ACSP Quality of Service (QoS) 3 — Questions and Answers
Question 1: On an Aruba AOS-CX switch, which QoS profile type defines the mapping between DSCP values and local priority queues?
- Schedule profile
- Queue profile
- DSCP map (Correct answer)
- Policy map
Correct answer: DSCP map
A DSCP map (configured with 'qos dscp-map') defines how incoming DSCP values are translated to local queue priorities on the switch.
Question 2: Which feature allows an Aruba switch to automatically configure QoS for Cisco IP phones detected via CDP/LLDP on an access port?
- Auto QoS (Correct answer)
- Trust boundary enforcement
- Dynamic ARP inspection
- Phone VLAN auto-provision
Correct answer: Auto QoS
Auto QoS detects IP phones via CDP or LLDP and automatically applies appropriate trust settings and queue configurations for voice traffic.
Question 3: What happens to packets that exceed the configured police rate when the action is set to 'drop' on an Aruba switch?
- Packets are buffered until rate decreases
- Packets are remarked to a lower DSCP and forwarded
- Packets are discarded immediately (Correct answer)
- Packets are queued in the lowest-priority queue
Correct answer: Packets are discarded immediately
With a police action of 'drop', packets exceeding the committed rate are immediately discarded rather than buffered or remarked.
Question 4: In AOS-CX QoS, what does the 'strict' scheduling mode mean when applied to a queue?
- The queue shares bandwidth equally with all other queues
- The queue is always serviced before lower-priority queues, regardless of their content (Correct answer)
- The queue uses token buckets to shape traffic
- The queue randomly drops packets to avoid congestion
Correct answer: The queue is always serviced before lower-priority queues, regardless of their content
Strict priority scheduling always services the strict queue before moving to lower-priority queues, which can starve lower queues if the strict queue is always busy.
Question 5: Which Layer 2 field is used to carry QoS markings in 802.1Q-tagged Ethernet frames on Aruba switch trunk ports?
- VLAN ID bits
- 802.1p Priority Code Point (PCP) (Correct answer)
- Ethernet Type field
- Frame Check Sequence (FCS)
Correct answer: 802.1p Priority Code Point (PCP)
The 802.1p PCP field (3 bits within the 802.1Q tag) carries Class of Service (CoS) values 0–7 for Layer 2 QoS on trunk links.
Question 6: An administrator needs to remark all DSCP values from untrusted endpoints to CS1 (DSCP 8) on ingress. Which Aruba AOS-CX configuration object would accomplish this?
- A QoS schedule profile with CS1 weight
- A QoS classifier with DSCP remarking action (Correct answer)
- A VLAN ACL blocking non-CS1 traffic
- A spanning tree port priority of 8
Correct answer: A QoS classifier with DSCP remarking action
A QoS classifier (class map + policy map) can match traffic from untrusted ports and apply a DSCP remark action to set the value to CS1.
Question 7: Which Aruba QoS concept defines the boundary point where traffic markings are trusted or enforced before entering the network core?
- Trust anchor
- Trust boundary (Correct answer)
- QoS domain edge
- Marking enforcement point
Correct answer: Trust boundary
The trust boundary is the network point (typically the access switch port) where an organization decides to honor or override incoming QoS markings from endpoints.
ACSP Quality of Service (QoS) 3
On an Aruba AOS-CX switch, which QoS profile type defines the mapping between DSCP values and local priority queues?