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

[Juergen Georgi]

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

After 12 hours all but one NS-RR have expired. Unfortunately
delphi.bsz-bw.de sits behind a firewall and cannot be reached.

This zone is definitey screwed up, I admit. Anyway, pdns-recursor
should still handle this situation gracefully. So if a RR set 
in a reply differs from an RR set in the cache, it should not
go into the cache.

Regards,

-Juergen Georgi