IP - Internet Protocol

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Developed during the 1970s, Internet Protocol (IP) is the fundamental network protocol used across the Internet, home networks and business networks. Internet Protocol is often used together with the Transport Control Protocol (TCP) and referred to interchangeably as both IP and TCP/IP.

IPv4 and IPv6

Most networks use the Internet Protocol version 4 (IPv4) standard that features IP addresses four bytes (32 bits) in length.

The newer Internet Protocol version 6 (IPv6) standard features addresses 16 bytes (128 bits) in length. See also - What Happened to IPv5?

How Internet Protocol Works

Data on an Internet Protocol network is organized into messages. These messages are sometimes called packets and sometimes datagrams, but in layman's terms, they all refer roughly to the same concept. Each IP datagram includes both a header (that specifies the source, destination, and other information about the data) and the message data itself.

Internet Protocol functions at layer 3 of the OSI model. IP can, therefore, run on top of different data link interfaces including Ethernet and Wi-Fi.

For more, see - Internet Protocol Tutorial.

IP Datagrams

Each IP datagram includes both a header (that specifies the source, destination, and other information about the data) and the message data itself. IP uses a base header of 20 bytes (5 longwords) in length, with additional expanded header options, followed by data.

The IP headers contain:

  • Word 1: Version - 4 bits, Header Length (in longwords) - 4 bits, Type of Service / Differentiated Services Code Point (DSCP) - 8 bits, Datagram Length (in bytes) - 16 bits
  • Word 2: ID Number - 16 bits, Fragmentation Flags - 3 bits, Fragmentation Offset - 13 bits
  • Word 3: Time to Live - 8 bits, Transport Protocol - 8 bits, Header Checksum - 16 bits
  • Word 4: Source IP Address - 32 bits
  • Word 5: Destination IP Address - 32 bits
  • Variable length fields (can be empty): Options, and Padding

IP datagram payloads can be of variable length. The minimum size of an IP datagram is 28 bytes, using the minimum 20 bytes of header information, followed by the minimum of 8 bytes of data. The maximum size of an IP datagram payload is 65,535 bytes minus the header size.

Internet Protocol does not use its own datagram footer.

Using Internet Protocol

Internet Protocol is used by many higher level protocols, principally TCP and UDP. All popular Internet software applications including Web browsers, FTP clients, and email programs, rely on IP.

IP supports unique addressing for computers on a network Most people who work with Internet Protocol do so through IP addresses.

The IPX/SPX protocols used by Novell NetWare were at one time a notable competitor to TCP/IP.  IPX/SPX was designed to offer similar functionality and also had some technical advantages over TCP/IP. However, with the decline of NetWare as a business operating system, IPX/SPX also faded into relative obscurity.