Checking Whether a Domain Name Is Registered

1.5.1 Problem

You want to check whether a particular domain name is already registered, or who has registered that domain name.

1.5.2 Solution

Use the whois service offered by the appropriate registration authority, or use a command-line version of whois to look up registration information about the domain name you're interested in.

The Internet Assigned Numbers Authority, or IANA, maintains a list of country-code top-level domains (ccTLDs) at http://www.iana.org/cctld/cctld-whois.htm,which includes links to the web pages of those ccTLDs registration authorities. Many of these web pages offer online whois lookups. The web site http://www.allwhois.com/also includes links to many whois lookup facilities.

If your host's operating system includes a command-line whois client, you can use that to look up to look up registration information about the domain name. Newer whois clients automatically determine which whois server to query, so you can simply run:

$ whois domain-name

Older whois clients may require you to specify the whois server to use. For these, you can try tld.whois-server.net. For example:

$ whois -h ca.whois-servers.net risq.ca

The whois output usually contains information about the registrant (the person or organization that registered the domain name). For example:

$ whois isc.org

produces output that includes:

Registrant:
Internet Software Consortium (ISC2-DOM)
 950 Charter Street
 Redwood City, CA 94062
 US

 Domain Name: ISC.ORG

 Administrative Contact, Billing Contact:
 Conrad, David Randolph (DC396) [e-mail]
 Internet Software Consortium
 950 Charter Street
 Redwood City, CA 94063
 1-650-779-7061 (FAX) 1-650-779-7055
 Technical Contact:
 Vixie, Paul (PV15) [e-mail]
 M.I.B.H., LLC
 950 Charter Street
 Redwood City, CA 94063
 +1.650.779.7000 (FAX) +1.650.779.7055

 Record last updated on 04-Mar-2002.
 Record expires on 05-Apr-2004.
 Record created on 04-Apr-1994.
 Database last updated on 14-Mar-2002 09:39:00 EST.

 Domain servers in listed order:

 NS-EXT.VIX.COM 204.152.184.64
 NS1.GNAC.COM 209.182.195.77

1.5.3 Discussion

If the registration authority for your prospective top-level domain doesn't offer a whois server, or you can't find it, you can look up NS records for the domain name you're interested in. For example:

$ dig ns domain-name

If the domain name has NS records, it's very likely registered. On the other hand, if a domain name lacks NS records, it may still be registered: some TLDs take a day or more to process a new registration and add the corresponding NS records.

1.5.4 See Also

"Using whois" in Chapter 3 of DNS and BIND.