Why IPv6 Is Needed
With the rapid expansion of the internet, the pool of traditional IPv4 addresses (approximately 4.3 billion) became insufficient. The central pool held by IANA finished handing out addresses in February 2011, and the regional internet registries (RIRs) exhausted their own pools one after another during the 2010s. Anticipating the growth of smartphones, IoT devices, and cloud services, IPv6 was designed in the 1990s with a virtually unlimited address space.
IPv6 is more than just an expansion of address capacity. It is a next-generation protocol that incorporates numerous improvements in security, efficiency, and auto-configuration. While IPv4's address space is 32 bits (approximately 4.3 billion addresses), IPv6 uses 128 bits (approximately 340 undecillion addresses) - an incomparably larger scale.
A common misconception is that "if IPv4 is exhausted, we can no longer connect to the internet." In reality, NAT (Network Address Translation) technology allows multiple devices to share a single global IPv4 address. However, NAT introduces communication complexity and performance overhead, making IPv6 migration the fundamental solution.
Why IPv6 Migration Has Been Slow
The IPv6 specification was established as RFC 2460 in 1998, and in July 2017 it was replaced by RFC 8200, which became an Internet Standard (STD 86). Even so, more than a quarter century after that first specification, full migration had not been achieved as of 2026. Several structural factors explain this delay.
First, the widespread adoption of NAT significantly extended IPv4's lifespan. By allowing hundreds of devices to share a single global IP address, NAT mitigated the impact of address exhaustion and reduced the urgency for migration. Second, IPv4 and IPv6 are not backward compatible. IPv6 is not a simple extension of IPv4 but an entirely different protocol, requiring updates to network equipment, software, and operational procedures. Third, there is the issue of migration costs. Upgrading existing network infrastructure for IPv6 requires significant investment in equipment replacement, configuration changes, and staff training. This burden is a major barrier, especially for small businesses and ISPs in developing countries.
Furthermore, IPv6 migration faces a "chicken and egg" problem. Content providers deprioritize IPv6 support when few users have it, while ISPs are slow to offer IPv6 when little content is available - a vicious cycle that persisted for years. World IPv6 Launch on 6 June 2012 prompted major services such as Google and Facebook to keep IPv6 permanently enabled, and the cycle has gradually eased since then.
IPv6 Address Notation
An IPv6 address is 128 bits long and is written as eight groups of hexadecimal digits separated by colons.
Full notation example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Rules for shortening the notation are also defined:
- Leading zeros in each group can be omitted:
2001:db8:85a3:0:0:8a2e:370:7334 - Consecutive groups of zeros can be replaced with "::" once:
2001:db8:85a3::8a2e:370:7334
Special addresses include the loopback address ::1 (equivalent to 127.0.0.1 in IPv4) and the unspecified address ::.
When including an IPv6 address in a URL, it must be enclosed in brackets (e.g., http://[2001:db8::1]:8080/). Without this notation, directly accessing an IPv6 address in a browser can be confusing.
Types of IPv6 Addresses
Global Unicast Address
A routable address on the internet, equivalent to a global IP address in IPv4. Allocated from the 2000::/3 range, the vast majority of IPv6 addresses actually in operation are of this type.
Link-Local Address
Belonging to the fe80::/10 range, these addresses are valid only within the same network segment. They are automatically assigned to every IPv6-enabled interface and are used for neighbor discovery and router discovery.
Unique Local Address
In the fc00::/7 range, these are the IPv6 equivalent of IPv4 private addresses (such as 192.168.x.x). Used within organizational networks, they are not routed on the internet.
Multicast Address
In the ff00::/8 range, these addresses are used to send data to multiple devices simultaneously. IPv6 has eliminated broadcast in favor of multicast.
The IP Check-san IPv6 analysis feature automatically determines and displays which type your IPv6 address belongs to. The type of IPv6 address also affects the accuracy of GeoIP-based location estimation, so knowing your address type is useful.
Coexistence and Migration Technologies with IPv4
The transition from IPv4 to IPv6 cannot happen overnight. Technologies that support coexistence during the transition period are essential. The three main migration technologies are dual stack, tunneling, and NAT64.
Dual Stack
A method where a device holds both IPv4 and IPv6 addresses and can communicate using either protocol. It is the most widely used coexistence approach during the migration period, and many ISPs offer dual-stack connectivity. You can check your connection status with the IP Check-san dual-stack detection feature.
In a dual-stack environment, IPv6 is used preferentially when the destination server supports it (Happy Eyeballs algorithm). However, if there are issues with the IPv6 route, the connection automatically falls back to IPv4, allowing communication to continue seamlessly without user awareness.
A drawback of dual stack is the increased complexity of network management, as both IPv4 and IPv6 addresses must be maintained. Firewall rules also need to be configured for both protocols, creating potential security risks from configuration oversights.
Tunneling
A technology that encapsulates IPv6 packets for transport over IPv4 networks. Methods such as 6to4 and Teredo exist, but migration to native IPv6 connectivity is recommended due to security concerns. In particular, using 6to4 by reaching relay routers through a shared anycast address was deprecated by RFC 7526 (BCP 196) in May 2015, so it should not be newly deployed.
