TechnitiumSoftware/DnsServer · error · DnsServerException

Invalid domain name [{value}]: IP address cannot be used for

Error message

Invalid domain name [{value}]: IP address cannot be used for DNS server domain name.

What it means

Thrown by the ServerDomain setter when the (Unicode->IDNA-normalized) value parses successfully as an IPAddress. The DNS server's domain must be a domain NAME, not an IP; using an IP would break SOA records, responsible-person mail, and NS generation.

Source

Thrown at DnsServerCore/Dns/DnsServer.cs:7108

        #endregion

        #region properties

        public string ServerDomain
        {
            get { return _serverDomain; }
            set
            {
                if (!_serverDomain.Equals(value, StringComparison.Ordinal))
                {
                    if (DnsClient.IsDomainNameUnicode(value))
                        value = DnsClient.ConvertDomainNameToAscii(value);

                    DnsClient.IsDomainNameValid(value, true);

                    if (IPAddress.TryParse(value, out _))
                        throw new DnsServerException("Invalid domain name [" + value + "]: IP address cannot be used for DNS server domain name.");

                    _serverDomain = value.ToLowerInvariant();
                    _fallbackResponsiblePerson = new MailAddress("hostadmin@" + _serverDomain);

                    _authZoneManager.TriggerUpdateServerDomain();
                    _allowedZoneManager.UpdateServerDomain();
                    _blockedZoneManager.UpdateServerDomain();
                    _blockListZoneManager.UpdateServerDomain();

                    UpdateThisServer();
                }
            }
        }

        public string ConfigFolder
        { get { return _configFolder; } }

        public IReadOnlyList<IPEndPoint> LocalEndPoints

View on GitHub (pinned to d0484b6c1e)

Solutions

1. Set ServerDomain to an actual hostname (e.g. ns1.example.com), and set the listen address separately via localEndPoints.
2. If you have no domain, register one or use a dynamic-DNS hostname.
3. Fix the configuration source (env var/UI/config file) that is feeding an IP into the domain field.
4. Validate that IPAddress.TryParse(value) is false before assignment.

Example fix

// before
server.ServerDomain = "10.0.0.5";

// after
server.ServerDomain = "ns1.example.com";
server.LocalEndPoints = new[] { new IPEndPoint(IPAddress.Parse("10.0.0.5"), 53) };

string SafeServerDomain(string value)
{
    if (DnsClient.IsDomainNameUnicode(value)) value = DnsClient.ConvertDomainNameToAscii(value);
    DnsClient.IsDomainNameValid(value, true);
    if (IPAddress.TryParse(value, out _)) throw new ArgumentException("Server domain must be a hostname, not an IP");
    return value.ToLowerInvariant();
}

static bool IsValidServerDomain(string value)
{
    if (string.IsNullOrWhiteSpace(value)) return false;
    if (IPAddress.TryParse(value, out _)) return false;
    try { DnsClient.IsDomainNameValid(value, true); return true; } catch { return false; }
}

try { server.ServerDomain = value; }
catch (DnsServerException ex) when (ex.Message.Contains("IP address cannot be used")) { return BadRequest("Provide a domain name, not an IP"); }

When it happens

Trigger: Setting ServerDomain to a string that is a valid IP literal (e.g. "192.168.1.1" or "::1") after IDNA conversion. The setter first validates the domain name, then explicitly rejects IP-form values.

Common situations: Operator confuses the server domain with the bind/listen address; copy-paste from a connection string; automation reading the listen IP into the domain field; misconfigured env var (e.g. SERVER_DOMAIN=10.0.0.5).

Related errors

• Network group map contains an invalid network address: {strN
• External to internal translation entries must have same addr
• External to internal translation entries must have same pref
• The SSO Authority URL length cannot be more than 255 chars.
• The SSO Authority URL scheme can be 'http' or 'https' only.

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/9ae0d2de9a291d8d. Report an issue: GitHub.