Version: 0.2 (using KDE 3.5.5, Kubuntu (edgy) 4:3.5.5-0ubuntu2) Compiler: Target: i486-linux-gnu OS: Linux (i686) release 2.6.17-10-generic The network configuration settings dialog in system settings does not allow to me manually specify a netmask. I am forced to select from a drop-down box which, in the case of one of my network configs, does not contain the required subnet mask of 255.255.248.0 . I am unable to use the network that I am trying to configure until I correct the configuration from the command line using ifconfig.
Press the button "Advanced Setting", then you can set your subnet mask manually not using drop-down box.