RPC server is unavailable Troubleshooting

When troubleshooting the COMException error, "The RPC server is unavailable," the issue usually involves the Remote Procedure Call (RPC) service or network connectivity. The RPC service enables a program to request services from another program on a networked computer. This error appears in the Cloudamize ADC log when it fails to establish a WMI (Windows Management Instrumentation) connection to a remote host. The ADC uses WMI commands, which depend on the RPC service, to collect data from Windows machines. This error signifies a communication breakdown between the ADC machine and the target host before any authentication attempts.

Troubleshooting Steps

Step 1: Check Network Connectivity

• Ensure both the ADC and target machines can communicate. Ping the server from the ADC to confirm it's reachable.

• Confirm the server is running and hasn't crashed or been powered off.

Step 2: Verify RPC Services on the Target Host

Ensure the Remote Procedure Call (RPC) service is running on the remote host you're trying to add. It should be set to start automatically.

• On the target host, open the Services snap-in (services.msc).

• Locate the following services and confirm they are running and set to an Automatic startup type:

  • Remote Procedure Call (RPC)

  • DCOM Server Process Launcher

  • RPC Endpoint Mapper

• If any of these services are not running, right-click and select Start.

Step 3: RPC Port Connectivity and Firewall Configuration.

The ADC needs to be able to reach specific ports on the target host. Please make sure the dynamic Port range is open. Also, please check if Firewalls on either the ADC machine or the target host are the most frequent cause of this error. They can block the necessary RPC traffic.

• Each Windows endpoint:

  • TCP port 445 open outbound to the machine with the Agentless Data Collector installed

  • TCP ports 135 and the dynamic RPC port ranges open inbound, appropriate for your OS versions:

    • Windows Server 2008 and later: TCP ports 49152 to 65535 open inbound

    • Windows Server 2003 and earlier: TCP ports 1025 to 5000 open inbound

  • The required port details are also available in our KB here.

  • Also, please refer to the Microsoft article for the RPC error troubleshooting. The steps are in the table for the error 0x800706BA (RPC_S_SERVER_UNAVAILABLE). The link to the Article is available here.

Step 4: Review DCOM Permissions.

The user account used by the Cloudamize ADC to connect to the remote server needs specific DCOM permissions.

• On the remote host, run dcomcnfg to open Component Services.

• Navigate to Computers -> My Computer, right-click, and select Properties.

• Go to the COM Security tab.

• Under "Access Permissions" and "Launch and Activation Permissions," ensure the account has "Remote Access" and "Remote Launch and Activation" rights.

Step 5: Test WMI Connectivity.

You can use the Wbemtest tool on the ADC server to test WMI connectivity to the remote host.

• Run wbemtest on the ADC server.

• Click Connect... and enter the remote host's IP address or hostname in the "Namespace" field (e.g., \\remote_host_ip\root\cimv2).

• Enter the credentials for the account you're using.

• If the connection fails, it confirms a deeper WMI or connectivity issue.

• The WBEMTEST steps are available in the Microsoft Article here.

Step 6: Review Group Policy Objects (GPOs).

GPOs can inadvertently block RPC communication by disabling the Remote Administration Exception in Windows Firewall. They can also force RPC, DCOM, or WMI services to be disabled or set to a manual startup. Verify these settings aren't preventing remote access required by the Cloudamize ADC.

If you are still experiencing issues, please send log files from the ADC machine to helpdesk@cloudamize.com. The log files are located in C:\Program Files (x86)\Cloudamize\log_backup.txt.