What does errno 101 (ENETUNREACH) mean?

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 ENETUNREACH distinct from EHOSTUNREACH, which is normally more specific to the target host.

Linux ip-route(8) · RFC 792: ICMP destination unreachable · Linux connect(2)

Looking for a different code? Search another status or error code.