VNC (Virtual Network Computing) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another

computer A computer is a machine that can be Computer programming, programmed to automatically Execution (computing), carry out sequences of arithmetic or logical operations (''computation''). Modern digital electronic computers can perform generic set ...

. It transmits the

keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Mus ...

and

mouse A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus'' ...

input from one computer to another, relaying the graphical- screen updates, over a

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

. Popular uses for this technology include remote technical support and accessing files on one's work computer from one's home computer, or vice versa. VNC is platform-independent, with clients and servers for many GUI-based operating systems and for

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

. Multiple clients may connect to a VNC server at the same time. There are a number of variants of VNC which offer their own particular functionality; e.g., some optimised for

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

, or offering

file transfer File transfer is the transmission of a computer file through a communication channel from one computer system to another. Typically, file transfer is mediated by a communications protocol. In the history of computing, numerous file transfer protoc ...

(not part of VNC proper), etc. Many are compatible (without their added features) with VNC proper in the sense that a viewer of one flavour can connect with a server of another; others are based on VNC code but not compatible with standard VNC. VNC was originally developed at the Olivetti & Oracle Research Lab in Cambridge, United Kingdom, whose developers subsequently created RealVNC Ltd and claimed VNC and RFB as

registered trademark A trademark (also written trade mark or trade-mark) is a form of intellectual property that consists of a word, phrase, symbol, design, or a combination that identifies a product or service from a particular source and distinguishes it from ot ...

s in the US and some other countries. The original VNC

source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...

and many modern derivatives are

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

under the

GNU General Public License The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

History

The Olivetti & Oracle Research Lab (ORL) at Cambridge in the UK developed VNC at a time when

Olivetti Olivetti S.p.A. is an Italian manufacturer of computers, tablets, smartphones, printers and other such business products as calculators and fax machines. Headquartered in Ivrea, in the Metropolitan City of Turin, the company has been owned b ...

and

Oracle Corporation Oracle Corporation is an American Multinational corporation, multinational computer technology company headquartered in Austin, Texas. Co-founded in 1977 in Santa Clara, California, by Larry Ellison, who remains executive chairman, Oracle was ...

owned the lab. Developers who worked on VNC while at the AT&T Research Lab include Tristan Richardson (inventor),

Andy Harter Andrew Charles Harter (born 5 April 1961 in Yorkshire, England) is a British computer scientist, best known as the founder of RealVNC, where he was CEO until March 2018. Education and early life Born in Yorkshire in 1961, Harter attended the ...

(project leader),

Quentin Stafford-Fraser James Quentin Stafford-Fraser is a computer scientist and entrepreneur based in Cambridge, England. He was one of the team that created the first webcam, the Trojan room coffee pot. Quentin pointed a camera at the coffee pot and wrote the XCoff ...

, James Weatherall and

Andy Hopper Sir Andrew Hopper (born 9 May 1953) is a British-Polish computer technologist and entrepreneur. He is Chairman of lowRISC CIC, a Commissioner of the Royal Commission for the Exhibition of 1851, former Treasurer and Vice-President of the Royal S ...

. The name ''Virtual Network Computer/Computing'' (VNC) originated with ORL's work on a

thin client In computer networking, a thin client, sometimes called slim client or lean client, is a simple (low-Computer performance, performance) computer that has been Program optimization, optimized for Remote desktop, establishing a remote connectio ...

called the Videotile, which also used the RFB protocol. The Videotile had an LCD display with pen input and a fast ATM connection to the network. At the time, ''

network computer In computer networking, a thin client, sometimes called slim client or lean client, is a simple (low-performance) computer that has been optimized for establishing a remote connection with a server-based computing environment. They are som ...

'' was commonly used as a synonym for a thin client; VNC is essentially a software-only (i.e. virtual) network computer. In 1999, AT&T acquired the lab, and in 2002 closed down the lab's research efforts. Following this, several members of the development team (including Richardson, Harter, Weatherall and Hopper) formed RealVNC in order to continue working on

open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

and commercial VNC software under that name. , RealVNC Ltd claims the term "VNC" as a registered trademark in the United States and in other countries. The original GPLed source code has fed into several other versions of VNC. Such forking has not led to compatibility problems because the RFB protocol is designed to be extensible. VNC clients and servers negotiate their capabilities with handshaking in order to use the most appropriate options supported at both ends.

Design and operation

The VNC

server Server may refer to: Computing *Server (computing), a computer program or a device that provides requested information for other programs or devices, called clients. Role * Waiting staff, those who work at a restaurant or a bar attending custome ...

is the program on the machine that shares some screen (and may not be related to a physical display: the server can be "headless"), and allows the client to share control of it. The VNC

client Client(s) or The Client may refer to: * Client (business) * Client (computing), hardware or software that accesses a remote service on another computer * Customer or client, a recipient of goods or services in return for monetary or other valuable ...

