IPv4 Deep Dive: Addressing, Subnetting, NAT, and Real-World Limitations

Internet Protocol version 4 (IPv4) is one of the most important technologies ever created for computer networking. Despite being designed in the early 1980s, IPv4 still carries the majority of global internet traffic today.

To understand networking, cloud infrastructure, security, and routing, you must understand IPv4 deeply — not just its address format, but how it behaves in real networks.

This article provides a deep, practical explanation of IPv4, covering addressing, subnetting, NAT, routing behavior, and why IPv4 still matters in a world moving toward IPv6.

What Is IPv4?

IPv4 is a connectionless, packet-switched network protocol responsible for identifying devices and routing packets across interconnected networks.

Each device on an IPv4 network is identified by a 32-bit address, written in dotted-decimal notation:

192.168.1.10

IPv4 operates at Layer 3 (Network Layer) of the TCP/IP and OSI models.

IPv4 Address Structure

An IPv4 address consists of four 8-bit octets, giving a total of 32 bits:

11000000.10101000.00000001.00001010

This allows for approximately 4.29 billion unique addresses:

2³² = 4,294,967,296

In practice, far fewer are usable due to reservations, special-purpose ranges, and inefficient early allocation.

Public vs Private IPv4 Addresses

IPv4 defines private address ranges that are not routable on the public internet.

These ranges are heavily used behind routers, firewalls, and cloud networks.

Subnetting Explained

Subnetting divides a larger network into smaller, manageable segments called subnets.

Subnets are defined using a subnet mask or CIDR prefix:

192.168.1.0/24

This means:

• 24 bits for the network
• 8 bits for host addresses
• 254 usable hosts

Subnetting improves:

• Routing efficiency
• Security isolation
• Broadcast control
• Address utilization

NAT: The Lifeline of IPv4

Network Address Translation (NAT) is the primary reason IPv4 has survived decades beyond its original limits.

NAT allows multiple private IP addresses to share a single public IPv4 address.

NAT hides private networks behind public IPs.

Common NAT types:

• SNAT (Source NAT)
• DNAT (Destination NAT)
• PAT (Port Address Translation)

While NAT conserves addresses, it breaks end-to-end connectivity and complicates modern applications.

IPv4 Routing Fundamentals

Routers forward IPv4 packets based on destination address and routing tables.

Routing decisions are influenced by:

• Prefix length (longest match wins)
• Routing protocols (OSPF, BGP, RIP)
• Administrative distance
• Metrics and policies

IPv4 routing scalability is one reason why CIDR and route aggregation were introduced.

Limitations of IPv4

• Address exhaustion
• No native encryption
• Heavy reliance on NAT
• Complex network designs
• Poor support for massive IoT scale

These limitations directly led to the development of IPv6.

Why IPv4 Still Dominates

Despite its flaws, IPv4 remains dominant due to:

• Universal support
• Legacy infrastructure
• Operational familiarity
• NAT-based workarounds

Modern networks operate in a dual-stack IPv4 + IPv6 world.

Final Thoughts

IPv4 is far more than a legacy protocol — it is the foundation upon which modern networking knowledge is built.

Understanding IPv4 deeply is essential for networking, security, cloud architecture, and troubleshooting real-world systems.