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Subnetting is a concept that helps you allocate IP addresses efficiently on a computer network. While there are many benefits to subnetting, it can be confusing. Read on to better understand the point of the process and how it works, and click through to read more in-depth networking articles. What is IP subnetting?IP subnetting is a method for dividing a single, physical network into smaller subnetworks, or subnets for short. This is accomplished by manipulating the 32-bits available in an IPv4 address, which can be divided into two parts: a network ID and a host ID.
The number of bits you assign to the network ID allows for either a greater number of total subnetworks or more hosts (devices that can be part of each subnet).With standard IPv4 address classes, there are three network ID sizes: 8 bits for Class A (which allows for more hosts), 16 bits for Class B, and 24 bits for Class C (which allows for more sub networks). However, in many cases, standard sizes do not fit all. Subnetting allows you to have more control over the length of the network ID portion of an IP address beyond the bounds of the standard 8-, 16- or 24- bit lengths, so your network ID can have any size your heart desires and you have more say over the number of host devices per subnetwork.The opposite of subnetting is supernetting, where you combine two or more subnets to create a single, supernet.
You can refer to this supernet using a Classless Inter-Domain Routing (CIDR) prefix. For more information, read. Why subnet?You may feel compelled to subnet for many reasons. Here is a brief summary of the main benefits of subnetting:. To more efficiently allocate a limited IP addresses from a limited range.
To improve network performance. Running lots of network devices on the same subnet can gum up the works, especially if there’s a lot of broadcast traffic. To make IP networks more secure and easier to manage.
Creating multiple networks partitions allows you to confine traffic and network breaches or virus outbreaks.What is a subnet mask?A subnet mask defines which chunk of an IP address is the host ID and which portion is the subnet network ID. This trick is accomplished using a subnet mask, another 32-bit number. A subnet mask works like a filter with the mask identifying the IP address bits that represent the network ID with a 1, and the bits that represent the host ID with a 0. The more host bits you have, the more devices that can connect to your subnet at the expense of the total number of sub networks you can set up, and visa-versa.
The subnet mask is always a string of ones on the left followed by a string of zeroes on the right.Keep in mind that the subnet mask is not the same thing as an IP address. It doesn’t uniquely identify any device or network. It just tells the router which portion of an IP address it should use to figure out the network ID. You can easily spot a subnet mask when it is represented in dotted-decimal notation. They always start with 255, which is not a valid first octet for any class of IP address.Default subnet mask tableEach class of IP address has its own default subnet mask.
The following table gives you a subnet cheat sheet that summarizes these defaults:ClassNetwork prefixDotted-DecimalFirstOctetSecond OctetThirdOctetFourth OctetClass A/8255.0.0.000Class B/16255.255.0.000Class C/24255.255.2000000Even if you do not plan to go outside of the default IP classes, you may need to express you network using a subnet mask. Most operating systems and networking hardware assume that subnetting is being used (because it is so awesome).How does subnetting work?When you subnet a network, how does traffic find its way to its destination?
Let’s imagine a network, with a gateway IP address of 139.12.0.0. Now imagine we split this network into two smaller subnets. The following diagram describes how the network looks with these two subnets.If you're wondering about how to actually subnet an IPv4 network, check out. You might also be interested in. And if you're just looking for tips on how to keep subnetting concepts straight, check our our.So the outside world considers the device at 139.12.16.15 to be a part of the 139.12.0.0 network.
Any packet sent to this device will be delivered to the router at 139.12.0.0. The router then does the work of figuring out the subnet portion of the host ID to decide whether the packet goes to subnet 16 or subnet 28.Calculating subnetsYou can calculate IPv4 subnet addresses by hand if you so desire, but it is much easier to just use a subnet calculator like.This network mask calculator quickly figures out how to optimize your network using subnetting, no matter how many subnets you need. Specify what IP range you’ll use, the number of subnets you need, and let us do the rest.
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