Free Subnet Calculator

What is subnetting?

Subnetting is the process of breaking down a single network into one or more smaller networks called “sub-networks” or “subnets” for short. The process of subnetting was initially created to solve the shortage of IP addresses over the internet but has since evolved into an IP management best practice for IP network utilization.

Every IP address is comprised of three different classes or major networks – Class A, Class B, and Class C. Without subnets, you’d only be able to use one network from each class, which isn’t the most efficient way to work.

Subnetting allows network administrators to take bits from the IP address’s host part and use these bits to create smaller networks inside the network. These smaller networks are built up of many other IP addresses sharing the same IP routing prefix as the original IP address used to create the subnets. Once you have these smaller networks, you create a network of interconnecting subnetworks to distribute your network’s load more efficiently.

It’s critically important for network administrators in large enterprises to subnet because reorganizing the network in such a way makes it more functional. For a single IP subnet to handle everything happening in a large enterprise, it would have to be incredibly large—which means it would be inherently unwieldy.

You might end up with:

• Unnecessary network traffic from hosts handling broadcasts sent over a single subnet
• Network security concerns caused by secured and unsecured servers using the same subnet
• A poorly organized overall structure

What is a subnet mask?

A subnet mask is a 32-digit number determining the possible range of IP addresses available in a network. One subnet mask limits how many IP addresses can exist on a single network, but multiple subnet masks can be used to organize an entire network into sub-subnets.

A subnet mask also indicates which part of the IP address refers to the host and which part refers to the subnet. Class A, B, and C networks have default masks, and an IP address on an unsubnetted Class A, B, or C network would have an address/subnet mask pair similar to the default mask. To find which part is the host and which part is the subnet, you must convert both numbers to binary numbers. This makes it easier to differentiate the host from the subnet. Address bits corresponding to 1 in the IP class’s default mask represent the subnet, and address bits corresponding to a 0 in the default mask represent the host.

One popular way of representing a subnet mask is by using Classless Inter-Domain Routing (CIDR) notation. The notation is simply a count of how many network bits (which are set to 1) there are within the subnet mask. So if there are 8 bits in the subnet mask, the CIDR number is 8. When it comes to notation, the CIDR number will usually follow the IP address and will be separated from it by a slash.

CIDR notation is popular not only because it works easily with a subnet mask calculator, but also because it’s more concise than other notation methods like Dotted Decimal notation.

By using CIDR notation, our subnet mask calculator can help you easily find the subnet mask—no binary code conversion necessary.

Why should I subnet a network?

You should use a network subnet calculator to subnet your network for three primary reasons.

1. Organizational Efficiency: When it comes to partitioning a large enterprise’s network and dividing resources accordingly, subnetting the network gives you several different options. For example, if you divide your network into subnets based on departments, you’ll be able to easily identify which department is having problems by looking at the IP address alone. This facilitates faster troubleshooting and makes it easier for you to find info related to a specific department. Subnetting with the help of a network subnet calculator allows you to compartmentalize and organize your network in a logical manner.
2. Network Security: One of the biggest disadvantages of working within an unsubnetted network is it can compromise network security. When devices use the same subnet, these devices can freely communicate with one another and share information. This can pose a problem if a server containing sensitive information and an employee workstation share the same subnet. At best, an employee might accidentally gain access to confidential information. At worst, a cyberattacker could gain access to confidential information and critical systems housed on the subnet by leveraging access to an employee workstation. Subnetting allows you to set and maintain clear barriers within the network to control departmental access.
3. Operational Efficiency: Network administrators first started subnetting because creating and setting aside millions of unused IPv4 was a waste of time and effort. Extending the range of your IP addresses by creating subnets helps you scale and makes your network more functional. If you have too many subnet masks, changing the size of the subnet by adjusting the subnet mask will free up more IP addresses for other subnets. Subnetting makes better use of your organization’s existing IP addresses and network resources.

These three benefits are only the beginning when it comes to subnetting—a network subnet calculator can help you unlock even more.

How to calculate a subnet?

