IP addresses and subnet masks can be a tough concept to grasp for network administrators just starting out in the field. And getting them wrong can have devastating effects either immediately with the routing process or down the line with IP address depletion. It is important to get it right the first time. This is why we’re presenting the 10 best subnet calculators to help you with that.
Today, we’ll first briefly explain how IP addresses work. Then, we’ll discuss subnetting and subnet masks. Since our discussion wouldn’t be complete without explaining classful addressing and CIDR, this is what we’ll do next. And before we dig into our core subnets, the best subnet calculators, we’ll explain the difference between public and private networks.
IP Addresses — Hosts And Networks
IP addresses, or Internet Protocol addresses, are used to uniquely identify each host, or device, connected to a network. That network could be as big as the Internet with millions of hosts or as small as your typical home network with just a handful of hosts.
IP addresses are binary numbers that are 32 bits long. Since it could be tedious and error-prone to write IP addresses in their binary form–such as 11000000101010000000000001101010–we devised a way to write them as a sequence of four decimal number, each representing eight bits, separated by a dot. Using this scheme, the previous address would be written as 192.168.0.106. Much easier to write, read, and remember, don’t you think? This notation is referred to as dotted decimal.
There are two parts to an IP address, the network part, and the host part. The first part specifies the subnet where that address is located while the host part specifies the exact host on that network. If IP addresses were postal addresses, the network part would be the city name and the host part would be the actual street address.
Now, you may ask yourself: which part is the network and which is the host? Well… you decide. Keep reading.
What You Should Know About Subnetting
Subnetting is the “art” of dividing a network into smaller parts, each called a subnet. Let’s say, for example, that your organization’s IP address is 10.11.0.0 and that the 10.11 part is net network part. That leaves you with a potential of 65534 hosts, from 0.1 to 255.254.
There are, however, many reasons why you should avoid big networks with thousands of hosts. In the early days of networks, when they were operating on coaxial cable, it had to do with collisions. You see, all hosts on a network “talked” on a common wire. Only one host could talk at a time. But hosts had no way of detecting if the cable was in use. They had, however, a way to detect that two devices had talked at the same time. That event was called a collision and, when it happened, both devices stopped talking for a random albeit very short amount of time and started talking again. You can imagine that, when collisions were too frequent, performance was adversely affected.
Nowadays, networks are switched and collisions don’t exist anymore but still, we try to keep networks as small as possible for another important reason, broadcasts. Broadcasts are packets of data that are received by all hosts on a network. Many communication protocols rely on them for different purposes and there can be lots of them on a network. And while the effect may not be as dramatic as high collision rates, they do slow down networks.
So, back to our example, we could decide that we want to split the 10.11 network into 255 networks of 254 hosts each. In our subnetted setup, the network part would then become 10.11.0 and the host part would be the final 0.
Now that we’ve elected to split a network into several subnets, how do we do it? How do we let equipment know which part is which? We use a subnet mask. A subnet mask will identify how many of the 32 bits are reserved for the network and how many are reserved for the host. To get back to our previous example, the subnet mask would be 11111111111111111111111100000000 indicating that the first 24 bits represent the network part and the last 8 represent the host part. Using the dotted decimal notation, we’d write this mask as 255.255.255.0.
In the recent years, a new notation has surfaced to facilitate writing subnet masks. Instead of specifying an IP address followed by a subnet mask we write the IP address followed by a forward slash and the number of bits in the network part of the address. Back to our previous example, we’d write 10.11.0.0/24
Classful vs CIDR
Back in the early days of the Internet, subnet masks were predefined according to the class of IP address. All addresses were categorized into 5 classes, A, B, C, D, and E. Class A addresses started with 10. and always had 255.0.0.0 as their mask. Class B addresses started with 127. and always had a subnet mask of 255.255.0.0. Class C addresses started with 192.168 and always had a subnet mask of 255.255.255.0. As for classes D and E, the former is used for multicasting and the latter is not used.
This was practical as you never had to specify the subnet mask. It was implied according to the IP address class. Eventually, network manager started to find IP address classes too restrictive and CIDR, or Classless Inter-Domain Routing was invented. With CIDR, admins could specify any subnet mask with any IP address.
