Unbound strange stub_zone behavior?

Jan Komissar (jkomissa) jkomissa at cisco.com
Mon Jul 13 18:55:25 UTC 2020

Hi Andrew,

I believe that stub-zones will not work correctly for +norecurse (RD (recursion desired) flag unset) queries. Also, if your blah.example.com has delegations to subzones (even on the same server) and you use a non-standard port, you would need a stub-zone for each sub-zone.

I would follow Eric's advice to use an auth-zone, either as primary or secondary server (depending on your authoritative requirements).



On 7/12/20, 12:00 PM, "Unbound-users on behalf of Eric Luehrsen via Unbound-users" <unbound-users-bounces at lists.nlnetlabs.nl on behalf of unbound-users at lists.nlnetlabs.nl> wrote:

    On 7/11/20 11:49 AM, Andrew Forgue via Unbound-users wrote:
    > I have an unbound server that acts as a recursive resolver for clients and also acts as a target for fully delegated DNS (i.e. unbound is the NS record). For the fully-delegated domain it is a simple stub zone with an upstream of localhost on a different port.  Let's call it "blah.example.com".
    > Occasionally, unbound (has happened on versions 1.10.1 and 1.7.3) will start responding to non-recursive queries with the list of root zones instead of a response from the stub-zone.  It seems that clients that use the `rd` flag are fine and continue to be able to resolve records in the stub-zone.  Only recursive desired clients will receive correct records from unbound (using the stub server).  All records in seemingly all stub zones have this behavior simultaneously.
    > I don't know what triggers it, but a full restart of unbound is the only thing that fixes it.  I've tried flushing cache, flushing infra, and everything, nothing seems to matter. I've seen only 2 things that may point to the issue.
    > - With verbosity turned up to 10, there's an entry produced in strace (but not in the actual log - maybe a misconfig): "unbound[2213085:5] debug: answer from the cache failed"
    > - stracing the "broken" unbound process is a very tight recvmsg() (of the request) and sendmsg() (with the root servers) with no syscalls in between.
    > Again, Using dig with +recurse works all the time, even when unbound gets in this state.  So seems like an unbound bug / cache corruption or something?

    If it is a bug, you may want to try a work around while waiting for a 
    fix. You could try "auth-zone:" instead of "stub-zone:" or as a 
    companion to "stub-zone:" You may need to give the authoritative server 
    permission for a wholesale zone transfer to the Unbound instance. This 
    may help avoid some undiscovered bug in piecemeal zone recursion.
    - Eric

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