| Previous | Next |
| ERROR_NETWORK_UNREACHABLE | ERROR_PROTOCOL_UNREACHABLE |
ERROR_HOST_UNREACHABLE
ERROR_HOST_UNREACHABLE identifies the host level of a reachability failure. Windows defines nearby codes for network, protocol, and port reachability, and the distinction can reflect information returned by the network stack or an ICMP error.
ICMP gives the categories technical meaning
For IPv4, RFC 792 defines separate destination-unreachable codes for network, host, protocol, and port. IPv6 uses its own ICMPv6 destination-unreachable reasons. Firewalls and middleboxes can suppress or translate these messages, so a missing ICMP packet does not prove that the application result is wrong.
What to correlate
- The destination address selected after DNS resolution.
- Local route and neighbor-resolution state.
- ICMP/ICMPv6 errors and the original packet quoted by the error.
- Whether alternate destination addresses are reachable.
- The transport API and time elapsed before the error surfaced.
Do not diagnose a closed TCP port from this code; that is closer to a refusal or port-unreachable condition. Likewise, a missing route to an entire network belongs to the network-reachability category.
Microsoft: system error codes · IETF: ICMPv4 destination unreachable · IETF: ICMPv6
Looking for a different code? Search another status or error code.