  Quantum networks comprised of entangled end nodes serve stronger than the
classical correlation for unparalleled quantum internet applications. However,
practical quantum networking is affected by noise, which at its worst, causes
end nodes to be described by pre-existing classical data. In such untrusted
networks, determining quantum network fidelity and genuine multi-node
entanglement becomes crucial. Here, we show that determining quantum network
fidelity and genuine $N$-node entanglement in an untrusted star network
requires only $N+1$ measurement settings. This method establishes a
semi-trusted framework, allowing some nodes to relax their assumptions. Our
network determination method is enabled by detecting genuine $N$-node
Einstein-Podolsky-Rosen steerability. Experimentally, using spontaneous
parametric down-conversion entanglement sources, we demonstrate the
determinations of genuine 3-photon and 4-photon quantum networks and the false
positives of the widely used entanglement witness, the fidelity criterion of
$1/2$. Our results provide a scalable method for the determination of
multipartite entanglement in realistic quantum networks.
