What does errno 65 (EHOSTUNREACH) mean?

EHOSTUNREACH

The network may exist, but this host cannot be reached

EHOSTUNREACH means the stack cannot reach the specific destination host. It is more specific than ENETUNREACH, where the destination network has no usable route, and it should not be mistaken for an application-level refusal.

A host-specific result can be influenced by route selection, neighbor resolution, tunnel state, address-family configuration, or filtering. The error alone does not identify which layer made the host unreachable, so the route and resolved address are more valuable than a generic retry count.

Collect the route decision

• Log the numeric target address, family, candidate source address, interface, gateway or route selection, and the original hostname if one was used.
• Test address families independently. A dual-stack name can produce a reachable IPv4 target and an unreachable IPv6 target, or the reverse.
• Compare another host in the same prefix and the same destination through a different interface only when that comparison preserves the relevant routing policy.

Different from endpoint refusal

ECONNREFUSED indicates an active negative response during connection establishment. EHOSTUNREACH means that connection establishment could not reach the host to obtain such a response.

References

• XNU: Darwin errno definitions
• FreeBSD manual: errno(2)
• POSIX: connect()

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