Bridge Protocol Data Units (BPDUs) How frequently are BPDUs (Bridge Protocol Data Units) sent out by a Layer 2 device in a Spanning Tree Protocol (STP) enabled network?

Introduction / Context:
BPDUs (Bridge Protocol Data Units) are messages exchanged by switches in a network running the Spanning Tree Protocol (STP). They are crucial in preventing loops and maintaining a loop-free topology. Their transmission frequency is standardized to ensure stable convergence.

Given Data / Assumptions:

• We are considering IEEE 802.1D STP standard.
• Default configuration is assumed.
• BPDU timers are unchanged (Hello Time = 2 seconds).

Concept / Approach:

In IEEE 802.1D, switches send BPDUs by default every 2 seconds. These Hello BPDUs allow switches to share spanning tree information and elect the root bridge.

Step-by-Step Solution:

Verification / Alternative check:

Cisco networking documentation and IEEE 802.1D confirm the Hello BPDU interval of 2 seconds as the default setting.

Why Other Options Are Wrong:

• Never: incorrect; BPDUs are the foundation of STP.
• 10 minutes or 30 seconds: too infrequent; would cause instability.
• 60 seconds: not a standard default timer.

Common Pitfalls:

• Confusing BPDU interval with Max Age timer (20 seconds).
• Assuming BPDUs are sent only by the root bridge; all switches generate them.

Final Answer:

Every 2 seconds