How does IPv4 work and why is it needed

The internet is a global system where devices constantly exchange data. For information to reach the correct destination, each device must have a unique identifier. This function is performed by an IP address, and IPv4 remains the oldest and most widely used addressing protocol, in operation since 1981.

What is IPv4

IPv4 (Internet Protocol version 4) is defined in RFC 791 and is responsible for delivering data packets between devices across interconnected networks.

An IPv4 address is a 32-bit numeric value. For удобства it is written as four decimal numbers ranging from 0 to 255, separated by dots, for example: 192.168.1.1 or 123.45.67.89. This format provides approximately 4.3 billion unique addresses, which was originally considered sufficient for all connected devices.

How IPv4 works

In a typical scenario, when a user opens a website, the request is divided into smaller data packets. Each packet receives a header containing both the sender’s and the recipient’s IP addresses.

• The packet moves through several stages: computer → local router → provider’s router → intermediate nodes → destination server.

At every step, routers analyze the destination address and determine where to forward the packet next. Once the data reaches the server, a response is generated and sent back using the same process.

Structure of an IPv4 packet

An IPv4 packet consists of a header and a data section. The header contains essential technical information required for delivery.

Main fields include:

• Version — specifies that IPv4 is being used
• IHL — indicates the header length (from 20 to 60 bytes)
• Type of Service — defines traffic priority
• Total Length — full packet size, including data
• Identification — used to reassemble fragmented packets
• Flags — control whether fragmentation is allowed
• Fragment Offset — shows the position of a fragment
• TTL (Time to Live) — limits packet lifetime to prevent infinite routing loops
• Protocol — specifies the upper-layer protocol (TCP, UDP, ICMP)
• Header Checksum — verifies header integrity
• Source IP Address — sender’s address
• Destination IP Address — recipient’s address
• Options — optional parameters (rarely used)
• Padding — ensures proper alignment

IPv4 addressing system

Initially, IPv4 used a class-based addressing model, but today CIDR (Classless Inter-Domain Routing) is the standard. In this approach, a subnet mask determines which part of the address represents the network and which part identifies the host.

Certain address ranges are reserved for specific purposes:

• 0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — private networks not accessible from the public internet
• 0.0.0/8 — loopback addresses for internal communication
• 254.0.0/16 — automatically assigned when DHCP fails
• 0.0.0/8 — refers to the current or unspecified network
• 0.0.0/4 — multicast addresses for group communication

Why IPv4 is still relevant

Simple structure

IPv4 addresses are easy to understand and configure, even without advanced networking knowledge.

Broad compatibility

All hardware, operating systems, and websites support IPv4 by default, making it a universal standard.

Default usage

Even in networks where IPv6 is implemented, IPv4 is almost always supported. Dual-stack configurations ensure compatibility with all resources.

Widespread adoption

Millions of corporate and home networks still rely on IPv4, as transitioning to IPv6 requires significant costs with limited immediate benefits.

Protocol support

Core internet protocols such as DNS, HTTP, SMTP, and FTP operate seamlessly over IPv4, forming the foundation of modern internet infrastructure.

Security and limitations of IPv4

The main limitation of IPv4 is the shortage of available addresses. The original pool of approximately 4.3 billion has already been exhausted. To address this, NAT (Network Address Translation) is used, allowing multiple devices to share a single public IP.

However, NAT introduces several challenges:

• Devices behind NAT cannot receive direct incoming connections
• Peer-to-peer applications require additional technologies such as STUN, TURN, and ICE, which can reduce performance
• Carrier-grade NAT (CGNAT) further complicates connectivity
• From a security perspective, IPv4 does not include built-in encryption. IPsec support is optional, so additional layers such as TLS or VPNs are required. The header checksum only verifies data integrity and does not provide authentication.

Additionally, the limited address space makes IPv4 networks more susceptible to scanning, as attackers can enumerate possible addresses relatively quickly.