IPv4 vs IPv6: A Complete Comparison
The internet is slowly transitioning from a 40-year-old addressing system (IPv4) to its modern replacement (IPv6). Here's what each one is, why it matters, and what the difference means for you — whether you're a curious beginner or a network engineer.
Quick answer
IPv4 is the original internet addressing system from 1981 — uses 32-bit addresses (like 192.168.1.1) with about 4.3 billion possible combinations. IPv6 is its modern replacement — uses 128-bit addresses (like 2001:0db8::8a2e:0370:7334) with effectively unlimited capacity. The internet ran out of free IPv4 addresses in 2011, and IPv6 is the long-term solution.
What is IPv4?
IPv4 (Internet Protocol version 4) is the addressing system the internet was built on. Standardized in 1981 by RFC 791, it's been the dominant protocol for over 40 years. When you see an address like 192.168.1.1 or 73.118.92.45, that's IPv4.
Each IPv4 address is a 32-bit number, usually written as four decimal numbers (0–255) separated by dots. Behind the scenes, the address 192.168.1.1 is really the binary number 11000000.10101000.00000001.00000001 — humans just find the dotted-decimal format easier to read.
That 32-bit space gives us 232 = about 4.3 billion possible addresses. In 1981, that seemed infinite. In 2026, with billions of phones, computers, smart TVs, security cameras, refrigerators, and other connected devices, it's clearly not enough.
What is IPv6?
IPv6 (Internet Protocol version 6) is the next-generation addressing system, designed to replace IPv4. It was standardized in 1998 by RFC 2460 (and updated by RFC 8200), and after a slow start, it's now actively used by major networks worldwide.
IPv6 uses 128-bit addresses written as eight groups of four hexadecimal digits separated by colons. For example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334.
That 128-bit space gives us 2128 — approximately 340 undecillion addresses. To put that in perspective: there are roughly enough IPv6 addresses to give every grain of sand on Earth its own unique address, with addresses to spare.
The design goals of IPv6 went beyond just more addresses. The new protocol also includes:
- Simplified packet headers for faster routing
- Built-in security (IPsec) as an optional standard
- Better mobile support with Mobile IPv6
- Automatic configuration via Stateless Address Autoconfiguration (SLAAC)
- No more NAT requirement — every device can have a unique global address
Why we ran out of IPv4 addresses
When IPv4 was designed in 1981, the internet had about 200 computers on it. The designers thought 4.3 billion addresses would last forever. They were wrong by several orders of magnitude.
The first warning signs appeared in the early 1990s. By 2011, the Internet Assigned Numbers Authority (IANA) handed out its last block of free IPv4 addresses. Regional registries (ARIN for North America, RIPE for Europe, APNIC for Asia-Pacific) have since exhausted their pools too.
For most of the last decade, the internet has been making do with workarounds:
- Network Address Translation (NAT): Lets many devices share one public IPv4 (this is why your home has one public IP for many devices).
- Carrier-Grade NAT (CGNAT): ISPs share one public IPv4 among many customers, especially in mobile networks.
- IP recycling and resale: Unused IPv4 blocks are now bought and sold for $30-50 per address.
These workarounds have kept IPv4 functional, but they add complexity, increase latency, break some applications (like peer-to-peer connections), and force ISPs to spend significant money on NAT infrastructure. IPv6 was created so we wouldn't need these workarounds at all.
IPv4 vs IPv6: Side-by-side comparison
| IPv4 | IPv6 | |
|---|---|---|
| Released | 1981 | 1998 |
| Address size | 32 bits | 128 bits |
| Address format | Dotted decimal: 192.168.1.1 |
Hexadecimal: 2001:0db8::1 |
| Total addresses | 4.3 billion | 340 undecillion |
| Header size | 20–60 bytes (variable) | 40 bytes (fixed) |
| NAT required? | Usually yes | No |
| Built-in encryption | No (separate IPsec) | Optional (IPsec) |
| Auto-configuration | DHCP required | SLAAC or DHCPv6 |
| Broadcast support | Yes | No (multicast only) |
| Checksum in header | Yes | No (handled by upper layers) |
| Current adoption | ~60% of traffic | ~40% of traffic |
Address format deep dive
IPv4 address structure
An IPv4 address has four "octets" (8-bit numbers) separated by dots:
192.168.1.1
Each octet can be 0–255 (because 28 = 256). The full range goes from 0.0.0.0 to 255.255.255.255. Certain ranges are reserved:
10.0.0.0/8,172.16.0.0/12,192.168.0.0/16— private networks127.0.0.0/8— loopback (your own device)169.254.0.0/16— link-local (when DHCP fails)224.0.0.0/4— multicast
IPv6 address structure
An IPv6 address has eight groups of four hexadecimal digits separated by colons:
2001:0db8:85a3:0000:0000:8a2e:0370:7334
That's 128 bits total (8 groups × 16 bits each). To save space, IPv6 has two abbreviation rules:
- Leading zeros can be omitted in any group.
