Root on lookback (RFC 7706)
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Knot Resolver developers decided that pure implementation of :rfc:`7706` is a bad idea so it is not implemented in the form envisioned by the RFC. You can get the very similar effect without its downsides by combining :ref:`prefill <mod-prefill>` and :ref:`serve_stale <mod-serve_stale>` modules with Aggressive Use of DNSSEC-Validated Cache (:rfc:`8198`) behavior which is enabled automatically together with DNSSEC validation.
