ACSP Quality of Service (QoS) 2 — Questions and Answers
Question 1: Which QoS mechanism on Aruba switches uses token bucket algorithms to control the rate of traffic egressing a port?
- Traffic shaping (Correct answer)
- Traffic policing
- Weighted Fair Queuing
- Priority queuing
Correct answer: Traffic shaping
Traffic shaping uses token bucket algorithms to buffer and pace traffic, smoothing bursts to conform to a configured rate.
Question 2: On an Aruba switch, which DSCP value is associated with the Expedited Forwarding (EF) per-hop behavior used for voice traffic?
- DSCP 0
- DSCP 46 (Correct answer)
- DSCP 34
- DSCP 10
Correct answer: DSCP 46
DSCP 46 (101110 binary) is defined as Expedited Forwarding (EF) and is the standard marking for voice traffic requiring low latency.
Question 3: Which Aruba AOS-CX command applies a QoS schedule profile to an interface?
- qos trust dscp
- apply qos schedule-profile <name> (Correct answer)
- service-policy <name> out
- qos schedule-profile apply <name>
Correct answer: apply qos schedule-profile <name>
The command 'apply qos schedule-profile <name>' under an interface context attaches a schedule profile to control queue servicing on that port.
Question 4: What is the primary purpose of the 'qos trust' command on an Aruba access port?
- Enables policing on ingress traffic
- Instructs the switch to honor incoming DSCP or CoS markings (Correct answer)
- Resets all packet markings to default
- Enables LLDP for QoS negotiation
Correct answer: Instructs the switch to honor incoming DSCP or CoS markings
'qos trust dscp' or 'qos trust cos' tells the switch to use the packet's existing markings rather than overriding them with a default value.
Question 5: In Aruba's QoS queuing model, which scheduling algorithm gives each queue a guaranteed minimum bandwidth while allowing unused bandwidth to be shared?
- Strict Priority
- Weighted Round Robin (WRR) (Correct answer)
- First In First Out (FIFO)
- Random Early Detection (RED)
Correct answer: Weighted Round Robin (WRR)
WRR assigns weights to queues, guaranteeing minimum bandwidth proportional to each weight while redistributing unused capacity to other queues.
Question 6: Which CoS value is typically recommended by Aruba for marking IP telephony voice bearer traffic on a trunk port?
- CoS 0
- CoS 3
- CoS 5 (Correct answer)
- CoS 7
Correct answer: CoS 5
CoS 5 is the IEEE 802.1p standard recommendation for voice bearer (RTP) traffic, mapping to the highest-priority queues.
Question 7: An Aruba switch is dropping voice packets during congestion. Which congestion avoidance mechanism would help by proactively dropping lower-priority TCP traffic before queues fill?
- Tail drop
- Weighted Random Early Detection (WRED) (Correct answer)
- Traffic shaping
- Committed Access Rate (CAR)
Correct answer: Weighted Random Early Detection (WRED)
WRED selectively drops lower-priority packets earlier in the congestion cycle, allowing TCP flows to back off before queues reach full capacity.
ACSP Quality of Service (QoS) 2
Which QoS mechanism on Aruba switches uses token bucket algorithms to control the rate of traffic egressing a port?