QoS practice questions

A network engineer is configuring QoS on a Cisco Catalyst 3850 switch to prioritize voice traffic. The switch is connected to an IP phone and a PC using a single access port. The engineer applies a service policy on the access port that marks CoS 5 for voice and CoS 0 for data. However, the IP phone is not receiving any voice packets. What is the most likely cause?

Trap 1: The IP phone is not configured with the correct VLAN for voice…

Incorrect because the scenario describes a QoS marking issue, not a VLAN assignment problem; voice VLAN configuration is separate from QoS trust.

Trap 2: The service policy is applied in the output direction instead of…

Incorrect because the service policy direction does not affect trust; trust is a port-level attribute, not part of the policy map.

Trap 3: The switch does not support CoS marking on access ports

Incorrect because Catalyst 3850 switches support CoS marking on access ports when trust is enabled.

A
The switchport is configured as an access port without 'mls qos trust cos'
Correct because without trusting CoS, the switch ignores the phone's markings and treats all traffic as best-effort.
B
The IP phone is not configured with the correct VLAN for voice traffic
Why wrong: Incorrect because the scenario describes a QoS marking issue, not a VLAN assignment problem; voice VLAN configuration is separate from QoS trust.
C
The service policy is applied in the output direction instead of input
Why wrong: Incorrect because the service policy direction does not affect trust; trust is a port-level attribute, not part of the policy map.
D
The switch does not support CoS marking on access ports
Why wrong: Incorrect because Catalyst 3850 switches support CoS marking on access ports when trust is enabled.

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Question 2hardmultiple choice

An engineer is deploying QoS on a WAN link between two sites using a Cisco ISR 4451 router. The link is a 10 Mbps MPLS circuit. The engineer wants to ensure that voice traffic (EF) is never dropped, even during congestion. The current policy uses a single class map for voice with a policer that drops excess traffic. During peak hours, users report choppy voice calls. What change should the engineer make?

Trap 1: Increase the policer rate to 20 Mbps to accommodate voice bursts

Incorrect because the link is only 10 Mbps; over-subscribing the policer can cause drops for other traffic and does not solve the congestion issue.

Trap 2: Remove the policer and rely on FIFO queuing

Incorrect because FIFO does not prioritize voice, leading to increased delay and jitter during congestion.

Trap 3: Apply the policy in the output direction only

Incorrect because the direction does not address the fundamental issue of dropping voice packets; the policy must provide priority queuing.

A
Change the policer to a shaper and apply it to the voice class
Correct because shaping buffers excess traffic instead of dropping it, reducing jitter and packet loss for voice.
B
Increase the policer rate to 20 Mbps to accommodate voice bursts
Why wrong: Incorrect because the link is only 10 Mbps; over-subscribing the policer can cause drops for other traffic and does not solve the congestion issue.
C
Remove the policer and rely on FIFO queuing
Why wrong: Incorrect because FIFO does not prioritize voice, leading to increased delay and jitter during congestion.
D
Apply the policy in the output direction only
Why wrong: Incorrect because the direction does not address the fundamental issue of dropping voice packets; the policy must provide priority queuing.

Question 3hardmultiple choice

A network engineer is troubleshooting QoS on a Cisco Nexus 9000 switch. The switch is configured with a policy map that uses a class-default with a bandwidth remaining percent of 100. However, during congestion, traffic in a priority queue (class-map for EF) is experiencing drops even though the priority queue is not fully utilized. What is the most likely cause?

Trap 1: The class-default bandwidth remaining percent should be set to 0

Incorrect because class-default bandwidth remaining percent does not affect priority queue drops; it only allocates leftover bandwidth.

Trap 2: The priority queue is not configured with a queue-limit

Incorrect because queue-limit controls buffer depth, not policing; drops due to policing occur before queuing.

Trap 3: The switch is using strict priority queuing without any shaping

Incorrect because strict priority queuing does not cause drops; it only prioritizes traffic. Drops occur due to policing.

