How does IPv4 work and why is it needed

The internet is a vast network in which devices exchange data. For a data packet to reach its recipient, every device must have a unique identifier. This role is fulfilled by an IP address, and the IPv4 protocol is the oldest and most widely used method of such addressing, operating since 1981.

What is IPv4

IPv4 (Internet Protocol version 4) is the fourth version of the internet protocol, described in RFC 791. Its main task is to transmit datagrams from the sender to the recipient across interconnected networks.

An IPv4 address is a 32-bit number. For convenience, it is written as four decimal numbers from 0 to 255 separated by dots. For example: 192.168.1.1 or 123.45.67.89 . This structure provides about 4.3 billion unique combinations — the theoretical number of devices that can be directly connected to the internet.

How IPv4 works

Let’s explain using the most common scenario: a computer sends a request to open a website. The data is split into packets, and each one receives a header with the sender’s and recipient’s addresses.

• The packet travels along the chain: computer → router in the local network → provider’s router → transit nodes → server hosting the website.

At each intermediate device, the router checks the destination address and decides where to send the packet next. When the packet reaches the server, it forms response packets and sends them back using the same principle.

Structure of an IPv4 packet

An IPv4 packet consists of a header and data. The header contains service information without which delivery is impossible.

Main fields:

• Version (4 bits) — indicates that IPv4 is used. This helps devices understand which protocol version to work with.
• IHL (4 bits) — header length. Minimum value is 5 (20 bytes), maximum is 15 (60 bytes). It shows where the header ends and the data begins.
• Type of Service (8 bits) — defines packet priority. It allows distinguishing, for example, between regular web traffic and voice calls that require low latency.
• Total Length (16 bits) — the size of the entire datagram including data. Maximum is 65535 bytes, but in practice packets are rarely that large.
• Identification (16 bits) — packet number. If the packet is fragmented, the receiver reassembles it using this identifier.
• Flags (3 bits) — control fragmentation. They indicate whether the packet can be split and whether more fragments follow.
• Fragment Offset (13 bits) — indicates the position of this fragment in the original packet.
• Time to Live (TTL, 8 bits) — a counter that decreases at each router. When TTL reaches zero, the packet is discarded. This protects the network from endlessly circulating lost packets.
• Protocol (8 bits) — indicates which upper-layer protocol (TCP, UDP, ICMP) should receive the data after delivery.
• Header Checksum (16 bits) — verifies the integrity of the header. If errors occur during transmission, the packet is discarded.
• Source IP Address (32 bits) — where the packet came from.
• Destination IP Address (32 bits) — where the packet is going.
• Options (variable length) — additional settings, rarely used.
• Padding — aligns the header to a 32-bit boundary.

IPv4 addressing system

All IPv4 addresses are divided into classes, but today classless addressing (CIDR) is more commonly used, where the subnet mask determines which part of the address belongs to the network and which to the host.

Some ranges are reserved for special purposes :

• 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — private addresses for local networks. They are not routed on the internet.
• 127.0.0.0/8 — loopback, addresses for a computer to communicate with itself.
• 169.254.0.0/16 — automatically assigned if no address is received from DHCP.
• 0.0.0.0/8 — denotes the “own” network, used during boot without an IP.
• 224.0.0.0/4 — multicast, for group data transmission.

Why IPv4 is still needed today

Simple structure

32-bit addresses are easy to remember and enter manually. Configuring IPv4 networks does not require specialized knowledge.

Broad compatibility

IPv4 is supported by absolutely all hardware and software. Any router, any operating system, and any website work with IPv4 “out of the box.” It is a universal standard that requires no additional checks.

Default use in most networks

Even where IPv6 has already been implemented, support for the fourth version is almost always retained. Dual stack (IPv4 + IPv6) is standard practice, ensuring that a device can access any resources.

Primary standard in corporate and home networks

Millions of local networks are built on IPv4, and no one is in a hurry to switch them to IPv6 because it is expensive and offers no obvious benefits to regular users.

Support by all internet protocols and services

DNS, HTTP, SMTP, FTP, and dozens of other protocols work perfectly over IPv4. The internet infrastructure is built around it.

Security and limitations of IPv4

The main problem with IPv4 is address exhaustion. The 4.3 billion unique combinations have long been depleted. For now, NAT (Network Address Translation) helps, allowing multiple devices to access the internet through a single public IP.

But NAT has its drawbacks:

• External devices cannot initiate connections to a computer behind NAT.
• P2P applications (games, video calls) require complex workarounds — STUN, TURN, ICE — which slow down traffic and sometimes fail altogether .
• Multi-layer NAT (CGNAT) used by providers complicates things even further.
• From a security standpoint, IPv4 has no built-in encryption mechanisms. IPsec for IPv4 is optional, so protection must be added on top (TLS for websites, VPN for connections) . The header checksum only verifies integrity, not authenticity.

In addition, the limited address space makes IPv4 networks vulnerable to scanning. An attacker can enumerate all possible addresses within a reasonable time.

Conclusion

Despite technical limitations and address shortages, IPv4 remains the most compatible and widely used protocol. Without it, websites, email, messengers, and thousands of other services would not function.

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