ACA Quality of Service & Traffic Management 2 — Questions and Answers
Question 1: Which DSCP value represents Expedited Forwarding (EF), typically used for VoIP traffic?
- DSCP 0
- DSCP 10
- DSCP 46 (Correct answer)
- DSCP 56
Correct answer: DSCP 46
DSCP EF is encoded as decimal 46 (binary 101110) and is reserved for low-latency, low-jitter, low-loss traffic such as VoIP.
Question 2: What is the valid range of 802.1p Class of Service (CoS) values in an 802.1Q tag?
- 0–3
- 0–7 (Correct answer)
- 0–15
- 0–63
Correct answer: 0–7
802.1p CoS uses a 3-bit Priority Code Point (PCP) field in the 802.1Q tag, providing 8 possible values from 0 to 7.
Question 3: Which queuing mechanism guarantees a minimum bandwidth to each class while still allowing unused bandwidth to be shared?
- Strict Priority Queuing
- FIFO
- Class-Based Weighted Fair Queuing (CBWFQ) (Correct answer)
- Tail-drop queuing
Correct answer: Class-Based Weighted Fair Queuing (CBWFQ)
CBWFQ assigns guaranteed minimum bandwidth to each defined class and distributes any remaining bandwidth proportionally among classes.
Question 4: What does WRED stand for and what problem does it solve?
- Weighted Random Early Detection — prevents tail-drop congestion by proactively dropping packets before queues fill (Correct answer)
- Wireless Routing Efficiency Design — optimizes wireless routing paths
- Wide-Range Error Detection — identifies transmission errors on WAN links
- Weighted Round-Robin External Delivery — balances load across WAN circuits
Correct answer: Weighted Random Early Detection — prevents tail-drop congestion by proactively dropping packets before queues fill
WRED (Weighted Random Early Detection) randomly drops packets before queues are completely full, preventing TCP global synchronization and favoring lower-priority traffic for drops.
Question 5: In Aruba AOS-CX switches, what is the default number of QoS queues available per port?
- 2
- 4
- 8 (Correct answer)
- 16
Correct answer: 8
Aruba AOS-CX switches support 8 egress queues per port, allowing granular traffic prioritization aligned to 802.1p CoS or DSCP values.
Question 6: What DSCP value is assigned to Best Effort (BE) traffic, which receives no special QoS treatment?
- DSCP 0 (Correct answer)
- DSCP 8
- DSCP 16
- DSCP 32
Correct answer: DSCP 0
DSCP 0 (Default Forwarding / DF) represents Best Effort traffic and receives no guaranteed service — it is the baseline with no QoS marking.
Question 7: Which Aruba feature allows network administrators to apply QoS policies based on identified application type rather than just IP/port?
- Application Visibility and Control (AVC) with AppRF (Correct answer)
- OSPF route redistribution
- Aruba Central NetConductor
- Spanning Tree Protocol (STP)
Correct answer: Application Visibility and Control (AVC) with AppRF
Aruba's Application Visibility and Control (AVC) using AppRF identifies applications through deep packet inspection and enforces QoS policies based on application type.
ACA Quality of Service & Traffic Management 2
Which DSCP value represents Expedited Forwarding (EF), typically used for VoIP traffic?