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This month I am discussing VNC. Virtual Network Computing (VNC) is a graphical desktop sharing system that uses RFB protocol to remotely control another computer. It transmits keyboard and mouse events from one computer to another, relaying the graphical screen updates back in the other direction, over a network.

VNC is platform-independent – a VNC viewer on one operating system may connect to a VNC server on the same or any other operating system. There are clients and servers for many GUI-based operating systems and for Java. Multiple clients may connect to a VNC server at the same time. 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 was originally developed at the Olivetti & Oracle Research Lab (ORL), which was then owned by Olivetti and Oracle Corporation. In 1999 AT&T acquired the lab, and in 2002 closed down the lab's research efforts. You may view their old website here. The original VNC source code and many modern derivatives are open source under the GNU General Public License.  Following the closure of ORL in 2002, several members of the development team formed RealVNC in order to continue working on open source and commercial VNC software under that name. The server sends small rectangles of the framebuffer to the client. In its simplest form, the VNC protocol can use lots of bandwidth, so various methods have been devised to reduce the communication overhead. There are various encodings (methods to determine the most efficient way to transfer numerous graphic rectangles). The VNC protocol allows the client and server to negotiate which encoding will be used.

A VNC system consists of a client, a server, and a communication protocol.

• The VNC server is the program on the machine that shares its screen. The server passively allows the client to take control of it.
• The VNC client (or viewer) is the program that watches, controls, and interacts with the server. The client controls the server.
• The VNC protocol (RFB) is very simple. In normal operation a viewer connects to a port on the server (default port 5900TCP). Alternatively a browser can connect to the server (default port 5800TCP). Other ports can be used as long as both client and server are configured accordingly. Using VNC over the Internet works well if broadband connections exist at both ends. VNC probably requires advanced NAT in firewall and router configuration such as port forwarding (read on).

There are a number of VNC variants which offer their own particular functionality including my favorite titled UltraVNC. UltraVNC offers encryption and file transfer (both not part of VNC proper). As I explained in an earlier article, I had a short term job monitoring a LAN with several hundred clients, email, and three file and print servers. Instead of driving daily to the location, I was able to VNC into the site to verify network connectivity, clear print queues, add and delete users and verify daily backups. On another occasion I also used VNC to help troubleshoot my sister's computer in Arizona.

UltraVNC was essential in the first instance since private data should not be transmitted unencrypted over the Internet. I setup the server component at the site on a Windows Server2003 to operate on port 5902 (a non-standard port to mask a quick hacker sweep). I installed UltraVNC Server as a service which begins whenever the computer is started (a necessity for connecting after rebooting).

Port 5902 had to be opened or forwarded on the Internet router or firewall. On the standard LinkSys router this is accomplished in the advanced settings / forwarding page for TCP connections (and remember to save this configuration).

On my home laptop I installed only the UltraVNC client. I left an icon on the desktop. When the client opens you type in the Internet address of the server as an IP number, add a colon and 5902 ( i.e. xxx.xxx.xxx.xxx:5902). Type the username and password selected for the server and you soon view the display screen of the monitored computer inside an UltraVNC window. All activity is slowed over the Internet but you now have access to everything as if you were standing in front of the server itself. A handy tool inside UltraVNC allows you to transfer files either way between the two computers.

My sister's home computer was slightly different. She needed to install UltraVNC and setup forwarding at her end. To simplify things we used the default 5900 port. She used the utility IP2 which I sent her as an email attachment to tell me her current IP address which was not fixed. At my end I typed this address followed by the colon 5900 and password. Soon I was moving her mouse pointer and understanding her problem.

UltraVNC is limited to Windows use but other VNC combinations can link Mac, Linux and Windows computers. The VNC protocol is open source, regularly updated and free.

FOSS stands for free and open source software. FOSS software is maintained worldwide by groups of volunteers committed to delivering quality products. There is never a charge for FOSS. You are invited to join the FOSS SIG on the last Thursday of each month from 1:00 to 3:00 PM in the TBCS Resource Center (no meetings in November and December).

Visit our online website at http://fosssig.com and I'll be back with something new next month inside FOSS Flap.

Cyber-blessings, Stew Bottorf This e-mail address is being protected from spambots. You need JavaScript enabled to view it
 

©  2009 TBCS and Stew Bottorf