XP SP2: RealVNC Will Not Connect. Unable to Resolve Host by Name.

   Posted December 4, 2005 by David Kirk in Windows networking

Last Updated on

Many systems with realVNC installed will not connect after sp2 is installed. Many XP sp2 systems have difficulty connecting even if realVNC is installed after the update. Here is the fix.

You install Real VNC on a new system. You leave it and start upgrading XP remotely. You install SP2 and suddenly you can not connect anymore:

VNC Viewer : Error
unable to resolve host by name: No such host is known. (11001)

SP2’s firewall is more rigid. As the realVNC server installs itself as a service, XP never asks the user if it should punch a hole in the firewall for it. Therefore, you must do it manually.

    1. Click Start
    2. Click Control Panel
    3. In the classic view, select Windows Firewall
    4. Under the exceptions tab, click Add Port button
    5. Name it RealVNC
    6. Port Number is 5900
    7. Select TCP
    8. If you only use VNC over your local network, you should press the Change Scope button and select the My Network (subnet) only
    9. Press OK until you are out of the firewall panel

Ann earned a shirt by adding the following:

    Your information is exactly correct for using the RealVNC Viewer
    program ONLY to access the RealVNC Server.
    RealVNC also allows access to the Server via a web browser (Internet Explorer).
    When you use the VNCViewer for access, it usually defaults to
    port 5900, but when you use a browser, you need to access the JAVA port
    that is usually on port 5800.

    Ergo, to make the SERVER available to any remote user whether they
    are running REALVNCViewer or not, one would setup the SERVER
    as mentioned in your document. This would allow the VNCViewer
    to work. And then go through your process a second time but use port 5800.
    Naturally, if you setup 5800, only, users trying to use the REALVNC Viewer
    will not be able to access, but the browser folks will.

    To access a SERVER using a BROWSER, the syntax is:
    where the #’s are those of the SERVER, same as in the REALVNC Viewer.

    IF REALVNC Viewer works& your browser doesn’t (using the syntax above).
    You can try this test.
    On your browser, use port 5900, in lieu of 5800.
    You should get a screen with something like: RFB 003,008.
    IF you get this, then you might have to recheck the server.
    make sure that you setup 5800 correctly.
    IF you don’t get this, you have some other issue.


About David Kirk

David Kirk is one of the original founders of tech-recipes and is currently serving as editor-in-chief. Not only has he been crafting tutorials for over ten years, but in his other life he also enjoys taking care of critically ill patients as an ICU physician.
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