[Dnsmasq-discuss] DNSMasq caching DNS query after restart?

[Matthias Andree]

Piero schrieb:
> Hi there,
> 
>    I have a strange issue with DNSMasq: it looks like it saves dns
> cached query and keep them after a restart.
> Here is the problem: the host opaplnx13 didn't reverse lookup and I
> saw this in DNSMasq logs. I fixed the problem in "master DNS servers"
> and they actually reverse lookup opaplnx13 correctly but DNSMasq
> actually does not. It doesn't even after a restart.
> 
> 10.145.3.71 and 10.145.3.72 are DNSMasq servers
> 10.145.1.121 is a master server
> 
> [root at opaplnx23 etc]# nslookup
>> server 10.145.3.71
> Default server: 10.145.3.71
> Address: 10.145.3.71#53
>> 10.145.3.41
> Server:         10.145.3.71
> Address:        10.145.3.71#53
> 
> ** server can't find 41.3.145.10.in-addr.arpa: NXDOMAIN
>> server 10.145.3.72
> Default server: 10.145.3.72
> Address: 10.145.3.72#53
>> 10.145.3.41
> Server:         10.145.3.72
> Address:        10.145.3.72#53
> 
> ** server can't find 41.3.145.10.in-addr.arpa: NXDOMAIN
>> server 10.145.1.121
> Default server: 10.145.1.121
> Address: 10.145.1.121#53
>> 10.145.3.41
> Server:         10.145.1.121
> Address:        10.145.1.121#53
> 
> 41.3.145.10.in-addr.arpa        name = opaplnx13.intra.azosp.vr.it.
> 
> In DNSMasq log I can see:
> Aug 25 16:21:06 dnsmasq[6373]: query[PTR] 41.3.145.10.in-addr.arpa
> from 10.145.3.69
> Aug 25 16:21:06 dnsmasq[6373]: config 10.145.3.41 is NXDOMAIN-IPv4
> 
> How is it possible? Is there a cache file somewhere?

1. don't use nslookup for any kind of testing, you often get very strange
results. Use dig instead, or host. dig for instance will also show the TTL,
which can be rather useful when dealing with "is this data cached" sort of
questions.

2. dnsmasq is a forwarder, and if the upstream server caches the result, then
dnsmasq will get a cached result.