What does errno 49 (EADDRNOTAVAIL) mean?

EADDRNOTAVAIL

The local source address cannot be assigned

EADDRNOTAVAIL indicates that the operation requested a local address that the system cannot currently use. An interface may no longer own that address, a source-address selection may be invalid for the chosen family, or an automatic local-address allocation may have no usable candidate.

This is local-address validation, not a claim that the remote host is offline. Changing the remote DNS name or service port does not repair a source address that is no longer configured or no longer belongs to the expected interface.

What to record

• Record whether the error came from explicit bind() or from connect() while the kernel was choosing an ephemeral local endpoint.
• Capture the selected local address, address family, interface index when available, and network-configuration changes around the failure.
• For code that pins a source address, distinguish the desired policy from the actual interface state; a VPN, sleep/wake event, or address renumbering can invalidate a cached value.

Related errors

EADDRINUSE is an ownership collision for a usable address. ENETUNREACH and EHOSTUNREACH concern the route to a destination after local addressing is valid.

References

• XNU: Darwin errno definitions
• POSIX: bind()
• POSIX: connect()

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