There are two main things to remember when trying to calculate subnets. The first is that that default subnet for a range is 255.255.255.0. This subnet, that we all recognize gives you one network with 255 different addresses from 1 to 255. Fairly easy stuff so far. The second thing to remember is the formula needed to calculate a new subnet. For this we have to go back to basics and remember that the number 255 is made up in binary of 8 bits. To get the number 255, all those 8 bits would be set to 1, each one representing a number in decimal in the following sequence. (1, 2, 4, 8, 16, 32, 64, 128). If you add all these numbers together you get 255.

In order to create our subnet mask we need to “borrow” a certain number of bits from our host address. The host address is the last number in the group of four that makes up our subnet. So in the subnet 255.255.255.0, the 0 is the host address.

We can use the formula (2^n – 2) to figure out how many networks we can make by borrowing certain number of bits. Lets say for example we wanted to make six networks; we would need to borrow 3 bits, because (2^3 – 2 = 6). So we take the three bits from the left of our binary sequence and add them together. (128 + 64 + 32 = 224). So the subnet we need to use for our 6-network system is 255.255.255.224.

Now we’ve calculated our subnet, the next thing we need to do is work out the ranges of our new networks. This is a fairly easy thing to do if you remember one rule. The lowest number in the bits we borrowed from our host address is our guide. In this case, the bits we borrowed were 128, 64 and 32. The lowest of these is 32, so this is our guide number we’re going to use to set up our network ranges.

What you want to do is start off with your guide number, and that gives you the first address of our first network. For example – 192.168.0.32. To get the starting address of the second network, you just add on 32. So the second network will begin at 192.168.0.64. Keep adding the number 32 to find the other network starting points, and you’ll end up with this network address range map:

• Network 1: 192.168.0.32 – 192.168.0.63
• Network 2: 192.168.0.64 – 192.168.0.95
• Network 3: 192.168.0.96 – 192.168.0.127
• Network 4: 192.168.0.128 – 192.168.0.159
• Network 5: 192.168.0.160 – 192.168.0.191
• Network 6: 192.168.0.192 – 192.168.0.223

Note that you cannot use the first 32 or last 32 addresses of the entire 255 address range, (unless you’re using specific equipment that allows it). And there you have it, we’ve calculated our subnet mask, and we’ve worked out the ranges our networks will use. Remember the formula (2^n – 2) and your binary numbers, and you’ll be able to work out any configuration of subnets and networks.

Naturally if you have such a server, you have to have the ability to configure that server. One of the configurations you most likely will need to undertake is the configuring of network settings for a static IP address on your headless, GUI-less server. Fortunately, when using Ubuntu Server 8.10 – that is a piece of cake.

In reality there are two files that must be configured and one file that can be configured. The “must files” are /etc/network/interfaces and /etc/resolv.conf. The “can file” is /etc/hosts. We will deal with the former two files in this article. The latter file (a file that deals with local IP to name mapping) has already been covered in my article “Ease Linux Networking with /etc/hosts” here on gHacks.

So let’s first take a look at the most important file, /etc/network/interfaces. Open that file up in your favorite editor (mine being nano).? What you will most likely see is this:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
iface eth0 inet dhcp

The last line is what you need to edit (and add to.) To configure eth0 (your network device) for a static IP address that last line should resemble:

iface eth0 inet static
address 192.168.1.10
netmask 255.255.255.0
gateway 192.168.1.1

Naturally you will need to change the last three lines to reflect your own networking setup.

Once that file has been edited you can restart your network connection with the command:

sudo /etc/init.d/networking restart

Your Ubuntu Server 8.10 should now be up and running with a static IP address.

DNS

There is one last file you will need to take care of. That file is /etc/resolv.conf. This file is in charge of holding your DNS server addresses. Open this file up in your editor. What you need are two lines:

nameserver 208.67.220.220

nameserver 208.67.222.222

The above example reflects using the OpenDNS servers. Your network will obviously have its own requirements for DNS addresses. Once you have edited that file save it and you’re done (no need to restart networking for the change in DNS addresses to take effect.)

Final Thoughts

That’s it. How simple is it to configure your Ubuntu Server with a static IP address – even when said server is a headless, GUI-less server. Of course there is much more you can do than simple Static IP address configuration, but this just highlights how easy a Linux server can actually be to administer.

Monitored Windows processes get killed at the moment after they are started instead of being blocked outright so that even a start is not possible anymore. A few small scripts can slip through at the moment because of this behavior as it takes some time to recognize a newly launched application and send the kill command to the computer system.

Process Blocker uses a simple text file that is placed in the same installation directory as the main application. This text file contains names of executables that are not allowed to be launched on a computer system. The program itself is added as a Windows Service to the system which has to be restarted after making changes to the text file.

Process Blocker will display a user notification in the Windows System Tray whenever a process has been blocked by the service. A similar application that provides a better user experience is the process manager Process Lasso. The developers of Process Blocker on the other hand are not even halfway through their roadmap. The next step will move the management of processes from the text file to a Group Policy administrative template. Other planned features are killing processes and applications using its crc (in case they get renamed) or full path, recording process errors and information in Windows Event log, allowing users to only run applications from specified folders (e.g. program files and Windows) and changing process killing to process execution prevention.