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+.. _mod-prefill:
+
+Cache prefilling
+----------------
+
+This module provides ability to periodically prefill DNS cache by importing root zone data obtained over HTTPS.
+
+Intended users of this module are big resolver operators which will benefit from decreased latencies and smaller amount of traffic towards DNS root servets.
+
+Example configuration is:
+
+.. code-block:: lua
+
+	modules.load('prefill')
+	prefill.config({
+              ['.'] = {
+                      url = 'https://www.internic.net/domain/root.zone',
+                      ca_file = '/etc/pki/tls/certs/ca-bundle.crt',
+                      interval = 86400  -- seconds
+              }
+        })
+
+This configuration downloads zone file from URL `https://www.internic.net/domain/root.zone` and imports it into cache every 86400 seconds (1 day). The HTTPS connection is authenticated using CA certificate from file `/etc/pki/tls/certs/ca-bundle.crt` and signed zone content is validated using DNSSEC.
+
+Root zone to import must be signed using DNSSEC and the resolver must have valid DNSSEC configuration. (For further details please see :ref:`enabling-dnssec`.)
+
+.. csv-table::
+ :header: "Parameter", "Description"
+
+ "ca_file", "path to CA certificate bundle used to authenticate the HTTPS connection"
+ "interval", "number of seconds between zone data refresh attempts"
+ "url", "URL of a file in :rfc:`1035` zone file format"
+
+Only root zone import is supported at the moment.
+
+Dependencies
+^^^^^^^^^^^^
+
+Depends on the luasec_ library.
+
+.. _luasec: https://luarocks.org/modules/brunoos/luasec