TechnitiumSoftware/DnsServer · error · ArgumentOutOfRangeException

QPM limit IPv4 prefix valid range is between 0 and 32.

Error message

QPM limit IPv4 prefix valid range is between 0 and 32.

What it means

Thrown by the QpmPrefixLimitsIPv4 property setter when any dictionary key (IPv4 prefix length) is outside 0-32. IPv4 addresses are 32 bits, so prefix lengths beyond that are invalid. Each entry is validated in a loop before assignment.

Source

Thrown at DnsServerCore/Dns/DnsServer.cs:7418

        public IReadOnlyDictionary<int, (int, int)> QpmPrefixLimitsIPv4
        {
            get { return _qpmPrefixLimitsIPv4; }
            set
            {
                if (value is null)
                {
                    _qpmPrefixLimitsIPv4 = new Dictionary<int, (int, int)>();
                }
                else if (value.Count > byte.MaxValue)
                {
                    throw new ArgumentOutOfRangeException(nameof(QpmPrefixLimitsIPv4), "QPM Prefix Limits for IPv4 cannot have more than 255 entries.");
                }
                else
                {
                    foreach (KeyValuePair<int, (int, int)> qpmPrefixLimit in value)
                    {
                        if ((qpmPrefixLimit.Key < 0) || (qpmPrefixLimit.Key > 32))
                            throw new ArgumentOutOfRangeException(nameof(QpmPrefixLimitsIPv4), "QPM limit IPv4 prefix valid range is between 0 and 32.");

                        if ((qpmPrefixLimit.Value.Item1 < 0) || (qpmPrefixLimit.Value.Item2 < 0))
                            throw new ArgumentOutOfRangeException(nameof(QpmPrefixLimitsIPv4), "QPM limit value cannot be less than 0.");
                    }

                    _qpmPrefixLimitsIPv4 = value;
                }

                ResetQpsLimitTimer();
            }
        }

        public IReadOnlyDictionary<int, (int, int)> QpmPrefixLimitsIPv6
        {
            get { return _qpmPrefixLimitsIPv6; }
            set
            {
                if (value is null)

View on GitHub (pinned to d0484b6c1e)

Solutions

1. Ensure all keys are integers in the range 0-32 inclusive.
2. Filter the dictionary before assignment to drop out-of-range keys.

Example fix

// before
server.QpmPrefixLimitsIPv4 =
    new Dictionary<int,(int,int)> { { 64, (100, 200) } }; // throws

// after
server.QpmPrefixLimitsIPv4 =
    new Dictionary<int,(int,int)> { { 24, (100, 200) } };

foreach (var key in qpmV4.Keys)
    if (key < 0 || key > 32)
        throw new InvalidOperationException($"Invalid IPv4 prefix key: {key}");
server.QpmPrefixLimitsIPv4 = qpmV4;

static bool IsValidV4PrefixKey(int key) => key >= 0 && key <= 32;

try { server.QpmPrefixLimitsIPv4 = qpmV4; }
catch (ArgumentOutOfRangeException) { qpmV4 = qpmV4.Where(kv => kv.Key >= 0 && kv.Key <= 32).ToDictionary(k=>k.Key,v=>v.Value); server.QpmPrefixLimitsIPv4 = qpmV4; }

When it happens

Trigger: Assigning QpmPrefixLimitsIPv4 a dictionary containing a key < 0 or > 32.

Common situations: Reusing an IPv6 prefix-length list (up to 128) for the IPv4 limits; off-by-one in generated config; typo in a manually-edited settings file.

Related errors

• QPM Prefix Limits for IPv4 cannot have more than 255 entries
• QPM limit value cannot be less than 0.
• QPM limit IPv6 prefix valid range is between 0 and 128.
• QPM Prefix Limits for IPv6 cannot have more than 255 entries
• Valid range is between 1 and 60 minutes.

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/f80f0835fa55fb52. Report an issue: GitHub.