IPv4 vs IPv6: What's the Difference?

The main difference between IPv4 and IPv6 is address capacity. IPv4 uses 32-bit addresses, allowing about 4.3 billion possible values. IPv6 uses 128-bit addresses, allowing about 340 undecillion, or 3.4 × 10³⁸, possible values. These are total address-space sizes; some ranges have special purposes.

Both versions help devices exchange data across networks. IPv6 provides much more room for growth, but IPv4 remains part of how the internet works. The address-size change is defined in the IPv6 specification, RFC 8200.

If the underlying concept is new to you, start with What Is an IP Address?.

IPv4 vs IPv6 at a glance

The example addresses are reserved for documentation under RFC 5737 and RFC 3849. They are illustrations, not live destinations.

What is IPv4?

IPv4 means Internet Protocol version 4. Its familiar address format looks like 192.0.2.10: four numbers, each between 0 and 255, separated by dots.

IPv4’s limited address space creates a practical constraint. Not every possible address can be assigned to a public internet connection, because some ranges are reserved for private networks and other uses.

Providers therefore need to manage available public IPv4 space carefully. For example, ARIN reports that its free pool was depleted in September 2015 and describes the remaining request and transfer options in its IPv4 addressing guide.

Exhaustion does not mean existing IPv4 addresses stop working. It means obtaining additional space is constrained.

What is IPv6?

IPv6 means Internet Protocol version 6. Its much larger address space allows networks to assign addresses without the same pressure to make many devices share a single public address.

A full IPv6 address has eight groups of hexadecimal digits. Leading zeros can be omitted, and one consecutive run of all-zero groups can be replaced with ::.

For example, these represent the same address:

• Full form: 2001:0db8:0000:0000:0000:0000:0000:0010
• Short form: 2001:db8::10

The shortening changes how the address is written, not its value. RFC 4291 defines the notation.

How do devices get their addresses?

IPv4 devices commonly use DHCP to receive an address automatically. Administrators can also configure fixed addresses.

IPv6 supports stateless address autoconfiguration, usually shortened to SLAAC. With SLAAC, a device can form an address using network-prefix information advertised by a router. A prefix identifies an address range belonging to the network. IPv6 networks can also use DHCPv6, and both methods can coexist. RFC 4862 explains SLAAC.

For most users, this happens in the background when a device joins a network.

Can IPv4 and IPv6 work together?

Yes, with the right network support. An IPv4-only endpoint and an IPv6-only endpoint cannot communicate directly using their native protocols alone.

One common approach is dual stack: a device or network supports both versions. It can use IPv4 for an IPv4 destination and IPv6 for an IPv6 destination. This approach is described in RFC 4213.

For example, a website can publish an A record for its IPv4 address and an AAAA record for its IPv6 address. A visitor’s software can then attempt a supported connection. Connection-selection methods such as Happy Eyeballs help avoid long delays when one path is unavailable or slow.

Translation is another approach. NAT64, usually paired with DNS64, can let IPv6-only clients reach IPv4 servers. It requires a translator in the network; it is not simply a change in how an address is written. RFC 6146 describes this mechanism.

Is IPv6 faster than IPv4?

Neither version is a universal speed upgrade. For a particular website, the two versions may take different routes or encounter different network conditions. Your provider, the destination, congestion, and the quality of each path all affect the result.

The Happy Eyeballs specification accounts for differences in connectivity and responsiveness between available paths. The practical conclusion is to measure performance on the network and services you actually use; the IP version alone does not predict it.

Is IPv6 more secure than IPv4?

Using IPv6 does not automatically encrypt traffic or protect a device. Both versions need appropriate firewall rules, software updates, and application security. IPv4 also supports IPsec, so support for that technology is not an exclusive IPv6 benefit. The Internet Society’s IPv6 security FAQ explains these distinctions.

IPv6 can give devices globally routable addresses without the address-sharing NAT common in IPv4 networks. A firewall can still restrict incoming traffic. Globally routable does not mean every service is open to everyone.

The distinction between address scope and access is covered in Public vs Private IP Addresses.

What should businesses consider?

For a public website or application, the useful question is whether customers can reach it reliably over the connections they have.

When adding IPv6, check the full service path: connectivity, DNS, hosting, load balancers, firewall rules, and monitoring. Test both versions if the service supports both. An IPv6 address on a server is only one part of making the application reachable.

If retaining public addresses across infrastructure providers matters, BYOIP is a separate consideration. Confirm which address families the provider supports for the specific service; IPv4 BYOIP support does not establish IPv6 support.

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