300-420 Question 251
Select 3A large enterprise is implementing QoS policies across its network to ensure that real-time applications like voice and video are prioritized over less critical traffic. The design team decides to classify and mark traffic at the access layer switches before forwarding it to the core. Which of the following statements about classification and marking are correct in this scenario?
- A
Classification refers to identifying the traffic type based on attributes such as IP address, port number, or DSCP values.
- B
Marking involves modifying packet headers with specific QoS values, such as DSCP or CoS, to indicate priority.
- C
Marking traffic at the access layer ensures that QoS policies are consistently applied across the network.
- D
Classification and marking are only necessary at the core layer as traffic handling policies are executed there.
- E
Marking is performed to directly enforce QoS treatment, such as bandwidth allocation and queuing.
Show answer and explanation
Correct answers: A, B, C
Explanation
In a QoS design, classification and marking are foundational steps that ensure traffic is identified and tagged appropriately before it traverses the network. By performing these tasks at the access layer, the network can apply consistent QoS policies end-to-end, ensuring real-time traffic like voice and video is prioritized. Marking does not directly enforce QoS treatment but provides the necessary information for downstream devices to apply QoS mechanisms such as queuing and scheduling.
- A. Correct.
Correct. Classification is the process of identifying traffic based on specific attributes, which is a necessary step before applying marking or other QoS policies.
- B. Correct.
Correct. Marking involves modifying packet headers (e.g., DSCP or CoS values) to indicate traffic priority, allowing downstream devices to handle the traffic appropriately.
- C. Correct.
Correct. Marking traffic at the access layer ensures that QoS policies can be consistently enforced throughout the network, including at the core and edge layers.
- D. Incorrect.
Incorrect. While the core layer enforces key QoS mechanisms, classification and marking at the access layer are critical to ensure traffic is properly identified and marked early in the forwarding path.
- E. Incorrect.
Incorrect. Marking itself does not enforce QoS treatment but rather provides classification information that downstream devices use to apply QoS policies such as bandwidth allocation and queuing.