Internet Protocol Version 4 Packet Header

What Does Internet Protocol Version 4 Packet Header Mean?

An Internet Protocol version 4 packet header (IPv4 packet header) contains application information, including usage and source/destination addresses. IPv4 packet headers contain 20 bytes of data and are normally 32 bits long.


A packet is a network communication data unit containing fixed or variable lengths. However, a single packet contains three portions: header, body and trailer.

Techopedia Explains Internet Protocol Version 4 Packet Header

A 20-byte header contains almost 13 multipurpose fields, which hold specific related object information such as application, data type and source/destination addresses. The following are detailed header field descriptions:

  • Version: This contains the Internet header format and uses only four packet header bits.
  • Internet header length (IHL): This 32-bit field stores IP header length information.
  • Type of service (ToS): This provides network service parameters.
  • Datagram size: This contains combined data and header length.
  • Identification: This 16-bit field contains a specific number for primary data identification.
  • Flags: This router fragment activity is controlled by three flags.
  • Fragmentation offset: This is a fragment identification via offset value.
  • Time to Live (TTL): This contains the total number of routers allowing packet pass-through.
  • Protocol: This 8-bit field contains header transport packet information.
  • Header checksum: It checks and monitors communication errors.
  • Source address: It stores source IP address.
  • Destination address: It stores destination IP address.
  • Options: This is the last packet header field and is used for additional information. When it is used, the header length is greater than 32 bits.

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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.