Which feature is enabled by default on a Cisco Catalyst Switch?

The Spanning Tree Protocol (STP) is enabled by default on Cisco Catalyst Switches to prevent network loops that can occur in Layer 2 switched networks. STP is crucial in network environments where multiple switches are interconnected; it ensures that there is a single, active path between two network devices while placing other redundant paths in a blocking state. This loop prevention is vital for maintaining network stability and performance.

In contrast, features like MAC Address filtering, VLAN trunking, and Static routing are not enabled by default. MAC address filtering is typically a security feature that needs to be manually configured to allow or block devices based on their MAC addresses. VLAN trunking, which allows multiple VLANs to be carried over a single physical link, requires configuration of trunk ports before it takes effect. Static routing, which is used for directing packets along specified paths in a network, also requires manual configuration by the administrator.

Thus, STP stands out as a foundational protocol that supports the proper functioning of existing switching operations automatically, contributing to a healthy Ethernet environment without additional input from users upon initial configuration.