Without a subnet calculator, you can subnet IP address manually using the binary method. To make a Class A, B, or C default subnet mask larger, convert the subnet mask to a binary number and borrow bits from the host ID portion of the IP address to create a subnetwork ID. After your calculations, you’ll be left with a list of possible subnets to use in your network.

If you don’t need the exact IP addresses of possible subnets but instead need to know how many subnets are contained within a given IP address, you only need a simple equation. Two to the power of x equals the number of subnets, in which x is the number of subnet bits. If the IP address has three subnet bits, then you can have two to the 3_rd power of subnets, or eight total subnets.

Not only is it time-consuming to manually calculate the full IP addresses of possible subnets, but it’s also an error-prone process. A subnet calculator automates the process of calculating a subnet and helps ensure an accurate result. Try out the IP address calculator above to see the benefits for yourself!

What is the difference between IPv4 and IPv6 subnetting?

Broadly speaking, the purpose of subnetting is to take a network and split it into multiple smaller networks to free up more public IP addresses and to simplify network security and management since networks are now segmented.

IPv4 and IPv6 subnetting are quite similar when it comes to their basic IP subnetting principles. Both should be thought of as binary and both can be simplified with the use of an IP subnet calculator. The only significant difference between the two comes down to scale and, to a lesser degree, their complexity. Unlike IPv4 addresses, IPv6 addresses are 128-bit in length. That includes 16 bits specifically designated for subnetting, which come after the most significant 48 bits that are already allocated to the network identifier. That means the most important 64 bits represent the network identifier, while the less important 64 bits are representative of the host identifier.

IPv4 subnetting came before IPv6 subnetting and, as such, is a bit more complicated in some areas. It began with a subnet mask that used dotted quad notation, but was later replaced by CIDR notation. IPv6 subnetting doesn't have a subnet mask at all, but instead has a Prefix Length, sometimes just called a “Prefix,” which works similarly to CIDR masking in that both denote the number of bits in the address that define the network it exists in. The prefixes used in IPv6 can be any number between 0 and 128, but they’re most often multiples of four.

A subnetting calculator like this one can work with both IPv4 and IPv6.

What is a supernet calculator?

A supernet calculator is a type of IP address calculator just like a subnet calculator, but instead of dealing with subnets it calculates supernets. To understand that distinction, it’s important to define a supernet.

Subnets or multiple networks that are combined into a single network with a single CIDR mask are called supernetworks, or supernets. The supernet’s common routing prefix is an aggregation of the prefixes from the given subnets or networks. It must be the same length or shorter than the smallest component network prefix in the supernet.

The process of creating a supernet is called routing aggregation or supernetting. It was introduced to solve the problems of rapidly growing routing tables and IPv4 address pool exhaustion. The main advantages of the process are fewer CPU power and memory requirements for processing and storing routes since there are now fewer routes to begin with.

A supernet calculator is a form of IP calculator that focuses just on the supernet and not on the individual subnets that it may contain. When you input networks into the IP calculator, it will summarize the supernet and exclude any invalid networks.

What are the difficulties connected to subnetting?

The process of subnetting simply means creating a subnetwork (or subnet) within a network. All of the network devices and interfaces within a subnet can communicate directly while routers facilitate communication between multiple subnets. An IP range calculator can deliver insights into individual subnets to simplify management.

Subnetting offers a number of benefits including better network performance and stronger network security. However, it also has some limitations. These include:

• Needing a router to communicate between subnets—if a router is poorly configured or failed, your organization’s network can suffer
• IP addresses can be wasted given that every subnet needs dedicated IP addresses as subnet IDs and broadcast addresses
• The potential for unnecessary complexity that interferes with the effectiveness of your network administration if you create too many subnets

Luckily, all of these difficulties can be addressed with the right tool. In addition to offering a powerful free subnetting calculator, SolarWinds also offers SolarWinds^® IP Address Manager (IPAM), management software that’s designed to make administrators’ lives easier while helping your network run more smoothly. IPAM not only makes subnetting (and managing subnets) simpler, helping you prevent the potential limitations of the process, but it also includes IP scanning, monitoring, and alerting features that ensure you’re aware any time an error arises within your subnets.

You can try IPAM free for 30 days.