whois is an essential query and response protocol used for querying databases that store registered domain names, IP addresses, and autonomous system information. For system administrators and security professionals, whois provides critical intelligence about domain ownership, registration dates, expiration dates, nameservers, and contact information for network resources.
📑 Table of Contents
Understanding who owns a domain or IP address is fundamental for network troubleshooting, security investigations, and compliance verification. The whois protocol connects to distributed databases maintained by regional internet registries (RIRs) and domain registrars to retrieve this authoritative information.
Key Features
- Domain Lookups – Query registration details for any domain name
- IP Address Queries – Find ownership information for IP blocks
- ASN Information – Look up autonomous system details
- Registrar Details – Identify domain registrars and their contacts
- Expiration Tracking – Check when domains expire
- Nameserver Information – View authoritative DNS servers
Installation
sudo apt install whois # Debian/Ubuntu
sudo dnf install whois # Fedora/RHEL
sudo pacman -S whois # Arch LinuxBasic Usage Examples
# Query domain information
whois example.com
# Query IP address ownership
whois 8.8.8.8
# Query specific whois server
whois -h whois.verisign-grs.com example.com
# Query ASN information
whois AS15169
# Verbose output
whois -v example.com
# Query with specific port
whois -p 43 example.comUnderstanding Output
A typical whois response includes domain name, registrar information, registration and expiration dates, nameservers, DNSSEC status, and registrant contact details (though many are now redacted for privacy under GDPR). For IP addresses, you’ll see the allocated network block, organization name, and abuse contact information.
Use Cases
- Security Investigations – Research suspicious domains or IPs
- Domain Management – Monitor expiration dates
- Network Troubleshooting – Identify network owners
- Competitive Analysis – Research competitor domains
- Abuse Reporting – Find correct contacts for complaints
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