WHOIS query and response protocol is widely used for databases holding various Internet resources like IPv4 assignments, IPv6 assignments, AS numbers and RIR(for example ARIN in USA or RIPE in Europe) members need(details depend on RIR) to keep their records in those databases. In addition, lot of automation in ISP world happens based on those objects in those RIR WHOIS databases. For example whois.ripe.net for RIPE region or whois.apnic.net for APNIC region. Now in which WHOIS databases are the domain names kept? Is it mandatory for domain registrar to make a record to this/those WHOIS database? I guess yes because otherwise the other domain registers would not know that the domain is in use? Is there a RFC which defines what information besides the domain name will go to this database?