HTTP/3 is the newest version of the protocol browsers use to load websites. It runs over QUIC, a transport built on UDP instead of TCP. LiteSpeed Web Server was one of the first servers to support it, and on MdmHost it is available for sites with SSL without any setup.
Before you start
- A site on MdmHost with a valid SSL certificate (see AutoSSL for customer accounts). HTTP/3 only works over HTTPS.
- A modern browser: current Chrome, Edge, Firefox and Safari support HTTP/3.
What HTTP/3 improves
| HTTP/2 over TCP | HTTP/3 over QUIC | |
|---|---|---|
| Connection setup | TCP handshake plus TLS handshake | Combined; faster first connection, 0-RTT on repeat visits |
| Packet loss | One lost packet stalls all streams | Only the affected stream waits |
| Network changes | Switching Wi-Fi to mobile drops the connection | Connection migrates without restarting |
| Encryption | TLS 1.2 or 1.3 | TLS 1.3 always |
The gains are largest on mobile and unreliable networks, which is where many of your visitors are.
How browsers find HTTP/3
- The first visit uses HTTP/2 over TCP.
- LiteSpeed sends an
alt-svcheader saying HTTP/3 is available on UDP port 443. - The browser uses HTTP/3 for later requests and visits.
Check your site uses HTTP/3
- Open your site in Chrome and press F12.
- Go to Network, right-click a column header and enable Protocol.
- Reload the page (twice if needed). Requests served over HTTP/3 show
h3; HTTP/2 showsh2. - Check the response headers for
alt-svc: h3=":443".
Note: Some corporate networks and firewalls block UDP traffic. Browsers then fall back to HTTP/2 automatically, so visitors are never cut off.
HTTP/3 and CDNs
If your site sits behind a CDN such as Cloudflare or QUIC.cloud, visitors connect to the CDN, so the CDN's HTTP/3 setting applies to them (see QUIC.cloud CDN). The connection between CDN and server is separate.
Do you need to do anything?
No configuration is needed on MdmHost. To get the most from HTTP/3:
- Keep SSL valid and force HTTPS (see forcing HTTPS).
- Avoid old optimisation tricks like domain sharding; HTTP/2 and HTTP/3 work best with one domain.
- Do not combine all CSS and JS into one file just for fewer requests; multiplexing makes many small files cheap (see page optimisation settings).
More on the server itself is in LiteSpeed Web Server explained.
Frequently asked questions
Does HTTP/3 help SEO?
Indirectly. Faster loading improves Core Web Vitals, which are part of how search engines judge page experience.
Can I turn HTTP/3 off?
It is controlled server-side and does no harm, because browsers fall back to HTTP/2 when needed.
Is QUIC.cloud related to QUIC?
QUIC.cloud is LiteSpeed's CDN service, named after the protocol. QUIC itself is an open internet standard.
Why do some requests still show h2?
The first request on a new connection uses HTTP/2 before the browser learns about HTTP/3. Third-party resources depend on their own servers.
Does HTTP/3 use more server resources?
Not noticeably for websites. LiteSpeed handles QUIC efficiently, and faster page loads can even reduce the time connections stay open.