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How IP Address Are Assigned By Internet Service Provider ?

Cubepost, Jul 27, 2020

ISP assigns a Public IP address for your computer or mobile when you connect. ISP provides you with Public IP Adress

Who Assigns The IP Addresses?

The Internet Assigned Numbers Authority (IANA) organization coordinates through all Regional Internet Registries and ISPs to allocates the IP addresses, Then ISP assigns you a Public IP address either IPv4 or IPv6 when you connect, which are allocated to them.

Types of IP Address

  • IPv4 - Internet Protocol Version 4 consists of 32 Bit Numbers
               IPv4 address Format: x.x.x.x where x is called an octet and must be a decimal value between 0 to 255
  • IPv6 -  Internet Protocol Version 6 consists of 128 Bit Numbers
               IPv6 address Format: Represented as eight groups of four hexadecimal digits, each group representing 16 bits
               eg. 2001:0db8:582:ae33::29

  Find YOUR IP AddresS HERE  

Will ISP assign me Public IP or Private IP?

ISP assigns you only a Public IP address.

Story: Your router connects through the internet is assigned one public IP by ISP, Then the router assigns a local private IP to each device it connects and manages. So all devices connected to the router have the same public IP, The router smartly manages with all devices connecting to and fro to the internet.

How does IP address assignment work?

ICANN coordinating the maintenance and procedures of several databases related to the namespaces and numerical spaces like domain names and IP addresses. 

IANA is responsible for the operation of assignment of IP in a hierarchy, ISPs obtain allocations of IP addresses from a local Internet registry (LIR) or National Internet Registry (NIR), or from their appropriate Regional Internet, Which are given by IANA.

IP Registries List

Registry Region
AFRINIC Africa Region
APNIC Asia/Pacific Region
ARIN Canada, USA, and some Caribbean Islands
Latin America and some Caribbean Islands
Europe, the Middle East, and Central Asia
Source: IANA Number Resources

Bytes: First and last IP of any subnet is reserved, First IP is used as the network number and Last IP is used as broadcast address

What is Public IP?

  • Public IP is an IP address assigned by the ISP to communicate to your device or devices in your network. 
  • Public IP is unique globally at any given time is assigned to only one device.
  • Public IP can be either IPv4 or IPv6.
  • It also can be Static IP or Dynamic IP.
  • Web Servers, Email Servers, Home Routers, Phone with the Internet is assigned with Public IP.

What is a Private IP?

  • Private IPs are used local networks assigned to all connected devices in a local area network (LAN). 
    Eg. A router with 10 devices connected, each is assigned a private IP address.
  • Network Address Translation (NAT) is used to map each local system to connect to the internet which has a single Public IP address with multiple local systems with each private IP.
  • IETF directed IANA to reserve the IPv4 address ranges for private networks. 

Static IP vs Dynamic IP

Static IP is one that is assigned by ISP or a device that never changes even on network reconnection. Usually when assigned by ISP as a static IP would cost a flat fee as it will not return to their IP Pool, Wheres the dynamic IP may not guarantee the same when reconnected.

For web servers, Email servers, and business, having static IP will make things easier as IP need not be frequently remapped in order to connect to the right server or system.

In a local network, DHCP controls the IP assignment for each connected device and avoid clashed between IP

Private IP Ranges

ClassIP RangeNo of IP Addresses
Class A10.0.0.0 -,777,216
Class B -
Class C -
Note: 4,294,967,296 IPv4 Addresses are there

IP Address Classes

  1. CLASS A - Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only. The IP range 127.x.x.x is reserved for loopback IP addresses.

  2. Class B  - IP Addresses range from 128.0.x.x to 191.255.x.x. The default subnet mask for Class B is 255.255.x.x.

  3. Class C IP addresses range from 192.0.0.x to 223.255.255.x. The default subnet mask for Class C is 255.255.255.x.

  4. Class D - IP address range from to Class D is reserved for Multicasting. In multicasting data is not destined for a particular host, that is why there is no need to extract the host address from the IP address, and Class D does not have any subnet mask.

  5. CLASS E - IP Class is reserved for experimental purposes only for R&D or Study. IP addresses in this class range from to Like Class D, this class too is not equipped with any subnet mask.

More Detailed Info Below on IP Addresses

What is CIDR Block

Classless inter-domain routing (CIDR) is a set of Internet protocol (IP) standards that are used to create unique identifiers for networks and individual devices. 
Eg. This is sample CIDR for Cloudflare IPs, CIDR is represented with a slash followed by a number.

CIDR is just a compact representation of an IP Block, It can be converted to IP Range also.

Network Address Translation (NAT)

NAT acts as an agent for local networks and the internet. As said above for a network only one public IP is assigned, Each other device connected in the network will be assigned only local private IP. But each device needs to access the internet and download it independently. But any device to connect to the internet needs Public IP.

To overcome the above problem NAT just maintains the local network mapping with each local Private IP and Public IP. So a packet request from your mobile A will get a response back to Mobile A and not to Mobile B though both have the same Public IP according to the outer world. The only difference is each has its unique private IP within a local network. 

Eg. Modem with Public IP -,
Two Devices with Private IP, &

More IP Tools Here

IANA Number Resources

Cubepost, Jul 27, 2020

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