Does port 443 use TCP or UDP?

HTTP/1.1 and HTTP/2 operate over TCP port 443. The modern HTTP/3 standard utilizes UDP port 443 via the QUIC protocol for reduced handshake latency.

Why does my browser show a certificate warning on port 443?

Warnings occur when the SSL certificate has expired, is self-signed, doesn't match the requested domain name, or is missing intermediate chain certificates.

How can I check if port 443 is open on my server?

Test your server's domain or IP in our Open Port Checker or run 'curl -Iv https://yourdomain.com' from your terminal.

Home/Open Port Checker/Port 443

Port 143 Port 465

Well-Known Port Reference

Port 443: HTTPS (HTTP Secure) (TCP/UDP)

Encrypted Hypertext Transfer Protocol secured by Transport Layer Security (TLS) and HTTP/3 QUIC.

Port Number

443

Transport

TCP/UDP

Security Risk

Low

Standard / RFC

RFC 9114

Test Port 443 Reachability Live

Verify whether Port 443 is open, closed, or filtered on your server or public IP address.

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Service Architecture & Function

Port 443 is the global standard for secure web browsing. All modern websites, REST APIs, and web applications serve traffic over port 443. Connections are encrypted using TLS 1.2 or TLS 1.3 over TCP, preventing eavesdropping and tampering. Modern HTTP/3 also utilizes port 443 over UDP via QUIC.

Security Profile & Hardening

While port 443 provides robust cryptographic transit security, the underlying web application remains vulnerable to application-layer attacks (SQL injection, XSS, CSRF). Ensure strong cipher suites, active SSL certificate renewal, and a Web Application Firewall (WAF).

Example Firewall Commands:

# UFW (Ubuntu/Debian)

sudo ufw allow 443/tcp

# iptables (Direct Kernel)

iptables -A INPUT -p tcp --dport 443 -j ACCEPT

Frequently Asked Questions

Technical answers and configuration advice for Port 443.

Port 443 is used for secure web browsing via HTTPS. It encrypts all communications between client browsers and web servers using Transport Layer Security (TLS).