TechnitiumSoftware/DnsServer · error · DhcpServerException

Scope with name '{newName}' already exists.

Error message

Scope with name '{newName}' already exists.

What it means

RenameScope found the source scope but the target newName is already taken by another scope, so TryAdd(newName, scope) fails. Rename is atomic: it adds the new key before removing the old.

Source

Thrown at DnsServerCore/Dhcp/DhcpServer.cs:1449

        }

        public Scope GetScope(string name)
        {
            if (_scopes.TryGetValue(name, out Scope scope))
                return scope;

            return null;
        }

        public void RenameScope(string oldName, string newName)
        {
            Scope.ValidateScopeName(newName);

            if (!_scopes.TryGetValue(oldName, out Scope scope))
                throw new DhcpServerException("Scope with name '" + oldName + "' does not exists.");

            if (!_scopes.TryAdd(newName, scope))
                throw new DhcpServerException("Scope with name '" + newName + "' already exists.");

            scope.Name = newName;
            _scopes.TryRemove(oldName, out _);

            SaveScopeFile(scope);
            DeleteScopeFile(oldName);
        }

        public void DeleteScope(string name)
        {
            if (_scopes.TryGetValue(name, out Scope scope))
            {
                UnloadScope(scope, true);
                DeleteScopeFile(scope.Name);
            }
        }

        public async Task<bool> EnableScopeAsync(string name, bool throwException = false)

View on GitHub (pinned to d0484b6c1e)

Solutions

1. Choose a newName not currently in use (check GetScope(newName) == null first).
2. Rename or delete the conflicting target scope first.
3. For a swap, rename through a temporary unique name.

Example fix

// before
_dhcpServer.RenameScope('a', 'b'); // 'b' exists
// after
if (_dhcpServer.GetScope('b') == null) _dhcpServer.RenameScope('a', 'b');

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

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

try { _dhcpServer.RenameScope(oldName, newName); }
catch (DhcpServerException ex) when (ex.Message.Contains("already exists"))
{ /* pick a unique name or delete/swap target, retry */ }

When it happens

Trigger: Calling RenameScope(oldName, newName) when a different scope already has Name == newName.

Common situations: Renaming onto an existing scope name. UI pre-fill collision. Swapping names without an intermediate.

Related errors

• Scope with same name 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/43e8359a295d1152. Report an issue: GitHub.