IPv4

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Internet Protocol Version 4.

Internet Protocol Version 4

This article should provide you with an overview of IPv4 and how it relates to Networking. The information that follows is designed to inform the more tech-savvy Internet users in an easy-to-read format.

[For a more in-depth discussion of IPv4 read the Wikipedia article about IPv4.]

What is IPv4?

IPv4 stands for Internet Protocol Version 4. Internet Protocol is a method of communication between electronic devices on a network. IPv4 was developed by the Defense Advanced Research Projects Agency (DARPA), a United States Department of Defense agency, as research project. IPv4 was implemented in the 1980’s and became the widespread network protocol that served as a foundation for other transport layer protocols. IPv6 is expected to replace IPv4 due to the world-wide shortage of IP addresses and the exponential increase in Internet enabled electronics. The official documentation for IPv4 can be found in RFC 791.

The IPv4 Datagram Format

IPv4 transmits information across the Internet in the form of a packet. At the network-layer of the OSI model, a transmitted packet is referred to as datagram.

There are 14 components of the IPv4 datagram packet:

  • Version Number
  • Header Length
  • Type of Service
  • Datagram Length (In Bytes)
  • Identifier (16-bits)
  • Flags
  • Fragmentation Offset (13-bits)
  • Time-to-Live (TTL)
  • Upper-Layer Protocol
  • Header Checksum
  • Source IP Address
  • Destination IP Address
  • Options
  • Data
32-bits
Version
Header Length
Type of Service
Datagram Length
Identifier
Flags
Fragmentation Offset
TTL
Upper-Layer Protocol
Header Checksum
Source IP Address
Destination IP Address
Options
Data


IPv4 Addressing

As seen from the diagram above, IPv4 addresses are 32 bits in length, which is roughly 4 bytes. That means that there are 2 32, or approximately 4 million possible IP addresses available using IPv4. This is why there is a shortage of IP addresses using the current protocol. Imagine everyone you know that owns a cell phone, a laptop, a tablet. There are enough people in the U.S. alone to exhaust the number of IP addresses available.

IPv4 addresses are usually written using dotted decimal notation. In dotted decimal notation, each byte of the IP address is written as a number and is separated by a period, or dot, from other bytes in the address. For example:

192.168.1.1

IP addresses must often be converted to binary to be useful to network devices. Each of the 4 bytes is converted individually when displayed in binary notation. For example, the dotted decimal address above would be the following in binary.

11000000 10101000 00000001 00000001