A network technician is working on a PC with a faulty NIC. The host is connected to a switch with secured ports. After testing the connection cables and using a known-good NIC, the host is still unable to connect to the network. Which of the following is causing the connection issue?

BPDU guard is a feature that protects the network topology by disabling ports that receive Bridge Protocol Data Units (BPDUs) on edge ports. However, in this scenario, BPDU guard is not the cause of the connection issue, as it would only disable the port if a BPDU was detected, which does not relate to the NIC's functionality or its MAC address.

Link aggregation combines multiple network connections to increase bandwidth and provide redundancy. If link aggregation settings were misconfigured, it could cause network issues; however, this would not be the root cause since the host's connection is blocked due to the MAC address of the NIC, not link aggregation.

Power over Ethernet (PoE) provides power to devices over network cables. While a PoE issue could affect devices requiring power, it does not apply here since the host's inability to connect is specifically due to the switch's MAC address filtering rather than insufficient power.