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copyright
years
2020, 2025
lastupdated 2025-07-04
keywords
subcollection cis

{{site.data.keyword.attribute-definition-list}}

HTTP protocols

{: #http-concepts}

HTTP/2 and HTTP/3 accelerate page load times are included in all {{site.data.keyword.cis_full}} plans. HTTP/2 is enabled by default and requires an SSL certificate at the {{site.data.keyword.cis_short_notm}} edge network. Domains on Trial plans can't disable HTTP/2. {: shortdesc}

Browsers and web servers automatically negotiate the highest protocol available, so HTTP/3 takes precedence over HTTP/2. {{site.data.keyword.cis_short_notm}} uses HTTP/1.x only for communication between the origin web server and {{site.data.keyword.cis_short_notm}} edge.

To determine the protocol used for your connection, enter example.com/cdn-cgi/trace in a web browser or HTTP client, replacing example.com with your domain. The http= value in the results indicates the protocol:

  • http=h2 means that the connection used HTTP/2
  • http=http2+quic/99 indicates HTTP/3
  • http=http/1.x indicates HTTP/1.x

HTTP/2

{: #http-2}

HTTP/2 improves page load times through:

Connection multiplexing : Retrieves multiple resources over a single network connection. Responses are sent as resources become available, helping to avoid delays in page rendering.

HTTP header compression : Compresses headers and simplifies HTTP requests to avoid resending headers.

HTTP/2 server push : To improve page load speed, {{site.data.keyword.cis_short_notm}} provides additional resources for a client to cache without waiting for additional requests.

Not all browsers support HTTP/2 and use HTTP 1.x instead. Connection multiplexing is handled on a per-domain basis. {: note}

HTTP/3

{: #http-3}

HTTP/3 enables fast, reliable, and secure connections. By default, HTTP/3 encrypts internet transport by using QUIC, a protocol developed by Google. You can enable HTTP/3 through the Cloudflare Network application. The following methods show you how to experiment with HTTP/3.

Using Google Chrome as your HTTP/3 client

{: #chrome-client}

To connect to your website over HTTP/3 using Chrome, first download and install the latest Chrome Canary build{: external}. Then, enable HTTP/3 support in Chrome Canary using the --enable-quic and --quic-version=h3-23 command-line arguments{: external}.

After Chrome starts, enter your domain in the address bar. To verify the protocol version, open Chrome’s Developer Tools and go to the Network tab. If http2+quic/99 doesn’t appear in the Protocol column, try reloading the page.

Using cURL

{: #using-curl}

The cURL command-line tool supports HTTP/3. Download the most recent version{: external} and follow the instructions to enable HTTP/3 support{: external}.

For macOS, use Homebrew to install cURL with HTTP/3 support:

brew install --HEAD -s https://raw.githubusercontent.com/cloudflare/homebrew-cloudflare/master/curl.rb

{: pre}

Then, run an HTTP/3 cURL with the --http3 command-line flag:

./curl -I https://blog.cloudflare.com/ --http3

{: pre}

Confirm that HTTP/3 appears in the response and that there are no error messages.