IPv6 (Internet Protocol version 6) is the successor of IPv4 and is specified in RFC 8200. It extends IP addresses from 32 to 128 bits, which allows far more addresses than IPv4’s roughly 4.3 billion.
How are IPv6 addresses written?
An IPv6 address consists of eight groups of four hexadecimal digits, separated by colons. Leading zeros in a group can be dropped, and one run of all-zero groups can be shortened to ::, but only once per address (RFC 4291). The range 2001:db8::/32 is reserved for documentation and examples (RFC 3849). In DNS, an AAAA record points a hostname to an IPv6 address, the counterpart of the A record for IPv4.
Why does IPv6 matter in SEO?
Most sites run IPv4 and IPv6 side by side. Server logs then contain requests from both address types, including from crawlers. Google’s published IP ranges for its crawlers include IPv6 prefixes, so a bot check against these lists, or a reverse DNS lookup, has to handle IPv6 as well as IPv4. Scripts that only parse IPv4 miss part of the traffic. IP addresses in logs can be personal data (CJEU, judgment of October 19, 2016, C-582/14 Breyer). This is not legal advice.
Example
2001:0db8:0000:0000:0000:ff00:0042:8329
2001:db8::ff00:42:8329
Both lines are the same address, the second in short form.
Sources
- RFC 8200: Internet Protocol, Version 6 (IPv6) Specificationrfc-editor.org
- RFC 4291: IP Version 6 Addressing Architecture (section 2.2, text representation)rfc-editor.org
- RFC 3849: IPv6 Address Prefix Reserved for Documentationrfc-editor.org
- Verifying Googlebot and other Google crawlers – Google Search Centraldevelopers.google.com
- Google common crawlers IP ranges (JSON)developers.google.com
- CJEU, judgment of 19 October 2016, C-582/14 (Breyer) – EUR-Lexeur-lex.europa.eu
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