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Expand blackhole description

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Clarify the behavior of negated addresses within the `blackhole`
statement to prevent common configuration misunderstandings.

(cherry picked from commit 2b23c7011e)
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Ondřej Surý 2026-02-26 17:13:04 +01:00 committed by Mark Andrews
parent 994cf44836
commit 78beb3a71a
1 changed files with 11 additions and 0 deletions
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doc/arm/reference.rst
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@ -3149,6 +3149,17 @@ for details on how to specify IP address lists.
from or use to resolve a query. Queries from these addresses are not
responded to. The default is ``none``.
When configuring this list, note that BIND evaluates Access Control Lists
sequentially (first match wins). A common misconception is that the directive
``!address;`` blocks everything except that address. In reality, it only
explicitly exempts ``address`` from the blackhole; all other IP addresses
reach the end of the list without matching, meaning they are also not
blackholed.
To successfully blackhole all traffic *except* specific addresses, you must
explicitly catch the remaining traffic with ``any;`` at the end of the list.
For example: ``!address; any;``
.. namedconf:statement:: keep-response-order
:tags: server
:short: Defines an :any:`address_match_list` of addresses which do not accept reordered answers within a single TCP stream.