A WHOIS lookup is a query and response protocol used to obtain various pieces of information about the registrant of an Internet resource, such as a domain name, an IP address block, or an autonomous system. This protocol is standardized by the Internet Corporation for Assigned Names and Numbers (ICANN) and is used to access a database that stores the registration data of these Internet resources.
Here’s a breakdown of the technical aspects of a WHOIS lookup:
- Protocol and Port: WHOIS traditionally operates over TCP using port 43. The client makes a TCP connection to a WHOIS server and sends a text request, which typically includes the domain name or IP address in question. The server then responds with the relevant WHOIS data.
- Data Retrieved: The WHOIS response may include various details such as the domain name’s availability, the registrant’s contact information (name, phone number, email address), registration and expiration dates, the status of the domain, the nameservers associated with the domain, and the registrar responsible for the domain registration.
- Servers and Databases: Each registrar maintains its own WHOIS database containing information about the domains it manages. Additionally, regional Internet registries (RIRs) maintain WHOIS databases for IP address allocations and related data.
- Privacy and Access: Due to privacy concerns, especially in the context of the General Data Protection Regulation (GDPR) in the European Union, WHOIS information may be redacted or restricted to protect the privacy of individuals. Some registrars and RIRs offer privacy services that replace registrant information with anonymized data.
- Uses of WHOIS: WHOIS lookups are commonly used for various purposes, including checking domain name availability, identifying domain name registrants for legal or business purposes, network troubleshooting, and enforcing compliance with domain registration requirements.
- Extensions and Alternatives: Due to the limitations of the traditional WHOIS protocol, such as lack of standardization in responses and concerns over data privacy, an alternative called RDAP (Registration Data Access Protocol) has been developed. RDAP provides a more standardized and secure approach to accessing registration data.
WHOIS lookups can be performed using various command-line tools, web-based interfaces, or through direct API integrations provided by domain registrars and data providers.