DNS Server failed to resolve the request '10.in-addr.arpa. IXFR IN' using forwarders

[micush]

Hi Shreyas,

I've been seeing this in the logs the last X days:

[2025-11-22 20:41:25 UTC] DNS Server failed to resolve the request '10.in-addr.arpa. IXFR IN' using forwarders: 1.1.1.1, 2.2.2.2.
DnsServerCore.Dns.DnsServerException: All name servers failed to answer the request '10.in-addr.arpa. IXFR IN'. Received last response with RCODE=FormatError from: 2.2.2.2
   at DnsServerCore.Dns.DnsServer.RecursiveResolverBackgroundTaskAsync(DnsQuestionRecord question, NetworkAddress eDnsClientSubnet, Boolean advancedForwardingClientSubnet, IReadOnlyList`1 conditionalForwarders, Boolean dnssecValidation, Boolean cachePrefetchOperation, Boolean cacheRefreshOperation, Boolean skipDnsAppAuthoritativeRequestHandlers, TaskCompletionSource`1 taskCompletionSource) in Z:\Technitium\Projects\DnsServer\DnsServerCore\Dns\DnsServer.cs:line 4503

A verbose tcpdump on the requesting host shows: FormErr- q: IXFR? 10.in-addr.arpa

All servers are Technitium now 14.2, but I was seeing it in 14.1 as well. Two servers are clustered and are Authoritative for 10.in-addr.arpa and another two are also clustered and are configured as forwarders for the zone 10.in-addr.arpa and point to the Authoritative hosts.

Upgrading from 14.1 to 14.2 did not bring an improvement. Can you have a look kind sir?

Regards,

micush

[roswitina]

Is 2.2.2.2 even an official nameserver?

[ShreyasZare]

Thanks for reporting this. It seems that you have that reverse forwarder zone which getting IXFR from secondary forwarder zone on another server. The auto prefetch feature is collecting stats which gets this IXFR queries in stats and is trying to "refresh" them in cache.

Will get the auto prefetch code updated to avoid this in the next release.

[micush]

Is 2.2.2.2 even an official nameserver?

The specifics were changed for privacy.

[micush]

Thanks for reporting this. It seems that you have that reverse forwarder zone which getting IXFR from secondary forwarder zone on another server. The auto prefetch feature is collecting stats which gets this IXFR queries in stats and is trying to "refresh" them in cache.

Will get the auto prefetch code updated to avoid this in the next release.

Thanks a lot. Appreciate it. It was kind of weird to me that a forward zone was trying to do an incremental transfer. :)

[ShreyasZare]

There is a workaround to avoid this issue till the next update. You can just increase the conditional forwarder zone's SOA REFRESH value to 1 hour so that the secondary forwarder zone does periodic IXFR queries only ones an hour. This will cause the auto prefetch to not consider it for "refresh" task since it wont be eligible anymore.

[ShreyasZare]

Technitium DNS Server v14.3 is now available which fixes this issue. Do update and let me know your feedback.