Summary: This article will explain to you about the classes in IP addresses or, in other words, classful networks/address classes.

An Internet Protocol address (IP address) is a layer three logical address assigned by a network administrator. IP addresses are used to identify specific devices on a network.

An IP address is a 32-bit binary address usually written in dotted decimal formats. These 32 bits are further subdivided into four 8 bit segments called octets. Each octet is separated by a period.

Also Read: How To Use grep Command In Linux With Regex.

Every IP address can be broken down into two main portions.

  1. Network Address Portion (Network ID)
  2. Host Address Portion (Host ID)

The Network address portion is used to identify a specific network. Routers maintain routing tables that contain the network addresses. The Host address portion is used to identify a specific endpoint on a network such as servers, printers, computers, mobile phones, etc. (Please Note – Routers build their routing tables based on network address not based on Host addresses.)

IP address Structure
IP address Structure

Types Of IP Address Classes (Address Classes/Classful Networks)

This is a network addressing architecture used in the internet from 1981 until the introduction of CIDR (Classless Inter-Domain Routing) in 1993.

This method divides IPv4 address space into five types of ip address classes.

  1. Class A
  2. Class B
  3. Class C
  4. Class D
  5. Class E

Class A, Class B, and Class C  provide unicast addresses. Class D is for multicast networking and the class E address range is reserved for future or experimental purposes.

These Address classes were determined and allocated by the Internet Assigned Numbers Authority (IANA)

Breaking Down Of Class A IP Address

In Class A addresses the first bit of the first octet is always set to Zero.

00000000 – 01111111

Therefore in Class A addresses the first octet ranges from 0 – 127.

0.0.0.0 – 127.255.255.255

But 127 is reserved for loopback IP addresses. For example, you can’t configure an IP address of 127.0.0.1 as a static IP on a PC. 0 is reserved for the default network. So that can’t be used either to configure an IP address on a PC. For example, you can’t configure an IP address of 0.1.1.1 as a static IP on a PC.

Because of the reasons mentioned above the actual range of Class A addresses is from 1 – 126.

1.0.0.0 – 126.255.255.255

In these addresses, the first 8 Bits denotes the Network Portion and the last 24 Bits denotes the Host Portion.

Class A IP Address Structure
Class A IP Address Structure

Breaking Down Of Class B IP Address

In Class B addresses first two bit of the first octet is always set to 10. (One and Zero).

10000000 – 10111111

Therefore in Class B addresses the first octet ranges from 128 – 191.

128.0.0.0 – 191.255.255.255

In these addresses, the first 16 Bits denotes the Network Portion and the last 16 Bits denotes the Host Portion.

Class B IP Address Structure
Class B IP Address Structure

Breaking Down Of Class C IP Address

In the first octet of Class C addresses first 3 Bits are set to 110. (One One Zero)

11000000 – 11011111

Therefore in Class C addresses the first octet ranges from 192 – 223.

192.0.0.0 – 223.255.255.255

In these addresses, the first 24 Bits denotes the Network Portion and the last 8 Bits denotes the Host Portion.

Class C IP Address Structure
Class C IP Address Structure

Breaking Down Of Class D IP Address

In Class D addresses the very first four bits of the first octet are set to 1110. (One One One and Zero)

11100000 – 11101111

Therefore in Class D addresses the first octet ranges from 224 – 239.

224.0.0.0 – 239.255.255.255

These addresses are reserved for Multicasting. In multicasting, data is not transmitted for a particular host. Therefore it’s not necessary to extract the host address from the IP address.

Breaking Down Of Class E IP Address

Class E is reserved for experimental purposes.

In Class E addresses the very first four bits of the first octet are set to 1111. (One One One and One)

11110000 – 11111110

Therefore in Class E addresses the first octet ranges from 240 – 254.

240.0.0.0 – 254.255.255.254

In Summery

Class1st Octet Decimal Range1st Octet High Order BitDefault Subnet MaskNumber of NetworksHosts Per Network
A1 – 1260255.0.0.012616,777,214
B128 – 19110255.255.0.016,38265,534
C192 – 223110255.255.255.02,097,150254
D224 – 2391110Reserved forMulti casting
E240 – 2541111Used for Research
IP Address Classes Summery Chart

Private IP Address Classes

According to RFC1918, private IP addresses are non-routable IP addresses. These addresses will be blocked by ISP and thus can not be used to send traffic.

When we sending traffic internally from an IP address such as 192.168.1.3 to a website such as learntechtutorials.com our IP address has to be NAT (Network Address Translation) to a public IP such as 104.24.104.42.

IANA has reserved the following three blocks of the IP spaces for private Internet.

ClassRange
A10.0.0.0 – 10.255.255.255
B172.16. 0.0 – 172.31. 255.255
C192.168.0.0 – 192.168.255.255 
Private IP Address Classes Summery Chart

So that’s it. I hope this article clearly explained to you the private IP address classes. Thank you for reading. I Hope you learned something new.

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