A
The priority queue is implicitly policed to a default rate on Nexus switches
Correct because Nexus switches enforce a default policer on the priority queue to protect other traffic, which can cause drops.
B
The class-default bandwidth remaining percent should be set to 0
Why wrong: Incorrect because class-default bandwidth remaining percent does not affect priority queue drops; it only allocates leftover bandwidth.
C
The priority queue is not configured with a queue-limit
Why wrong: Incorrect because queue-limit controls buffer depth, not policing; drops due to policing occur before queuing.
D
The switch is using strict priority queuing without any shaping
Why wrong: Incorrect because strict priority queuing does not cause drops; it only prioritizes traffic. Drops occur due to policing.

Question 4mediummultiple choice

An engineer is configuring QoS on a Cisco ASR 1000 router to support three traffic classes: voice (EF), video (AF41), and data (default). The link is a 50 Mbps Ethernet circuit. The engineer wants to guarantee 10 Mbps for voice, 20 Mbps for video, and the remaining for data. The current policy uses bandwidth percent statements. During congestion, voice traffic is not receiving its guaranteed bandwidth. What is the most likely cause?

Trap 1: The voice class should use priority instead of bandwidth

Incorrect because priority provides strict priority, not guaranteed bandwidth; it could starve other classes.

Trap 2: The video class should use bandwidth remaining percent

Incorrect because bandwidth remaining percent allocates leftover bandwidth, not a fixed guarantee; it does not solve the voice under-allocation.

Trap 3: The policy map is applied in the input direction

Incorrect because input direction does not support bandwidth guarantees; bandwidth is only for output policies.

A
The interface bandwidth command is not set to 50000 kbps
Correct because bandwidth percent uses the interface bandwidth value; if it is set to a default (e.g., 1000000 for Ethernet), the percentages do not match the actual link speed.
B
The voice class should use priority instead of bandwidth
Why wrong: Incorrect because priority provides strict priority, not guaranteed bandwidth; it could starve other classes.
C
The video class should use bandwidth remaining percent
Why wrong: Incorrect because bandwidth remaining percent allocates leftover bandwidth, not a fixed guarantee; it does not solve the voice under-allocation.
D
The policy map is applied in the input direction
Why wrong: Incorrect because input direction does not support bandwidth guarantees; bandwidth is only for output policies.

Question 5mediummultiple choice

A network engineer is troubleshooting voice quality issues on a Cisco Catalyst 9300 switch. The switch is configured with auto QoS for voice, which enabled trust on the access ports. However, voice packets are being marked with DSCP EF but are still experiencing jitter. The engineer checks the interface queue statistics and sees that the priority queue is not being used. What is the most likely reason?

Trap 1: The switch does not support DSCP-based queuing

Incorrect because Catalyst 9300 switches support DSCP-based queuing when a proper policy is applied.

Trap 2: The voice VLAN is not configured on the access port

Incorrect because voice VLAN affects VLAN assignment, not queuing; the priority queue issue is unrelated.

Trap 3: The switch is using default CoS-to-queue mapping which maps EF to a…

Incorrect because auto QoS does modify CoS-to-queue mapping, but it does not enable the priority queue without a service policy.

A
Auto QoS does not create a priority queue; a manual policy is required
Correct because auto QoS only sets trust and marks; the queuing policy must be applied separately to prioritize voice.
B
The switch does not support DSCP-based queuing
Why wrong: Incorrect because Catalyst 9300 switches support DSCP-based queuing when a proper policy is applied.
C
The voice VLAN is not configured on the access port
Why wrong: Incorrect because voice VLAN affects VLAN assignment, not queuing; the priority queue issue is unrelated.
D
The switch is using default CoS-to-queue mapping which maps EF to a non-priority queue
Why wrong: Incorrect because auto QoS does modify CoS-to-queue mapping, but it does not enable the priority queue without a service policy.

Question 6hardmultiple choice

An engineer is configuring QoS on a Cisco ISR 4331 router for a site-to-site VPN tunnel. The tunnel interface is configured with a service policy that uses a class map matching DSCP EF. The engineer notices that the policy is not shaping traffic as expected; the tunnel bandwidth is 20 Mbps but the shaper is set to 10 Mbps. However, traffic still exceeds 10 Mbps. What is the most likely cause?

Trap 1: The shaper rate should be set to 20 Mbps to match the tunnel…

Incorrect because increasing the shaper rate would allow even more traffic, not solve the problem of shaping not working.

