A technician troubleshooting a slow file transfer to a radiology workstation notices the interface shows a high number of late collisions and the port is running at half duplex, while the connected switch port on the other end is configured for full duplex. What should the technician conclude?

Duplex mismatch occurs when one end of a link operates half duplex, using collision-based access to the medium, while the other end operates full duplex, assuming it can send and receive simultaneously without needing to detect collisions; the half-duplex side then reports collisions, including late collisions, whenever the full-duplex side transmits during what it thinks should be an idle period. This produces exactly the symptom described: degraded throughput and rising collision counters, even though the link stays up and passes some traffic. A wrong VLAN assignment would misroute or block traffic entirely or send it to the wrong broadcast domain, but it does not produce duplex-related collision counters, since VLAN membership operates above the physical and MAC-layer duplex mechanism. A spanning-tree alternate port role applies to a redundant link that STP has intentionally put in a blocking-like state to prevent a loop, which is unrelated to a duplex setting and would not, by itself, generate collision counters on an actively forwarding port. An unreachable default gateway would affect routed connectivity beyond the local subnet, not local-link collision behavior. A concrete check is aligning both ends to the same duplex setting, ideally by allowing auto-negotiation to complete correctly on both sides, then confirming the collision counters stop increasing.