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IPV4 Address - Subnetting Tutorial

IPV4 Address

IPV4 Address is 32bit.

IPV4 has public and private IP Address.

Public IP Addresses is routable over the internet.

Private IP Addresses as it names implies is private,  which is basically for private use and is not routable over the internet. Use by private companies or private individuals.

Logically, private IP just goes with the saying. What happens in LA stays in LA. Likewise a private IP Address if it use at home then that IP Address stays at home. It won’t even go out to the neighbor, unless you have a Wifi and the neighbor crack your Wifi or wireless password, then that’s an exemption.

Private IP Address Classes and Range

Class A
10.0.0.0 – 10.255.255.255
Class B
172.16.0.0 – 172.31.255.255
Class C
192.168.0.0 – 192.168.255.255


IPV4 is 32 bit or four octets, each octet  is separated by dot or period.

Example of an IPV4 Address, if you count the number of x it’s  32 x’es.

xxx xxxx . xxxx xxxx . xxxx xxxx . xxxx xxx

Since IPV4 is  32 bit, so it is compose of  32 bits of either 1’s or  0’s.

Example in binary is: 1100 0000 . 1010 1000 . 0000 0001 . 0000 0001

Decimal equivalent  of above binary address is a private IP which is 192.168.1.1

If you’re tired of doing manually the conversion, pull out windows calculator to verify.

But if you’re preparing for a Cisco Certification suggests you do the conversion manually for practice and use windows calculator to verify the correct answer.

If you issue the command  “IPCONFIG” in a Windows OS.

It will always  display the result with a standard format, which is an IP Address, Subnet Mask and Gateway.

But if you issue “IPCONFIG /ALL” it will have more detailed result but I’m not going to talk about it.

IP Address gives a unique information of the device or a computer in the network so it will be able to communicate with other computers or devices on the network.

If there’s a duplicate IP Address on the network, Windows OS normally will prompt a message like “IP Conflict Address”.  And the computer or device is disconnected from the network.

Subnet mask, is used to extract information about the host address and the network address.

Gateway  is like the baseline of the communication on the local network, a common setup in local network, is that a  gateway IP Address is the IP Address of the router. But of course it’s not always a router it depends on the setup of your network.

In the CISCO world or network environment, “Gateway of last resort” is a common phrase.

If you’re preparing for a Network Certification such as Cisco Certification.

CCNA certification requires the candidate to have a solid knowledge of subnetting.

To determine the host address and the network address, is the job of the subnet mask.

So how does a subnet mask does it job?

IPV4  Address is 32 bit, so it’s prefix length will start from prefix 1 until prefix 32.

So the IP Prefix Length table will be like this: (it’s just in two rows just for a good display, but it will be better to write it down in one row)

/1
/2
/3
/4
/5
/6
/7
/8
/9
/10
/11
/12
/13
/14
/15
/16
/17
/18
/19
/20
/21
/22
/23
/24
/25
/26
/27
/28
/29
/30
/31
/32


Private IPV4 Address has Class A, Class B and Class C. Class A IP Address is sometimes called an /8 network, likewise a Class  B is /16 and Class C is /24.

/8, /16, /24 refers to the number of bits used by the network address.

Class A will have a subnet mask of 255.0.0.0 (/8)

Class B will have a subnet mask of 255.255.0.0. (/16)

Class C will have a subnet mask of 255.255.255.0 (/24)


In binary Class A will be 1111 1111 . 0 . 0 . 0

Class B – 1111 1111 . 1111 1111 . 0 . 0

Class C – 1111 1111 . 1111 1111 . 1111 1111 . 0

If you pop up a Windows calculator and convert binary 1111 1111 to decimal, answer would be 255.

Why 255? Because that’s the way it is?

      To come up with 255, it has this decimal value.

Let’ use the Prefix Table:

/1
/2
/3
/4
/5
/6
/7
/8

128
64
32
16
8
4
2
1
 add all = 255

/9
/10
/11
/12
/13
/14
/15
/16

128
64
32
16
8
4
2
1
add all = 255

/17
/18
/19
/20
/21
/22
/23
/24

128
64
32
16
8
4
2
1
add all = 255

/25
/26
/27
/28
/29
/30
/31
/32

128
64
32
16
8
4
2
1
add all = 255

So that’s the mystery behind the subnet mask, as you can see there’s  a pattern.