Trap 2: The class map should match on the outer IP header instead of the…

Incorrect because the inner DSCP is preserved in the tunnel; matching on the outer header would not match the original DSCP.

Trap 3: The service policy should be applied in the input direction

Incorrect because shaping is only supported on output policies; input direction does not shape.

A
The shaper should be applied to the physical interface instead of the tunnel interface
Correct because tunnel interfaces encapsulate traffic; shaping on the tunnel does not control the actual output rate on the physical link.
B
The shaper rate should be set to 20 Mbps to match the tunnel bandwidth
Why wrong: Incorrect because increasing the shaper rate would allow even more traffic, not solve the problem of shaping not working.
C
The class map should match on the outer IP header instead of the inner DSCP
Why wrong: Incorrect because the inner DSCP is preserved in the tunnel; matching on the outer header would not match the original DSCP.
D
The service policy should be applied in the input direction
Why wrong: Incorrect because shaping is only supported on output policies; input direction does not shape.

Question 7easymultiple choice

A network engineer is deploying QoS on a Cisco Catalyst 4500 switch to support four queues per port. The engineer wants to assign voice traffic to queue 1 (priority), video to queue 2, critical data to queue 3, and best-effort to queue 4. The switch is configured with the default CoS-to-queue mapping. However, video traffic is being placed in queue 1 along with voice. What should the engineer do to separate them?

Trap 1: Change the video traffic marking to DSCP AF41 and rely on…

Incorrect because the switch uses CoS-to-queue mapping by default; DSCP mapping is not used unless explicitly configured.

Trap 2: Apply a service policy that uses a priority queue for voice only

Incorrect because a priority queue does not change the queue assignment; it only provides strict priority within the queue.

Trap 3: Increase the number of queues to eight

Incorrect because the number of queues is hardware-limited; adding more queues does not solve the mapping issue.

A
Modify the CoS-to-queue mapping using the 'mls qos srr-queue output cos-map' command
Correct because this command allows the engineer to map specific CoS values to specific queues, separating voice and video.
B
Change the video traffic marking to DSCP AF41 and rely on DSCP-to-queue mapping
Why wrong: Incorrect because the switch uses CoS-to-queue mapping by default; DSCP mapping is not used unless explicitly configured.
C
Apply a service policy that uses a priority queue for voice only
Why wrong: Incorrect because a priority queue does not change the queue assignment; it only provides strict priority within the queue.
D
Increase the number of queues to eight
Why wrong: Incorrect because the number of queues is hardware-limited; adding more queues does not solve the mapping issue.

Question 8hardmultiple choice

An engineer is troubleshooting QoS on a Cisco ASR 1002 router. The router is configured with a policy map that includes a class for voice with a priority command. During congestion, the engineer notices that voice traffic is being dropped even though the priority queue is not congested. The router logs show 'QoS: priority queue overflow'. What is the most likely cause?

Trap 1: The interface bandwidth is set too low, causing the priority queue…

Incorrect because the priority queue is not bandwidth-constrained; the policer is independent of interface bandwidth.

Trap 2: The class map is not matching the voice traffic correctly

Incorrect because if the class map did not match, the traffic would not enter the priority queue at all.

Trap 3: The router is using WRED on the priority queue

Incorrect because WRED is not applied to priority queues; it is used for non-priority queues to manage congestion.

A
The priority queue has a default policer that drops traffic exceeding a certain rate
Correct because on ASR routers, the priority command includes an implicit policer to prevent starvation of other queues; exceeding this policer causes drops.
B
The interface bandwidth is set too low, causing the priority queue to be under-provisioned
Why wrong: Incorrect because the priority queue is not bandwidth-constrained; the policer is independent of interface bandwidth.
C
The class map is not matching the voice traffic correctly
Why wrong: Incorrect because if the class map did not match, the traffic would not enter the priority queue at all.
D
The router is using WRED on the priority queue
Why wrong: Incorrect because WRED is not applied to priority queues; it is used for non-priority queues to manage congestion.

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Question 9easymultiple choice

A network engineer is configuring QoS on a Cisco Catalyst 2960-X switch to support marking of traffic based on VLAN. The switch has two VLANs: VLAN 10 (voice) and VLAN 20 (data). The engineer wants to mark all traffic from VLAN 10 with CoS 5 and all traffic from VLAN 20 with CoS 0. The engineer applies a policy map that matches on VLAN using a class map. However, the marking is not being applied. What is the most likely reason?

