Unbound and intermittent network connectivity?

W.C.A. Wijngaards wouter at nlnetlabs.nl
Mon Jan 4 09:29:10 UTC 2016

Hash: SHA256

Hi Robert,

On 18/12/15 20:05, Robert Edmonds via Unbound-users wrote:
> Hi,
> I have a few recent bug reports from Debian users that Unbound
> stops resolving after brief interruptions in network connectivity.
> Especially from users on laptops, which are typically not as
> well-connected as servers or workstations with wired Ethernet
> connections.
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=791659
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=808204
> A few questions:
> Is my guess that Unbound stores unreachability information for 
> particular nameservers in the "infra cache" correct?  Does this
> also apply to forwarders?  Does that mean if a user is running
> Unbound in forwarding mode and has a brief network outage, they
> have to wait until an "infra-host-ttl" expiration (default 15
> minutes) occurs before resolution service works again?

Yes it applies to forwarders.

> Is the format of the "dump_infra" output documented anywhere?
> I've started reading source code to figure it out, but it would be
> nice to have some "this is good" and "this is bad" examples.  E.g.,
> at first glance I misread "lame dnssec 0" to mean "this server is
> lame, and does not support DNSSEC", which appears to be the
> opposite of what it means :-)

It is not documented.  It also changed between versions of unbound as
the internal cache contents contains different values.
daemon/remote.c:dump_infra_host() has the print statement.  The ping
value is the interesting "how may millisecond" value.  Values of
120000 indicate unbound thinks it is unreachable.

> Should distros be doing something on network change events to get 
> Unbound to purge unreachability information?  I think "flush_infra
> all" would do it, but isn't this quite disruptive?  (Maybe
> unreachability information could be cached with a different TTL
> than the other attributes for entries in the infra cache?)

Yes that is a good idea.  It is not disruptive.  (it could be
disruptive for a high-load server, that is now going to probe distant
servers that are experiencing a high packet rate).

> Should distros lower "infra-host-ttl" in general, or for laptop
> users in particular?

I would distinguish between end-hosts and recursive-servers.

> How should we deal with brief interruptions in network connectivity
> past the first hop (say, outage inside the ISP backbone) that don't
> trigger events?

That is what the TTL is for.

Best regards, Wouter

> Thanks!

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