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Unlike TCP, UDP does not establish a transport connection before sending a datagram. A missing response can mean filtering, packet loss, an invalid request, or an application that does not reply. Use a valid protocol-level health check and capture at sender and receiver when diagnosing the path.

TCP connection establishment and retransmission make a port-connectivity test meaningful, but application message boundaries still need framing. UDP has no handshake, so silence may mean a dropped packet, invalid request, or a service that does not answer probes. Test using a valid protocol request and inspect both ends when possible.