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What is a subnet mask?

At first glance, your IP address might look like a bunch of random numbers. However, there is a hidden logic behind this combination, and you don’t need to be a tech expert to crack it. It’s called a subnet mask, and if you’re wondering what a subnet mask is and how to find it, you’re in the right place.

Karolis Bareckas

Karolis Bareckas

What is a subnet mask?

What is a subnet?

There are millions of networks around the world, and they all vary in size. However, the larger a network is, the harder it is to manage and maintain. When a network is divided into smaller pieces, those pieces are called subnets. A subnet is a small network.

Subnetting is beneficial in many ways:

  • Easier maintenance;
  • Advanced network security so that one subnet can’t access the other one;
  • Reduced network traffic;
  • When you can subnet your network, you don’t need to acquire additional IP addresses from ISPs (internet service providers).

However, subnetting often requires additional hardware such as routers, so it also comes with a cost.

Subnet mask explained

IP address explained

Just like every address is defined by a street name and a house number, an IP address consists of a network component and a host component. Let’s take 192.168.123.132 as an example. The first three octets (192.168.123.) represent the network and the last octet identifies a machine on your network.

IP addresses consist of 32 binary bits (4 x 8), but since they are long and complex, we use a dot decimal system.

192.168.123.132 = 11000000.10101000.01111011.10000100

The subnet mask reflects the network portion in an IP address. It might look look something this:

255.255.255.0 = 11111111.11111111.11111111.00000000

When you combine them, you get:

11000000.10101000.01111011.00000000 (network address: 192.168.123.0) 00000000.00000000.00000000.10000100 (host address: 000.000.000.132)

192.168.123.0 is your subnet, while 192.168.123.132 is a destination address (a device in your subnet). However, if you’re using a VPN, your IP will change depending on the server you’re connected to.

What are the different classes of IP addresses?

IP addresses are divided into three classes: A, B, and C. Classes D and E also exist, but they are not used by end users. Each class has a different default subnet mask, and you identify the class by looking at the first octet of an IP address. However, there are also different types of IP addresses: static, dynamic, public, and private.

Class A IP address

Class A networks use a subnet mask of 255.0.0.0 and have 0-127 as their first octet. It allows 126 networks and almost 17 million hosts per network.

Class B IP address

Class B uses a subnet mask of 255.255.0.0 and has 128-191 as its first octet. It is used by medium and large networks. Class B allows around 16,000 networks and 65,000 hosts per network.

Class C IP address

Class C is used for local area networks (LAN) and allows 2 million networks with 254 hosts each. Class C uses a subnet mask of 255.255.255.0 and has 192-223 as its first octet.

Class D IP address

Class D is reserved for multicasting (transmitting streaming media and other data for multiple users). It ranges from 224 to 239 and doesn't have a subnet mask as multicasting is not destined for a particular host.

Class E IP address

Class E ranges from 240 to 255 and also doesn’t have a subnet mask. It is used for experimental and study purposes.

It’s worth noting, however, that the classful IP addressing is outdated. Classless Inter-Domain Routing, or CIDR, is a much more efficient way of allocating IP addresses.

What is Classless Inter-Domain Routing?

Classless Inter-Domain Routing, or CIDR, was introduced in 1993 as a way to get rid of the classful network structure and significantly improve the method of allocating different IP addresses. It also aimed to reduce the stress across routing tables.

A routing table can be found in a router or some other network host. It’s essentially a table of rules and designations that tell a data packet which route it needs to take in a network to reach the desired location. Obviously, as IPv4 addresses spiraled out of control, routing tables needed to grow with them.

While originally planned as a temporary fix to stop the rapid exhaustion of IPv4 addresses, CIDR is still being used over twenty years later.

CIDR is based on variable-length subnet masking, or VLSM. Rather than using a mask to denote which IP address a network belongs to, a specific suffix can be combined with the IP address. This suffix contains the variable number of bits. This shortening of the display allows CIDR to create even more precise and numerous network divisions.

For example, here is a CIDR IP address:

192.168.123.132/12

The prefix is a standard IP address. The suffix (12) tells us how many bits the address has altogether.

The most important feature of CIDR is the ability to create supernets. This is done by combining CIDR blocks, groups of IP addresses with the same bits and network prefixes. By creating a supernet, an organization can reduce the stress on routing devices, while simultaneously saving address space.

