TechnitiumSoftware/DnsServer · error · ArgumentException

Exclusion ending address must be greater than or equal to st

Error message

Exclusion ending address must be greater than or equal to starting address.

What it means

Exclusion constructor validates that the ending address is not numerically before the starting address (using ConvertIpToNumber). An exclusion is an address range removed from a DHCP scope, so it must be a valid ordered range.

Source

Thrown at DnsServerCore/Dhcp/Exclusion.cs:40

using TechnitiumLibrary.Net;

namespace DnsServerCore.Dhcp
{
    public class Exclusion
    {
        #region variables

        readonly IPAddress _startingAddress;
        readonly IPAddress _endingAddress;

        #endregion

        #region constructor

        public Exclusion(IPAddress startingAddress, IPAddress endingAddress)
        {
            if (startingAddress.ConvertIpToNumber() > endingAddress.ConvertIpToNumber())
                throw new ArgumentException("Exclusion ending address must be greater than or equal to starting address.");

            _startingAddress = startingAddress;
            _endingAddress = endingAddress;
        }

        #endregion

        #region properties

        public IPAddress StartingAddress
        { get { return _startingAddress; } }

        public IPAddress EndingAddress
        { get { return _endingAddress; } }

        #endregion
    }
}

View on GitHub (pinned to d0484b6c1e)

Solutions

Swap the two addresses so starting <= ending (numerically).
Validate/sort the pair before constructing: pass (min, max).

Example fix

// before
var ex = new Exclusion(Parse('192.168.1.200'), Parse('192.168.1.100'));
// after
var (lo, hi) = (Parse('192.168.1.100'), Parse('192.168.1.200'));
var ex = new Exclusion(lo, hi);

Defensive patterns

Strategy: validation

Validate before calling

if (startingAddress.ConvertIpToNumber() > endingAddress.ConvertIpToNumber())
    (startingAddress, endingAddress) = (endingAddress, startingAddress);

Type guard

static bool ExclusionOrdered(IPAddress start, IPAddress end) => start.ConvertIpToNumber() <= end.ConvertIpToNumber();

Try / catch

try { new Exclusion(start, end); }
catch (ArgumentException ex) when (ex.Message.Contains("greater than or equal to starting"))
{ /* swap start/end, retry */ }

Prevention

Normalize (min, max) before constructing an Exclusion.
Sort range endpoints at the UI/config boundary.
Unit-test exclusion parsing with reversed inputs.

When it happens

Trigger: new Exclusion(startingAddress, endingAddress) with startingAddress.ConvertIpToNumber() > endingAddress.ConvertIpToNumber().

Common situations: UI form fields entered in the wrong order. Copy-paste of gateway/high-address into the 'from' field. IPv4 ordering assumption error.

Related errors

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/9e55a0e67662a35d. Report an issue: GitHub.