Trap 1: The policy map is applied in the wrong direction

Incorrect because direction does not affect the ability to match on VLAN; the feature is simply not supported.

Trap 2: The class map should use 'match access-group' instead of 'match…

Incorrect because while ACLs can match on VLAN, the switch does not support VLAN-based ACLs for QoS classification.

Trap 3: The switch requires the 'mls qos' command to be enabled globally

Incorrect because 'mls qos' is required for QoS, but even with it enabled, VLAN-based matching is not supported.

A
The switch does not support VLAN-based classification in QoS
Correct because Catalyst 2960-X switches lack the ability to match on VLAN in a class map; they rely on CoS or DSCP.
B
The policy map is applied in the wrong direction
Why wrong: Incorrect because direction does not affect the ability to match on VLAN; the feature is simply not supported.
C
The class map should use 'match access-group' instead of 'match vlan'
Why wrong: Incorrect because while ACLs can match on VLAN, the switch does not support VLAN-based ACLs for QoS classification.
D
The switch requires the 'mls qos' command to be enabled globally
Why wrong: Incorrect because 'mls qos' is required for QoS, but even with it enabled, VLAN-based matching is not supported.

Question 10mediummultiple choice

A network engineer runs the following command on Router R1:

R1# show policy-map interface GigabitEthernet0/1

GigabitEthernet0/1

Service-policy output: QOS_POLICY

Class-map: VOICE (match-any) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: ip dscp ef (46) Queueing queue limit 64 packets (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 0/0 police cir 1000000 bc 15625 be 15625 conformed 0 packets, 0 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop

Class-map: class-default (match-any) 100 packets, 10000 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: any Queueing queue limit 64 packets (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 100/10000

Based on this output, what can be concluded?

Trap 1: Voice traffic is being marked with DSCP EF and is being policed at…

The voice class shows 0 packets, so no voice traffic has been matched.

Trap 2: All traffic is being dropped due to the police action.

The class-default shows 100 packets output, so traffic is being forwarded.

Trap 3: The policy-map is applied in the input direction.

The output says 'Service-policy output', so it is applied outbound.

A
Voice traffic is being marked with DSCP EF and is being policed at 1 Mbps.
Why wrong: The voice class shows 0 packets, so no voice traffic has been matched.
B
Voice traffic is not being classified because no packets match the VOICE class.
The VOICE class has 0 packets, meaning no traffic matched the DSCP EF criteria.
C
All traffic is being dropped due to the police action.
Why wrong: The class-default shows 100 packets output, so traffic is being forwarded.
D
The policy-map is applied in the input direction.
Why wrong: The output says 'Service-policy output', so it is applied outbound.

Question 11hardmultiple choice

A network engineer runs the following command on Router R2:

R2# show class-map

Class Map match-any VOICE (id 1) Match ip dscp ef (46) Class Map match-any DATA (id 2) Match ip dscp af31 (26) Class Map match-any class-default (id 0) Match any

R2# show policy-map

Policy Map QOS_POLICY Class VOICE priority level 1 police cir 1000000 bc 15625 be 15625 Class DATA bandwidth remaining percent 50 Class class-default bandwidth remaining percent 50

R2# show policy-map interface GigabitEthernet0/1

GigabitEthernet0/1

Service-policy output: QOS_POLICY

Class-map: VOICE (match-any) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: ip dscp ef (46) Queueing strict priority queue limit 64 packets (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 0/0 police cir 1000000 bc 15625 be 15625 conformed 0 packets, 0 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop

Class-map: DATA (match-any) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: ip dscp af31 (26) Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 0/0 bandwidth remaining percent 50 (0 kbps)

Class-map: class-default (match-any) 100 packets, 10000 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: any Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 100/10000 bandwidth remaining percent 50 (0 kbps)

Based on this output, what can be concluded?

Trap 1: Voice traffic is being prioritized with strict priority queuing and…

No voice traffic is being matched (0 packets), so the priority and police are not applied.

Trap 2: Data traffic is being guaranteed 50% of the remaining bandwidth.

DATA class has 0 packets, so no data traffic is being classified.

