[Bug 1472510] Re: Unbound returns SERVFAIL for specific query on dual stacked machine

[Patrik Lundin]

[Impact]
* Unbound is not able to look up certain hostnames in the default configuration when running on a dual stacked (IPv4 and IPv6) host.
* The impact of this on users is that it can lead to a nasty surprise when a currently IPv4-only host gets IPv6 connectivity.

[Test Case]
* On a machine that is currently dual stacked, you can verify the problem with unbound-host. Forcing it to IPv4- and IPv6 only should work, while allowing both will fail.
* IPv4-only (works):
===
unbound-host -4 -f /var/lib/unbound/root.key a.root-servers.net
===

* IPv6-only (works):
===
unbound-host -6 -f /var/lib/unbound/root.key a.root-servers.net
===

* Both (fails):
===
unbound-host -f /var/lib/unbound/root.key a.root-servers.net
===

[Regression Potential] 
* I am not aware of any regression risks. Looking at the upstream tree I am not able to identify any diffs surrounding r3127 that seem relevant to this bump.

[Other Info]
* See attachement for debdiff against wily.

** Patch added: "unbound_1.4.22-1ubuntu6.patch"
   https://bugs.launchpad.net/ubuntu/+source/unbound/+bug/1472510/+attachment/4429922/+files/unbound_1.4.22-1ubuntu6.patch

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Title:
  Unbound returns SERVFAIL for specific query on dual stacked machine

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