[Dnsmasq-discuss] Caching issue question

Nick nick at double-stroke.com
Fri May 18 11:29:13 BST 2012


Hi Simon,
sorry I did not know that I have to specify the CNAME for A and AAAA. I 
will add the entries to our DNS then. Would it be possible to have a 
CNAME for the A and AAAA entry even when the CNAMEs point to different 
locations? I always thought that the cached response gets stored with 
the type of the entry (A or AAAA).

Best Regards
Nick

Am 18.05.2012 12:14, schrieb Simon Kelley:
> On 18/05/12 10:14, Nick wrote:
>> Hi,
>> I will provide a little bit more debug output. We are using Ubuntu
>> 11.10, so I rebuild the Ubuntu 12.04 package for Ubuntu 11.10.
>>
>> Here is the current config which we use for dnsmasq (without 
>> defaults):
>>
>> """
>> domain-needed
>> resolv-file=/etc/dnsmasq.upstreams
>> strict-order
>> listen-address=127.0.0.1
>> no-dhcp-interface=127.0.0.1
>> bind-interfaces
>> no-hosts
>> cache-size=300
>> """
>>
>> Here is the log output of dnsmasq (syslog) when I do alternating 
>> queries
>> with dig and enabled logging:
>>
>> <restarted dnsmasq before to clear cache; TTL is 60 seconds; doing 
>> "dig
>> session-storage.fd.corp" and "dig AAAA session-storage.fd.corp">
>> """
>> May 18 12:08:05 pzk-node-9 dnsmasq[1367]: query[A]
>> session-storage.fd.corp from 127.0.0.1
>> May 18 12:08:05 pzk-node-9 dnsmasq[1367]: forwarded
>> session-storage.fd.corp to 10.193.3.133
>> May 18 12:08:05 pzk-node-9 dnsmasq[1367]: reply 
>> session-storage.fd.corp
>> is <CNAME>
>> May 18 12:08:05 pzk-node-9 dnsmasq[1367]: reply 
>> cb-node-1.poz.fd.corp is
>> 10.190.2.1
>>
>> # now doing a AAAA request
>> May 18 12:08:08 pzk-node-9 dnsmasq[1367]: query[AAAA]
>> session-storage.fd.corp from 127.0.0.1
>> May 18 12:08:08 pzk-node-9 dnsmasq[1367]: cached 
>> session-storage.fd.corp
>> is <CNAME>
>> # why is CNAME cached for the first AAAA query?
>
> CNAMES are for a domain, not for a type of query, dnsmasq has cached
> that session-storage.fd.corp is a CNAME for cb-node-1.poz.fd.corp, 
> hence
> this line. But then it finds it has no AAAA record cached for
> cb-node-1.poz.fd.corp, so it forwards the query anyway, and gets.
>>
>> May 18 12:08:08 pzk-node-9 dnsmasq[1367]: forwarded
>> session-storage.fd.corp to 10.193.3.133
>> May 18 12:08:08 pzk-node-9 dnsmasq[1367]: reply 
>> session-storage.fd.corp
>> is NODATA-IPv6
>
> session-storage.fd.corp has no value for AAAA. This is WRONG, if an A
> query for session-storage.fd.corp returns a CNAME, then an AAAA query
> should return a CNAME too. If there's no AAAA record, it should be 
> for
> cb-node-1.poz.fd.corp.
>
>
>>
>> # now doing again A request
>> May 18 12:08:11 pzk-node-9 dnsmasq[1367]: query[A]
>> session-storage.fd.corp from 127.0.0.1
>> May 18 12:08:11 pzk-node-9 dnsmasq[1367]: forwarded
>> session-storage.fd.corp to 10.193.3.133
>> May 18 12:08:11 pzk-node-9 dnsmasq[1367]: reply 
>> session-storage.fd.corp
>> is <CNAME>
>> May 18 12:08:11 pzk-node-9 dnsmasq[1367]: reply 
>> cb-node-1.poz.fd.corp is
>>
>> # it got forwarded, but it should be in cache (first request was on
>> 12:08:05)
> Because the NODATA reply for session-storage.fd.corp removed the 
> CNAME
> from the cache.
>
>>
>> # doing same stuff again
>> May 18 12:08:14 pzk-node-9 dnsmasq[1367]: query[AAAA]
>> session-storage.fd.corp from 127.0.0.1
>> May 18 12:08:14 pzk-node-9 dnsmasq[1367]: cached 
>> session-storage.fd.corp
>> is <CNAME>
>> May 18 12:08:14 pzk-node-9 dnsmasq[1367]: forwarded
>> session-storage.fd.corp to 10.193.3.133
>> May 18 12:08:14 pzk-node-9 dnsmasq[1367]: reply 
>> session-storage.fd.corp
>> is NODATA-IPv6
>> May 18 12:08:17 pzk-node-9 dnsmasq[1367]: query[A]
>> session-storage.fd.corp from 127.0.0.1
>> May 18 12:08:17 pzk-node-9 dnsmasq[1367]: forwarded
>> session-storage.fd.corp to 10.193.3.133
>> May 18 12:08:17 pzk-node-9 dnsmasq[1367]: reply 
>> session-storage.fd.corp
>> is <CNAME>
>> May 18 12:08:17 pzk-node-9 dnsmasq[1367]: reply 
>> cb-node-1.poz.fd.corp is
>> 10.190.2.1
>> """
>>
>> I hope that helps.
>>
>
> So I think this is DNS misconfiguration upstream, the A query returns
>
> session-storage.fd.corp   CNAME  cb-node-1.poz.fd.corp
> cb-node-1.poz.fd.corp     A      10.190.2.1
>
>
> and the AAAA query SHOULD return
>
> session-storage.fd.corp   CNAME  cb-node-1.poz.fd.corp
>
> but it's in fact returning no data for session-storage.fd.corp
>
>
> If I'm wrong, someone will no doubt be along soon to tell me why.
>
>
> Simon.
>
>
>
>
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