Rapid Recovery Core VMware Agentless Protection Fails with "The server refused connection" When ESXi Advertises an APIPA NFC Address (4384201)

Core and VMware Proxy logs show VDDK failures such as:

• The server refused connection
• HTTP 500 Internal Server Error
• Unable to open virtual disk
• NBD_ERR_NETWORK_CONNECT

The issue occurs because vCenter advertises a 169.254.x.x (APIPA) address as the NFC (Network File Copy) endpoint for one or more ESXi hosts. Since APIPA addresses are not routable, the Rapid Recovery Core cannot establish the required VDDK connection to open the virtual disks.

Products

• Rapid Recovery Core 6.x
• VMware Agentless Protection
• VMware vCenter
• VMware ESXi

Symptoms

One or more VMware virtual machines fail with:

• Unknown protection status
• Metadata Refresh fails
• Agentless backups fail
• VMware snapshots are created and removed successfully, but backups never begin reading disk data.

Core logs may report:

Unable to open virtual disk

POST /vmwareproxy/vddk/open
HTTP 500 InternalServerError

VMware Proxy logs report:

The server refused connection

or

VixDiskLib Error 14009
DiskLib error 2338: NBD_ERR_NETWORK_CONNECT

Rapid Recovery uses VMware's VDDK libraries to access VMware virtual disks.

During this process:

1. Rapid Recovery communicates with vCenter.
2. vCenter authenticates successfully.
3. vCenter instructs the VMware Proxy to connect to the ESXi host's NFC endpoint.
4. The ESXi host advertises an NFC IP address.
5. If that address is a 169.254.x.x (APIPA) address, the Rapid Recovery Core cannot establish a TCP connection.
6. VMware VDDK fails before opening the virtual disk.

This results in VMware Proxy returning an Internal Server Error to the Core.

This issue is external to Rapid Recovery and originates from the VMware networking configuration.

Example Log Entries

VMware Proxy

NBD_ClientOpen:
attempting to create connection to
vpxa-nfcssl://...
@nfcip:169.254.xxx.xxx

followed by

CnxOpenTCPSocket:
Cannot connect to server
169.254.xxx.xxx:902

followed by

VixDiskLib Error 14009

The server refused connection

Correct the VMware VMkernel networking so that the ESXi host advertises a valid routable NFC endpoint.

Step 1

Open the VMware vSphere Client.

Navigate to:

Hosts and Clusters
→ Select ESXi Host
→ Configure
→ Networking
→ VMkernel adapters

Step 2

Identify the VMkernel adapter used for Management/NFC traffic.

Verify that it is not configured with a:

169.254.x.x

address.

If an APIPA address is present, the interface has likely:

• failed DHCP assignment, or
• has an incorrect network configuration.

Step 3

Assign a valid routable IP address to the Management/NFC VMkernel interface.

This may be:

• Static IP
• DHCP-assigned IP

The address must be reachable from the Rapid Recovery Core server.

Step 4

From the Rapid Recovery Core server verify connectivity:

Test-NetConnection -ComputerName <ESXi Hostname> -Port 902

Expected result:

TcpTestSucceeded : True

Step 5

Repeat this verification for all ESXi hosts participating in the cluster.

If multiple hosts advertise APIPA addresses, multiple virtual machines may be affected.

Step 6

After correcting the ESXi networking:

• Refresh VMware metadata in Rapid Recovery.
• Protect the virtual machine again (if necessary).
• Execute a test backup.

No Rapid Recovery repair or reinstallation should be required.