.co (second-level domain) .co (second-level domain) In a number of countries, .co is used as a second-level domain to mean "commercial" and domain registrants register second-level domains of the form .co.xx, where xx is the country code top level domain (e.g., .co.uk in the U.K. and .co.jp in Japan). Some of the countries using .co as a second-level domain include: Barbados (.bb), Cook Islands (.ck), Costa Rica (.cr), India (.in), Indonesia (.id), Israel (.il), Japan (.jp), New Zealand (.nz), South Africa (.za), South Korea (.kr), Thailand (.th) and the United Kingdom (.uk). .co is also a country top-level domain corresponding to Colombia. Its
Top-level domain Dynamic Delegation Discovery System, and e164.arpa for telephone number mapping based on NAPTR DNS records. For historical reasons, arpa is sometimes considered to be a generic top-level domain. RFC 6761 reserves the following four top-level domain names to avoid confusion and conflict. Any such reserved usage of those TLDs should not occur in production networks that utilize the global domain name system: RFC 6762 reserves the use of .local for link-local host names that can be resolved via the Multicast DNS name resolution protocol. RFC 7686 reserves the use of .onion for the self-authenticating names of Tor hidden services. These