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IPv4 and IPv6

IPv4 and IPv6 are two versions of the Internet Protocol (IP), the system that lets devices address and send data to one another across networks. IPv4 is the older version and uses 32-bit addresses, commonly written as four decimal (base-ten) numbers, such as 192.0.2.25. IPv6 uses 128-bit addresses, commonly written as groups of hexadecimal numbers (using digits and the letters a to f) separated by colons, such as 2001:db8::25.

Why are there two versions?

The growth of the Internet made the supply of IPv4 addresses insufficient for the number of devices and services that need addresses. IPv6 provides many more possible addresses. It was designed to coexist with IPv4 during a gradual transition, so networks and services may support IPv4, IPv6, or both.

The two formats are not interchangeable. An IPv4-only connection cannot directly use an IPv6 destination without a system that translates between the two versions, and IPv6 support at a server does not mean every visitor's network can reach it. In practice, organizations often operate both versions to reach more users.

How do the versions appear in DNS?

DNS uses different record types for the two address versions. An A record gives an IPv4 address; an AAAA record gives an IPv6 address. A domain can publish both. For instance, www.example.com could have one A record and one AAAA record, each pointing to a server address for its version. A visitor whose device and network support the relevant version can then connect using an available route.

The record type only tells DNS what kind of address is stored. It does not switch a network from one version to the other, guarantee that both routes work, or prove the website is healthy. If a site publishes an incorrect IPv6 address, some visitors may fail even though the IPv4 address works.

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