I have a guest-VM installed in OVM Server. OVM Server is running on top of VirtualBox. From the HOST-OS, I can ping to the guest-VM. I attempted vncviewer into the guest-VM, however no luck. I did 192.168.1.51:5900
However, I can launch through the console via OVMM and can see the guest-VM.
I have turn off firewall in guest-VM (linux). I was able to use vncviewer the day before.
Dude.... The VM console feature using VNC is proxied through the VM Manager. The VNC viewer connects through the VM Manager. You can't connect directly to the VM guest using VNC... unless.... You have VNC Server installed on that guest. Even then, it might not be running on 5900 unless you're running a windows VM guest. In which case, 5900 is the default port. On many linux distributions, you have define the port in the setup and no one I know runs VNC on port 5900 in Linux. If its a Linux guest with rpm based packaging do a
rpm -qa | grep vnc
This will tell if the package is at least installed.
The x windows environment has to be installed and configured. It may already be installed. At the console prompt, do a startx. If not, then you will need to load the packages to run GNOME or KDE.... and then configure the X environment. I don't use any of the base OS templates from Oracle. They are extremely stripped down installations. I don't know if they come with any x-windows environment or not. I suggest you learn how to use kickstart and build your own base configs with what you want/need into them already.
You should run the VNC session as user "oracle". This account is created by "oracle-rdbms-server-11gR2-preinstall".
The password will need to be set: as "root" "passwd oracle".
Details on YUM are here Oracle Public Yum Server