The correct answer is C . Versa’s bandwidth and throughput troubleshooting documentation specifically instructs administrators to check link speed and half-duplex conditions with the command show interfaces detail interface-name. The example output shows an interface operating at half-duplex / 100 Mbps , and the documentation states that the interface should not be in half-duplex mode and that 100 Mbps was incorrect in that scenario.

A duplex mismatch or incorrect negotiated speed can severely reduce effective throughput, cause collisions or retransmissions, and make SD-WAN overlay performance appear poor even when the overlay itself is functioning. Versa recommends fixing half-duplex and link-speed issues by correcting the configuration on the device to which the VOS device is connected and checking the ISP-side transmission mode, such as auto/auto.

SLA probing, Controller route advertisement, and VXLAN encapsulation may affect SD-WAN path selection or tunnel formation, but the evidence in the question directly points to a physical or underlay Ethernet negotiation problem.