Oneupweb : Basic IP Subnetting
The other day I was attempting to assist a friend with setting up a printer on their network. As I began describing the steps necessary, it became obvious that this person was lacking even the most basic understanding of networking. Somehow, they had a mix of wired and wireless devices connected and were able to connect to the Internet, but they had no idea how or why it worked.
It all started with the question, “What subnet are you using?”—”Huh?” was all I got. This is an important question, because devices need to be on the same network in order to communicate with each other. Different networks require a router to connect and manage the routing between the networks, such as the Internet. We’ll leave routing for another day though.
Most networks are TCP/IP networks, because that is what the Internet uses and most people want to communicate with the Internet—So TCP/IP is king. In addition to being on the same network, each device has to be uniquely identified on the network in order to communicate with each other. Asking what the subnet was, was simply asking what is the network they are using. All devices on a TCP/IP network have IP addresses that uniquely identify them and allow them to find and communicate with other devices on their network. An IPv4 address is a 32-bit number consisting of 4 octets separated by periods. This is used in combination with the Subnet Mask to define the network.
The Subnet Mask defines which part of the IP address is the network portion and which part of it is the host. All devices on the network will have the same network portion of their IP address and as mentioned before, the host portions must be unique. As an example, let’s say the computer has an IP address of 192.168.11.100 with a Subnet Mask of 255.255.255.0, the network portion is the 192.168.11 and the host is .100. To add the printer to this network, it will need to have the same network and a different host. For instance 192.168.11.200 would be OK. Since we are only using the last octet to define our hosts, a quick bit of math tells us that we can have a total of 254 unique hosts on this network which is plenty for most home and small office setups. Now that we know that the computer and printer are on the same network, we can create a TCP/IP printer port that points to the printer so the computer knows how to print to it. Now when you get your new laptop or printer for Christmas, you will know how to assign an IP address that will allow it to communicate with the rest of your network. For additional information on IPv4 addresses, just Google it or check out this Wikipedia article to get the scoop.