350-401 Question 57
Select 3A network engineer is troubleshooting a Quality of Service (QoS) issue on a wired network. The engineer runs a command on a Cisco switch and sees the following configuration snippet:
class-map match-any VOICE-TRAFFIC
match dscp ef
policy-map QOS-POLICY
class VOICE-TRAFFIC
priority level 1
interface GigabitEthernet0/1
service-policy output QOS-POLICY
Which of the following statements are true about this configuration?
- A
The configuration prioritizes voice traffic using Expedited Forwarding (EF) marking.
- B
The policy applies to incoming traffic on interface GigabitEthernet0/1.
- C
The 'priority' command ensures low-latency queuing (LLQ) for the VOICE-TRAFFIC class.
- D
Traffic that does not match the VOICE-TRAFFIC class will be dropped.
- E
The 'match dscp ef' command classifies packets with a DSCP value of 46.
Show answer and explanation
Correct answers: A, C, E
Explanation
This configuration snippet demonstrates a QoS policy designed to prioritize voice traffic. The class map identifies voice traffic by matching packets marked with the EF DSCP value (46). The policy map applies low-latency queuing for this class, ensuring bandwidth prioritization while applying the policy to outgoing traffic on the specified interface. Traffic that does not match the VOICE-TRAFFIC class is not dropped but handled by default queueing mechanisms.
- A. Correct.
Correct: The
match dscp efcommand specifies the EF (Expedited Forwarding) DSCP value, which is typically used for voice traffic, ensuring prioritization. - B. Incorrect.
Incorrect: The
service-policy output QOS-POLICYcommand applies the policy to outgoing traffic, not incoming traffic. - C. Correct.
Correct: The
prioritycommand in the policy map triggers Low-Latency Queuing (LLQ), ensuring that voice traffic receives preferential treatment with guaranteed bandwidth. - D. Incorrect.
Incorrect: Traffic that does not match the VOICE-TRAFFIC class will not be dropped automatically; it will fall into the default class and be handled according to default queueing rules.
- E. Correct.
Correct: The
match dscp efline explicitly matches traffic with a DSCP value of 46, which is the standard value for EF.