(or viewer) is the program that represents the screen data originating from the server, receives updates from it, and presumably controls it by informing the server of collected local input. The VNC

protocol Protocol may refer to: Sociology and politics * Protocol (politics) Protocol originally (in Late Middle English, c. 15th century) meant the minutes or logbook taken at a meeting, upon which an agreement was based. The term now commonly refers to ...

(

RFB protocol RFB ("remote framebuffer") is an open simple protocol for remote access to graphical user interfaces. Because it works at the framebuffer level it is applicable to all windowing systems and applications, including Microsoft Windows, macOS, the ...

) is very simple, based on transmitting one graphic primitive from server to client ("Put a rectangle of

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

data at the specified X,Y position") and event messages from client to server. In the normal method of operation a viewer connects to a port on the server (default port: 5900). Alternatively (depending on the implementation) a browser can connect to the server (default port: 5800). And a server can connect to a viewer in "listening mode" on port 5500. One advantage of listening mode is that the server site does not have to configure its firewall to allow access on port 5900 (or 5800); the duty is on the viewer, which is useful if the server site has no computer expertise and the viewer user is more knowledgeable. The server sends small rectangles of the

framebuffer A framebuffer (frame buffer, or sometimes framestore) is a portion of random-access memory (RAM) containing a bitmap that drives a video display. It is a memory buffer containing data representing all the pixels in a complete video frame. Mode ...

to the client. In its simplest form, the VNC protocol can use a lot of

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

, so various methods have been devised to reduce the communication overhead. For example, there are various ''encodings'' (methods to determine the most efficient way to transfer these rectangles). The VNC protocol allows the client and server to negotiate which encoding they will use. The simplest encoding, supported by all clients and servers, is ''raw encoding'', which sends pixel data in left-to-right

scanline A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode-ray tube (CRT) display of a television set or computer monitor. On CRT screens the horizontal scan lines are visually discernib ...

order, and after the original full screen has been transmitted, transfers only rectangles that change. This encoding works very well if only a small portion of the screen changes from one frame to the next (as when a mouse pointer moves across a desktop, or when text is written at the cursor), but bandwidth demands get very high if a lot of pixels change at the same time (such as when scrolling a window or viewing full-screen video). VNC by default uses

TCP port The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is common ...

5900+''N'', where ''N'' is the display number (usually :0 for a physical display). Several implementations also start a basic

HTTP HTTP (Hypertext Transfer Protocol) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, wher ...

on port 5800+''N'' to provide a VNC viewer as a

Java applet Java applets were applet, small applications written in the Java (programming language), Java programming language, or another programming language that Compiled language, compiles to Java bytecode, and delivered to users in the form of Ja ...

, allowing easy connection through any Java-enabled web-browser. Different port assignments can be used as long as both client and server are configured accordingly. A HTML5 VNC client implementation for modern browsers (no plugins required) exists too. Although possible even on low bandwidth, using VNC over the Internet is facilitated if the user has a

broadband In telecommunications, broadband or high speed is the wide-bandwidth (signal processing), bandwidth data transmission that exploits signals at a wide spread of frequencies or several different simultaneous frequencies, and is used in fast Inter ...

connection at both ends. However, it may require advanced

network address translation Network address translation (NAT) is a method of mapping an IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic Router (computing), routing device. The te ...

(NAT),

firewall Firewall may refer to: * Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts * Firewall (construction), a barrier inside a building, designed to limit the spre ...

and router configuration such as

port forwarding In computer networking, port forwarding or port mapping is an application of network address translation (NAT) that redirects a communication request from one address and port number combination to another while the packets are traversing a netwo ...

in order for the connection to go through. Users may establish communication through

virtual private network Virtual private network (VPN) is a network architecture for virtually extending a private network (i.e. any computer network which is not the public Internet) across one or multiple other networks which are either untrusted (as they are not con ...

(VPN) technologies to ease usage over the Internet, or as a LAN connection if VPN is used as a proxy, or through a VNC repeater (useful in presence of a NAT). In addition, the display that is served by VNC is not necessarily the same display seen by a user on the server. On Unix/Linux computers that support multiple simultaneous X11 sessions, VNC may be set to serve a particular existing X11 session, or to start one of its own. It is also possible to run multiple VNC sessions from the same computer. On Microsoft Windows the VNC session served is always the current user session. In July 2014 RealVNC published a Wayland developer preview.

Security

By default, RFB is not a secure protocol. While

password A password, sometimes called a passcode, is secret data, typically a string of characters, usually used to confirm a user's identity. Traditionally, passwords were expected to be memorized, but the large number of password-protected services t ...

s are not sent in plain-text (as in

telnet Telnet (sometimes stylized TELNET) is a client-server application protocol that provides access to virtual terminals of remote systems on local area networks or the Internet. It is a protocol for bidirectional 8-bit communications. Its main ...

