Cisco Certified Network Professional 2025 – 400 Free Practice Questions to Pass the Exam

The correct answer is Bridge Protocol Data Unit (BPDU). STP, or Spanning Tree Protocol, uses BPDUs as the primary means of communication between switches in a network. These BPDUs contain essential information about the network topology, such as the switch identifiers, port roles, and path costs, which are crucial for making decisions about redundant paths and preventing loops in the network.

BPDUs are utilized for both configuration and topology change notifications. They are generated by switches to share their state and topology information with other switches. Only switches participate in STP by exchanging BPDUs to build a consistent view of the network topology and establish a loop-free environment.

Topology Change Notifications (TCNs) are specific types of BPDUs that indicate a change in the topology, but they are not the general message type used for ongoing computations. Configuration BPDUs, while related, refer specifically to one type of BPDU that carries information used for STP operations. Data packets, in contrast, do not participate in the STP calculations and are used for the transport of user data across the network.