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Why does named log an error 'disabling RFC 1918 empty zones' when starting up?
Author: ISC Support Reference Number: AA-00804 Views: 42301 Created: 2012-09-27 16:57 Last Updated: 2013-08-15 22:10 0 Rating/ Voters

In BIND 9.6-ESV-R5, 9.7.4, 9.8.1 (and newer versions of 9.6-ESV, 9.7 and 9.8 that supersede them), the warning message below may be encountered when named is starting:

Warning: 'empty-zones-enable/disable-empty-zone' not set:
disabling RFC 1918 empty zones

This is emitted when the empty-zones-enable option is not set and when named does not encounter any RFC 1918 zones in named.conf - either explicitly configured or explicitly disabled as an empty zone via option disable-empty-zone (in which case the default is to disable the RFC 1918 empty zones).  Its purpose is to highlight to the administrator that these empty zones are now available to be enabled, but were not included by default.

The warning is not generated if any RFC 1918 zones are encountered since it's assumed that the administrator is already aware of and using these zones and would not want or expect named's behaviour to change on a minor BIND version or ESV revision upgrade.

When upgrading to BIND 9.9 or later, note that empty zones with RFC 1918 prefixes will be loaded by default.

The treatment of the newly-introduced RFC 1918 automatic empty zones is subtly different on 9.9. 

In BIND 9.6-ESV-R5, 9.7.4, 9.8.1 (and newer versions of 9.6-ESV, 9.7 and 9.8 that supersede them), all of the empty zones except the new RFC 1918 empty zones are added automatically when empty-zones-enable has not been declared as an option.  These new RFC 1918 empty zones will not be loaded unless named.conf explicitly includes option empty-zones-enable yes; (i.e, the default is 'yes', but not fully 'yes'.  This was done to minimize the likelihood of unexpected behaviour being encountered by users following small incremental upgrades within the same major version.)

From BIND 9.9.0, the new RFC 1918 empty zones have equal status with those in the earlier set and are all included by default.

All empty zones that named loads automatically are logged as they are created and loaded when named starts up, or you can refer to the list in the Administrator Reference Manual, which can be found in the BIND source code distributions (see also An Overview of BIND 9 Documentation ).

For a longer and more detailed article on the implementation of automatic empty zones, see: Automatic empty zones (including RFC 1918 prefixes) (you will need to login to view this article, but registration is open to all).

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Feedback 2
  • #
    [ Ulrik]: 9.9 behaviour 2013-02-01 16:36

    I realise this page is not mainly about Bind 9.9 but a link to the appropriate manual describing Bind 9.9 behaviour would be helpful for those of us sent here via Google.

  • #
    [Brian Conry]: Re: 9.9 behaviour 2013-08-15 22:11

    Hi Ulrik,

    I have updated the previously-broken documentation link to point to an overview page that covers all versions, including 9.9.

    The best place, however, to read about the behavior of 9.9 is the "Automatic empty zones (including RFC 1918 prefixes)" article mentioned above.

    Brian Conry
    ISC Support

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