Port 443 HTTPS · TCP and UDP

What runs on port 443

HTTPS: HTTP over TLS, the port the web runs on. Since HTTP/3, UDP 443 carries QUIC as well, so a firewall that allows only TCP 443 forces browsers to fall back to HTTP/2. Almost everything else now tunnels over 443 too (APIs, WebSockets, VPNs, DNS over HTTPS), which is why "only 443 is open" rarely means only web traffic.

Software that uses it: nginx · Apache · Caddy · HAProxy · Cloudflare and other CDNs · Traefik · IIS

Should port 443 be open?

Designed to face the internet. This port exists to be reachable from anywhere, so the usual question is not whether to open it but how the service behind it is configured and patched.

• Allow UDP 443 outbound if you want HTTP/3 to work for your users.
• openssl s_client -connect host:443 -servername host shows the certificate chain and the negotiated protocol.
• Test the configuration with our HTTP headers analyzer and SSL certificate decoder.

Check port 443

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :443'
ss -lunp 'sport = :443'
sudo lsof -i :443

# from another machine: is it reachable?
nc -zv host 443
nmap -p 443 host
nc -zuv host 443
sudo nmap -sU -p 443 host
curl -v telnet://host:443      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 443

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 443 proto tcp
sudo ufw allow from 10.0.0.0/8 to any port 443 proto udp
sudo ufw deny 443/tcp
sudo ufw deny 443/udp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 meta l4proto { tcp, udp } th dport 443 accept
nft add rule inet filter input meta l4proto { tcp, udp } th dport 443 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
iptables -A INPUT -p udp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 443 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=443 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 443" with no source is just "open".

Putting it behind nginx

server {
    listen 443 ssl;
    server_name app.example.com;
    location / {
        proxy_pass http://127.0.0.1:443;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
    }
}

Then make the application listen on 127.0.0.1:443 only. Test which location block a request hits with the nginx location tester.

Related ports

• 80 HTTP — Web, unencrypted
• 8443 HTTPS alt — Tomcat, Plesk, Unifi
• 4443 HTTPS alt
• 853 DNS over TLS

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions