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WSAEPROTONOSUPPORT
WSAEPROTONOSUPPORT means that the selected Windows Sockets provider has no implementation for the requested transport protocol. This is a local capability or configuration problem at socket creation time, not an indication that a remote service rejected a connection.
Where to look first
Check the family, type, protocol number, and any supplied WSAPROTOCOL_INFO. A protocol can be legitimate in another provider or on another host but unavailable in the local catalog or inconsistent with the requested provider selection. The distinction matters: a protocol mismatch with the socket type is WSAEPROTOTYPE; an unavailable protocol is WSAEPROTONOSUPPORT.
Recovery strategy
- Do not retry the same creation tuple in a loop; the local capability will not change immediately.
- Use the default protocol where appropriate, or intentionally select a provider that advertises the required protocol.
- For deployment failures, compare installed networking components and provider configuration between a working and failing host.
Microsoft: WSASocket · Microsoft: Winsock error codes · The Open Group: protocol selection
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