unbound flooding syslog with 'sendto failed: Cannot assign requested address'

W.C.A. Wijngaards wouter at nlnetlabs.nl
Fri Oct 16 11:28:12 UTC 2015

Hash: SHA1

Hi Hendrik,

On 10/16/2015 12:47 PM, Hendrik Jaeger via Unbound-users wrote:
> Hi,
> I’m running unbound 1.4.22 from debian unstable on my laptop. Since
> yesterday unbound started behaving strangely, flooding the syslog 
> with failure messages. Example: Oct 16 10:23:20 frustcomp unbound:
> [26958:0] notice: sendto failed: Cannot assign requested address 
> Oct 16 10:23:20 frustcomp unbound: [26958:0] notice: remote address
> is 2001:500:3::42 port 53

The newer versions of unbound have many fixes.  Several of them have
related to squelching log messages.

> The pattern is always the same: 'sendto failed' followed by
> 'remote address is' with varying IPv6 addresses. You can find full
> unbound-logs for yesterday in [0], created using this command: grep
> 'unbound' /var/log/syslog.1 > /tmp/unbound_failures.log (Careful:
> this file is 339M big and has 3642512 lines.)

That is big!  I did not check, because you already give lots of
information here :-)

> IPv6 is disabled on this system, it has neither an IPv6 address on
> any interface nor a route set.

Unbound does not know IPv6 is disabled, so it tries.  The failure is
harmless (apart from annoying with a log message in this unbound
version you are using).  You could do-ip6: no in unbound.conf to make
the log messages go away.  Or upgrade to a newer version.

> Today I tried just restarting unbound and that failed as well: #
> service unbound restart Restarting recursive DNS server:
> unbound[1444991903] unbound[22562:0] error: can't bind socket:
> Cannot assign requested address [1444991903] unbound[22562:0]
> debug: failed address ::1 port 8953 [1444991903] unbound[22562:0]
> error: cannot open control interface ::1 8953 [1444991903]
> unbound[22562:0] fatal error: could not open ports failed!
> # ss -apen | grep 8953 returns nothing listening on that port, just
> to make sure that’s not the problem. Since the message refers to
> 'requested address' and probably means ::1, I doubt it is. ::1 is
> not configured on any interface, as IPv6 is disabled.
> I can’t figure out either of these problems, and I’m not sure if
> they are related but the timing seems to suggest that.

Well if you disable IPv6 and then ::1 does not exist, then you'd also
have to disable ::1 for unbound, i.e. do-ip6: no.  In any case, you
could either disable ipv6 for unbound, or configure it with
as the interface to bind to with interface: and control-interface:.

In later versions of unbound this error may also go away, but there
have been many releases in the meantime, so I am not sure.  (it would
detect ipv6 is disabled and not fail and not bother you about it).

> Can anyone help me understand any of the error messages please?
> What might cause them? Why do they appear on a system without IPv6 
> configured?

Apart from all of the above, would you enable IPv6?  This is not to
fix the issue you have with your Unbound configuration, but because
IPv6 is necessary for connecting future internet users?

Best regards, Wouter

> Please tell me (off-list maybe) what other info I should provide.
> Thank you very much.
> Sincerely
> henk
> [0]: http://henk.hnjs.ch/20151015_unbound_failures.txt

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