SUBNNETTING | How to Subnet a Network? | Part 1 - For the IP Beginners |

How to Subnet a Network? | Part 1 - For the IP Beginners 

IP Network Addresses

          To understand network IP addressing, let’s take a look at postal addresses. Every building must have its own unique address in order for mail to be delivered. An address consists of different parts such as the street, number, and city. In a network, every device must have its own unique IP address. That is, every network device (printer, server, router, etc.)
must be identified with a separate IP address.

Many Devices or Hosts

                       Using the postal example, think about an apartment building. In order for the mail to arrive at the right apartment, each apartment must have its own unique identifier (apartment number) in addition to the street name and address.

           With IP addresses, an organization is assigned a unique IP network, such as 192.168.1.0, but a single IP address must be assigned for each network device. For example, let's assume that ABC company has 5 devices in one of their buildings that need IP addresses, and that ABC is assigned the network address 192.168.1.0. The IP addresses could be assigned as follows:

Device 1 (router): 192.168.1.1
Device 2 (office printer): 192.168.1.2
Device 3 (Ms. Chung's laptop):  192.168.1.3
Device 4 (Receiptionist's computer): 192.168.1.4
Device 5 (company server): 192.168.1.5

Hosts .1, .2, .3, .4, and .5 are all on the 192.168.1 network, just as apartments 1, 2, 3, 4, and 5 might be located in the apartment building at 123 First Street.


           When you see an IP address, you will always see another number associated with it that looks something like one of the following:

♦ 255.255.255.0
♦ 255.255.0.0
♦ 255.0.0.0

                  This number is called the subnet  mask. A subnet mask is used to show  which portion of the IP address identifies the network and which portion identifies a specific host on the network. This may seem unnecessary at first since the first three numbers of an IP address starting from the left (such as 192.168.1) always identify the network, and the last number (such as .1) always identifies an individual device in networks like the one in our example, which is called a standard Class C network. However, this is not true for other networks. That's why subnet masks are used to differentiate the network portion of the address from the host portion. The following table shows the subnet mask 255.255.255.0, which is always the subnet mask for a standard Class C network, applied to one of our example addresses. Notice how the mask reveals which portion of the string 192.168.1.1 is the individual host address.

NOTE: Class C addresses have a number from 192 to 223 in the first octet.

           Network portion                   Host portion                                

           192             168               1                    1                                 
            255             255             255                  0                                

              The number 255 indicates that the corresponding section of the address is part of the network address. The 0 indicates that the corresponding section is the host portion of the address.


             This document and the Subnet game refer only to Class C networks. Once you understand IP addressing for Class C networks, it will be much easier for you to understand IP addressing for any network.