Just a little bit of theory

IP classes

There are 3 different classes of networks: A class networks, B class networks and C class networks. As said before, any IP address consist of 4 triplets of digits separated by dots. Each triplet is the decimal representation of 1 byte actually. So 4 bytes are needed to define an IP address. 4 bytes are equal to 32 bits. 1 byte can represent up to 2⁸ = 256 different values. '0' is a value too, so a generic IP address can range from 0.0.0.0 to 255.255.255.255.

With A classes, first triplet on the left represents the network whereas the other 3 triplets on the right represent hosts.

                                           --------------------->  HOST
               |
                -----------
            XXX.yyy.yyy.yyy
---
 |
                  |--------> NETWORK


With B classes, first  2 triplets on the left represent the network whereas the other 2 triplets on the right represent hosts.

                                          --------------------->  HOST
               |
                -------
        XXX.XXX.yyy.yyy
-------
  |
                   |--------> NETWORK


With C classes, first  3 triplets on the left represent the network whereas the other triplet on the right represents hosts.

                                               --------------------->  HOST
                    |
                    ---
        XXX.XXX.XXX.yyy
   -----------
    |
                     |--------> NETWORK

But, didn't this guide have to be 'practical'? Of course, but a little of theory was needed! ;o) Go on to the practice. If you want to set up a home computers network or, better, a LAN (Local Area Network) you can't use any IP address. You have to use a particular range of IP addresses. IANA in fact, has reserved 3 specific ranges of IP addresses for private networks (LANs): from 10.0.0.0 up to 10.255.255.255 (i.e. 1 class A network) from 172.16.0.0 up to 172.31.255.255 (i.e. 16 class B networks) from 192.168.0.0 up to 192.168.255.255 (i.e. 256 class C networks) (refer to the RFC1918 for more information). 10.x.x.x addresses are designed for large networks (not little home LANs) that's networks up to 3354443 different computers (class A networks)! 172.16.x.x addresses are designed for smaller networks (but not for little home LAN again). 172.16.x.x addresses can manage up to 16 different networks, each of them containing up to 32766 different computers (class B networks). Finally, 192.168.x.x addresses are designed for little networks (LANs of course!). 192.168.x.x addresses can handle up to 256 class C networks. Each network can contain up to 254 different computers. Finally, there are 2 special IP addresses: 0.0.0.0 (the default route) and 127.0.0.1 (the local loop or loop back). Each computer is named 'host'. Notice that 'networks' and 'hosts' are not the same thing! For example, 192.168.1.1 is a host whereas 192.168.1.0 is a network. Again, 192.168.3.0 is a network whereas 192.168.3.1 is a host. But 192.168.3.255 is not a host! In fact the '255' value is used to send messages to *ALL* computers connected to a specific network (broadcast address). So 192.168.3.255 is an IP address used to transmit information to all hosts inside of the 192.168.3.0 network. So there are 256 networks from 192.168.0.0 up to 192.168.255.0. Each triplet is a byte represented in decimal form and its values can range from 0 up to 255. As said before 192.168.3.0 is a network, so you can't use 0 as the last digit to identify a host. The value 255 is used for broadcasting so you can't use it to identify a host. Hence, you can identify 254 different hosts only. Anyway, a specification is needed: IP addresses identify interfaces, not hosts actually...An interface is a network card (Ethernet card). In fact if you want to connect your computer to any network, it must have at least one network card.

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