What issue can occur in a network due to the existence of an active loop?

An active loop in a network can lead to the issue where the network gets congested with duplicate frames. In simple terms, when a loop exists, data packets sent across the network can circulate indefinitely, meaning they keep being transmitted over and over again without reaching their intended destination. This results in multiple copies of the same data being present on the network simultaneously.

The consequence of this is that the network's bandwidth is consumed by these duplicate frames, leading to congestion. Devices on the network can become overwhelmed trying to process or forward these multiple copies, which can degrade performance significantly. Network protocols, such as Spanning Tree Protocol (STP), are implemented to prevent loops and mitigate such issues by blocking redundant paths.

This situation contrasts with other options; for instance, while network failures and outages can occur due to various reasons, those are typically associated with configuration errors or equipment failures rather than directly caused by loops. Additionally, the network cannot speed up due to loops; quite the opposite occurs. Therefore, the correct understanding of an active loop is its capability to create redundancy and congestion, ensuring that the network remains functional but inefficient.