), cracking could prove successful if both the

encryption In Cryptography law, cryptography, encryption (more specifically, Code, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the inf ...

key and encoded password were sniffed from a network. For this reason it is recommended that a password of at least 8 characters be used. On the other hand, there is also an 8-character limit on some versions of VNC; if a password is sent exceeding 8 characters, the excess characters are removed and the truncated string is compared to the password. UltraVNC supports the use of an open-source encryption plugin which encrypts the entire VNC session including password authentication and data transfer. It also allows authentication to be performed based on

NTLM In a Windows network, NT (New Technology) LAN Manager (NTLM) is a suite of Microsoft security protocols intended to provide authentication, integrity, and confidentiality to users. NTLM is the successor to the authentication protocol in Microsoft ...

and

Active Directory Active Directory (AD) is a directory service developed by Microsoft for Windows domain networks. Windows Server operating systems include it as a set of processes and services. Originally, only centralized domain management used Active Direct ...

user accounts. However, use of such encryption plugins makes it incompatible with other VNC programs. RealVNC offers high-strength AES encryption as part of its commercial package, along with integration with Active Directory. Workspot released

AES encryption The Advanced Encryption Standard (AES), also known by its original name Rijndael (), is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is a variant ...

patches for VNC. According to TightVNC, TightVNC is not secure as picture data is transmitted without encryption. To circumvent this, it should be tunneled through an SSH connection (see below). VNC may be tunneled over an

SSH The Secure Shell Protocol (SSH Protocol) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH was designed for Un ...

VPN Virtual private network (VPN) is a network architecture for virtually extending a private network (i.e. any computer network which is not the public Internet) across one or multiple other networks which are either untrusted (as they are not c ...

connection which would add an extra security layer with stronger encryption. An additional security concern for the use of VNC is to check whether the version used requires authorization from the remote computer owner before someone takes control of their device. This will avoid the situation where the owner of the computer accessed realizes there is someone in control of their device without previous notice.

Implementations

''Xvnc'' is the Unix VNC server, which is based on a standard

X server X server may refer to: * a display server for the X Window System * X.Org Server, the X.Org Foundation's display server for the X Window System * HPE Integrity Superdome X Server, a line of HPE Integrity Servers HPE Integrity Servers is a ser ...

. To applications, Xvnc appears as an X "server" (i.e., it displays client windows), and to remote VNC users it is a VNC server. Applications can display themselves on Xvnc as if it were a normal X display, but they will appear on any connected VNC viewers rather than on a physical screen. Alternatively, a machine (which may be a workstation or a network server) with screen, keyboard, and mouse can be set up to boot and run the VNC server as a service or daemon, then the screen, keyboard, and mouse can be removed and the machine stored in an out-of-the way location. Users commonly deploy VNC as a

cross-platform Within computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several Computing platform, computing platforms. Some ...

remote desktop system. For example,

Apple Remote Desktop Apple Remote Desktop (ARD) is a Macintosh application produced by Apple Inc., first released on March 14, 2002, that replaced a similar product called ''Apple Network Assistant''. Aimed at computer administrators responsible for large numbers of ...

for

Mac OS X macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

(and "

Back to My Mac Back to My Mac was a feature introduced with Mac OS X Leopard (10.5) that used Wide-Area Bonjour to securely discover services across the Internet and automatically configure ad hoc, on-demand, point-to-point encrypted connections between comput ...

" in versions 10.5 through 10.13) interoperates with VNC and will connect to a Unix user's current desktop if it is served with

x11vnc x11vnc is a Virtual Network Computing (VNC) server program. It allows remote access from a remote client to a computer hosting an X Window session and the x11vnc software, continuously polling the X server's frame buffer for changes. This allows ...

, or to a separate X11 session if one is served with

TightVNC TightVNC is a Free and open-source software, free and open-source remote desktop software server and client application for Linux and Windows. A server for macOS is available under a commercial software, commercial source code license only, with ...

. From Unix, TightVNC will connect to a Mac OS X session served by Apple Remote Desktop if the VNC option is enabled, or to a VNC server running on Microsoft Windows. Other programs or software libraries which implement VNC include Krfb, Libvncserver, PocketVNC,

Remmina Remmina is a free and open source remote desktop client for POSIX-based computer operating systems. It supports the Remote Desktop Protocol (RDP), VNC, NX technology, NX, XDMCP, SPICE (protocol), SPICE, X2Go and Secure Shell, SSH protocols and us ...

TigerVNC TigerVNC is an open source Virtual Network Computing (VNC) server and client software, started as a fork of TightVNC in 2009. The client supports Windows, Linux and macOS. The server supports Linux. There is no server for macOS and as of release ...

VirtualGL VirtualGL (VGL) is an open-source software package that redirects the 3D rendering commands from Unix and Linux OpenGL applications to 3D accelerator hardware in a dedicated server and sends the rendered output to a ( thin) client located elsewhe ...

, and

Vinagre Vinagre is a discontinued Virtual Network Computing, VNC, Secure Shell, SSH, Remote Desktop Protocol, RDP and Simple Protocol for Independent Computing Environments, SPICE client for the GNOME desktop environment, it is superseded by GNOME Con ...

References

External links

RFB 3.8 Protocol Standard

Original AT&T-Cambridge VNC website {{Use dmy dates, date=January 2019 Free network-related software Remote desktop protocols