# Test connection gives connection refused

When you click  Test connection to test the LDAP connection, an error appears:

> Unable to connect to LDAP - LDAP => LdapConnectionError - <Error_details>

The Synctool fails to connect to the server. The issue could be related to the AD server, the authorized user, or the allowed connections between the Synctool server and the AD server.

## Causes and solutions

### Cause 1

The host name is incorrect.

### Solution 1

Try the host name with and without the domain name. For example, use `DC01` if the Synctool runs on the AD server. If it does not run on the AD server, try `DC01.zivver.org`.

### Cause 2

The port number is not 636 (recommended) or 389.

### Solution 2

Make sure to use port 636 (recommended) or 389.

### Cause 3

A connection over port 636 or 389 is not allowed to the AD server.

### Solution 3

Ask your network administrator to verify the firewall settings.

### Cause 4

The **Use implicit TLS** setting does not match the port number.

### Solution 4

Ensure **Use implicit TLS** is **enabled** for port 636 or **disabled** for port 389.

### Cause 5

The authorized user name is incorrect.

### Solution 5

- Check for typos.
- Try using a domain prefix. Example: `ZIVVERTEST\serviceaccount`.
- Try without a domain prefix. Example: `serviceaccount`.

### Cause 6

The password is incorrect.

### Cause 7

The authorized user cannot log in to the AD server because of security restrictions.

### Solution 7

1. On the **AD server**, open ADUC.
2. Right-click the service account > **Properties** > **Account** > **Log On To…** _A window opens showing the following information_:
   - Whether the authorized user can log in (for example, to **All computers**).
   - Which DNS names are configured for computers the service account can access.

### Cause 8

Windows blocks the Synctool executable file.

### Solution 8

1. In the Windows file system, locate the executable file.
2. Right-click the file icon.
3. In the **Properties** window, select **Unblock**.

Updated on 2026-02-16