IPv4 vs IPv6: What's the Difference?

You're probably using IPv4 right now — it's what your router gives to your computer and phone. But IPv6 is coming, and it's worth understanding why.

The short version: IPv4 has about 4.3 billion addresses. IPv6 has enough to give every atom on Earth its own IP — and then some.

IPv4: The System That Ran Out of Space

IPv4 (Internet Protocol version 4) has been around since 1983. An IPv4 address looks like this:

192.168.1.100
172.16.0.1
8.8.8.8

That's 32 bits of addressing space, giving us approximately 4.3 billion unique addresses. In 1983, that seemed like plenty. But fast forward to today — every phone, tablet, laptop, smart TV, smart speaker, and IoT device needs an IP. We've simply run out.

The internet now uses a technique called NAT (Network Address Translation) to share public IPs across many private addresses. A single public IP can serve hundreds of devices behind it. But this is a workaround, not a solution.

IPv6: The New Kid on the Block

IPv6 addresses look very different:

2001:0db8:85a3:0000:0000:8a2e:0370:7334
fe80::1
2001:4860:4860::8888

That's 128 bits — giving us 340 undecillion addresses. (That's 340 followed by 36 zeros.) The number is so large we just say "practically unlimited."

IPv6 Addresses Are Shorter to Write!

Notice in the examples above, some parts are just "::" — that's called zero compression. IPv6 lets you:

Skip leading zeros: 0db8 → db8
Collapse runs of zeros: 0000:0000:0000:0000 → ::

Full:     2001:0db8:85a3:0000:0000:8a2e:0370:7334
Compressed: 2001:db8:85a3::8a2e:370:7334

IPv4 vs IPv6: Side-by-Side

Feature	IPv4	IPv6
Address length	32 bits	128 bits
Total addresses	~4.3 billion	~340 undecillion
Written as	192.168.1.100	2001:db8::1
Subnet mask	255.255.255.0	/64
DHCP	Required	Optional (autoconfig)
Security	Optional (IPsec)	Required (IPsec)
Header size	20 bytes	40 bytes
Fragmentation	Router/host	Source only

What IPv6 Means for You

Benefits of IPv6:

No more NAT: Every device can have a unique public address — direct connections are easier
No more address shortages: Never worry about running out
Better security: IPsec is built into the protocol, not optional
Auto-configuration: Devices can assign themselves an IP without a DHCP server
Simpler headers: Faster routing for better performance

The Challenge:

Switching isn't instant. Every device, router, and service on the internet needs to support IPv6. We call this "dual stack" — running both IPv4 and IPv6 simultaneously during the transition.

⚠️ The Big Problem: IPv4 and IPv6 are not compatible! An IPv4 device can't directly talk to an IPv6 server without translation. That's why the transition will take years.

Checking Your Connection

Want to see if your network supports IPv6?

Test your IPv6 connectivity:

Visit ipv6-test.com

See your IPv6 address (Windows):

ipconfig | findstr "IPv6"

See your IPv6 address (Mac/Linux):

ifconfig | grep "inet6"

The Future: Both Coexist

We're in a transitional period. Your network probably has both:

A private IPv4 address (like 192.168.1.100)
A private IPv6 address (like fe80::1)
A public IPv4 address from your ISP
An IPv6 address if your ISP supports it

Most services still work via IPv4. But as more networks enable IPv6, you'll eventually switch over. The subnetting concepts stay the same — /64 is the standard home network size in IPv6.

👉 Coming Soon: IPv6 Subnet Calculator