What represents a main feature of port security on switches?

A main feature of port security on switches is the ability to limit the number of allowed MAC addresses per port. This function enhances network security by preventing unauthorized devices from connecting to the network through a switch port. By specifying a maximum number of MAC addresses that can be learned on a particular port, the switch can block traffic from any additional devices that attempt to connect. This provides a mechanism to protect the network by ensuring that only trusted devices can send and receive data on that port, effectively reducing the risk of unauthorized access or potential security threats.

The other options, while relevant to network management or functionality, do not specifically relate to the fundamental purpose of port security. Monitoring of network traffic pertains to network analysis and performance evaluation rather than access control. Increasing the switch's data handling capacity is typically associated with hardware specifications and overall switch efficiency, not a direct feature of port security. Configuring VLANs automatically involves dynamic VLAN assignment processes and does not pertain to the enforcement of device access control like port security does. Thus, the essence of port security is best captured by the ability to manage and restrict MAC address learning on individual switch ports.