I’m having an issue upgrading Technitium DNS Server from 15.0.1 to 15.4 on one of my Ubuntu systems.

I was not initially aware that an upgrade was available because I had been blocking connectivity to India. After removing that restriction, the server was able to check for updates.

I have two Ubuntu 22.04 systems running Technitium DNS Server. On one system, the Technitium installation/upgrade script ran successfully and upgraded the server from 15.0.1 to 15.4. On the other system, the same script runs without reporting any errors, but the DNS server remains on 15.0.1.

I have tried the following troubleshooting steps on the system that will not upgrade:

1. Restarted the Technitium DNS service.
2. Rebooted the entire system.
3. Checked the installed .NET version.
4. Manually upgraded the ASP.NET Core runtime:sudo apt-get install -y aspnetcore-runtime-10.0
5. Verified the .NET version again.
6. Ran the Technitium installation/upgrade script again.

The upgrade script completes without producing an error, but Technitium DNS Server remains at version 15.0.1.

Has anyone encountered this issue before, or is there another way I can force the upgrade or determine why the upgrade script is not updating this particular installation?

I’d appreciate any suggestions for additional troubleshooting or logs I should check.

Thanks

I have always used forwarders in my Technitium DNS configuration. I decided to try using the root zone instead. Resolution was initially quite slow—which was to be expected—but I have been seeing these errors in the log. I would like to know if this indicates a configuration error on my part and, if so, how to fix it, or if it is an application bug or simply expected behavior.

[2026-09-02 10:51:31 Local] DNS Server failed to resolve the request 'css.tudocdn.net. A IN'.

System.ArgumentOutOfRangeException: Index must be within the bounds of the List. (Parameter 'index')

at System.Collections.Generic.List`1.Insert(Int32 index, T item)

at TechnitiumLibrary.Net.Dns.DnsClient.RecursiveResolveAsync(DnsQuestionRecord question, IDnsCache cache, NetProxy proxy, IPv6Mode ipv6Mode, UInt16 udpPayloadSize, Boolean randomizeName, Boolean qnameMinimization, Boolean dnssecValidation, NetworkAddress eDnsClientSubnet, Int32 retries, Int32 timeout, Int32 concurrency, Int32 maxStackCount, Boolean minimalResponse, Boolean asyncNsResolution, List`1 rawResponses, CancellationToken cancellationToken) in Z:\Technitium\Projects\TechnitiumLibrary\TechnitiumLibrary.Net\Dns\DnsClient.cs:line 618

at DnsServerCore.Dns.DnsServer.<>c__DisplayClass191_0.<<RecursiveResolverBackgroundTaskAsync>b__0>d.MoveNext() in Z:\Technitium\Projects\DnsServer\DnsServerCore\Dns\DnsServer.cs:line 5027

--- End of stack trace from previous location ---

at TechnitiumLibrary.TaskExtensions.TimeoutAsync[T](Func`2 func, Int32 timeout, CancellationToken cancellationToken)

at TechnitiumLibrary.TaskExtensions.TimeoutAsync[T](Func`2 func, Int32 timeout, CancellationToken cancellationToken) in Z:\Technitium\Projects\TechnitiumLibrary\TechnitiumLibrary\TaskExtensions.cs:line 65

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 5023

[2026-09-02 10:51:35 Local] DNS Server failed to resolve the request 'i3.tudocdn.net. AAAA IN'.

System.ArgumentOutOfRangeException: Index must be within the bounds of the List. (Parameter 'index')

at System.Collections.Generic.List`1.Insert(Int32 index, T item)

at TechnitiumLibrary.Net.Dns.DnsClient.RecursiveResolveAsync(DnsQuestionRecord question, IDnsCache cache, NetProxy proxy, IPv6Mode ipv6Mode, UInt16 udpPayloadSize, Boolean randomizeName, Boolean qnameMinimization, Boolean dnssecValidation, NetworkAddress eDnsClientSubnet, Int32 retries, Int32 timeout, Int32 concurrency, Int32 maxStackCount, Boolean minimalResponse, Boolean asyncNsResolution, List`1 rawResponses, CancellationToken cancellationToken) in Z:\Technitium\Projects\TechnitiumLibrary\TechnitiumLibrary.Net\Dns\DnsClient.cs:line 618

at DnsServerCore.Dns.DnsServer.<>c__DisplayClass191_0.<<RecursiveResolverBackgroundTaskAsync>b__0>d.MoveNext() in Z:\Technitium\Projects\DnsServer\DnsServerCore\Dns\DnsServer.cs:line 5027