IPv4 vs IPv6: Key Differences Developers Should Know

Jan 18, 2026 · 6 min read

The internet is slowly transitioning from IPv4 to IPv6, and this shift affects everything from network configuration to IP geolocation accuracy. Here's what you need to know as a developer.

Quick Comparison

Why IPv4 Is Running Out

IPv4 supports about 4.3 billion unique addresses. That sounds like a lot, but with smartphones, IoT devices, and cloud infrastructure, we passed that number years ago. The last blocks of IPv4 addresses were allocated by IANA in 2011.

The workaround has been NAT (Network Address Translation) — multiple devices sharing a single public IP. Your home router does this: all your devices share one public IPv4 address. This works but creates problems for geolocation and peer-to-peer connections.

How IPv6 Solves This

IPv6 has 340 undecillion addresses (3.4 × 10³⁸). That's enough to assign a unique address to every atom on Earth's surface — multiple times over. With IPv6, every device can have its own globally unique address, eliminating the need for NAT.

Impact on IP Geolocation

The IPv4-to-IPv6 transition has real implications for geolocation accuracy:

IPv4 Geolocation

• Well-established databases with decades of mapping data
• NAT means multiple users share one IP — location resolves to the NAT gateway
• Carrier-grade NAT (CGNAT) can put thousands of mobile users behind one IP
• Generally accurate to city level in developed countries

IPv6 Geolocation

• Each device can have a unique address — potentially more precise mapping
• Newer databases, less historical data — accuracy is still catching up
• ISPs assign large IPv6 blocks to regions, making country/region detection reliable
• Privacy extensions (RFC 4941) rotate addresses, making tracking harder

What This Means for Your Code

If you're using a geolocation API like Kamero, the IPv4/IPv6 distinction is handled transparently — the API returns location data regardless of which protocol the visitor uses:

// Works the same for IPv4 and IPv6 visitors
const { ip, city, country } = await fetch(
  "https://geo.kamero.ai/api/geo"
).then(r => r.json());

// ip might be "203.0.113.42" (IPv4)
// or "2607:f8b0:4004:800::200e" (IPv6)
console.log(ip, city, country);

Handling Both Formats in Code

If you're storing or validating IP addresses, make sure your code handles both formats:

// JavaScript: Check if an IP is IPv4 or IPv6
function isIPv6(ip: string): boolean {
  return ip.includes(":");
}

function isIPv4(ip: string): boolean {
  return /^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/.test(ip);
}

// Database: Use a column type that supports both
// PostgreSQL: inet type handles both IPv4 and IPv6
// MySQL: Use VARCHAR(45) — max IPv6 length is 45 chars
// MongoDB: Store as string

IPv6 Adoption by Region (2026)

These numbers mean a significant portion of your visitors are already on IPv6. If your infrastructure or logging only handles IPv4, you're missing data.

Key Takeaways

• IPv6 adoption is accelerating — plan for both protocols in your code
• Geolocation works for both, but IPv6 databases are still maturing
• Use APIs that handle both transparently (like Kamero) so you don't have to worry about it
• Store IPs in formats that support both (VARCHAR(45) or inet type)
• Don't assume all IPs are IPv4 — validate and handle both