Why IPv6 Is Needed
With the rapid expansion of the internet, the pool of traditional IPv4 addresses (approximately 4.3 billion) was exhausted in 2011. To accommodate the explosive growth of smartphones, IoT devices, and cloud services, IPv6 was developed 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.
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 ::.
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 in use today 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 Kakunin-san IPv6 analysis feature automatically determines and displays which type your IPv6 address belongs to.
Coexistence Technologies with IPv4
The transition from IPv4 to IPv6 cannot happen overnight. Technologies that support coexistence during the transition period are essential.
Dual Stack
A method where a device holds both IPv4 and IPv6 addresses and can communicate using either protocol. This is currently the most common coexistence approach, and many ISPs offer dual-stack connectivity. You can check your connection status with the Kakunin-san dual-stack detection feature.
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.
NAT64/DNS64
A translation technology that allows IPv6-only networks to access IPv4 servers. Adoption is growing in mobile networks.
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: RFC 4941
"Privacy Extensions" were introduced to address this issue. By generating random interface IDs and changing them periodically, they prevent MAC address exposure. Most modern operating systems enable Privacy Extensions by default.
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.
Kakunin-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
According to Google's statistics, over 40% of global internet traffic already uses IPv6. In Japan, major ISPs offer IPv6 connectivity, and the adoption of IPoE (native IPv6 connections) is steadily progressing.
You can easily check whether your connection supports IPv6 on the Kakunin-san homepage. If you are connected via IPv6, detailed address analysis results are also displayed.