The main goal of this article is to explain to you what is (or 19216811) IP address, why is it important and why do you need it but in the process, we are going to explain so much more in order to come to this subject. So, concentrate and try to follow and you will find out all you need to know about networks, internet protocols, public and private IP addresses. In the end, you will have much better understanding of IP addresses and of this particular IP address.

Invention and First Use of IP Addresses

Our story begins in 1970. Back then, there was no standard method for networks to communicate. This was one of the crucial prerequisites for the internet to evolve and become global network as we know it today. So, the networks had to be able to communicate with each other and every device had to be able to communicate with any other device. Thanks to two guys – Vint Cerf and Bob Kahn and their work, the standard for communication was established and it was named Internet Working Protocol (or Internet Protocol). This standard was the base for development of the thing we now call the Internet.

So, what is internet today? It can be described as a system of millions interconnected networks all over the world. All those networks communicate with each other thanks to IP (Internet Protocol). Let’s say you have a laptop or a phone. You connect your phone or a laptop to a router through Wi-Fi; that router is connected to your Internet Service Provider (ISP) and ISP connects you to billions of other devices around the world through all those interconnected networks. Internet Protocol is, in fact, a number of rules and standards, which allows the communication between devices if they accept those rules.

What is Actually an IP Address?

Just like every phone has its own number, and every house has its address (state, city, street, number) as well as geographical location (longitude and latitude), every device on the internet has its own address. That address is a number (just like a phone number, or your home number, but a little bit different). Every device must have it in order to communicate with other devices on the internet. In order to send a letter to someone, for example, you don’t have to know his/her exact name but you do have to know the correct address. The same rule applies to devices on the internet. These addresses are assigned to all of your devices (and all devices in the world) in accordance with Internet Protocol (IP). That’s why we call them IP addresses.

Whenever you access some website, what really happens is that your computer is trying to communicate with some other computer. Your computer then sends a message (or an inquiry, if you want) along with its own IP address so the other computer could know where to send the feedback.

You have probably seen an IP address before. That’s actually a group of four numbers separated by dots (like Each of those numbers can have any value from 0 to 255. Since every data on the internet and on every computer is digital (zeros and ones), these decimal notations (these four numbers separated by dots) are in fact four 8-bit groups (32 bits in total).

So, IP address is in fact 11000000.10101000.00000001.00000001 when you translate it into bits.

Every computer, phone, iPad, router, as well as every website on the internet, has its own IP address made of 32 bits.

Internet Protocols – IPv4 and IPv6

The protocol used to assign a 32-bit IP address to every device is called IPv4. There is one big flaw in this protocol. When it was invented in 1973, no one could predict how big will internet be. With 32 zeros and ones, it is possible to assign only limited number of IP addresses. That number is 4, 294,967,296 or 232 (nearly 4.3 billion). In 1973, that was a huge number of IP addresses, but with the expansion of internet and the expansion of human population (there are 7.5 billion people living on Earth), this number will be insufficient in a few years (a decade at most). It’s, in fact, already insufficient but there were some tricks that allowed multiple computers to use the same IP address and we are going to talk about this later. That’s why new version of IP protocol is invented. This protocol assigns new and larger IP address to every device. The new IP address consists of 128 bits instead of 32 and it consists of eight 16-bit sequences. These sequences are not separated by dots but with colons.

Every 32-bits IPv4 address can be translated to IPv6. For example: = 0:0:0:0:0:FFFF:C0A8:0101

If you want to know how would 0:0:0:0:0:FFFF:C0A8:0101 look in binary form, here is an answer:


But, this IPv6 protocol can also be used for assigning completely new IP addresses.

If you see some IPv6 address in binary form, you will notice that it is much longer than any IPv4 address (see the example above), so there are much more possible combinations of zeros and ones. In other words, there are much more possible IP addresses. To be precise, there are 2128 possible IP addresses (that’s 3.4 *1038 or 340 undecillions, and yes, undecillion is a real number).

We are now in transition period from IPv4 to IPv6 addresses, and this transition will last for at least a few years. So, we are stuck with IPv4 addresses for now and we are going to focus our attention on IPv4 protocol and IP addresses assigned in accordance with it.

