IPv4 Header Format Explained | Key Elements and Their Significance

The IPv4 header serves as the starting point of every IPv4 packet and plays a vital role in routing the packet to its intended destination. This fixed-size data structure contains essential information used by networking hardware. The fields within the IPv4 header are listed below in sequential order:

IPv4 Header Format Overview:

Version (4 bits) – Indicates the version of the IP protocol being used. Always set to 4 for IPv4 packets.
Header Length (4 bits) – Indicates the length of the header in 32-bit words, ranging from 5 to 15 due to optional fields.
Type of Service (8 bits) – Describes handling needs and packet priority.
Total Length (16 bits) – Indicates the overall packet length in bytes, including header and data.
Identification (16 bits) – Used for fragmentation and reassembly, assigns a unique identification number to the packet.
Flags (3 bits) – Regulates fragmentation with “More Fragments” (MF) and “Don’t Fragment” (DF) flags.
Fragment Offset (13 bits) – Indicates the offset of data in the packet relative to the original unfragmented packet.
Time to Live (8 bits) – Specifies the maximum number of hops a packet can make before being discarded.
Protocol (8 bits) – Identifies the protocol used in the data section, e.g., TCP, UDP, or ICMP.
Header Checksum (16 bits) – Used to check the header’s integrity.
Source Address (32 bits) – Contains the IP address of the sender.
Destination Address (32 bits) – Contains the IP address of the recipient.
Options (variable) – Optional field for additional information, like security and routing data.