Constant errors concerning in-addr.arpa SOA (insecure response)

[vom513]

Hello all,

I've searched the list - and there is a thread from 7 years ago that seems to match what I am seeing:

https://lists.isc.org/pipermail/bind-users/2013-March/090003.html

I am seeing this on a fresh Debian 10 install, using the Debian bind9 packages (specifically as of this moment I have: BIND 9.11.5-P4-5.1+deb10u1-Debian (Extended Support Version) <id:998753c>).  I have stayed as close as possible to the vanilla shipped config.  So to that point - DNSSEC validation works fine out of the box.

I am getting this frequently:

May 30 14:15:33 orbital named[10379]:   validating in-addr.arpa/SOA: got insecure response; parent indicates it should be secure
May 30 14:19:47 orbital named[10379]:   validating in-addr.arpa/SOA: got insecure response; parent indicates it should be secure
May 30 14:19:58 orbital named[10379]:   validating in-addr.arpa/SOA: got insecure response; parent indicates it should be secure
May 30 14:23:12 orbital named[10379]:   validating in-addr.arpa/SOA: got insecure response; parent indicates it should be secure

Absolutely maddening.  This box is also my mail server, so it’s constantly doing reverse lookups, and hence frequently triggering this log...

I have two other boxes (one Debian 9, one Ubuntu (16.04 ?)).  Both also run bind 9.x - distro packages.  Neither of those boxes give me the frequent errors for in-addr.arpa.

I thought this was perhaps an MTU / frag (IPv6 ?) issue ?  I can ping 1500 packets with DF from here to other places across the net.

I also ran a tcpdump filtering for the IP/IPv6 addresses of the [a-f].in-addr-servers.arpa… either I missed something or I’m not seeing it.  Nothing stands out to me there.

No idea if this is red herring, or not, but I notice that b and c instances give back answers that are 200+  bytes larger than a,d,e,f:

vom at orbital:~$ for i in a b c d e f; do echo -n "$i: "; dig -4 +norecurse +dnssec @$i.in-addr-servers.arpa in-addr.arpa soa | grep rcvd: ; done
a: ;; MSG SIZE  rcvd: 309
b: ;; MSG SIZE  rcvd: 547
c: ;; MSG SIZE  rcvd: 547
d: ;; MSG SIZE  rcvd: 309
e: ;; MSG SIZE  rcvd: 313
f: ;; MSG SIZE  rcvd: 281
vom at orbital:~$ for i in a b c d e f; do echo -n "$i: "; dig -6 +norecurse +dnssec @$i.in-addr-servers.arpa in-addr.arpa soa | grep rcvd: ; done
a: ;; MSG SIZE  rcvd: 309
b: ;; MSG SIZE  rcvd: 547
c: ;; MSG SIZE  rcvd: 547
d: ;; MSG SIZE  rcvd: 309
e: ;; MSG SIZE  rcvd: 313
f: ;; MSG SIZE  rcvd: 281

Does anyone know what could be causing this ?  I feel like I’m missing a troubleshooting step.  I would love some clue on some specific dig commands I could run to recreate/diagnose this.

Thanks in advance - this is my “white whale” for this weekend...