Difficulty: Easy
Correct Answer: To prevent switching loops in Ethernet networks that have redundant switched paths
Explanation:
Introduction / Context:
Redundancy is an important design principle in modern Local Area Networks because it provides high availability. In a switched Ethernet network, redundant links between switches can create logical loops. Unlike routers, switches forward broadcast and unknown unicast frames out of all ports except the incoming port. If loops exist, these frames can circulate indefinitely and cause a broadcast storm, bringing the network down. The Spanning Tree Protocol is specifically designed to prevent this scenario by creating a loop free logical topology over a physically redundant mesh of switches.
Given Data / Assumptions:
Concept / Approach:
Spanning Tree Protocol operates at Layer two of the Open Systems Interconnection reference model. It was originally defined in IEEE 802.1D. STP elects a root bridge, calculates a loop free tree topology, and blocks certain redundant ports to break logical loops while still allowing quick reconvergence if a link fails. The goal is not to manage routing tables or monitor performance but to ensure there is exactly one active path between any two switches at any time. This preserves redundancy at the physical level while eliminating layer two loops that would cause broadcast storms.
Step-by-Step Solution:
1. Identify that the network described is a switched Local Area Network, not a Layer three routed network.
2. Acknowledge that redundant links are present and that these create the risk of Ethernet switching loops.
3. Recall that Spanning Tree Protocol is the standard mechanism to control loops in such environments.
4. STP works by electing a root bridge and then determining which switch ports should be forwarding and which should be blocking.
5. As a result, a loop free logical topology is constructed even though redundant physical paths still exist for backup.
6. Therefore, the primary purpose of STP is to prevent switching loops in networks with redundant switched paths.
Verification / Alternative check:
Real networks that disable STP while keeping redundant links often experience symptoms like slowly increasing broadcast traffic, duplicate frames, and ultimately network collapse due to broadcast storms. Re enabling STP or using newer variants such as Rapid Spanning Tree Protocol quickly restores stability. Documentation and practical experience both confirm that the main function of STP is loop prevention at Layer two, rather than routing optimisation or performance monitoring.
Why Other Options Are Wrong:
To provide a mechanism for detailed network performance monitoring: While some features in switches provide monitoring, STP is not a monitoring protocol but a loop prevention protocol.
To prevent routing loops in networks that use multiple redundant router paths: Routing loops are handled by Layer three routing protocols and techniques such as split horizon and time to live. STP handles switching loops, not routing loops.
To manage and synchronise the VLAN database across multiple switches: VLAN Trunking Protocol or other mechanisms manage VLAN databases. STP does not synchronise VLAN information.
To compress Ethernet frames in order to save bandwidth on links: There is no frame compression feature in STP. The protocol simply controls which links forward and which block.
Common Pitfalls:
Learners sometimes confuse switching loops with routing loops and may think that STP is related to Layer three routing protocols. Another pitfall is confusing STP with VLAN management protocols such as VTP. To avoid these mistakes, remember that STP operates at Layer two, works with bridges and switches, and its core goal is to block certain ports to eliminate loops while preserving redundancy. It is one of the foundational protocols in any enterprise switched network design.
Final Answer:
To prevent switching loops in Ethernet networks that have redundant switched paths
Discussion & Comments