Which two techniques are commonly used to implement QoS?

• A. IPsec tunneling and NAT traversal
• B. VLAN tagging and MAC filtering
• C. Traffic marking (DSCP/CoS) and queuing and shaping
• D. Peer aging and ARP suppression

Answer: (C)

Quality of Service aims to ensure that important traffic gets the network resources it needs even when congestion occurs. The two common techniques to implement QoS are traffic marking and how traffic is queued and shaped.

Traffic marking attaches a priority label to each packet, typically using DSCP in the IP header or CoS in Ethernet frames. This label travels with the packet across devices, allowing routers and switches to recognize its importance and treat it accordingly as it moves toward the destination. Queuing and shaping then control how packets are actually transmitted: different queues prioritize higher‑priority traffic, and shaping limits or smooths the rate of sending to prevent bursts from overwhelming the network. Together, marking tells the network what’s important, and queuing/shaping ensures those priorities translate into timely delivery.

Other options describe security or network management features rather than performance guarantees. IPsec tunneling and NAT traversal relate to secure communication and address translation. VLAN tagging and MAC filtering deal with segmentation and access control, not prioritizing traffic. Peer aging and ARP suppression focus on neighbor discovery efficiency, not QoS behavior.