Classes of IP Addresses

As you already know, there are almost 4.3 billion of IPv4 addresses. 4.3 billion is still a huge number, and that’s why all the addresses, from to, are divided into 5 classes – A, B, C, D, E.

Class A includes IP addresses ranging from to

Class B includes IP addresses ranging from to

Class C includes IP addresses ranging from to

Class D includes IP addresses ranging from to

Class E includes IP addresses ranging from to

Before we start explaining these classes, you should know that there are some special IP addresses:, 127.x.x.x (every IP address from to, and

We are going to dedicate another article to this one. For now, you should know that this one is also known as default network and it’s used for routing.


All the addresses from this range are known as loopback addresses or localhost addresses. They are used for web servers, and if you don’t have a web server you won’t have any benefit from these addresses. When you type in any of these addresses in your browser, you will get an error message unless you have a web server. By typing one of these IP addresses, you are actually trying to communicate with your own device.

This is one more special address also known as the broadcast address. All the hosts connected to one network can receive the message sent to this address.

CLASS A addresses

This type of addresses usually belongs to large companies. There are only 126 Class A networks and only the largest companies can have those IP addresses (multinational companies, for example). One Class A network offers up to 16.8 million different IP addresses.

CLASS B addresses

Class B addresses are usually given to Internet Service Providers (ISP) and other large companies. There are 16,384 available Class B networks and inside every network, there are 65,534 available unique IP addresses.

CLASS C addresses

These addresses are assigned to smaller companies. There are more than 2 million different class C networks (2,097,152 to be precise) with 255 unique IP addresses within every network.

CLASS D addresses are assigned to Multicast services and CLASS E addresses are meant for experimental use.

Public and Private IP Addresses

All the addresses assigned to different companies that you can access or route through internet are considered public addresses. Inside Class A, Class B, and Class C there are blocks (or ranges) of IP addresses that can’t be routed through internet. These IP addresses are meant for internal use within companies and for home networks. If you check your router IP address, you will find one of these IP addresses. They are called private IP addresses. All the companies can use these addresses internally for communication within the company but they will only be unique inside company’s private network. If any company needs a unique public IP address, it has to contact IANA (Internet Assigned Numbers Authority) to get it.

Within Class A addresses, block with private IP addresses spans from to

Within Class B addresses, block with private IP addresses spans from to

Within Class C addresses, block with private IP addresses spans from to

As you can see, the address that is the main subject of our article is private IP address within Class C.

Before we start our story about this specific address, we are going to mention one more term that is important for understanding IP addresses. The term is SUBNETTING and it is essential for maximum utilization of all the private IP addresses. Subnetting also extends the life of IPv4 protocol and enables smooth transition to IPv6.

Any company can function on a single network but it is much easier if you divide (subnet) one single network into bunch of smaller networks (separated networks for each department). That way, you will get more efficient network, it will be easier to administrate the whole network, and you will improve the security.

The first thing you should understand before understanding the process of subnetting is subnet mask. The subnet mask, just like IP address, contains 32 bits and it basically looks the same like an IP address. A subnet mask is not independent of IP address. It always comes along with IP address and when you apply subnet mask to IP address, you get two parts of the address – one that refers to network address and the other that refers to host (any device) address.

There are default subnet masks for private IP addresses for Class A, Class B, and Class C networks

Class A – from to; Default subnet mask –

Class B – from to; Default subnet mask –

Class C – from to; Default subnet mask –

Every number that is not zero in these subnet masks represents network address (for class A – 255, for class B – 255.255, for class C – 255.255.255) and zeros represent host address. In binary form, the left part of the address (the one with ones) is the network address and the part with zeros is the host address.

Class A default subnet mask: = 11111111.00000000.00000000.00000000

Class B default subnet mask: = 11111111.11111111.00000000.00000000

Class C default subnet mask: = 11111111.11111111.11111111.00000000

Considering the number of zeros, you can conclude, that if you use some Class A network you have 16,777,214 hosts at your disposal (224 – 2, 24 is the number of zeros, and 224 – 2 is the number of possible hosts (usable IP addresses) since the first and the last IP address are always reserved). If you use class B network, you have 65,534 hosts or unique IP addresses at your disposal (216 – 2, 16 is the number of zeros), and if you use Class C network you have 254 hosts (unique IP addresses) at your disposal (28 – 2, 8 being the number of zeroes).