Trap 3: The police command on VOICE is causing drops for voice traffic.

No voice traffic is matched, so no drops occur.

A
Voice traffic is being prioritized with strict priority queuing and policed at 1 Mbps.
Why wrong: No voice traffic is being matched (0 packets), so the priority and police are not applied.
B
Data traffic is being guaranteed 50% of the remaining bandwidth.
Why wrong: DATA class has 0 packets, so no data traffic is being classified.
C
All traffic is being handled by class-default, which gets 100% of the bandwidth.
Only class-default has traffic (100 packets), and since it is the only class with traffic, it uses all bandwidth.
D
The police command on VOICE is causing drops for voice traffic.
Why wrong: No voice traffic is matched, so no drops occur.

Question 12mediummultiple choice

A network engineer runs the following command on Router R3:

R3# show mls qos interface GigabitEthernet0/1

GigabitEthernet0/1 trust state: trust DSCP trust mode: trust dscp COS override: dis default COS: 0 DSCP Mutation Map: default dscp mutation map trust device: none qos mode: port-based

R3# show mls qos

QoS is enabled globally QoS global counters: total packets not matching QoS criteria = 0 Total packets with known CoS = 0 Total packets dropped by policing = 0

Based on this output, what can be concluded?

Trap 1: The interface is configured to trust CoS values.

The output shows 'trust dscp', not CoS.

Trap 2: The interface will overwrite incoming DSCP values with default CoS.

Trust DSCP means the DSCP values are preserved, not overwritten.

Trap 3: QoS is disabled globally.

The output says 'QoS is enabled globally'.

A
The interface is configured to trust CoS values.
Why wrong: The output shows 'trust dscp', not CoS.
B
The interface will overwrite incoming DSCP values with default CoS.
Why wrong: Trust DSCP means the DSCP values are preserved, not overwritten.
C
The interface trusts the DSCP markings of incoming packets.
The output clearly states 'trust state: trust DSCP' and 'trust mode: trust dscp'.
D
QoS is disabled globally.
Why wrong: The output says 'QoS is enabled globally'.

Question 13mediummultiple choice

A network engineer runs the following command on Router R4:

R4# show policy-map interface GigabitEthernet0/1

GigabitEthernet0/1

Service-policy input: SHAPE_POLICY

Class-map: class-default (match-any) 1000 packets, 100000 bytes 5 minute offered rate 100000 bps, drop rate 0 bps Match: any Queueing shape (average) cir 500000, bc 5000, be 5000 target shape rate 500000

Based on this output, what can be concluded?

Trap 1: Traffic is being policed to 500 kbps.

The command is 'shape', not 'police'. Shaping buffers traffic, while policing drops.

Trap 2: The policy is applied to output traffic.

The output says 'Service-policy input'.

Trap 3: The offered rate exceeds the shaping rate, causing drops.

The offered rate is 100 kbps, which is below the 500 kbps shaping rate.

A
Traffic is being shaped to an average rate of 500 kbps.
The shape command specifies cir 500000, which is 500 kbps.
B
Traffic is being policed to 500 kbps.
Why wrong: The command is 'shape', not 'police'. Shaping buffers traffic, while policing drops.
C
The policy is applied to output traffic.
Why wrong: The output says 'Service-policy input'.
D
The offered rate exceeds the shaping rate, causing drops.
Why wrong: The offered rate is 100 kbps, which is below the 500 kbps shaping rate.

Question 14mediummultiple choice

A network engineer runs the following command on Router R5:

R5# show queueing interface GigabitEthernet0/1
 Interface GigabitEthernet0/1 queueing strategy:  weighted fair

Queueing on output: Weighted Fair Queueing Current fair queue configuration: Number of queues: 256 Dynamic queues: 256 Reserved queues: 0 Current WFQ global configuration: Total dynamic queues: 256 Total reserved queues: 0 Class based weighted fair queueing: enabled Queueing on input: FIFO

Based on this output, what can be concluded?

Trap 1: The interface uses FIFO queuing for output.

The output says 'Queueing on output: Weighted Fair Queueing'.

Trap 2: The interface uses Class-Based Weighted Fair Queueing (CBWFQ).

Although CBWFQ is enabled, the output shows WFQ, not CBWFQ. CBWFQ would show classes.

