Port 43 — WHOIS
Quick reference for TCP/UDP port 43, used by WHOIS. Includes what the service does, security guidance and related ports.
What is port 43?
Domain registration lookup.
What port does WHOIS use?
WHOIS listens on port 43 by default.
Is port 43 open? How to check
Run one of these from your computer, replacing HOST with the IP address or domain you want to test.
nc -zv HOST 43
Test-NetConnection HOST -Port 43
nmap -p 43 HOST
A refused or timed-out connection means the port is closed or filtered by a firewall.
Security guidance
Medium risk — open with care
Port 43 (WHOIS) can safely face the internet if you keep the software up to date, restrict admin endpoints, and use TLS where possible. Audit who can reach it and watch your logs.
Frequently asked
What is port 43 used for?+
Port 43 is the standard TCP/UDP port for WHOIS. Domain registration lookup.
What port does WHOIS use?+
WHOIS listens on port 43 by default.
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