What is a IP Address? A Unique network IDentifier

Map Of Internet 1973


An IP address is:


With Ipv4: /




An Unicast address is an identifier for a single interface. adapter

A packet sent to a unicast address is delivered to the interface identified by that address.


The Wildcard Address indicates the absence of an address.

It's used mostly as the target of bind, which allows a server to accept a client connection on any interface, in case the server host has multiple interfaces.

It's also known as:

  • the anylocal
  • the Unspecified address.

It must:

  • never be assigned to any node.
  • not be used as the destination address of an IP packet.


The Loopback Addresses is the address assigned to the loopback interface.

Anything sent to this IP address loops around and becomes IP input on the local host.

This address is often used when testing a client.


A multicast address is an identifier for a set of interfaces (typically belonging to different nodes).

A packet sent to a multicast address is delivered to all interfaces identified by that address.


An IP address is comprised of:

All hosts on a subnetwork have the same mask (ie network prefix), unlike the host identifier which is a unique local identification.


The IP Address is an attribute of the Internet Protocol (ie tcp or udp packet).


There are 2 version:

The main difference between IPv4 and IPv6 is the number of bytes and therefore the number of possible ip addresses. IPv6 was introduced in 1995 to ensure that the world would not run out anytime soon of IP number.

IP Version Number of bytes Bit Address Space Possible addresses
Ipv4 4 32 4 billion
Ipv6 16 128 <math>3.4 \times 10^{38}</math>



Public Vs Private Ip Address



Public IP are global addresses that are unique across the internet.

See What is a public IP?.


The devices that do not require public access may be assigned a private IP address and make it uniquely identifiable within one organization.

For example, a network printer may be assigned a private IP address to prevent rest of the world from printing from it.

To allow organizations to freely assign private IP addresses, the NIC has reserved certain address blocks for private use. See private

To hostname

See DNS - rDNS - Reverse DNS (lookup|resolution) - from IP to name

Database Owner

You can query a whois database to see the owner of an IP address.

Reference / Architecture

The IP address architecture is defined by:



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