Overview

While having Kerio Control non-transparent proxy server enabled, you might receive a DNS lookup failed. This message was created by Kerio Control Proxy error.

Such a message is shown in the web browser while accessing certain websites.

While setting the browser's Proxy to use a custom proxy.pac configuration, the ERR_PROXY_CONNECTION_FAILED is being shown.

The webpage reports having no Internet connection.

This article provides information on how to resolve Proxy connection failures in browsers.

Important: custom proxy.pac config is enabled to resolve "DNS lookup failed" error.

Solution

Proxy connection failed error may occur due to ISP issues or incorrect browser settings.

Note: contact your ISP to verify nothing is blocked from their side.

In this particular scenario, the Proxy configuration should be changed both in Kerio Control Webadmin and clients' browsers.

1. In Kerio Control Webadmin > Proxy server > enable "Allow browsers to use configuration script automatically via DHCP server".
   
   Optionally, enable HTTP caching for a non-transparent proxy server so Kerio Control will retain the website data.
2. Make sure the DHCP server is enabled on Kerio Control. You might need to configure the DHCP scopes manually.
3. Verify the custom DNS forwarding and cache settings are in place.
   
4. (Optional) In certain environments with many users connected concurrently, it might be required to create an exclusion from connection limits for the LAN IP addresses.
5. On the browser's side, revert the custom proxy configuration to Automatically detect settings. Make sure the Proxy URL address is empty.