Let’s say, you have a small enterprise and you want to use some Class C network ( for example). This class allows you to have 254 hosts (different devices connected to this network). You probably don’t need 254 different devices and that’s your first problem. In order to optimize the utilization of unique IP addresses, you need to divide this network into two or more subnetworks and use these smaller subnetworks. The second problem is that you don’t want all of your devices to be able to access every part of this small network. For example, you don’t want other devices to be able to access human resources department through this network. This problem can also be solved by dividing one network with 254 possible hosts into two or more subnetworks. That way, you can limit the access to some sensitive data and improve security. That’s basically the point of subnetting.

How to subnet in practice?

So, how could you possibly make bunch of smaller networks from one network?

Let’s say you want to use network with 254 possible hosts and you need more subnetworks (not one network with 254 hosts but 2 or 4 or 8 (or even more) smaller networks).

Since you have network, you know that this is Class C network and you know what’s the default subnet mask (

Default subnet mask for Class C network is written down (in binary form).


The part with ones, as you already know, is the part of the IP address that refers to network address, and the part with zeros refers to host. With the default subnet mask for Class C, you have 254 hosts at your disposal (28 – 2, 2 IP addresses are reserved (one for the network and one for broadcast)).

Your network with 254 unique IP addresses (with default subnet mask can be written like this where 24 is the number called CIDR notation (CIDR stands for Classless Inter-Domain Routing). This number is basically the number of bits in the mask referring to the network (when you have default subnet mask for class C, you have 24 ones or the first three octets – look at the binary form written above). But, this network offers 254 different IP addresses and you don’t need that much. Let’s say you need to break this number of IP addresses into two smaller groups (you need two subnets). You can do this by adding one more bit to the existing portion of 24 bits that refers to network address. How to do that? Just change the first 0 in the host part of the default mask for Class C into 1

So, instead of


You will now have


The new subnet mask has 25 bits referring to the network and 7 bits referring to the host (which means 27 – 2 (2 addresses are always reserved for network and for broadcast – usually the first one and the last one) or 126 unique IP addresses). So, instead of previous 254 usable IP addresses within single network, you will now have two smaller subnetworks and each will have 126 IP addresses and you can choose to use only one subnetwork for your business or you can restrict devices on one subnetwork to access the other subnetwork.

Let’s now see what has changed

Network ID
Subnet Mask
Available IP addresses block – –
Number of possible hosts 254 126

There is maybe one thing you don’t understand and it’s the new subnet mask The subnet mask is not the same anymore. You probably remember that we have changed one 0 from the host part of the mask to 1 and that’s how our subnet mask changed from

11111111.11111111.11111111.00000000 to 11111111.11111111.11111111.10000000

Eight ones in binary code give 255, and 8 zeros give zero. All the numbers between 0 and 255 are written as a different combination of eight ones and zeros. The last octet in our binary form is 10000000 instead of 00000000. The easiest way to turn number written in binary form to a real number is to use this simple table below

27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
1 0 0 0 0 0 0 0
128 0 0 0 0 0 0 0

The first two rows are the values of 2n where n takes values from 0 to 7 (we use 8 different values for n because the binary number we have to turn into decimal notation consists of 8 digits (bits). If you want to crack a binary number with 16 digits, you have to use the corresponding number of values for n, which is in that case 16 (from 0 to 15)).

The third row represents our number in binary form. Every cell is one digit (bit) from the binary form.

The last two rows will tell you the equivalent decimal notation (a real number, if you want) of the number written in binary form. In the fourth row, you will write 2n value whenever 2n value from the second row corresponds to 1 in the third row, and you will write 0 whenever 2n value from the second row corresponds to 0 from the third row. In the end, you will sum all the values from all the cells in the fourth raw and you will get the number you needed.

So, that’s how subnet mask turned from to and this is only one of the possible ways of calculating subnet mask but it’s not the only one. We will show some other methods when the things get complicated a little bit more. Remember, we have now only 2 subnetworks.

Let’s try to find decimal equivalent for another binary number. Just to be sure we got the things right. We are not going to explain everything this time, you can probably understand everything from the table.