Trap 3: The interface uses Priority Queuing.

The output shows WFQ, not priority queuing.

A
The interface uses FIFO queuing for output.
Why wrong: The output says 'Queueing on output: Weighted Fair Queueing'.
B
The interface uses Weighted Fair Queueing for output with 256 queues.
The output clearly states 'Weighted Fair Queueing' and 'Number of queues: 256'.
C
The interface uses Class-Based Weighted Fair Queueing (CBWFQ).
Why wrong: Although CBWFQ is enabled, the output shows WFQ, not CBWFQ. CBWFQ would show classes.
D
The interface uses Priority Queuing.
Why wrong: The output shows WFQ, not priority queuing.

Question 15hardmultiple choice

A network engineer runs the following command on Router R6:

R6# show policy-map interface GigabitEthernet0/1

GigabitEthernet0/1

Service-policy output: QOS_POLICY

Class-map: VOICE (match-any) 500 packets, 50000 bytes 5 minute offered rate 50000 bps, drop rate 0 bps Match: ip dscp ef (46) Queueing strict priority queue limit 64 packets (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 500/50000 police cir 1000000 bc 15625 be 15625 conformed 500 packets, 50000 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop

Class-map: DATA (match-any) 1000 packets, 100000 bytes 5 minute offered rate 100000 bps, drop rate 0 bps Match: ip dscp af31 (26) Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 1000/100000 bandwidth remaining percent 50

Class-map: class-default (match-any) 2000 packets, 200000 bytes 5 minute offered rate 200000 bps, drop rate 0 bps Match: any Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 2000/200000 bandwidth remaining percent 50

Based on this output, what can be concluded?

Trap 1: Voice traffic is being dropped because it exceeds the police rate.

The voice offered rate is 50 kbps, below the 1 Mbps police rate, so no drops.

Trap 2: All traffic is being shaped to a CIR of 1 Mbps.

There is no shape command; only police on voice and bandwidth remaining on others.

Trap 3: The policy-map is applied to input traffic.

The output says 'Service-policy output'.

A
Voice traffic is being dropped because it exceeds the police rate.
Why wrong: The voice offered rate is 50 kbps, below the 1 Mbps police rate, so no drops.
B
Data traffic is being guaranteed 50% of the remaining bandwidth.
The DATA class has 'bandwidth remaining percent 50', meaning it gets 50% of the bandwidth left after priority queuing.
C
All traffic is being shaped to a CIR of 1 Mbps.
Why wrong: There is no shape command; only police on voice and bandwidth remaining on others.
D
The policy-map is applied to input traffic.
Why wrong: The output says 'Service-policy output'.

Question 16hardmultiple choice

A network engineer runs the following command on Router R7:

R7# show mls qos interface GigabitEthernet0/1 statistics

GigabitEthernet0/1 Ingress statistics: dscp: incoming no_change classified policed dropped default: 0 0 0 0 0 ef: 100 100 100 0 0 af31: 200 200 200 0 0 other: 300 300 300 0 0

Egress statistics: dscp: queued dropped default: 0 0 ef: 100 0 af31: 200 0 other: 300 0

Based on this output, what can be concluded?

Trap 1: Packets with DSCP EF are being dropped at ingress.

The dropped column for EF is 0.

Trap 2: Policing is dropping packets with DSCP AF31.

The dropped column for AF31 is 0.

Trap 3: The interface is not using any QoS policy.

The statistics show classification, indicating a policy is applied.

A
Packets with DSCP EF are being dropped at ingress.
Why wrong: The dropped column for EF is 0.
B
All packets are being queued without drops at egress.
The egress statistics show queued packets equal to incoming, with zero drops.
C
Policing is dropping packets with DSCP AF31.
Why wrong: The dropped column for AF31 is 0.
D
The interface is not using any QoS policy.
Why wrong: The statistics show classification, indicating a policy is applied.

Question 17mediummultiple choice

A network engineer runs the following command on Router R8:

R8# show policy-map interface GigabitEthernet0/1

GigabitEthernet0/1

Service-policy output: QOS_POLICY

Class-map: class-default (match-any) 0 packets, 0 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: any Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 0/0 bandwidth remaining percent 50

Based on this output, what can be concluded?