Private vs Public Networks
This was especially useful with private networks. While IP addresses were originally created for the Internet and originally, every host connected to it used a public IP address with no two hosts having the same address, it quickly became obvious that a shortage of IP address was bound to happen sooner or later. Think of huge corporations with tens of thousands of computers and it’s easy to see how it could have been a problem,
This is why organizations starting to use private networks that do use IP addresses but in a private context. Their IP addresses do not have to be unique outside the organization. Today, even small networks use private addressing, For example, most home networks use the 192.168.0.0/24 network. The local Internet router is in charge of address translation, converting internal IP addresses to public ones and back.
The Ten Best Subnet Calculators
Since calculating IP addresses and subnet masks and subnetting networks can be a challenge to many beginning network administrators, several subnet calculators have been created. They can be very handy in optimizing IP address usage and ensuring that your IP addressing is done correctly. We’ve searched the web for the best of these and we’re presenting our top ten finds. Although we weren’t necessarily looking free software, it turns out that the best ten are all available free of charge.
Our first entry is from SolarWinds, a well-known company that makes some of the best network administration tools. The company is also known to publish several very useful free tools. Its Advanced Subnet Calculator is one such tool. In the early stages of being a network administrator, when one is starting out, this is often how many are introduced to SolarWinds.
The Advanced Subnet Calculator–which runs on Windows–can be used to find available addresses and save you a lot of time. It features an IP calculator, a subnet creator, and a CIDR calculator. It can also generate address lists for subnets and do forward and reverse DNS resolution–which has nothing to do with addressing per se but still is a very useful feature.
FREE TRIAL of Engineer’s Toolset from SolarWinds at https://www.solarwinds.com/engineers-toolset/
(contains the Advanced Subnet Calculator)
2. Tech-FAQ Subnet Calculator
Technology website Tech-FAQ published its own subnet calculator. It is a free utility that runs on Windows The software has three tabs. On the first one, you’ll find a classic subnet calculator that will help you figure out classful addressing and subnetting. The next tab is similar but it is specifically for CIDR addressing and subnetting. And on the last tab, you’ll find a wildcard mask calculator, another useful tool.
The tool uses Java so you’ll need to download and install Java from its own website prior to installing this software. Other than that prerequisite, installing the utility should be an easy task.
3. Subnet Ninja
The Subnet Ninja is a simple yet useful tool. Contrary to our previous entries, this one requires no installation as it is web-based. You can, therefore, use it from any device that has a web browser. That makes it usable from mobile devices, for instance.
Using the tool could hardly be easier. You simply enter an IP address and subnet mask. You can also enter CIDR slash notation–such as “/27” in lieu of a subnet mask. You then click the “Calculate” button and you’re presented with the results, a table with most of the information pertaining to the specified subnet. You’ll get the network address, the broadcast address, the first and last host addresses and a handful of other useful data.
4. Spiceworks Subnet Calculator
The Spiceworks Subnet Calculator is another on-line web-based calculator. It is simple and basic and using it is easy and intuitive. The tool is best used to subnet a range of IP addresses. Let’s say, for example, that your organization’s assigned IP addresses range from 10.11.0.0 to 10.11.255.0. Once you browse to the calculator’s page, you enter the first and last IP addresses. Then, you have the option to either specify the number of subnets you require or the minimum number of hosts you need in each subnet.
You then click the “Generate” button and a table specifying the parameters of each subnet is generated. For each subnet, it will give you the network address, the first and last available IP addresses and the subnet mask.
5. Online IP Subnet Calculator
The Online IP Subnet Calculator is another free online tool. It is actually very similar in look and functionality to the Tech-FAQ subnet calculator introduced earlier. At first glance, you’d be tempted to conclude that it only deals with classful subnetting but, if you read the small print to the right of the calculator, you’ll find that there are actually three different tools available.
The calculator enables subnet network calculations using network class, IP address, subnet mask, subnet bits, mask bits, maximum required IP subnets and maximum required hosts per subnet. And from the calculator, you can access the CIDR calculator, the supernet calculator, and the ACL wildcard mask calculator, three more useful tools that complete this one nicely.