The classful network structure eats up IPv4 addresses quickly. CIDR slowed the usage of IPv4 addresses down until the advent of IPv6 addresses, which would take a much longer time to deplete, if at all.

How do you find the subnet mask?

On macOS

  1. Go to System Preferences > Network.
  2. Select your network and click Advanced.
  3. Click on TCP/IP tab and you will find your IP address along with the subnet mask.

On Windows

  1. Go to Control Panel > Network and Sharing Centre.
  2. Click on your network name and then click Details.
  3. You will find the subnet mask along with other network details.

On iOS

  1. Go to Settings > Wi-Fi.
  2. Find the network you’re connected to and click the “i” icon.
  3. You will find the subnet mask along with other network details.

On Android

  1. Go to Settings > Wireless & Networks > Wi-Fi.
  2. Tap on the network you’re connected to.
  3. You will find the subnet mask along with other network details.

What is a subnet mask calculator?

Subnet calculators give users a range of information: a subnet mask, network addresses, an IP class, usable host ranges, and more. There are different types of websites and apps designed to help manage your network and to allocate IP addresses to certain teams.

  • A subnet range calculator provides start and end addresses;
  • An IPv4 to IPv6 converter allows you to convert IP addresses from IPv4 to IPv6;
  • Subnet mask calculators provide users with available subnets and subnet masks;
  • An IPv4 CIDR calculator allows you to enter a subnet range and see IP address information in that range.

Subnet mask cheat sheet

CIDRSubnet maskNumber of IP addressesWildcard mask
/32255.255.255.25510.0.0.0
/31255.255.255.25420.0.0.1
/30255.255.255.25240.0.0.3
/29255.255.255.24880.0.0.7
/28255.255.255.240160.0.0.15
/27255.255.255.224320.0.0.31
/26255.255.255.192640.0.0.63
/29255.255.255.24880.0.0.7
/28255.255.255.240160.0.0.15
/27255.255.255.224320.0.0.31
/26255.255.255.192640.0.0.63
/25255.255.255.1281280.0.0.127
/24255.255.255.02560.0.0.255
/23255.255.254.05120.0.1.255
/22255.255.252.010240.0.3.255
/21255.255.248.020480.0.7.255
/20255.255.240.040960.0.15.255
/19255.255.224.081920.0.31.255
/18255.255.192.0163840.0.63.255
/17255.255.128.0327680.0.127.255
/16255.255.0.0655360.0.255.255
/15255.254.0.01310720.1.255.255
/14255.252.0.02621440.3.255.255
/13255.248.0.05242880.7.255.255
/12255.240.0.010485760.15.255.255
/11255.224.0.020971520.31.255.255
/10255.192.0.041943040.63.255.255
/9255.128.0.083886080.127.255.255
/8255.0.0.0167772160.255.255.255
/7254.0.0.0335544321.255.255.255
/6252.0.0.0671088643.255.255.255
/5248.0.0.01342177287.255.255.255
/4240.0.0.026843545615.255.255.255
/3224.0.0.053687091231.255.255.255
/2192.0.0.0107374182463.255.255.255
/1128.0.0.02147483648127.255.255.255
/00.0.0.0 4294967296255.255.255.255

Why should I hide my IP address?

Having your IP address publicly exposed is a risky business. It’s like driving around the city in a Ferrari with your home address written on the hood.

NordVPN masks your IP address and encrypts traffic, thus enhancing your security and privacy. It’s an easy-to-use app, allowing you to secure up to 6 devices. With a VPN turned on, your traffic is redirected through an encrypted tunnel, which is your safe harbor.

  • Hiding your internet activity from ISPs. Your provider could choose to throttle your connection based on your online activities. They can’t choose to throttle you if they can’t see what you’re up to.
  • To hide your physical address. Some hackers with enough tech-savvy can determine your physical location based on your IP address.
  • Staying secure on public Wi-Fi. Public Wi-Fi can be notoriously patchy when it comes to security. By hiding your IP address before connecting to it, you remove yourself from the list of other potential victims on the network.

When it comes to cybersecurity, it’s always best to stay ahead of the curve. Having a proactive attitude towards your online security will keep you a step ahead of any hackers or snoopers.

Online security starts with a click.

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Karolis Bareckas
Karolis Bareckas Karolis Bareckas
Karolis is a tech geek who writes about cybersecurity, online privacy, and the latest gadgets. When not rattling his keyboard, he’s always eager to try a new burrito recipe or explore a new camping spot.