When does rndc reconfig flush the cache?
  • 12 Oct 2018
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When does rndc reconfig flush the cache?

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Why does rndc reconfig flush the cache sometimes but not on other occasions?

Usually when issuing rndc reconfig to make changes to a running BIND 9 nameserver, you expect it to retain the current working cache of learned RRsets.

However, there are a few changes that you can make to the configuration that might be incompatible with what has already been cached - and in those circumstances, named will also start with a new and empty cache following the reconfig. Here are the settings that, if changed, will result in rndc reconfig clearing cache:

  • check-names
  • zero-no-soa-ttl
  • max-cache-size
  • max-cache-ttl
  • max-ncache-ttl
  • dnssec-validation
  • dnssec-accept-expired

See also the limitations on views that share cache
The criteria for whether or not two (or more) views configured in a BIND nameserver may share cache are that the policy settings listed above are consistent between views. The attach-cache option is used to configure cache-sharing.