[Pdns-users] cache expiry problem with pdns-recursor 3.1.4

[Darren Gamble]

Hi all,

> -----Original Message-----
> From: pdns-users-bounces at mailman.powerdns.com [mailto:pdns-users-
> bounces at mailman.powerdns.com] On Behalf Of Juergen Georgi
> Sent: Friday, May 04, 2007 4:23 AM
> To: pdns-users at mailman.powerdns.com
> Subject: [Pdns-users] cache expiry problem with pdns-recursor 3.1.4
> 
> Hi,
> 
> today I noticed that pdns-recursor failed to resolve RR
> zfl.bsz-bw.de, whereas our second recursor running BIND-9
> had no problems. It turned out, that zone bsz-bw.de was
> served by two master servers with different NS RR sets
> and different default TTLs. At some point, the different
> NS sets get mixed:
> 
> # ns -T bsz-bw.de
> bsz-bw.de               43200   NS      dns1.belwue.de
> bsz-bw.de               43200   NS      dns3.belwue.de
> bsz-bw.de               43200   NS      uranos.rz.uni-konstanz.de
> bsz-bw.de               43200   NS      konstanz.bsz-bw.de
> 
> # ns -T bsz-bw.de
> bsz-bw.de               43139   NS      uranos.rz.uni-konstanz.de
> bsz-bw.de               43139   NS      dns1.belwue.de
> bsz-bw.de               86370   NS      delphi.bsz-bw.de
> bsz-bw.de               43139   NS      konstanz.bsz-bw.de
> bsz-bw.de               43139   NS      dns3.belwue.de

I remember troubleshooting this issue with Bert last year, which we
believed was resolved back in 3.1.2, IIRC.  Perhaps not?

rrsets should never become merged; either the cache should keep its old
set or dump it for the new set.  This appears to be causing this
problem.  So yes, it does unfortunately still look like a problem with
the recursor.

Note also that a DNS server can not (is not supposed to, by RFC) return
and/or keep a rrset where any of the TTLs differ.  This is because,
well, it can cause exactly the issue you're seeing.

============================
Darren Gamble
Systems Architect, Regional Services
Shaw Cablesystems GP
630 - 3rd Avenue SW
Calgary, Alberta, Canada
T2P 4L4
(403) 781-4948