What QUIC and HTTP/3 Versions Does LSWS Support?

Initially, LSWS supported QUIC versions Q035, Q037. HTTP/3 support was introduced in July 2019. As of December 2019, the latest version of LSWS supports QUIC versions Q039, Q043, Q046 and HTTP/3 drafts ID-23 and ID-24, but this will continue to change, as both Chrome and LiteSpeed Web Server evolve.

LSWS will automatically show the supported QUIC versions through the headers.

There are a few ways to check which versions of QUIC and HTTP/3 are supported by a website. You can look up the alt-svc response header as shown below, or you can visit HTTP/3 Check and enter the site's URL. HTTP/3 Check provides a free detailed report of any site's QUIC and HTTP/3 capabilities.

Please do not change the LSWS QUIC versions setting! Leave it as Not Set, and the alt-svc response header will automatically display the currenly-supported versions.

Sometimes you cannot see the latest supported version from the QUIC header, even if LSWS's latest release supports them. For example, let's say, LSWS supports the fictional QUIC versions Q0XX, Q0YY, and Q0ZZ, but the page header only shows XX,YY. Why?

One possible reason is that you are using an old version of LSWS. You should always upgrade to the latest build of the latest version.

If you have upgraded to the latest version but still see the above inaccuracy, the most likely explanation is that you manually set QUIC Versions in LSWS's QUIC settings.

When QUIC Versions is not left as Not Set, the manual configuration will soon become outdated or wrong.

Why have a QUIC Versions setting at all, if you are not supposed to use it?

The idea behind exposing supported versions is to give the user the ability to disable a particular QUIC version in the case of a security vulnerability or bug. This is the only occasion during which you should set QUIC Versions manually.

Don't forget to revert the setting back to Not Set once the bug is fixed. Failure to do so will cause your configuration to become outdated in the future.

You can learn more about the history of LiteSpeed's QUIC and HTTP/3 support on our website.