What is the primary function of a switchport set to mode access?

The primary function of a switchport set to mode access is to limit connectivity to a single VLAN and, optionally, a Voice VLAN. When a switchport is configured in access mode, it is designed to connect end devices such as computers, printers, or IP phones. This configuration means that all frames sent and received on this port will belong to a single VLAN, which simplifies network management and enhances security by isolating traffic.

In some cases, if the access port is configured to allow a Voice VLAN, it can support both data and voice traffic from devices like IP phones. However, the fundamental purpose remains the same: to restrict the port's functionality to a single VLAN for data traffic, facilitating simpler network design and operation.

The other options do not correctly align with the function of an access mode switchport. For instance, trunks are used for carrying traffic from multiple VLANs, while access ports explicitly do not support this. Disabling DTP and sending DTP frames pertain to trunk negotiation and the dynamic establishment of trunk links, which is irrelevant in the context of an access port that follows a fixed VLAN configuration.