300-420 Question 248
Select 3An enterprise network administrator is tasked with prioritizing voice traffic over the WAN while ensuring that other critical applications receive appropriate service levels. The administrator decides to use Classification and Marking to implement QoS policies. Which of the following actions are appropriate for this task?
- A
Classify traffic using Access Control Lists (ACLs) to identify voice packets and assign them to a specific Class of Service (CoS) value.
- B
Mark all traffic with a default DSCP value without distinguishing between different traffic types.
- C
Use NBAR (Network-Based Application Recognition) to classify application traffic and assign it appropriate DSCP markings.
- D
Configure a policy to classify traffic based on port numbers and assign appropriate DSCP markings.
- E
Apply random DSCP values to packets to ensure traffic distribution is uniform across the network.
Show answer and explanation
Correct answers: A, C, D
Explanation
Classification and Marking are key components of QoS implementation. They allow traffic to be identified and marked with appropriate values (e.g., CoS or DSCP) to ensure proper prioritization and treatment across the network. Valid techniques include using ACLs, NBAR, or port-based classification to identify traffic types and assign markings. Methods like random marking or marking all traffic identically fail to achieve QoS goals.
- A. Correct.
Classifying traffic using ACLs is a valid method to identify specific types of traffic like voice and assign them to a Class of Service (CoS) or DSCP value. This helps prioritize voice traffic effectively in QoS policies.
- B. Incorrect.
Marking all traffic with a default DSCP value does not distinguish between traffic types, which defeats the purpose of classification and prioritization. This is not suitable for ensuring voice traffic is prioritized.
- C. Correct.
Using NBAR is another valid approach to dynamically identify application traffic, such as voice or video, and assign appropriate DSCP markings to enforce QoS policies.
- D. Correct.
Classifying traffic based on port numbers (e.g., port 5060 for SIP) is a valid and commonly used method to identify application-specific traffic, like voice, and mark it with the correct DSCP value for prioritization.
- E. Incorrect.
Applying random DSCP values is not a valid strategy. It introduces inconsistency and does not support effective QoS policies.