This type of protection is disabled by default because it can reduce performance and frustrate users if it is not correctly configured. Do not enable client blacklisting if using a gateway, such as a Unified Access Gateway appliance, which presents all client connections as the same IP address.

If enabled, connections from clients on the blacklist are delayed for a configurable period before processing. If many connections from the same client are being delayed at the same time, further connections from that client are refused, rather than delayed. This threshold is configurable.

You can enable this feature by adding the following property to the file:

secureHandshakeDelay = delay_in_milliseconds

For example:

secureHandshakeDelay = 2000

To disable blacklisting of HTTPS connections, remove the secureHandshakeDelay entry or set it to 0.

When a TLS handshake over-run occurs, the client's IP address is added to the blacklist for a minimum period equal to the sum of handshakeLifetime and secureHandshakeDelay.

Using the values in the examples above, the IP address of a misbehaving client is 22 seconds:

 (20 * 1000) + 2000 = 22 seconds

The minimum period is extended each time a connection from the same IP address misbehaves. The IP address is removed from the blacklist after the minimum period has expired and after the last delayed connection from that IP address has been processed.

A TLS handshake over-run is not the only reason to blacklist a client. Other reasons include a series of abandoned connections, or a series of requests ending in error, such as multiple attempts to access non-existent URLs. These various triggers have differing minimum blacklist periods. To extend monitoring of these additional triggers to port 80, add the following entry to the file:

insecureHandshakeDelay = delay_in_milliseconds

For example:

 insecureHandshakeDelay = 1000

To disable blacklisting of HTTP connections, remove the insecureHandshakeDelay entry or set it to 0.