Now let’s derive the Subnet Mask value from the table above:


/1
/2
/3
/4
/5
/6
/7
/8

128
64
32
16
8
4
2
1

128 + 0 = 128
128 + 64 = 192
192 + 32 = 224
224 + 16 = 240
240 + 8 = 248
248 + 4 = 252
252 + 2 = 254
254 + 1 = 255
Subnet Mask
128
192
224
240
248
252
254
255

.
/9
/10
/11
/12
/13
/14
/15
/16

128
64
32
16
8
4
2
1

128 + 0 = 128
128 + 64 = 192
192 + 32 = 224
224 + 16 = 240
240 + 8 = 248
248 + 4 = 252
252 + 2 = 254
254 + 1 = 255
Subnet Mask
128
192
224
240
248
252
254
255

.
/17
/18
/19
/20
/21
/22
/23
/24

128
64
32
16
8
4
2
1

128 + 0 = 128
128 + 64 = 192
192 + 32 = 224
224 + 16 = 240
240 + 8 = 248
248 + 4 = 252
252 + 2 = 254
254 + 1 = 255
Subnet Mask
128
192
224
240
248
252
254
255

.
/25
/26
/27
/28
/29
/30
/31
/32

128
64
32
16
8
4
2
1

128 + 0 = 128
128 + 64 = 192
192 + 32 = 224
224 + 16 = 240
240 + 8 = 248
248 + 4 = 252
252 + 2 = 254
254 + 1 = 255
Subnet Mask
128
192
224
240
248
252
254
255


If you notice the table, there’s a pattern for the subnet mask.

It’s always  128, 192, 224, 240, 248, 252, 254 and 255.

Let’s take an example of:  10.11.1.0 /10

So it’s a Class A IP Address but the subnet mask falls on the 2nd octet.

IP Address: 10.11.1.0  Subnet Mask: 255.192.0.0

Subnet mask is /10 and based on the table above /10 is equivalent to 192.

If you will notice below the increment is 64.

Like: 10.0.0.1 to 10.63.255.254 and the next subnet is 10.64.0.0. and next subnet is 10.128.0.0

Why is it a 64 increment?

If you look at the table above, you will notice that /10 falls under a 64 bit decimal value.

But there’s an easy way, you can always minus the subnet number by  256.

So, 256 – 192 = 64

So you will have this range:

Subnet          ,   Valid Hosts                       ,   Broadcast      
10.0.0.0        ,   10.0.0.1 to 10.63.255.254         ,   10.63.255.255  
10.64.0.0       ,   10.64.0.1 to 10.127.255.254       ,   10.127.255.255 
10.128.0.0      ,   10.128.0.1 to 10.191.255.254      ,   10.191.255.255 
10.192.0.0      ,   10.192.0.1 to 10.255.255.254      ,   10.255.255.255 
11.0.0.0        ,   11.0.0.1 to 11.63.255.254         ,   11.63.255.255  
11.64.0.0       ,   11.64.0.1 to 11.127.255.254       ,   11.127.255.255 
11.128.0.0      ,   11.128.0.1 to 11.191.255.254      ,   11.191.255.255 
11.192.0.0      ,   11.192.0.1 to 11.255.255.254      ,   11.255.255.255 
12.0.0.0        ,   12.0.0.1 to 12.63.255.254         ,   12.63.255.255  
12.64.0.0       ,   12.64.0.1 to 12.127.255.254       ,   12.127.255.255 
12.128.0.0      ,   12.128.0.1 to 12.191.255.254      ,   12.191.255.255 
12.192.0.0      ,   12.192.0.1 to 12.255.255.254      ,   12.255.255.255 
13.0.0.0        ,   13.0.0.1 to 13.63.255.254         ,   13.63.255.255  
13.64.0.0       ,   13.64.0.1 to 13.127.255.254       ,   13.127.255.255 
13.128.0.0      ,   13.128.0.1 to 13.191.255.254      ,   13.191.255.255 
13.192.0.0      ,   13.192.0.1 to 13.255.255.254      ,   13.255.255.255 
14.0.0.0        ,   14.0.0.1 to 14.63.255.254         ,   14.63.255.255  
14.64.0.0       ,   14.64.0.1 to 14.127.255.254       ,   14.127.255.255 
14.128.0.0      ,   14.128.0.1 to 14.191.255.254      ,   14.191.255.255 
14.192.0.0      ,   14.192.0.1 to 14.255.255.254      ,   14.255.255.255 


You can always make your own questions to practice. To verify your answers, you can download a subnet calculator. Boson subnet calculator is one of them and it is free. Just trawl the web and you will be able to find it.

Hope it will help a little bit to those who are struggling on how subnetting works.
Just my 2 cents of advice, to those who will sit for a CCNA Cisco Certification.  Don’t sit for the exam if you can’t subnet within 1 to 2 minutes.

In your examination day, before you click the start button. You can write down the subnet table on a scratch pad provided. So you don’t have to think about it during the exam.


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