TechnitiumSoftware/DnsServer · error · DhcpServerException

Scope with same name already exists.

Error message

Scope with same name already exists.

What it means

The new scope's Name already exists in the concurrent scopes dictionary, so TryAdd fails. Names are the unique key for scopes.

Source

Thrown at DnsServerCore/Dhcp/DhcpServer.cs:1235

                if (throwException)
                    throw;
            }

            return false;
        }

        private async Task LoadScopeAsync(Scope scope, bool waitForInterface)
        {
            foreach (KeyValuePair<string, Scope> entry in _scopes)
            {
                Scope existingScope = entry.Value;

                if (existingScope.IsAddressInRange(scope.StartingAddress) || existingScope.IsAddressInRange(scope.EndingAddress))
                    throw new DhcpServerException("Scope with overlapping range already exists: " + existingScope.StartingAddress.ToString() + "-" + existingScope.EndingAddress.ToString());
            }

            if (!_scopes.TryAdd(scope.Name, scope))
                throw new DhcpServerException("Scope with same name already exists.");

            if (scope.Enabled)
            {
                if (!await ActivateScopeAsync(scope, waitForInterface))
                    scope.SetEnabled(false);
            }

            _log.Write("DHCP Server successfully loaded scope: " + scope.Name);
        }

        private void UnloadScope(Scope scope, bool removeDnsEntries)
        {
            if (scope.Enabled)
                DeactivateScope(scope, removeDnsEntries, false);

            if (_scopes.TryRemove(scope.Name, out Scope removedScope))
            {
                removedScope.Dispose();

View on GitHub (pinned to d0484b6c1e)

Solutions

1. Pick a unique scope Name before adding.
2. Delete the existing scope with the same name first, or rename it.
3. Remove duplicate scope files from the scopes directory.

Example fix

// before
_dhcpServer.AddScope(new Scope('lan', ...)); // 'lan' already exists
// after
_dhcpServer.DeleteScope('lan');
_dhcpServer.AddScope(new Scope('lan', ...));

if (_dhcpServer.GetScope(scope.Name) != null)
    throw new InvalidOperationException($"Scope name '{scope.Name}' already exists");

static bool ScopeNameFree(Func<string, Scope> getScope, string name) => getScope(name) == null;

try { await _dhcpServer.LoadScopeAsync(scope, true); }
catch (DhcpServerException ex) when (ex.Message.Contains("same name already exists"))
{ /* rename or delete existing scope, retry */ }

When it happens

Trigger: Loading/adding a scope whose Name equals an already-loaded scope's Name; `_scopes.TryAdd(scope.Name, scope)` returns false.

Common situations: Duplicate scope file in the scopes directory. Renaming then re-adding without deleting the old. Race where two scope files share a name.

Related errors

• Scope with name '{newName}' already exists.
• Scope with overlapping range already exists: {existingScope.
• Scope with name '{oldName}' does not exists.
• The scope name contains an invalid character: {invalidChar}
• The address must be an IPv4 address: {startingAddress}

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/2de81941cb2b6b1d. Report an issue: GitHub.