IPv4 vs IPv6: What Changed and Why It Matters

The Internet Protocol version 4 (IPv4) has powered the internet since 1981. It was designed when the entire network consisted of a few hundred computers, and the 4.3 billion addresses it offered seemed like an impossible number to exhaust. Four decades later, that number was not enough. IPv6 was created to replace it with an address space so large that running out is not a realistic concern.

Understanding the difference between IPv4 and IPv6 matters if you manage a home network, troubleshoot connectivity problems, or simply want to know why your router now shows two different types of IP addresses.

IPv4 Address Format and Structure

IPv4 uses a 32-bit addressing system. Each address is written as four decimal numbers separated by dots, like 192.168.1.1. Each number (called an octet) represents 8 bits and ranges from 0 to 255. This dotted-decimal notation makes the address human-readable while the underlying binary format is what network equipment actually processes.

The total number of unique IPv4 addresses is 2 to the power of 32, which works out to 4,294,967,296. Not all of those are usable for public devices. Large blocks are reserved for private networks, loopback testing (127.0.0.0/8), multicast (224.0.0.0/4), and other special purposes. The actual number of publicly routable IPv4 addresses is closer to 3.7 billion.

Each IPv4 address splits into a network portion and a host portion. The subnet mask determines where that split happens. For a typical home network with a /24 subnet, the first three octets identify the network and the last octet identifies the device.

IPv4 headers carry 20 bytes of mandatory information including source address, destination address, time to live (TTL), and protocol type. Optional header fields can extend this up to 60 bytes, which adds processing overhead for routers.

IPv6 Address Format and Structure

IPv6 uses a 128-bit addressing system, written as eight groups of four hexadecimal digits separated by colons. A full IPv6 address looks like this: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. That is significantly longer than IPv4, but shorthand rules make it manageable.

Leading zeros within a group can be dropped. One consecutive sequence of all-zero groups can be replaced with a double colon (::). So the address above shortens to 2001:db8:85a3::8a2e:370:7334. These compression rules keep addresses readable without ambiguity.

The total number of unique IPv6 addresses is 2 to the power of 128, which equals roughly 340 undecillion (340 followed by 36 zeros). That is enough to assign billions of addresses to every square metre of Earth’s surface. The number is deliberately excessive to allow for flexible subnetting and to prevent the scarcity problem from ever recurring.

IPv6 addresses divide into a network prefix (typically the first 64 bits) and an interface identifier (the remaining 64 bits). The network prefix identifies the subnet, while the interface ID is often derived from the device’s hardware address or generated randomly for privacy.

Why IPv4 Ran Out

The Internet Assigned Numbers Authority (IANA) distributed the last blocks of unallocated IPv4 addresses in February 2011. Regional Internet Registries (RIRs) across different continents exhausted their pools over the following years. APNIC (Asia-Pacific) ran out first in 2011. RIPE NCC (Europe) followed in 2012. ARIN (North America) exhausted its free pool in 2015. LACNIC (Latin America) hit its limit in 2014. AFRINIC (Africa) was the last, reaching exhaustion in 2022.

Several factors drove the shortage. The original allocation system gave out addresses in enormous Class A and Class B blocks to organizations that never used them all. Millions of early adopters hold far more IPv4 addresses than they need. The mobile revolution added billions of smartphones, each wanting internet access. The Internet of Things expanded addressable devices from computers and phones to thermostats, cameras, doorbells, and light bulbs.

Network Address Translation (NAT) has been the primary workaround. NAT allows hundreds of devices behind a single router to share one public IPv4 address. Carrier-Grade NAT (CGNAT) extends this further, putting thousands of customers behind a single public address at the ISP level. These techniques buy time but add complexity and break certain applications that need direct device-to-device connections.

Dual-Stack: Running Both Protocols

Dual-stack is the transition strategy that keeps the internet functional during the shift from IPv4 to IPv6. A dual-stack device or network runs both protocols simultaneously, choosing IPv4 or IPv6 on a per-connection basis depending on what the destination supports.

When your computer connects to a server that has both an IPv4 address and an IPv6 address (which most major sites do), your operating system uses a preference algorithm. Modern systems typically prefer IPv6 when available, falling back to IPv4 when the destination or the path only supports the older protocol. This selection happens in milliseconds during DNS resolution and connection setup.

Your router likely already supports dual-stack. Most ISPs have been rolling out IPv6 alongside their existing IPv4 service. When dual-stack is active, your router maintains two address pools: one for IPv4 private addresses assigned via DHCP and one for IPv6 addresses assigned via DHCPv6 or SLAAC (Stateless Address Autoconfiguration).

The dual-stack period will last as long as significant portions of the internet remain IPv4-only. Given the installed base of older equipment and the slow pace of enterprise migration, this period will extend well into the 2030s.

Adoption Rates and Current Status

IPv6 adoption varies significantly by country, ISP, and network type. Google’s public statistics show that roughly 45% of connections to their services now use IPv6. India leads adoption at over 70%, driven by mobile carrier Reliance Jio deploying IPv6 natively. The United States sits around 50%. Germany, France, and Japan have crossed 60%. Countries with newer network infrastructure tend to adopt faster because they have less legacy IPv4 equipment to maintain.

Major content providers including Google, Facebook, Netflix, and Cloudflare have been fully IPv6-enabled for years. Cloud platforms like AWS, Azure, and GCP offer IPv6 support across their services. The backbone of the internet is largely dual-stack.

The holdouts are primarily enterprise networks, smaller ISPs, and older consumer equipment. Many businesses rely on IPv4-only applications, firewalls, and network monitoring tools that have not been updated. Some ISPs in developing regions lack the technical resources or business incentive to deploy IPv6.

What This Means for Home Users

For most home users, the IPv4 to IPv6 transition happens silently. Your router handles both protocols automatically. Your devices connect over whichever version works best for each destination. You do not need to configure anything manually in most cases.

There are a few practical differences worth knowing. If your ISP uses Carrier-Grade NAT (CGNAT) to share IPv4 addresses among customers, you may notice issues with port forwarding, online gaming, or hosting any kind of server. IPv6 can bypass this because each device can receive its own globally routable address, eliminating the need for NAT entirely.

IPv6 also changes how firewalling works on your network. With IPv4 and NAT, your devices are naturally hidden behind your router. With IPv6, each device has a public address and relies on the router’s firewall rules rather than NAT obscurity for protection. Modern routers handle this properly, but it is worth checking that your router’s IPv6 firewall is enabled.

If you are buying a new router, confirm it supports both IPv4 and IPv6 with a proper firewall for each. Check whether your ISP provides native IPv6 or only IPv4. The default gateway page on your router’s admin panel will typically show both your IPv4 and IPv6 addresses when dual-stack is active.