A subnet mask is essensially a mathematic tool that allow you to divide an IP address pool into smaller sections, or subnets. If many device are attached to a network, they will frequently send broadcast traffic to other device on that network. If a network do not use subnetting, the broadcast traffic from all of the device on the network will flood the network, causing it to slow down in performance.
Subnetting, however, allow organizations to divide an IP address pool into smaller groups of subnets. This process ensures that the traffic that flow between device within one group will not effect the traffic from other group on the network. An IP address consist of two parts: the network bits and the host bits.
How Subnet Masks Work
The subnet mask will help to determine which portion of an IP address are comprised of network bits and which portion of an IP address consist of host bits. The network bits will identify the network to which a device belong, while the host bits identify the specific device from that network. By borrowing bit from the host portion of an IP address, an organization can create additional subnet.
However, by borrowing bits from the host portion of an IP address, the number of device that can be added to each subnet will decrease. Since bits are represented as powers of two, subnetting itself is based upon powers of two as well. By using a subnet mask to divide an IP address pool, an organization can create separate subnet to which different type of device can be attached to the network.
For instance, a subnet can be created for guest user of a location, while a separate subnet can be created for the work machine that may be located at that same location. While it may seem like using subnets for an organization reduce the total number of available IP address for device on the network, it actualy ensures that traffic from device does not interfere with the traffic from other device on the network. Furthermore, the first IP address within a subnet is the network ID for that subnet, while the last IP address in a subnet is the broadcast address for that subnet.
Since these two address cannot be assigned to a device, an organization must subtract two from the total number of available address in a subnet to determine the number of device that can be added to that subnet. Subnetting itself can be understood through the use of binary math. A subnet mask can be represented as a string of one and zero.
The ones represent the portion of an IP address that represent the network, while the zeros represent the portion of an IP address that represents the host of that network. The prefix length of a subnet mask is represented by the number of ones in the binary representation of the subnet mask. By understanding the math behind binary, an organization can calculate the size of the subnet that can be created in their network.
Furthermore, by understanding the math behind binary, an organization will also understand how many device can be added to those subnet. Organizations of different size have different need regarding their IP subnet. The size of each subnet that is created within a network will depend upon the number of device that are to be added to that network.
Small organization may only require one subnet for the device in that organization. However, medium and large organization may require more subnet to provide for the device in those organization. Should an organization select a subnet that is too small for the device that are to be added to that network, it will eventually run out of IP address for those device.
In contrast, should the organization select a subnet that is too large, there may be too much broadcast traffic on the network. Variable Length Subnet Masking, or VLSM for short, is a process that allow for different size of subnet mask to be used on a network. Through the use of VLSM, an organization can allocate a small subnet mask to a point-to-point link between two network, while also using a much larger subnet mask for a subnet that must accommodate many device.
Through VLSM, the use of IP address is made more efficient by allocating IP address to each network according to the need of each network. However, care must be taken when implementing this process, as any misstep in planning can lead to the IP address being fragmented into small subnet that are not of great use to an organization. To avoid fragmentation of IP address, the subnet mask that is used on a network should always be constructed with number that are based off powers of two.
Furthermore, a subnet mask should always follow the rule of binary math. A variety of different software tool can be used to assist in the management of subnet. Software tool and calculator can help to reveal any error in a network before the hardware is configured for the device on that network.
One such tool is a subnet calculator, which will reveal the network ID for a network, the broadcast address for that network, and the number of usable IP address for the device on that network. Additionally, this tool will help to avoid the issue of overlapping subnet. Ensuring that the gateway for a network is configured correct will allow device on that network to communicate with device on other subnet.
Through the proper use of subnetting, an organization will be able to control the traffic that flow through their network, as well as easily scale that network as they add new device.