# Probe-Central connection issues and their resolutions

The Probe-Central connection should be established for proper functioning of OpManager Enterprise Edition. The Probe connection to the Central server can be checked in the corresponding Probe server under **Settings > Configuration > Central Details**.

Common problems faced with Probe-Central connection are discussed below.

## I. ConnectException

- **Connection refused: connect :** The Probe server is unable to contact the Central server port.  
  **Reason #1:** The Central server port contacted by the Probe server is invalid.  
  **Reason #2:** IP address of the Central server specified is wrong.  
  **Reason #3:** The Central server is not running.

- **Connection Timeout:** The Probe server could not establish a connection with the Central server.  
  **Reason #1:** Network has connectivity issues.  
  **Reason #2:** The Central server is overloaded with requests.  
  **Reason #3:** The connection request is blocked by Windows Firewall.

- **Connection Failure :** The Probe server is unable to establish connection with the Central server. Verify the protocol the Probe server uses for communication.  
  **Reason:** The protocol configured in the Probe server is wrong.

## II. SocketException

- **No route to host: connect :** The Probe server is unable to find a path to contact the Central server.  
  **Reason #1:** The connection is not established due to routing issues.  
  **Reason #2:** The network connection has been changed.

- **UnknownHostException:** The probe server is unable to identify the Central server.  
  **Reason #1:** IP address of the given host name is not found.  
  **Reason #2:** There is a problem with address resolution.

- **Connection reset:** The Probe server request is not received by the Central server.  
  **Reason:** Firewall in the Central server network is blocking the Probe server connection request.

- **Connection timed out:** The Central server is unable to respond to the request of the Probe server.  
  **Reason:** The Central server is unable to respond due to outbound firewall rules.

- **No Buffer space available:** Probe server could not establish a connection.  
  **Reason:** Ports in the Probe server are unavailable for establishing a connection with the Central server.

## III. IOException

- **HTTP response code 400:** Server returned HTTP response code: 400 for the specified URL.  
  **Reason:** There is no such available host.

These connection issues can be rectified by following the troubleshooting steps given below.

**Step 1: Verify the Central server details**

Check if the Central server details specified in the Probe server (under **Settings > Configuration > Central Details**) are valid. If not, provide the valid details.

**Step 2: Verify the Probe-Central connection**

Check if the connection is established between the Probe and the Central servers using ping and netstat commands. If not, fix the issue causing the connection failure.

**Step 3: Check port status**

Check if the port is occupied by another service/application using utility tools such as Resource Monitor for Windows and netstat command for Linux.

**Step 4: Analyze data packets**

Analyze data packets using a packet analyzer and check if:

- The data is sent from Probe and received by the Central server
- The Central server is responding to the request from the corresponding probe.
- The Probe server is receiving the response

If not, fix the issue.

**Step 5: Check firewall**

Disable firewall and check if data transfer occurs (Case: when connection check passes and data transfer fails)

If the above steps do not work, please contact [opmanager-support@manageengine.com](mailto:opmanager-support@manageengine.com), with the following details:

- Packet capture data
- Screenshot of Step 2