An IP address is a numeric label that identifies a device or server in a network that uses the Internet Protocol, and it tells other devices where to send data. Every web server has an address, and every visitor or crawler request arrives from one.
IPv4 and IPv6
- IPv4 uses 32 bits and is written as four numbers separated by dots, such as
192.0.2.10. It provides about 4.3 billion addresses. - IPv6 uses 128 bits and is written in hexadecimal groups separated by colons, such as
2001:db8::8a2e:370:7334. It provides about 3.4 × 10^38 addresses and was introduced because IPv4 addresses became scarce.
A website can be reachable over both. DNS records connect a domain name to the addresses: an A record holds an IPv4 address, an AAAA record an IPv6 address.
Public, private, static and dynamic
Public addresses can be reached from the internet. Private ranges, for example 192.168.0.0/16, are used inside local networks and are not routed on the public internet. A static address stays the same, while a dynamic address, often assigned by DHCP, can change when a device reconnects.
Why IP addresses matter for SEO
IP addresses appear in server logs, and each request lists the address it came from. IP addresses can be personal data (CJEU, judgment of October 19, 2016, C-582/14, Breyer). This is not legal advice. Because the user agent string of a request can be faked, the address is what site owners use to check whether a request really comes from a search engine. Google offers lists of its crawler IP ranges as JSON files, and a reverse DNS lookup on the address is the second method it documents.
Example
66.249.66.1 - - [06/Oct/2026:08:12:44 +0000] "GET /shoes/ HTTP/1.1" 200 ...
The first field in a common log format line is the client’s IP address.
Common mistakes
- Checking only the user agent. The user agent can be faked. Google documents the verification because others can claim to be Google.
- Doing only the reverse DNS lookup. Google’s instructions also require a forward DNS lookup on the hostname found, and its result has to match the original IP address.
- Accepting only
googlebot.com. Depending on the kind of Google request, the hostname ends ingooglebot.com,google.comorgoogleusercontent.comaccording to the documentation. - Storing IP addresses from logs without considering data protection. IP addresses can be personal data (CJEU, judgment of October 19, 2016, C-582/14, Breyer). This is not legal advice.
Sources
- IP address – Wikipediaen.wikipedia.org
- What is an IP address? – Fortinetfortinet.com
- Verifying Googlebot and other Google crawlers – Google Search Centraldevelopers.google.com
- RFC 8200 Internet Protocol, Version 6 (IPv6) Specification – IETFrfc-editor.org
- Judgment of the CJEU of 19 October 2016, C-582/14 (Breyer)eur-lex.europa.eu
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