IP Address Basics

IP address basics

 There are two versions of IP addresses: IPv4 and IPv6. Here, we will explain about IPv4.

An IP address is a 32-bit number assigned to each terminal that joins a network.

1 bit is either "0" or "1".

An IP address is a string of 32 0's and 1's.

If you express a certain IP address as it is with "0" and "1", the string of "1" and "0" will continue.

It's like this.


Don't you feel something when you look at the numbers above?

Can you remember this number just by looking at it?

It's a bit impossible, isn't it? For humans, this combination of long 0's and 1's looks just like a pattern!

It may be easy for computers to handle, but it's a bit difficult for humans!

Look at the following IP addresses.




are different addresses, can you tell them apart instantly?

Difficult, isn't it!

 So, for convenience, we divide by 8 digits. Separating by 8 digits (8 bits) is called octet separation. I put "." in the delimiter so that I can understand the delimiter. It will then be divided into 4 parts.

And it is designed to convert binary numbers of each 8 digits into decimal numbers.


Convert each of the four partitions into a decimal number.

 (10010111) 2  = (151) 10

 (01111111) 2  = (127) 10

 (00011010) 2  = (26) 10

 (00001001) 2  = (9) 10

Ultimately, this binary IP address can be represented in decimal as follows:

This expression should make it easier to understand.

The diagram below illustrates this transformation in a graphical way.

 Each value is 8 bits, so up to 255. That is, each octet-separated part has a minimum value of 0 and a maximum value of 255.

The minimum IP address is "" and the maximum is "".

In addition, since the IP address consists of 32 bits,

 2 32  = 4,294,967,296

It turns out that there are about 4.3 billion IP addresses.

network address and host address

What if this IP address was just a simple sequence of numbers, a flat address system?

A computer in Tokyo with ""

Change to a computer in New York

Change to a computer in Sydney

Suppose we allocate to

 If you assign IP addresses in this way, every time you send an email, you have to find the corresponding computer from computers all over the world.

 If IP addresses are randomly assigned in this way, different IP addresses will exist within the same network, making management difficult. Let's check what kind of addressing is used for the address information that we live in.

The address of "Tokyo Disneyland" is

1-1 Maihama, Urayasu City, Chiba Prefecture

This is the address.

You can see that "Tokyo Disneyland" is located in Chiba Prefecture.

You don't have to open up a world map to find Tokyo Disneyland, do you?

All you have to do is open up a map of Japan and look for it in Chiba Prefecture.

In this way, addressing is definitely more convenient if there is address information that points to the region.

Therefore, IP addresses, like address information, have a hierarchical address structure.

An IP address consists of a "network address" and a "host address".

A TCP/IP network is a complex of networks that are connected to each other.

The flow of packets when sending mail to a computer is as follows.

 When sending a packet, it is first sent to the destination network. Once it reaches the destination network, it can look for the destination computer. By creating a hierarchical address structure in this way, packet delivery becomes more efficient and IP address management becomes easier.

 Since an IP address consists of a "network address" and a "host address", it would be inefficient if the IP addresses were assigned separately.

IP addresses with the same network address will be assigned to one network.

broadcast address

 Some IP addresses are reserved among IP addresses. Among its reserved special IP addresses are network addresses and broadcast addresses. Here, we will explain the broadcast address.

 An IP address consists of a network address portion and a host address portion. A broadcast address is an address where the host address part is all "0".

For example, the broadcast address for "" is "".

 This address means that you know the network address of "150.10.XX", but you don't know the host address.


 If you send data as "", all hosts belonging to "150.10.XX" will be the terminals of "" to "".

Sending data to all hosts belonging to one network in this way is called broadcasting.

This broadcast is used by each network device to query information.

A packet sent by "" will reach all terminals within "".

 The packet is never delivered beyond the router to the next network. Routers block broadcasts and do not forward them to other networks.