ACSP Quality of Service (QoS) 5 — Questions and Answers
Question 1: On an Aruba AOS-CX switch, which QoS feature can detect when a queue is persistently congested and alert administrators via SNMP?
- Queue depth monitoring with SNMP traps (Correct answer)
- WRED threshold notification
- QoS policy violation syslog
- Traffic shaping alarm
Correct answer: Queue depth monitoring with SNMP traps
AOS-CX supports queue depth monitoring that can trigger SNMP traps when configured thresholds are exceeded, alerting administrators to persistent congestion.
Question 2: Which AF (Assured Forwarding) DSCP class provides the highest drop precedence within that class on an Aruba switch?
- AF11 (DSCP 10)
- AF13 (DSCP 14)
- AF41 (DSCP 34)
- AF43 (DSCP 38) (Correct answer)
Correct answer: AF43 (DSCP 38)
Within each AF class, the third drop precedence level (AFx3) has the highest probability of being dropped during congestion; AF43 (DSCP 38) is class 4, drop precedence 3.
Question 3: An Aruba switch is configured to use 802.1Q trunking to an IP phone. What VLAN configuration ensures the voice traffic gets QoS treatment separate from data traffic?
- Configure the phone port as an access port in the data VLAN
- Configure a voice VLAN (auxiliary VLAN) separate from the data VLAN on the port (Correct answer)
- Disable 802.1Q tagging and rely on native VLAN
- Use LACP to bundle phone and PC ports
Correct answer: Configure a voice VLAN (auxiliary VLAN) separate from the data VLAN on the port
A voice VLAN (auxiliary VLAN) separates phone traffic from PC data traffic, allowing independent QoS policies, DSCP marking, and queue assignment for each.
Question 4: In the context of Aruba QoS, what does 'remarking' accomplish at the trust boundary for traffic from a PC endpoint?
- It increases the bandwidth allocated to the PC
- It overrides the PC's self-assigned DSCP markings with switch-defined values (Correct answer)
- It enables LLDP QoS negotiation with the PC
- It places the PC in a dedicated VLAN for QoS
Correct answer: It overrides the PC's self-assigned DSCP markings with switch-defined values
Remarking at the trust boundary replaces potentially arbitrary DSCP values set by endpoints with network-policy-defined values the administrator controls.
Question 5: Which AOS-CX command displays the number of packets dropped per queue on an Aruba switch interface, useful for diagnosing QoS issues?
- show qos queue-profile
- show interface <port> queues
- show qos statistics interface <port> (Correct answer)
- show traffic-policy drops
Correct answer: show qos statistics interface <port>
'show qos statistics interface <port>' provides per-queue packet counters including drops, helping identify which queues are congested.
Question 6: What is the significance of the 'minimum bandwidth' parameter in an Aruba WRR queue profile?
- It sets the maximum rate the queue can transmit
- It guarantees the queue will receive at least this percentage of link bandwidth when congested (Correct answer)
- It defines the burst size for the queue's token bucket
- It sets the DSCP value for traffic entering the queue
Correct answer: It guarantees the queue will receive at least this percentage of link bandwidth when congested
The minimum bandwidth parameter in WRR ensures that even under congestion, a queue receives at least its configured bandwidth share before unused capacity is redistributed.
Question 7: Which Aruba QoS mechanism is most appropriate when an ISP requires traffic to be shaped to a specific rate before sending it across a WAN link to avoid ingress policing drops at the ISP edge?
- Ingress traffic policing
- Egress traffic shaping (Correct answer)
- DSCP remarking to CS0
- Strict priority queuing only
Correct answer: Egress traffic shaping
Egress traffic shaping smooths traffic to match the ISP's contracted rate using token buckets, preventing drops at the ISP's ingress policer.
ACSP Quality of Service (QoS) 5
On an Aruba AOS-CX switch, which QoS feature can detect when a queue is persistently congested and alert administrators via SNMP?