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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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