What Is IPv4? | NOC.org

What Is IPv4?

IPv4 (Internet Protocol version 4) is the fourth revision of the Internet Protocol and the first version to be widely deployed. Defined in RFC 791 in 1981, IPv4 has been the foundation of internet communication for over four decades. It is the protocol responsible for identifying and locating devices on a network through numerical addresses, enabling packets to be routed from source to destination across interconnected networks.

Despite the ongoing rollout of IPv6, IPv4 still carries the majority of internet traffic today. Understanding how IPv4 works remains essential for anyone managing web infrastructure, DNS, or security systems.

32-Bit Addressing and Dotted Decimal Notation

IPv4 uses a 32-bit address space, meaning each address is a sequence of 32 binary digits (ones and zeros). To make these addresses human-readable, they are written in dotted decimal notation — four groups of numbers separated by periods, where each group (called an octet) represents 8 bits and ranges from 0 to 255.

For example, the address 203.0.113.42 is the decimal representation of the binary address 11001011.00000000.01110001.00101010. Each octet maps to one byte, and the full address is exactly 4 bytes (32 bits) long.

A 32-bit address space provides 2³² possible addresses — approximately 4.3 billion. After subtracting reserved ranges (private addresses, multicast, loopback, and other special-purpose blocks), the number of usable public IPv4 addresses is significantly lower.

IPv4 Address Exhaustion

The most critical challenge facing IPv4 is address exhaustion. When the protocol was designed in the early 1980s, 4.3 billion addresses seemed more than sufficient. No one anticipated that billions of smartphones, IoT devices, cloud servers, and connected appliances would each need an address.

The Internet Assigned Numbers Authority (IANA) allocated the last blocks of IPv4 addresses to the regional internet registries (RIRs) in 2011. Most RIRs have since exhausted their free pools, and new IPv4 addresses are now only available through transfers on a secondary market — often at prices exceeding $50 per address.

This scarcity has driven several workarounds:

• NAT (Network Address Translation): Allows multiple devices on a private network to share a single public IPv4 address. NAT is ubiquitous in home and enterprise networks, but it introduces complexity for peer-to-peer applications and can complicate logging and forensics.
• CGNAT (Carrier-Grade NAT): ISPs use CGNAT to share a single public IP among many subscribers, further stretching the available pool but adding another layer of address translation.
• IPv6 adoption: The long-term solution. IPv6 provides a virtually unlimited address space and eliminates the need for NAT.

IPv4 vs. IPv6

While IPv4 has served the internet well, IPv6 addresses its fundamental limitations:

• Address space: IPv4 offers 4.3 billion addresses. IPv6 offers 340 undecillion (3.4 x 10³⁸).
• Header format: IPv6 uses a simplified fixed-length header, improving routing efficiency. IPv4 headers are variable-length and require more processing.
• NAT requirement: IPv4 relies heavily on NAT to conserve addresses. IPv6 gives every device a globally unique address, eliminating the need for NAT.
• Security: IPv6 was designed with IPsec support built in, though in practice both protocols can use IPsec.
• Auto-configuration: IPv6 supports stateless address auto-configuration (SLAAC), allowing devices to generate their own addresses without a DHCP server.

IPv4 in DNS and CDN Infrastructure

In DNS configuration, IPv4 addresses are stored in A records (Address records). When a browser resolves example.com, the authoritative DNS server returns an A record containing the site's IPv4 address. If IPv6 is also configured, a corresponding AAAA record provides the IPv6 address.

Modern CDN and security platforms operate dual-stack infrastructure, accepting connections over both IPv4 and IPv6. This ensures compatibility with the existing IPv4 internet while supporting the growing number of IPv6-only or IPv6-preferred clients.