Let’s take a random binary number 01001001. If you are a fan of The Big Bang Theory, you are probably familiar with this number since it’s Sheldon’s favorite.

27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
0 1 0 0 1 0 0 1
0 64 0 0 8 0 0 1
0+64+0+0+8+0+0+1 = 73

Even though the writers of the show made a mistake by stating that 73 is a palindrome in binary (the word or phrase (or a binary number, in our case) that is read the same forwards or backwards) when it really isn’t, it served as a good example of how to calculate number from binary form.

Ok, now you know how to subnet one larger network into two smaller ones and how to calculate a real number from its binary form. But, that’s not the end of our story. You can divide one network into 4 or 8 or 16 or 32 smaller subnetworks. How? The same way we divided it in two. Let’s write again our default subnet mask for Class C addresses

Or in binary


By changing one 0 from the host part of the mask to 1 we’ve got 2 networks, by changing another 0 to 1 we will get 4(22) subnetworks, by changing 3 0s to 1s we will get 8 (23) subnetworks, by changing 4 zeros to ones we will get 16 subnetworks (24), and so on. By changing 6 zeros to ones we will get 64 small subnetworks (26), each with only two IP addresses (two hosts or two devices) available in every subnetwork.

Let’s now try to make those 64 networks.

The default mask was


And the new one is


If you need decimal notation, you can use our table from above

27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
1 1 1 1 1 1 0 0
128 64 32 16 8 4 0 0
128+64+32+16+8+4+0+0 = 252

So, our new subnet mask in decimal notation is

Our new network ID is (30 represents the number of bits referring to the network)

Inside the first subnetwork, you will have two available IP addresses for your devices and ( is reserved for network, and is reserved for broadcast).

Just like you can determine what’s the subnet mask you have to use based on your needs (based on the number of IP addresses needed) you can determine the network ID and CIRD notation based only on a subnet mask and a specific IP address. You just have to go the other way around.

Let’s say you have subnet mask and an IP address

So, what can we see? Let’s look first at the subnet mask. It’s slightly changed default mask for C class addresses ( The last number in this decimal notation differs, which means that you are dealing with a subnetwork of a bigger network. Based on the number 192, you can determine how many zeros from the host part of the network is changed to ones. You can use one part of our previous table, specifically, the second raw.

128 64 32 16 8 4 2 1

Look at this small but very useful table and start adding numbers one by one until you get to 192 (from left to right). The first two number from our table will give you the desired result. That means that two zeros from the host part of the network ID are changed into ones and the other 6 zeros stayed unchanged. This means that you are dealing with 4 (22) subnetworks. You also know that CIDR notation is 26 (24+2).

To determine network ID, we have to analyze our IP address now:

Our address is

Since we know that our subnet mask is, the first three octets (the first three numbers of the IP address will be part of the network ID). So, our network will look something like this: 192.168.46.?? /26

Based on the last number in the IP address (55), we are going to determine what is going to be the last number of our network (or subnetwork) ID.

The last number is 55, or in binary form 00110111 (we are using the table again and trying to sum these values until we get 55)

128 64 32 16 8 4 2 1
0 0 1 1 0 1 1 1

The last octet of our IP address 00110111.

We know that two first bits from this octet are reserved for the network. The last number of our network ID actually depends on these two bits. Since the first two bits on 00110111 are 00, the last number of our network ID will be 0. And there you have it.

Our network ID will be

And our subnet mask is

Since we know that 2 bits are taken from the host part and changed into the network part of the address, we know that there are 4 (22) possible networks with different IDs and inside every network, there are 62 unique IP addresses (possible hosts) + 2 reserved addresses for network and broadcast.

The last number in our network ID could have been different if the last number in that given IP address was different. For example:

Let’s say that the last number in IP address is 73 ( You already know that 73 is 01001001. The first two bits from this octet are 01 which leaves us with number 64 (if you don’t understand how, just try to imagine that there are six more zeros behind 01 and try to transform it into decimal notation (into a real number) – 01000000 = 64).

In this case, our network ID is and subnet mask stays the same.

