Introduction

When LiteSpeed is installed on a cPanel & WHM server, QUIC support is enabled by default for HTTPS virtual hosts. QUIC uses UDP port 443 to improve connection performance and reduce latency.

In some environments, administrators may need to disable QUIC globally or for specific domains due to firewall restrictions, compatibility concerns, or troubleshooting requirements.

Prerequisites

Before proceeding, ensure the following:

• Root access to the server
• LiteSpeed installed on a cPanel & WHM server
• Access to modify server configuration files
• Basic knowledge of Linux commands
• Backup of existing configuration files before making changes

Implementation

I. Disable QUIC for All Domains

To disable QUIC globally across the server, follow these steps.

Step 1: Edit the Global Apache Include File

Open the following file:

/etc/apache2/conf.d/includes/pre_main_global.conf

Add the following configuration:

<IfModule LiteSpeed>
QuicEnable off
</IfModule>

Step 2: Rebuild Apache Configuration and Restart LiteSpeed

Run the following command:

/usr/local/cpanel/scripts/rebuildhttpdconf && /usr/local/cpanel/scripts/restartsrv_apache

This rebuilds the Apache configuration and restarts the LiteSpeed service.

II. Disable QUIC for a Specific Domain

To disable QUIC only for a particular domain or virtual host, create custom userdata include files for both SSL and non-SSL virtual hosts.

Step 1: Create the Non-SSL Userdata Directory

mkdir -p /etc/apache2/conf.d/userdata/std/2_4/$user/$domain/

Step 2: Create the SSL Userdata Directory

mkdir -p /etc/apache2/conf.d/userdata/ssl/2_4/$user/$domain/

Replace:

• $user with the cPanel account username
• $domain with the target domain name

Step 3: Create the QUIC Configuration File

Inside both directories, create the file:

quic_vhosts.conf

Add the following content:

<IfModule LiteSpeed>
QuicEnable off
</IfModule>

Step 4: Rebuild Configuration and Restart LiteSpeed

Run the following command:

/usr/local/cpanel/scripts/rebuildhttpdconf && /usr/local/cpanel/scripts/restartsrv_apache

Verification

After applying the configuration changes, verify that QUIC is disabled by checking the HTTP response headers or using online HTTP/3/QUIC testing tools.

Notes

• QUIC primarily affects HTTP/3 connections.
• Disabling QUIC does not disable HTTPS functionality.
• Ensure UDP port 443 handling aligns with your firewall and network configuration.

Conclusion

Disabling QUIC in LiteSpeed can help resolve compatibility, firewall, or networking issues in certain environments. Administrators can either disable QUIC globally for all hosted domains or selectively for specific virtual hosts based on operational requirements. After making configuration changes, always rebuild the Apache configuration and restart the LiteSpeed service to apply the updates successfully.