Cold migration fails at 12% with "Address family for hostname not supported" in dual-stack environments

Products

• VMware vCenter Server

Issue/Introduction

When performing a cold migration (offline migration) of a virtual machine between vCenter Server instances or across ESXi hosts, the task fails consistently at 12%.

Symptoms:

• The vCenter Server Task console displays the error: Cannot connect to host.

• The source ESXi host hostd.log contains the following entry: Local address lookup for <IP_ADDRESS> failed: Address family for hostname not supported

• The log further indicates a failure in the NFC (Network File Copy) connection: CnxAuthdConnectTCP failed Failed to connect to server <IP_ADDRESS>:902

• Standard network connectivity tests (ICMP ping and Netcat to port 902) are successful over IPv4.

Environment

VMware Esx

Cause

This issue occurs due to a DNS resolution mismatch in environments where ESXi hosts are configured with dual-stack (IPv4 and IPv6) networking.

The ESXi NFC client initiates the migration and attempts to use the IPv6 stack because IPv6 is enabled and preferred on the VMkernel interface (typically vmk0). However, if the destination host's FQDN or IP does not have a corresponding AAAA (IPv6) record in the DNS server, the "Address Family" lookup fails. The NFC agent is unable to map the connection request to the appropriate protocol stack, preventing the initialization of the data transfer.

Resolution

To resolve this issue, ensure consistent DNS resolution for all IP families enabled on the ESXi hosts.

1. Update DNS Records:

   • Verify if the destination ESXi host has an IPv6 address assigned to its management or provisioning VMkernel interface.

   • Create a corresponding AAAA record and PTR record for the destination host in your DNS infrastructure.

   • Confirm resolution from the source ESXi host shell using: nslookup <Destination_FQDN>

2. Alternative Workaround (Disable IPv6):

   • If IPv6 is not required in the environment, disable IPv6 on the ESXi hosts to force all NFC traffic over the IPv4 stack.

   • Note: This typically requires a host reboot to take effect.

Workaround:

If the migration continues to fail, ensure the Provisioning service is enabled on the VMkernel adapter intended for cold migration traffic.

If a dedicated provisioning network is not configured, the migration defaults to the Management network. Ensure the Management VMkernel port has the "Provisioning" stack enabled if necessary.