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ENETUNREACH
ENETUNREACH indicates a routing failure at the network level. The system cannot select a usable path to the destination network, so the connection or send attempt fails before the application reaches a remote service. It is therefore usually more useful to inspect local routing policy than to restart the destination process.
On Linux, the route type matters: the ip route documentation describes a missing route lookup represented by a throw route as yielding ENETUNREACH to local senders. In IPv4, ICMP also defines a distinct “network unreachable” destination-unreachable code. Operating systems may surface errors from local lookup, cached state, or network feedback, so the errno is a symptom rather than a complete path diagnosis.
What to check
- Inspect the route chosen for the exact destination and address family, including policy-routing tables, VRFs, and network namespaces.
- Verify the default gateway, egress interface state, and source-address selection.
- Compare IPv4 and IPv6 results; a hostname can resolve to both and only one family may have a route.
- Keep
ENETUNREACHdistinct fromEHOSTUNREACH, which is normally more specific to the target host.
Linux ip-route(8) · RFC 792: ICMP destination unreachable · Linux connect(2)
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