Cisco CCNA (200-301)IP ServicesMedium
A network administrator is configuring a Cisco router to prioritize voice traffic over data traffic. They have identified the voice traffic using an access control list (ACL) and classified it. Which QoS mechanism should be used next to mark this voice traffic with a specific CoS value for prioritization across the network?
- AMarking
- BTraffic Shaping
- CClassification
- DTraffic Policing
Show answer & explanationAnswer & explanation
Correct answer: A. Marking
After traffic is classified (identified), the next logical step in a QoS strategy is marking. Marking applies a label (like a CoS or DSCP value) to the packets, allowing subsequent network devices to apply the appropriate QoS policies based on this mark, ensuring prioritization for voice traffic.
Why the other options are wrong
- B. Traffic Shaping buffers and delays excess packets to smooth out traffic flow, not directly for marking after classification.
- C. Classification is the act of identifying traffic, which the question states has already been done.
- D. Traffic Policing limits the data rate of traffic, dropping excess packets, which is not the next step after classification for prioritization.
QoS Marking
QoS Marking is the process of adding or modifying a QoS label (like CoS or DSCP) within a packet header after traffic has been classified, enabling downstream devices to apply appropriate prioritization.
- Follows classification in the QoS process.
- Applies a tag to the packet (e.g., CoS in Layer 2, DSCP in Layer 3).
- Allows other network devices to enforce QoS policies.
- Critical for end-to-end QoS implementation.
Memory trick: Classify, Mark, Queue, Police, Shape!