Guidance for Registrars on Use of the Whois Service
Many CentralNic registrars use the CentralNic Whois service (located at whois.centralnic.com on TCP port 43) to perform large volume, automated domain availability checks. CentralNic wishes to clarify its position on the use of the Whois service for this purpose.
The Whois protocol (described in RFC 3912) provides information in a human-readable format. It was not designed for consumption by automated systems, but serves to provide information regarding domain name registrations.
Use of the Whois for perfoming domain name availability checks is STRONGLY DISCOURAGED. CentralNic does not guarantee, and registrars should not assume, the accuracy or timeliness of the data produced by the Whois system. Furthermore, CentralNic may change the layout or content of WHOIS records at any time, which may break automated parsers of WHOIS responses.
Furthermore, in order to ensure the stability of the service in the face of abusive activity, we may impose temporary rate limits and minimum round-trip times without notice.
Registrars wishing to do high volume domain name availability checks are STRONGLY ADVISED to use EPP, which offers significant benefits over the Whois service.
The EPP system also provides additional methods for obtaining information about domain name registrations, in a format that is strictly defined and easy to parse.
Rate Limiting
To prevent abuse of the WHOIS system and the information stored in the WHOIS database, CentralNic has imposed the following service limits on its Whois system:
- For the purposes of rate limiting, all queries coming from the same IPv4 /24 prefix or /48 IPv6 prefix are counted as coming from the same source.
- Queries are rate-limited at a maximum query rate of 1,800 queries per 15 minutes. Any queries in excess of this query rate will be refused until the query rate falls below this limit.
- CentralNic reserves the right to temporarily block query sources where needed to ensure the stability of the whois service, or to protect personal data from bulk collection. We periodically analyse query logs to detect patterns of abusive activity and will take steps to prevent or mitigate any abusive activity found.
Registrars should note that the above policy is applied globally and is not per-TLD. Similarly, if an IP address appears on the access list of multiple registrars, the permitted query rate is not increased.