ACSP - Aruba Certified Switching Professional Quality of Service (QoS) Questions and Answers — Questions and Answers
Question 1: An administrator connects an IP phone with a daisy-chained PC to an ArubaOS-CX switch port. The phone correctly marks its voice traffic with DSCP EF (46). The goal is to trust the phone's markings while ensuring any unmarked traffic from the PC is handled by a default policy. Which command should be configured on the switch interface?
- qos trust cos
- qos trust dscp (Correct answer)
- qos trust device-type phone
- no qos trust
Correct answer: qos trust dscp
The `qos trust dscp` command configures the interface to honor the incoming Layer 3 Differentiated Services Code Point (DSCP) markings. Since the IP phone is marking its own traffic at Layer 3 with DSCP EF, this setting ensures the switch preserves this high-priority marking. Unmarked traffic from the PC will be processed according to the switch's default QoS settings.
Question 2: A network requires that real-time video surveillance traffic is always serviced before any other traffic during periods of congestion, even if it means other applications experience delays. Which queuing mechanism on an ArubaOS-CX switch should be used to meet this requirement?
- Deficit Weighted Round Robin (DWRR)
- Weighted Fair Queuing (WFQ)
- Strict Priority (SP) (Correct answer)
- Egress Queue Shaping
Correct answer: Strict Priority (SP)
Strict Priority (SP) queuing services the highest-priority queue until it is empty before servicing any lower-priority queues. This is ideal for latency-sensitive traffic like real-time video or voice, as it provides absolute priority. However, it carries the risk of starving lower-priority queues if the high-priority traffic is continuous.
Question 3: A network engineer has created a QoS policy named `VIDEO-PRIORITY` to classify and mark video traffic. Which of the following commands correctly applies this policy to interface 1/1/5 for inbound traffic on an ArubaOS-CX switch?
- interface 1/1/5 qos policy VIDEO-PRIORITY in
- apply policy VIDEO-PRIORITY interface 1/1/5 in type qos
- interface 1/1/5 service-policy input VIDEO-PRIORITY
- interface 1/1/5 apply policy VIDEO-PRIORITY in type qos (Correct answer)
Correct answer: interface 1/1/5 apply policy VIDEO-PRIORITY in type qos
On ArubaOS-CX switches, policies are applied within the interface context. The correct syntax is `apply policy <policy-name> <direction> type qos`. In this case, `VIDEO-PRIORITY` is the policy name, `in` specifies the ingress direction, and `qos` defines the policy type.
Question 4: A company wants to ensure that all traffic from a public Wi-Fi VLAN is treated as low-priority, regardless of any markings client devices might send. An administrator creates a class matching this VLAN traffic. Within the QoS policy, which action re-marks all matching traffic with the low-priority DSCP value of CS1?
- local-priority 1
- dscp cs1 (Correct answer)
- trust dscp
- police rate 10 mbps
Correct answer: dscp cs1
The `dscp cs1` action within a QoS policy explicitly re-marks the Differentiated Services Code Point value in the IP header of all matching packets to CS1 (Code Point 8). This overrides any pre-existing DSCP value sent by the client device, enforcing the low-priority policy.
Question 5: Which of the following statements accurately describes a primary difference between Class of Service (CoS) and Differentiated Services Code Point (DSCP) for implementing QoS?
- CoS is a Layer 3 marking, while DSCP is a Layer 2 marking.
- CoS provides 64 priority levels, while DSCP provides 8.
- CoS is a 3-bit value in the 802.1Q tag, while DSCP is a 6-bit value in the IP header. (Correct answer)
- CoS is used for routing decisions, while DSCP is used for switching decisions.
Correct answer: CoS is a 3-bit value in the 802.1Q tag, while DSCP is a 6-bit value in the IP header.
Class of Service (CoS) is a Layer 2 marking mechanism that uses a 3-bit Priority Code Point (PCP) field in the 802.1Q VLAN tag, allowing for 8 priority levels (0-7). Differentiated Services Code Point (DSCP) is a Layer 3 marking mechanism that uses a 6-bit field in the IP header, allowing for 64 priority levels (0-63).
Question 6: An administrator needs to enforce a hard limit on the amount of inbound traffic from a specific server on port 1/1/10 to 20 Mbps. Any traffic exceeding this rate must be dropped immediately. A class has been created to match the server's traffic. Which QoS policy action should be used?
- shape average 20m
- police rate 20 mbps (Correct answer)
- min-bandwidth 20 percent
- rate-limit all 20000 kbps
Correct answer: police rate 20 mbps
The `police` action is used within a QoS policy to enforce a rate limit. By default, its violate-action is to drop packets that exceed the configured rate. This is the correct mechanism for applying a hard ceiling to a specific class of traffic. The `rate-limit` command is applied directly to an interface for broad traffic types (like broadcast/multicast) rather than specific classes defined in a policy.
ACSP - Aruba Certified Switching Professional Quality of Service (QoS) Questions and Answers
An administrator connects an IP phone with a daisy-chained PC to an ArubaOS-CX switch port.
The phone correctly marks its voice traffic with DSCP EF (46).
The goal is to trust the phone's markings while ensuring any unmarked traffic from the PC is handled by a default policy.
Which command should be configured on the switch interface?