ACSP - Aruba Certified Switching Professional Quality of Service (QoS) 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?

Accepted Answer

qos trust dscp

Answer

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?

Accepted Answer

Strict Priority (SP)

Answer

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?

Accepted Answer

interface 1/1/5 apply policy VIDEO-PRIORITY in type qos

Answer

On ArubaOS-CX switches, policies are applied within the interface context. The correct syntax is `apply policy 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?

Accepted Answer

dscp cs1

Answer

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?

Accepted Answer

CoS is a 3-bit value in the 802.1Q tag, while DSCP is a 6-bit value in the IP header.

Answer

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).

(ACSP) Aruba Certified Switching Professional Practice Test

(ACSP) Aruba Certified Switching Professional Practice Test

ACSP - Aruba Certified Switching Professional Quality of Service (QoS) Questions and Answers