IPv4 Header – Version Field (4 bits)

Definition

• The Version field tells a device which Internet Protocol (IP) version the packet uses.
• It is the first field the receiver checks before reading the rest of the IPv4 header.

What Problem It Solves

• Different IP versions have different header formats.
• The Version field prevents a device from interpreting an IPv6 packet as IPv4 (or vice versa), avoiding incorrect packet processing.

What Happens If Not Used

• A router or computer would not know how to read the packet.
• It could misinterpret the header fields, causing the packet to be dropped or processed incorrectly.

Easy Wording

It tells the receiver which "language" the IP packet is written in.

Layman Example

Imagine receiving a book without knowing whether it's written in English or Arabic. You must first identify the language before reading it. The Version field does exactly that for IP packets.

Technical Example

Request Flow:

• Your browser sends a request to example.com.
• DNS returns an IPv4 address.
• Your computer creates an IPv4 packet and sets Version = 4.
• Each router first checks Version = 4, then knows to process the remaining IPv4 header correctly.
• The packet reaches the web server.

Limitation: The Version field only identifies the IP format. It doesn't tell where the header ends if optional fields exist. IHL (Internet Header Length), solves this.