What are public and private IP addresses?


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What are public and private IP addresses? IP addressing space is divided into 2 parts: public location number distributed by net providers or Internet Assigned Numbers Authority (IANA) organizations and private number being beyond the IANA control and appointed to internal nodes by network administrators’ discretion.

Public IP addresses

Stability of internet operation bases on uniqueness of public network addresses being in use. Responsibility for enforcing numbers’ uniqueness is taken by the Internet Network Information Center (InterNIC) or IANA being its successor. IANA distributes remaining resource IP addresses avoiding duplications that may cause the Internet to instability and unapproved packages delivery to the net utilizing repeated locations.

If a company gets an IP address in public network, all net nodes route traffic directly to the web and can be accessible from the net.

Examples of public IP addresses:

Network Class

Public IP Ranges

A to to

B to to

C to to

D to

E to

Private IP addresses

Private not-networked hosts can use any available location number until it preserves its uniqueness in private net.

Private connection systems aimed to function in the Internet can use IP addresses dedicated for private use.

If internal nodes have private IP addresses, proxy server or Network Address Translation protocol (NAT) grant them access to the Internet. In the simplest way, NAT organizes a company service using one registered IP address.

NAT addresses’ translation mechanism transforms numbers from private addressing space to registered open address IP area. Usually, NAT functions are completed my router or firewall covering numbers in IP packets headers.

Private IP addresses area is composed from 3 groups:

  1. for one A class network;
  2. is an addresses range consisting of 16 nets of B class – from to;
  3. (for C class net composed from 256 addresses from to

What is more, there is Automatic Private IP Addressing applying for automatic IP configuration for network interface with lack of DHCP server.

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