TechnitiumSoftware/DnsServer · error · InvalidOperationException

MaxMind database not initialized.

Error message

MaxMind database not initialized.

What it means

Thrown by GeoCountryApp Address.ProcessRequestAsync in the A/AAAA branch when _maxMind is null. Functionally identical to error 26 but for country-level geo routing: the MaxMind reader was not built at startup (see error 31), so a country lookup cannot run and raises InvalidOperationException.

Source

Thrown at Apps/GeoCountryApp/Address.cs:170

            else
            {
                _groups = new Dictionary<string, List<string>>();
            }
        }

        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);

            switch (question.Type)
            {
                case DnsResourceRecordType.A:
                case DnsResourceRecordType.AAAA:
                    if (_maxMind is null)
                        throw new InvalidOperationException("MaxMind database not initialized.");

                    using (JsonDocument jsonDocument = JsonDocument.Parse(appRecordData, _jsonParseOptions))
                    {
                        JsonElement jsonAppRecordData = jsonDocument.RootElement;
                        JsonElement jsonCountry = default;

                        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. Deploy GeoLite2-Country.mmdb (or GeoIP2-Country.mmdb) into the ApplicationFolder.
  2. Restart the DnsServer service so the GeoCountryApp MaxMind constructor succeeds.
  3. Verify startup log shows no 'MaxMind Country file is missing!' (error 31).
Defensive patterns

Strategy: try-catch

Validate before calling

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

Try / catch

try { return await ProcessCountryAsync(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 DNS A/AAAA query matches a GeoCountryApp record, but the GeoLite2/GeoIP2-Country.mmdb file was missing at startup, leaving _maxMind null.

Common situations: GeoCountryApp configured without deploying the MaxMind country database, or the database removed after initial setup. Country-based answers fail for every client.

Related errors

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/b88605cfb8863900. Report an issue: GitHub.