WHOIS rate limiting provides you with access to the OpenSRS WHOIS server while preventing abuse from unscrupulous users trying to mine data.
Access limits for port 43 WHOIS
The default limit for each IP or IP range is one (1) lookup per second. A daily rate-limit for each IP or IP range has also been set. Contact support to discuss the daily rate-limit applied to your IP.
Daily and per second rate-limits ensure system stability and load management, while still allowing Registrars to perform daily lookups required to properly perform transfers.