What does errno 116 (ENETDOWN) mean?

ENETDOWN

ENETDOWN describes a local network-subsystem failure state. It is broader than one unreachable endpoint: the interface, transport stack, or required network service is not operational for the attempted socket action.

Native Winsock reports WSAENETDOWN through WSAGetLastError(). Treat this status as a signal to inspect local platform state before retrying application protocol work. Retrying the same request on the same socket without restoring the network path cannot prove that the remote peer is at fault.

Local-state checks

• Record interface operational state, route table snapshot, VPN or virtual-adapter status, and the time of any network-change notification.
• Identify whether the failure follows a suspend/resume, adapter reset, VPN reconnect, firewall policy update, or loss of required Winsock initialization.
• Invalidate or revalidate pooled connections after a local transport reset; an old socket may no longer represent the desired path.
• Use bounded reconnection with backoff and publish a local-network health signal separately from per-host errors.

References

• Microsoft: connect() errors
• Microsoft: WSAENETDOWN
• POSIX: ENETDOWN

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