Internet Protocol Version 4 Packet Header (IPv4 packet header)

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.