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HTTP/2 and HTTP/3 significantly improve page load performance over HTTP/1.1 by multiplexing requests over a single connection and reducing latency. Both require HTTPS to be enabled first.

Prerequisites

• Nginx installed with an active SSL certificate
• Nginx version 1.25+ for built-in HTTP/3 support (check with nginx -v)

Enabling HTTP/2

Edit your site's SSL server block:

sudo nano /etc/nginx/sites-available/example.com

server {
    listen 443 ssl;
    http2 on;

    server_name example.com;

    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
}

On older Nginx versions, the syntax is instead:

listen 443 ssl http2;

sudo nginx -t && sudo systemctl reload nginx

Verifying HTTP/2 Is Active

curl -I --http2 -s https://example.com | head -1

You should see HTTP/2 200. You can also check via browser developer tools (Network tab → Protocol column).

Enabling HTTP/3 (QUIC)

HTTP/3 runs over UDP rather than TCP, so it requires an additional listener and firewall rule:

server {
    listen 443 ssl;
    listen 443 quic reuseport;
    http2 on;
    http3 on;

    add_header Alt-Svc 'h3=":443"; ma=86400';

    server_name example.com;
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
}

Opening UDP Port 443 for QUIC

sudo ufw allow 443/udp

Verifying HTTP/3

curl -I --http3 https://example.com

Note this requires a curl build with HTTP/3 support; alternatively, check via browser developer tools or an external tool like HTTP/3 Check.

Common Errors

"unknown directive http3" — your Nginx build doesn't include HTTP/3 support; verify with nginx -V 2>&1 | grep -o with-http_v3_module, and upgrade to a build/version that includes it if missing.

HTTP/2 not showing in browser — confirm HTTPS is actually active on the connection being tested; HTTP/2 only applies over TLS in virtually all real-world Nginx configurations.

Best Practices

• Enable HTTP/2 on every HTTPS site — there's no real downside
• Treat HTTP/3 as an enhancement layered on top of working HTTP/2, not a replacement
• Confirm your hosting provider's network doesn't block UDP before troubleshooting HTTP/3 issues

FAQ

Do I need HTTP/3 if I already have HTTP/2?
Not strictly — HTTP/2 already provides most performance benefits; HTTP/3 further helps primarily on unstable/high-latency networks by avoiding TCP head-of-line blocking.

Related Articles

• How to Install Nginx on Ubuntu & Debian
• How to Install Let's Encrypt SSL with Certbot (Nginx & Apache)
• Nginx Performance Tuning: Worker Processes, Caching & Gzip