearType font-smoothing technology.
Support for remoting Windows Presentation Foundation applications: compatible clients
that have .NET Framework 3.0 support can display full Windows Presentation Foundation effects
on a local machine.
Rewrite of device redirection to be more general-purpose, allowing a greater variety of devices to be
accessed.
Fully configurable and scriptable via Windows Management Instrumentation.
Improved bandwidth tuning for RDP clients.
Support for Transport Layer Security 1.0 on both server and client ends.
Multiple monitor support for allowing one session to use multiple monitors on the client
Release 7.1 of RDP in 2010 introduced the following feature:
RemoteFX: RemoteFX provides virtualized GPU support and host-side encoding; it ships as
part of Windows Server 2008 R2 SP1.
Security issues The RDP protocol in its default configuration
is vulnerable to a man-in-the-middle attack.
Administrators can enable transport layer encryption to mitigate this risk.
RDP sessions are also susceptible to in-memory credential harvesting, which can be used to
launch pass the hash attacks.
In March 2012, Microsoft released an update for a critical security vulnerability in the
RDP protocol.
The vulnerability allowed a Windows computer to be compromised by unauthenticated clients
and computer worms.
RDP client version 6.1 can be used to reveal the names and pictures of all users on the
RDP Server in order to pick one, if no username is specified for the RDP connection.
Non-Microsoft implementations There are numerous non-Microsoft implementations
of RDP clients and servers that implement subsets of the Microsoft functionality.
For instance, the open-source command-line client rdesktop is available for Linux/Unix
and Microsoft Windows operating systems.
There are many GUI clients, like tsclient and KRDC, that are built on top of rdesktop;
CoRD is such a client for the Macintosh.
Unlike the Microsoft client for OS X, CorRD uses a single tabbed window for all remote
sessions, which a ZDNet reviewer found less confusing.
Another 2011 review found CoRD's connections more stable than Microsoft's OS X client.
In 2009, rdesktop was forked as FreeRDP, a new project aiming at modularizing the code,
addressing various issues, and implementing new features.
FreeRDP comes with its own command-line-client xfreerdp, which supports Seamless Windows
in RDP6.
There’s also a GTK-Application named Remmina.
An open-source implementation of a Remote Desktop Protocol server on Unix is FreeRDP
and xrdp.
The Windows' Remote Desktop Connection client can be used to connect to a server.
Proprietary RDP client solutions such as rdpclient are available as a stand-alone application
or embedded with client hardware.
A new access paradigm, browser-based access, has enabled users to access Windows desktops
and applications on any RDP hosts, such as Microsoft Remote Desktop Session Hosts and
virtual desktops.
There are now solutions that run directly within a browser, for example 2X Software
ApplicationServerXG and 2X Client which is a free RDP client.
There is also a so-called VRDP protocol used in the VirtualBox virtual machine implementation
by Oracle.
This protocol is compatible with all RDP clients, such as that provided with Windows but, unlike
the original RDP protocol, can be configured to accept unencrypted and password unprotected
connections, which may be useful in secure and trusted networks, such as home or office
LANs.
By default, Microsoft's RDP server refuses connections to user accounts with empty passwords.
External and guest authorization options are provided by VRDP as well.
It does not matter which operating system is installed as a guest because VRDP is implemented
on the virtual machine level, not in the guest system.
The proprietary VirtualBox Extension Pack is required.
Patents Microsoft considers necessary that third-party
implementations license the relevant RDP patents from them.
As of February 2014, the extent to which open source clients meet this requirement is unknown.
See also Comparison of remote desktop software
Ulteo OVD Citrix ICA
Desktop virtualization HP RGS
SPICE Virtual Network Computing
Virtual private server References
External links Microsoft Remote Desktop Connection for Mac
Technical Overview of Terminal Services - a more detailed feature list.
Remote Desktop Protocol - from Microsoft's Developer Network
Understanding the Remote Desktop Protocol - from support.microsoft.com
MS-RDPBCGR: Remote Desktop Protocol: Basic Connectivity and Graphics Remoting Specification
- from Microsoft's Developer Network