[nsd-users] nsd AXFR flood on NOT IMPL error code

[Andreas Schwarz]

Hi fellow nsd users,

due to an error in my configuration, I ended up having a secondary zone configured, which queried a DNS server, that sent me "NOT IMPL" error code.

I noticed, that according to the log messages, NSD seems to somewhat flood the respective server instead of aborting.

Excerpt from my log (please note the very short interval between timestamps):
#----------##----------##----------##----------##----------##----------#
[...]
[2020-04-27 14:24:23.860] nsd[22219]: error: xfrd: zone XYZ received error code NOT IMPL from 1.2.3.4
[2020-04-27 14:24:23.872] nsd[22219]: error: xfrd: zone XYZ received error code NOT IMPL from 1.2.3.4
[2020-04-27 14:24:23.882] nsd[22219]: error: xfrd: zone XYZ received error code NOT IMPL from 1.2.3.4
[2020-04-27 14:24:23.893] nsd[22219]: error: xfrd: zone XYZ received error code NOT IMPL from 1.2.3.4
[...]
#----------##----------##----------##----------##----------##----------#

At another occasion I noticed, that NSD seems to abort the XFR activity when receiving a NOT AUTHORITATIVE or even REFUSED.

Is the behaviour for "NOT IMPL" a bug? Do I misinterpret the logs? How can this behavior be adjusted to not flood the server (besides not pointing the zone to it in the first place, duh)?

NSD version is 4.2.4 but I did not find any commits for the xfrd code, that would indicate changes in this direction.

Any feedback appreciated. Thanks.

Cheers
Andreas