6. Subnet Calc
If you’re a Macintosh computer user, the Subnet Calc is for you. It runs on Mac osX and provides all the subnet calculating you may need. It is an open-source project released under the GPL license. It supports both classful and CIDR subnetting. And like most Mac tools, it has a nice looking user interface.
A functionality we particularly love with this subnet calculator is the possibility to export all calculated subnets to either the clipboard or to a CSV file.
7. VLSM (CIDR) Subnet Calculator
The VLSM (CIDR) Subnet Calculator is another free online calculator. As its name implies, it specializes in variable length subnetting, which is just another name for CIDR. To use it, you first enter the IP address that you want to variably subnet in CIDR notation. For example, you could enter 10.11.0.0/22. You then need to specify the number of subnets you need–the default is set to 6–then click the “Change” button. Next, you fill in the size of each subnet you require. That’s the maximum number of available IP addresses you’ll need in each subnet. You may also supply a name for each subnet if you want. When you’re done filling the form, you simply click the “Submit” button.
The result you get is a table with the parameters of each of the subnets. You’ll see the network address, the subnet mask, the range of assignable IP addresses and the broadcast address of each subnet.
8. IP Calculator
The IP Calculator is also an online calculator. the functionality it provides is very basic but its usage is simple. The tool takes an IP address and netmask and calculates the resulting broadcast, network, Cisco wildcard mask, and host range. Furthermore, By giving a second netmask, you can create subnets and/or supernets. The IP Calculator is also intended to be a teaching tool. As such, it also presents the subnetting results as easy-to-understand binary values.
Let’s say you want to subnet the 10.11.0.0/22 network intro several /28 subnets. All you need to do is enter 10.11.0.0 as the IP address, 22 as the first netmask and 28 as the second one. You then click “Calculate” and you’re presented with the detailed specification of each of the possible subnets. This is not only an online tool and you may download a Linux package to install on a local machine if you prefer.
Contrary to all other entries on our list, Sipcalc is a command-line utility for Linux computers. As such, you can expect its learning curve to be somewhat steeper. Once you master its ropes, though, it is a very powerful and efficient tool.
sipcalc -d -bcix -n 4 -e -r -t lo 220.127.116.11/28 -6 www.6bone.net -[ipv6 : 3ffe:b00:c18:1::10] - 0 [IPV6 INFO] Expanded Address - 3ffe:0b00:0c18:0001:0000:0000:0000:0010 Compressed address - 3ffe:b00:c18:1::10 Subnet prefix (masked) - 3ffe:b00:c18:1:0:0:0:10/128 Address ID (masked) - 0:0:0:0:0:0:0:0/128 Prefix address - ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff Prefix length - 128 Address type - Aggregatable Global Unicast Addresses Network range - 3ffe:0b00:0c18:0001:0000:0000:0000:0010 - 3ffe:0b00:0c18:0001:0000:0000:0000:0010 [V4INV6] Expanded v4inv6 address - 3ffe:0b00:0c18:0001:0000:0000:000.000.000.016 Compr. v4inv6 address - 3ffe:b00:c18:1::0.0.0.16 [IPV6 DNS] Reverse DNS (ip6.arpa) - 0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.18.104.22.168.8.1.c.0.0.0.b.0.e.f.f.3.ip6.arpa.
While this might not be for everyone, we felt we had to include it on our list as it is possibly the only command-line tools for IP addressing calculations.
10. IP Subnet Calculator
Our last entry, the IP Subnet Calculator is, despite its similar name, a very different product from our number five, the Online IP Subnet Calculator. For starters, this is not an online calculator. It is a piece of software that you need to download and install on a computer running Windows. It is also said to be executable under Linux/Mono.
The tool’s user interface is easy to comprehend and use. You fill in the IP address and subnet mask, click the “Start” button and see the resulting subnets displayed on the left side of the tool’s window.
No matter which one of these tools you choose, all will provide some welcome assistance. Some will event built complete IP addressing plans and let you export the data or copy and paste it. And with several of these available online, you often don’t even have to install anything on your computer. And last but not least, since all these tools are free, you can try them all and see which one is the best for you. You could even device to use a combination of them for greater functionality.