0000:0db8becomes0:db8. - Consecutive groups of zeros can be replaced with
::(but only once per address).2001:0db8:0000:0000:0000:0000:0000:0001becomes2001:db8::1.
So the full address above can be written more concisely as 2001:db8:85a3::8a2e:370:7334.
IPv6 has reserved ranges too:
::1— loopback (equivalent to127.0.0.1)fe80::/10— link-local addresses (auto-assigned)fc00::/7— unique local addresses (private)2000::/3— global unicast (public IPv6 addresses)ff00::/8— multicast
Engineer note: IPv6's elimination of broadcast in favor of multicast was a deliberate design choice. Broadcast traffic was a major contributor to IPv4 network congestion at scale. IPv6 also dropped header checksums because modern data-link layers (Ethernet) and transport layers (TCP/UDP) already perform checksum validation — the redundancy in IPv4 was wasted CPU cycles.
Current adoption status (2026)
IPv6 adoption has grown steadily but slowly. As of 2026, Google reports that approximately 40–45% of users access its services over IPv6, with significant regional variation:
- India: Over 70% IPv6 adoption (one of the highest globally)
- United States: Around 50% adoption, driven by Comcast, AT&T, and T-Mobile
- Germany, France: Around 50–75% adoption
- China: Rapidly growing past 30%
- Russia, much of Latin America: Still under 10%
Major content providers (Google, Facebook, Cloudflare, Netflix, AWS) have full IPv6 support. Mobile networks have been the fastest adopters because they had the most pressure from device counts.
For home internet in the US: most major ISPs offer IPv6 by default, but some still don't enable it on all customer accounts. Check our homepage tool to see if your connection has IPv6 enabled.
How the transition works
Switching the entire internet from IPv4 to IPv6 in a single day was never realistic. Instead, the transition uses several gradual techniques:
Dual stack
The most common approach: devices and networks support both IPv4 and IPv6 simultaneously. When you visit a website, your device tries IPv6 first; if that fails, it falls back to IPv4. This is called "Happy Eyeballs" (RFC 8305) when implemented at the application layer.
Tunneling
IPv6 packets are wrapped inside IPv4 packets to cross networks that only speak IPv4. Common protocols include 6in4, 6to4, and Teredo. Mostly used as a bridge during the transition.
NAT64 + DNS64
Lets IPv6-only clients reach IPv4-only servers by translating addresses at the network edge. Common in mobile networks where end devices speak IPv6 but many older services still require IPv4.
CGNAT (for IPv4 survival)
Not really a transition technology, but worth mentioning: ISPs use Carrier-Grade NAT to share a single public IPv4 among many customers. This buys time for IPv6 deployment but creates problems for applications that need direct addressability (peer-to-peer, gaming, hosting servers).
Which one are you using right now?
The easiest way to check is to visit our homepage tool. The "IP version" indicator tells you whether your current connection is using IPv4 or IPv6. If you see "IPv6 address" populated with a hexadecimal string, your network supports IPv6. If it shows "Not available," your connection is IPv4-only.
Most modern devices and routers use IPv6 automatically when available. You don't need to configure anything — the protocol is selected based on what the destination server and your network both support.
Frequently asked questions
What is the main difference between IPv4 and IPv6?
IPv4 uses 32-bit addresses with about 4.3 billion possible combinations, written like 192.168.1.1. IPv6 uses 128-bit addresses with effectively unlimited combinations, written like 2001:0db8:85a3::8a2e:0370:7334. IPv6 was created because the internet ran out of IPv4 addresses.
Is IPv6 faster than IPv4?
Slightly, in some cases. IPv6 eliminates the need for Network Address Translation (NAT), which can reduce latency. But in real-world tests, the difference is usually negligible for typical browsing. Most speed differences come from infrastructure quality, not the protocol itself.
Should I use IPv6 or IPv4?
Most modern devices and networks support both simultaneously, called "dual stack." You don't need to choose — your device will use IPv6 when available and fall back to IPv4 when not. Adoption of IPv6 is growing but IPv4 is still dominant in most regions.
Is IPv6 more secure than IPv4?
IPv6 includes IPsec (encryption) as an optional standard, but in practice this is rarely used at the address level. IPv6 also exposes individual devices directly (instead of hiding them behind NAT), which can be either a security risk or a feature depending on configuration. Net security difference is minimal for most users.
Can IPv4 and IPv6 work together?
Yes. The standard transition approach is called "dual stack," where networks support both protocols simultaneously. Your device picks whichever protocol the destination server supports. Other techniques like NAT64 and tunneling let IPv6-only networks communicate with IPv4-only services.
Will IPv4 ever be turned off?
Not anytime soon. Despite the address shortage, IPv4 is too deeply embedded in legacy systems, business applications, and embedded devices to be removed quickly. Most network engineers expect IPv4 to coexist with IPv6 for decades.
How do I switch to IPv6?
You usually don't need to. If your ISP offers IPv6, your modern router and devices will use it automatically. To check, visit our homepage tool. If your IPv6 shows as "Not available," contact your ISP — some require you to opt in to IPv6, and some still don't support it.