IPv4

IPv4 moves packets across interconnected networks. It does not promise delivery, preserve order, or recover lost data. Its job is narrower: label each packet with addresses and give routers enough information to forward that packet toward a destination.

That narrow job is why IPv4 sits at the center of many network designs. Applications use transport protocols such as TCP or UDP. Those transport messages become IPv4 payloads. A local network then carries each IPv4 packet to either the destination or the next router.

The packet is the unit of work

IPv4 is connectionless. Each packet, also called a datagram, is handled as an independent unit. A packet contains a header followed by its payload.

The header includes:

• A version value that identifies IPv4
• A source address and destination address
• A protocol value that identifies the next-layer payload
• A time to live value that limits how long the packet can circulate
• Length, checksum, and fragmentation fields

The header checksum protects the IPv4 header, not the payload. IPv4 itself does not acknowledge packets or retransmit missing ones. Higher-layer protocols add reliability when an application needs it.

Addresses identify interfaces