Internet-Security.com TCP port 43 details

TCP port 43 is used by the WHOIS/NICNAME protocol (RFC 3912) for domain, IP, and ASN registration lookups.
Domain registries run WHOIS on 43, e.g., Verisign’s whois.verisign-grs.com (.com/.net), PIR’s whois.pir.org (.org), Nominet’s whois.nic.uk (.uk), and IANA’s whois.iana.org.
Regional Internet Registries provide WHOIS on 43: ARIN (whois.arin.net), RIPE NCC (whois.ripe.net), APNIC (whois.apnic.net), LACNIC (whois.lacnic.net), and AFRINIC (whois.afrinic.net).
Internet Routing Registry services use port 43 with IRRd software, including RADB (whois.radb.net) and NTT’s IRR (whois.gin.ntt.net).
Common client software includes GNU whois and BSD whois (the whois CLI on Linux/BSD/macOS), jwhois, and Windows tools like Sysinternals Whois.
Registrars also expose WHOIS on 43, such as GoDaddy (whois.godaddy.com) and Namecheap (whois.namecheap.com).
Network intelligence services use port 43 WHOIS interfaces, notably Team Cymru’s whois.cymru.com for IP-to-ASN mapping.
Although RDAP over HTTPS is replacing classic WHOIS, port 43 WHOIS remains widely deployed and actively used.

TCP 43