What is a subnet mask? (Powercert animated videos)

What is Subnet Mask?

This article is a translation of the following link video ：
【IT Hard core animation handling / Chinese and English double characters 】 What is a subnet mask ？

Example of subnet mask

Suppose you have a small business ,IP Address :192.168.1.0, Subnet mask :255.255.255.0, Now suppose your small business has a total of 12 Computers , all 12 All computers are on the same network , These computers belong to different departments , Represented by color , But suppose you want to divide these computers into three different networks , In this way, each department can not see the network traffic of other departments .

therefore , You want to split a network in your enterprise into three small networks .

The method of splitting this network into smaller networks is realized through subnets , The method is to change the default subnet mask by borrowing some bits specified by the host and using them to create a subnet .

• In this subnet mask , We will change some zeros in the host part to one , So we can create more networks .
• If we keep the subnet mask unchanged , It will get a containing 256 Network of hosts , Technically speaking , We must now subtract the host , Because the values are 1,0 Reserved for broadcast and network addresses respectively , So we actually have 254 Available hosts .

We need to change this subnet mask , So we can generate the three networks we need

for example , Let's borrow one from the mainframe section , This is our new subnet mask , So now the fourth binary octet is 128, Because when you calculate the first bit of the binary octet , It's equal to 128.

1) Borrow a bit , This will divide the network in two , So now it is no longer a containing 254 Network of hosts , Instead, provide two networks or each subnet that contains 126 Of hosts .
2) Now let's continue borrowing another bit from the host section , Now we have borrowed two people from the host , So this is the new subnet mask in our fourth binary octet 192, So by borrowing two , This will further divide the network , Now we will have four subnets , Each subnet has 62 Console host .

3) Let's borrow another bit from the host part again , This is a new subnet mask , By borrowing 3 position , This will divide the network into 8 Subnet , Each subnet has 30 Console host .

4) If we borrow four bits , We will get 16 Subnet , Each subnet has 14 Console host

5) If we borrow 5 A bit , We will get 32 Subnet , Each subnet has 6 Host computer .

6) If we borrow 6 position , We will get 64 Subnet , Each subnet has two hosts

7) If we borrow 7 position , It will provide us with 128 Subnet , But no hosts are available .

The more bits the network portion borrows from the host portion , The number of networks that can be created doubles , However, the number of hosts per network will also be reduced by half at each bidding .

If we want to divide this network into three smaller networks or subnets , We have to borrow two bits from the host part , So even if we only need three networks , This subnet mask at least allows the network to work with it . Therefore, the new custom subnet mask of our three subnets is 255.255.255.192

So now our network is divided into three smaller subnets .

IP Address classification

• Addresses and subnet masks fall into five different categories , namely A To E class .
• A,B,C Classes are used for commercial purposes
• You can IP The number in the first octet of the address and the default subnet mask to distinguish which category they belong to .

A、B and C Class IP Diagram of address and default subnet mask

Now? , When organizations need to be connected , They will need one according to the needs of the organization IP Address category , This category is based on the number of hosts they have . therefore , If an organization has many hosts , They will need one A class IP Address , One A class IP Addresses can be generated up to 1600 Ten thousand hosts .

A class IP The host part of the address is very large , The host uses three octets , This is why it can generate so many hosts . An example of an organization needing so many hosts is similar to Internet Service provider , Because they need to put millions IP Address distribution to all customers .

One B class IP The address can generate up to 65000 hosts . This category is applicable to large and medium-sized organizations .

One C class IP Addresses can generate 254 Console host . One C class IP Addresses are used for small organizations and families with few hosts .

CIDR

The subnet mask can also be called CIDR To represent .CIDR Represents classless inter domain routing , Also known as slash notation . Slash notation is a shorter way to write a subnet mask , It does this by writing a forward slash , Then write a number in the count subnet mask to achieve this

for example , If you see IP The address is denoted by a slash 24. This means that the length of the subnet mask is 24 position , That is to say, its length is 24 position .

If the sign is a slash 25, This means that the length of the subnet mask is 25 position , Or if it's a slash 26, This means that the length of the subnet mask is 26 position , Or if CIDR The notation is a slash 8, This means that the length of the subnet mask is 8 position .