TechnitiumSoftware/DnsServer · error · InvalidOperationException

MaxMind database not initialized.

Error message

MaxMind database not initialized.

What it means

Thrown by GeoCountryApp CNAME.ProcessRequestAsync when _maxMind is null. Same root cause as error 29 but reached on a CNAME query against a country-routed record: no MaxMind reader is available, so the lookup fails with InvalidOperationException.

Source

Thrown at Apps/GeoCountryApp/CNAME.cs:82

        #region public

        public Task InitializeAsync(IDnsServer dnsServer, string? config)
        {
            _dnsServer = dnsServer;
            _maxMind = MaxMind.Create(dnsServer);

            return Task.CompletedTask;
        }

        public Task<DnsDatagram?> ProcessRequestAsync(DnsDatagram request, IPEndPoint remoteEP, DnsTransportProtocol protocol, bool isRecursionAllowed, string zoneName, string appRecordName, uint appRecordTtl, string appRecordData)
        {
            DnsQuestionRecord question = request.Question[0];

            if (!question.Name.Equals(appRecordName, StringComparison.OrdinalIgnoreCase) && !appRecordName.StartsWith('*'))
                return Task.FromResult<DnsDatagram?>(null);

            if (_maxMind is null)
                throw new InvalidOperationException("MaxMind database not initialized.");

            using JsonDocument jsonDocument = JsonDocument.Parse(appRecordData, Address._jsonParseOptions);
            JsonElement jsonAppRecordData = jsonDocument.RootElement;
            JsonElement jsonCountry = default;
            string? countryCode = null;

            byte scopePrefixLength = 0;
            EDnsClientSubnetOptionData requestECS = request.GetEDnsClientSubnetOption();
            if (requestECS is not null)
            {
                long? asn = null;

                if ((_maxMind.IspReader is not null) && _maxMind.IspReader.TryIsp(requestECS.Address, out IspResponse? csIsp) && (csIsp.Network is not null))
                {
                    scopePrefixLength = (byte)csIsp.Network.PrefixLength;
                    asn = csIsp.AutonomousSystemNumber;
                }
                else if ((_maxMind.AsnReader is not null) && _maxMind.AsnReader.TryAsn(requestECS.Address, out AsnResponse? csAsn) && (csAsn.Network is not null))

View on GitHub (pinned to d0484b6c1e)

Solutions

  1. Put GeoLite2-Country.mmdb (or GeoIP2-Country.mmdb) in the ApplicationFolder.
  2. Restart the service so the MaxMind constructor initialises _maxMind.
  3. Confirm error 31 no longer appears at startup.
Defensive patterns

Strategy: try-catch

Validate before calling

if (_maxMind is null)
    _log.Warn("GeoCountryApp CNAME query for {0} skipped: MaxMind database not loaded.", appRecordName);

Try / catch

try { return await ProcessCountryCnameAsync(request, ...); }
catch (InvalidOperationException ex) when (ex.Message.Contains("MaxMind database not initialized"))
{ _log.Error("GeoIP country database missing — deploy GeoLite2-Country.mmdb."); return Task.FromResult<DnsDatagram?>(null); }

Prevention

When it happens

Trigger: A CNAME query matches a GeoCountryApp record while _maxMind is null, i.e. the country database file was absent at startup.

Common situations: Country database not deployed, moved, or deleted; CNAME country records then surface the failure.

Related errors

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/4baa4c2b56e18602. Report an issue: GitHub.