If the last number in IP address was 155 ( then binary form of 155 would be 10011011 (we won’t draw a table every time, you can try doing it by yourself). The first two bits are 10 which means that the last number of our network ID is 128 (again, try to imagine that all the bits beyond 10 are zeros and try to turn this binary form into a real number – 10000000 = 128).

In this case, our network ID is and subnet mask stays the same.

If the last number in that given address was 230 ( the binary form of the last number would be 11100110. The first two bits in this binary form are 11 which leaves us with 192 (and again, try to imagine that all the other bits beyond 11 are zeros and try to convert that binary number into a real number – 11000000 = 192).

In this third case, our network ID would be and subnet mask would stay the same again.

One more real-life example that could help you understand how subnetting works. Let’s assume that your Internet Service Provider got a base address (this is class A with a default subnet mask and in order to utilize the most of it, ISP subnets this address with a subnet mask which means that ISP subtracts 15 bits from the host part of the address and makes 215 or 32,768 new networks. The host part consists of 9 bits which means that there are 29-2 or 512 hosts on every network. That’s how Internet Service Provider utilizes the most of its base address. IP Address – Default Gateway

If you have read the whole article, then you probably know that is part of the bigger block of private addresses within Class C (that block spans from to This address is often used by many router and modem manufacturers as a default gateway address for their routers and modems. This address (or your router, if you want) is actually a default gateway that allows your device (or devices) to connect to the internet and communicate with other devices in different networks. Default gateway is a mediator that allows devices within your local network to connect to the internet. So, if you want to visit some website and enter its address in your browser, your request has to go through this gateway before reaching the internet.

When communicating with other devices, you don’t actually use your device’s IP but the IP of your router (default gateway). Since the number of private IP addresses is very limited, there is high possibility that many devices share one IP address but they are not in conflict because they only have to be unique inside their own subnetworks, and that’s why subnetting is important and why Internet Service Providers subnet their base addresses.

What you need to know is that there is great chance that your router’s IP address is (or 19216811) It’s a convention (not a rule) established by router manufacturer Linksys and many other manufacturers followed. This address can’t be seen or routed on the internet because it’s private (and that’s a rule).

What can you do with this address in practice? Well, you can type it in your browser and access your router’s settings and you can adjust different aspects of your internet connection – change the name of your Wi-Fi, change the password of your Wi-Fi, change firewall settings, change DNS, change username and password of your router, restrict access to some websites, etc.

Is The Only Default Gateway?

We have already said that router manufacturers use this IP address by convention, but convention is not a rule or a law, so it happens sometimes that other manufacturers use other IP addresses as the default gateway for their routers. Even Linksys (which established this convention) uses different IP addresses for different models. The most common default gateway IP addresses (besides are:

Since there is no explicit rule, any IP address from those blocks of private IP addresses can be used as a default gateway, but manufacturers tend to stick with these well-known IP addresses.

How to check your router’s IP Address on Windows, Linux, or Mac OS

If you don’t know what is the default gateway for your router and you need to know that in order to change some settings, don’t worry. There are very simple ways to check your default IP address whether you use Windows, Linux, or Mac OS.


Step 1. Enter Command Prompt – click on Start and in the search field type in cmd, and click on Command Prompt (it will appear as the result of your search)

Step 2. Type in ipconfig and press ENTER

Step 3. Look for Default Gateway – that’s where you will see default IP address for your router


If you use Linux, you are probably used to Terminal. If you are new to Linux, this is the path to follow: Applications – System Tools – Terminal.

Step 1. Open Terminal

Step 2. Type in netstat -r and hit ENTER

Step 3. Look for the default IP address just under the Gateway

Mac OS

If you are Mac OS user, then you can also use Terminal. You can find it by following this simple path: Finder – Applications – Utilities – Terminal

Step 1. Open Terminal

Step 2. Type in netstat -rn and hit ENTER

Step 3. You will find your default IP address next to default


Step 1. Go to System Preferences

Step 2. Click on Network icon

Step 3. In Network tab, choose the type of your internet connection (usually Wi-Fi) and click on Advanced tab

Step 4. Got to TCP/IP tab and click on it

Step 5. Your router’s IP is the last one on the list and you will also see your computer’s IPv4 address as well as subnet mask address.

In any of these cases, there is a great chance that your router’s default gateway will be (19216811) since it’s the most common gateway.

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