Cisco Certified Support Technician (CCST) NetworkingIP ServicesHard
A network administrator implements a QoS policy to mark all Voice over IP (VoIP) traffic with a Differentiated Services Code Point (DSCP) value of 'EF' (Expedited Forwarding). Which of the following is the primary purpose of applying this specific marking?
- ATo limit the bandwidth consumed by VoIP traffic.
- BTo ensure VoIP traffic is routed through a specific path.
- CTo encrypt VoIP packets for security.
- DTo indicate to network devices that VoIP traffic requires low latency and high priority.
Show answer & explanationAnswer & explanation
Correct answer: D. To indicate to network devices that VoIP traffic requires low latency and high priority.
DSCP EF (Expedited Forwarding) is a well-known QoS marking specifically designed to provide a low-loss, low-latency, low-jitter, assured-bandwidth service. By marking VoIP traffic with EF, network devices are instructed to give it preferential treatment over other traffic types, crucial for real-time applications like VoIP.
Why the other options are wrong
- A. DSCP marking indicates priority, not primarily for limiting bandwidth, though it can be part of a broader policy that includes rate limiting.
- B. While QoS can influence routing (e.g., policy-based routing), the primary purpose of DSCP EF is prioritization, not explicit path selection.
- C. DSCP marking is for prioritization, not encryption.
DSCP Expedited Forwarding (EF)
A specific Differentiated Services Code Point (DSCP) value (46) used to mark network traffic that requires low-loss, low-latency, low-jitter, and assured-bandwidth characteristics, typically for real-time applications like VoIP.
- Commonly used for VoIP.
- Signals high priority and low latency requirements.
- Value is 46 (101110 in binary).
- Part of the Differentiated Services (DiffServ) architecture.
Memory trick: EF = Express Fast, for urgent packets.