problems resolving CNAME's with pdns_recursor 3.1.7

[Tom Mueller]

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Hash: SHA1

Hi,

sometimes the pdns_recursor doesn't send all A or AAAA records where
the requested CNAME points to.
There are no cascading CNAMES, the CNAME points to an A record.
In the first query the A records are missing, some seconds (and
several more requests) later the A records were sent, too
The TTL shows that the records are fetched by pdns_recursor in the
same second.
Hint: the 'X' in hostnames and IP addresses is a replacement of other
chars and digits.

Additional informations:
We are running 2 instances of pdns_recursor listening at different
ports on this IP to scale the amount of queries.
The  concerning instance has a load average of round about 1500 qps.


There are no error messages in the log - so I wonder what's happened?
There is another issue that sometimes existing AAAA records of another
host not sent but only the A records.

I think, when there was an error condition during recursion the
pdns_recursor has to sent a SERVFAIL, but it didn't.
So it may be possible that there is an issue in the cache management
when a refresh is needed it is not performed immediately?
Any idea?

- ------------------------------------------------

~ # dig XXftp.rz-ip.net

; <<>> DiG 9.3.4 <<>> XXftp.rz-ip.net
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36210
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;XXftp.rz-ip.net.                        IN      A

;; ANSWER SECTION:
XXftp.rz-ip.net.         1545    IN      CNAME   XXXservices.rz-ip.net.

;; Query time: 2 msec
;; SERVER: 85.214.7.22#53(85.214.7.22)
;; WHEN: Thu Jul 16 00:25:24 2009
;; MSG SIZE  rcvd: 56

- ---------------------------------------------

~ # dig XXftp.rz-ip.net

; <<>> DiG 9.3.4 <<>> XXftp.rz-ip.net
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42761
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;XXftp.rz-ip.net.                        IN      A

;; ANSWER SECTION:
XXftp.rz-ip.net.         1510    IN      CNAME   XXXservices.rz-ip.net.
XXXservices.rz-ip.net.    1800    IN      A       XXX.XXX.XXX.XXX
XXXservices.rz-ip.net.    1800    IN      A       XXX.XXX.XXX.XXX

;; Query time: 1 msec
;; SERVER: 85.214.7.22#53(85.214.7.22)
;; WHEN: Thu Jul 16 00:25:59 2009

;; MSG SIZE  rcvd: 88

- -----------------------------------------------------

Best regards

- --
Tom Mueller
Entwicklung Dedicated Servers
- ------------------------------------------------------------
Telefon: + 49 (0)30 - 398 02 - 0
Telefax: + 49 (0)30 - 398 02 - 222
E-Mail:  t.mueller@...
- ------------------------------------------------------------
Strato Rechenzentrum AG
Pascalstr. 10
10587 Berlin
- ----------------------------- -------------------------------
Aufsichtsrat: Damian Schmidt (Vorsitz), Stephan Esch, Andreas Sand
Vorstand: Julien Ardisson, Christian Mueller, Christoph Steffens,
Rene Wienholtz
Amtsgericht Berlin-Charlottenburg HRB 75629

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[bert hubert-2]

On Thu, Jul 16, 2009 at 2:13 PM, Tom Mueller<t.mueller@...> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hi,
>
> sometimes the pdns_recursor doesn't send all A or AAAA records where
> the requested CNAME points to.

Tom,

Do you run with an IPv6 local query address enabled? Can you,
privately, send me the full host names involved?

And a copy of your configuration file too?

Do you see this problem only on rz-ip.net?

Thanks.

> There are no cascading CNAMES, the CNAME points to an A record.
> In the first query the A records are missing, some seconds (and
> several more requests) later the A records were sent, too
> The TTL shows that the records are fetched by pdns_recursor in the
> same second.
> Hint: the 'X' in hostnames and IP addresses is a replacement of other
> chars and digits.
>
> Additional informations:
> We are running 2 instances of pdns_recursor listening at different
> ports on this IP to scale the amount of queries.
> The  concerning instance has a load average of round about 1500 qps.
>
>
> There are no error messages in the log - so I wonder what's happened?
> There is another issue that sometimes existing AAAA records of another
> host not sent but only the A records.
>
> I think, when there was an error condition during recursion the
> pdns_recursor has to sent a SERVFAIL, but it didn't.
> So it may be possible that there is an issue in the cache management
> when a refresh is needed it is not performed immediately?
> Any idea?

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