On Wed, 23 Dec 2015, martin f krafft via Unbound-users wrote:

I am running unbound (1.5.7 on Debian unstable) on a laptop as
a recursive resolver for localhost and a number of test VMs running
on the machine. I am aware that others use dnsmasq for this, but
I don't particularly like this monolithic do-everything tool and am
rather familiar with unbound already.

Unfortunately, I am experiencing problems at regular intervals. One
such problem is that occasionally, unbound will be unable to resolve
records, returning SERVFAIL:

 % host debian.org
 Host debian.org not found: 2(SERVFAIL)

According to the log (full log below), unbound thinks that the
forward server is failing:

 unbound: [1144:0] debug: configured forward servers failed -- returning 
SERVFAIL

However, querying the configured forwarding server works just fine.

 unbound: [1144:0] debug: processQueryTargets: targetqueries 0, currentqueries 
0 sentcount 0
 unbound: [1144:0] info: DelegationPoint<.>: 0 names (0 missing), 1 addrs (0 
result, 1 avail) parentNS
 unbound: [1144:0] debug:    ip4 192.168.1.1 port 53 (len 16)
 unbound: [1144:0] debug: attempt to get extra 3 targets
 unbound: [1144:0] debug: servselect ip4 192.168.1.1 port 53 (len 16)
 unbound: [1144:0] debug:    rtt=120000
 unbound: [1144:0] debug: No more query targets, attempting last resort
 unbound: [1144:0] debug: configured forward servers failed -- returning 
SERVFAIL
 unbound: [1144:0] debug: store error response in message cache

Did your forwarder perhaps not answer (in time) ?

Maybe try setting cache-max-negative-ttl: to something like 5 seconds ?

Paul

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