In Japan, IPv4 over IPv6 tunneling technologies such as MAP-E and DS-Lite are widely adopted. These tunnel IPv4 traffic over IPv6 IPoE connections and are offered as services like v6 Plus and transix. Compared to traditional PPPoE connections, this design makes it easier to avoid the congestion that arises when traffic is funneled through network termination equipment. Actual speeds still depend on the line you subscribe to and the state of the route, so the connection method alone does not determine how fast a link feels.
NAT64/DNS64
A translation technology that allows IPv6-only networks to access IPv4 servers. NAT64 functions as a gateway that converts IPv6 packets to IPv4 packets, while DNS64 synthesizes IPv4-only DNS records (A records) into synthetic IPv6 addresses (AAAA records).
Adoption is growing in mobile networks. Apple has required IPv6 support for iOS apps since 2016, mandating testing in NAT64 environments. T-Mobile US has run NAT64 on its IPv6-only network since 2014, with NAT64 mediating connections to services that are reachable only over IPv4.
IPv6 and Privacy
IPv6 raises important privacy considerations.
The EUI-64 Address Problem
The original IPv6 specification used the "EUI-64" method, which generated the interface ID from the device's MAC address. This meant a device could be uniquely identified from its IPv6 address - a significant privacy concern.
Privacy Extensions (Temporary Addresses)
"Privacy Extensions" (RFC 4941) were introduced to address this issue. Revised as RFC 8981 in 2021, they generate random interface IDs and change them periodically to prevent MAC address exposure.
When Privacy Extensions are enabled, the OS generates "Temporary Addresses" and preferentially uses them for outbound communication. The lifetime of temporary addresses varies by OS but typically rotates every 24 hours or so.
However, even with Privacy Extensions enabled, complete anonymity is not guaranteed. The upper 64 bits (prefix) of an IPv6 address are a fixed value assigned by the ISP, so communication from the same network can still be identified. For complete anonymity, using a VPN in combination is recommended.
Checking Privacy Extensions on Each OS
- Windows: Check with
netsh interface ipv6 show privacy. Enabled by default - macOS: Check with
sysctl net.inet6.ip6.use_tempaddr. A value of 1 means enabled. Enabled by default - Linux: Check with
sysctl net.ipv6.conf.all.use_tempaddr. A value of 2 means temporary addresses are preferred
IPv6 Address Tracking Risks
Because IPv6 eliminates the need for NAT, each device holds a globally unique address. Compared to IPv4 NAT environments, individual devices can be more easily tracked, making VPN usage and Privacy Extensions all the more important. Additionally, if a DNS leak occurs, your IPv6 address may be exposed even when using a VPN, so DNS leak protection should also be verified.
IP Check-san automatically determines whether your IPv6 address is a privacy address or an EUI-64 address. If an EUI-64 address is detected, we recommend reviewing your OS's Privacy Extensions settings.
IPv6 Adoption Status
Google publishes statistics compiled from access to its own services, and as of July 2026 they show that around half of all access worldwide arrives over IPv6. How far adoption has progressed varies enormously by country: in India and parts of Western Europe most access is already IPv6, while some countries with very large networks still see almost no IPv6 use.
In Japan too, IPv6 accounted for the majority of access as of 2026. The widespread deployment of IPoE (native IPv6 connections) built on NTT East/West's NGN (Next Generation Network) has been a major contributor, with IPv4 over IPv6 services such as v6 Plus and transix also widely used. On the other hand, IPv4-only setups remain common in corporate systems and business equipment, so migration is not necessarily as far along as it is on consumer lines.
Cloud service providers (AWS, Google Cloud, Azure) all support IPv6 across their major services, and CDN providers (Cloudflare, Akamai, Fastly) have enabled IPv6 delivery by default. In mobile networks, the rollout of 5G has widened the use of configurations that combine IPv6-only networks with NAT64.
Practical Steps to Check IPv6 Support
Follow these steps to check whether your network environment supports IPv6:
- Visit the IP Check-san homepage and check whether the displayed IP address is in IPv6 format (colon-separated hexadecimal)
- Review the dual-stack detection results to confirm whether you can connect via both IPv4 and IPv6
- If an IPv6 address is displayed, check whether it is identified as a privacy address or an EUI-64 address
- If an EUI-64 address is detected, enable Privacy Extensions using the OS-specific instructions above
- When using a VPN, verify that IPv6 traffic passes through the VPN tunnel (no IPv6 leak)
IPv6 is the protocol that will form the foundation of the future internet. Understanding your connection environment and properly managing your privacy settings is the first step toward safe internet usage.
Related Glossary Terms
Frequently Asked Questions
Will the internet stop working if I do not move to IPv6?
Not any time soon. Many environments run a dual-stack configuration in which IPv4 and IPv6 coexist, so devices without IPv6 support can keep communicating. That said, new IPv4 allocations are almost impossible to obtain, so a move to IPv6 is necessary in the long run.
Is IPv6 more secure than IPv4?
Not inherently. IPv6 includes IPsec in its standard specification, but implementing it is optional. Actual security depends on the protocols and configuration you use.