Internet Protocol Version 4 Packet Header (IPv4 packet header)

Last Updated: August 18, 2011

Definition - What does Internet Protocol Version 4 Packet Header (IPv4 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 (IPv4 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.