What do the error messages of the firewall or the CDN mean?

If your website is not accessible as usual, the EuropeanSEC firewall displays a special error page. This page contains general information as well as an error code, which helps you to identify the cause more quickly. Using the codes listed below, you can check for yourself whether an adjustment in the firewall settings is necessary or if your hosting provider or developer should intervene.

Typical error codes and solutions

Error code 8

Description: The connection between the firewall and the web server was rejected by a TCP reset response.
Details: The EuropeanSEC firewall could not establish a connection to the hosting server where the website is located.
Solution: Check if you have entered the correct IP address of your web server in the firewall settings, and make sure that the EuropeanSEC IP addresses are allowlisted on the hosting server.

Error code 15

Description: The request was blocked by security policies.
Details: The block is based on the firewall settings (such as "Blocked requests" or "Blocked IPs").
Solution: Check the relevant rules under Settings > Blacklist. If no issue is apparent, you can manually allow the affected IP address (Settings > IP Whitelist).

Error code 16

Description: The request was blocked by security policies.
Details: The block is based on rules such as Automated access (bots) or Unauthorized resource access.
Solution: Go to Settings > Firewall policies and check the policy settings. If everything is correct, add the IP address to the whitelist (Settings > IP Whitelist).

Error code 17

Description: The request was blocked.
Details: The block was triggered by the firewall's country settings.
Solution: Check your settings under Settings > Blacklist > Add countries. If the block is not intended, you can add the affected IP address to the whitelist (Settings > IP Whitelist).

Error code 20

Description: Connection to the web server could not be established due to a TCP timeout.
Details: Either the hosting server is unreachable or the IP address of your hosting server stored in the firewall is incorrect.
Solution: Check the IP address under Settings > Firewall settings > Your server IP address. If it is incorrect, correct it and wait up to 15 minutes for the change to take effect. If the IP is correct, contact your hosting provider to have server outages checked. If necessary, your hosting provider may need to add the EuropeanSEC IP addresses to their firewall whitelist. You can find more information and the required IP ranges in the FAQ article "Which IP addresses do I need to allow in my firewall to avoid a block by EuropeanSEC?".

Error code 22

Description: Domain could not be resolved by the proxy.
Details: This error often occurs when the domain has just been added or when services have expired or been cancelled before the DNS records were updated.
Solution: Update the A record of your domain as well as the "www" CNAME to the hosting IP. Allow 1–4 hours for DNS propagation.

Error code 23

Description: Domain could not be resolved because multiple entries exist with the same hostname configuration.
Details: There may be a duplicate EuropeanSEC entry or a conflict with existing services.
Solution: Contact our support to check for and clear any possible duplicate accounts.

Error code 26

Description: SSL is not supported.
Details: The cause is a faulty SSL/TLS configuration between the firewall and hosting server.
Solution: Make sure that the SSL certificate is correctly installed both on the hosting server and in the EuropeanSEC firewall (Settings > Firewall settings > Upload your own certificate). Depending on the situation, support from your hosting provider or our support may be required.

If you receive another error that is not described in the list, we kindly ask you to contact our support.