Trap 1: Voice traffic is being prioritized but not policed.

No traffic is present, so no conclusion about prioritization can be drawn.

Trap 2: Data traffic is being dropped due to policing.

No traffic is present, so no drops occur.

Trap 3: The policy-map is applied to input traffic.

The output says 'Service-policy output'.

A
Voice traffic is being prioritized but not policed.
Why wrong: No traffic is present, so no conclusion about prioritization can be drawn.
B
The interface is not passing any traffic.
All counters are zero, indicating no traffic has been forwarded.
C
Data traffic is being dropped due to policing.
Why wrong: No traffic is present, so no drops occur.
D
The policy-map is applied to input traffic.
Why wrong: The output says 'Service-policy output'.

Question 18hardmultiple choice

A network engineer runs the following command on Router R9:

R9# show queueing interface GigabitEthernet0/1
 Interface GigabitEthernet0/1 queueing strategy:  class-based weighted fair

Queueing on output: Class-based Weighted Fair Queueing Queueing on input: FIFO

R9# show policy-map interface GigabitEthernet0/1

GigabitEthernet0/1

Service-policy output: QOS_POLICY

Class-map: VOICE (match-any) 100 packets, 10000 bytes 5 minute offered rate 10000 bps, drop rate 0 bps Match: ip dscp ef (46) Queueing strict priority queue limit 64 packets (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 100/10000 police cir 1000000 bc 15625 be 15625 conformed 100 packets, 10000 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop violated 0 packets, 0 bytes; actions: drop

Class-map: DATA (match-any) 200 packets, 20000 bytes 5 minute offered rate 20000 bps, drop rate 0 bps Match: ip dscp af31 (26) Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 200/20000 bandwidth remaining percent 50

Class-map: class-default (match-any) 300 packets, 30000 bytes 5 minute offered rate 30000 bps, drop rate 0 bps Match: any Queueing (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 300/30000 bandwidth remaining percent 50

Based on this output, what can be concluded?

Trap 1: The interface uses WFQ for output queuing.

The output shows 'class-based weighted fair', which is CBWFQ, not WFQ.

Trap 2: Voice traffic is being dropped because it exceeds the police rate.

All voice packets conform; no drops.

Trap 3: The policy-map is applied to input traffic.

The output says 'Service-policy output'.

A
The interface uses WFQ for output queuing.
Why wrong: The output shows 'class-based weighted fair', which is CBWFQ, not WFQ.
B
Voice traffic is being dropped because it exceeds the police rate.
Why wrong: All voice packets conform; no drops.
C
Data traffic is guaranteed 50% of the remaining bandwidth after priority queuing.
The DATA class has 'bandwidth remaining percent 50'.
D
The policy-map is applied to input traffic.
Why wrong: The output says 'Service-policy output'.

Question 19mediummultiple choice

Examine the following configuration snippet on a Cisco IOS-XE router:

interface GigabitEthernet0/1

service-policy output QOS_POLICY

policy-map QOS_POLICY

class VOICE

priority percent 10

class VIDEO

bandwidth percent 30

class class-default

fair-queue

What is the effect of this configuration?

Trap 1: VOICE traffic is limited to 10% of bandwidth, VIDEO to 30%, and all…

Incorrect. The 'fair-queue' command does not drop traffic; it provides fair sharing.

Trap 2: VOICE traffic is given priority over VIDEO, but VIDEO can use up to…

Incorrect. The 'priority' command gives strict priority, but VIDEO is guaranteed bandwidth regardless of VOICE usage.

Trap 3: The policy-map is invalid because 'priority' and 'bandwidth' cannot…

Incorrect. 'priority' and 'bandwidth' can be used in different classes within the same policy-map.

A
VOICE traffic is guaranteed 10% of the interface bandwidth with strict priority queuing, VIDEO traffic is guaranteed 30%, and all other traffic shares the remaining bandwidth using fair-queuing.
Correct. The 'priority' command provides strict priority queuing with a bandwidth guarantee, and 'fair-queue' enables fair sharing among the default class.
B
VOICE traffic is limited to 10% of bandwidth, VIDEO to 30%, and all other traffic is dropped if the interface is congested.
Why wrong: Incorrect. The 'fair-queue' command does not drop traffic; it provides fair sharing.
C
VOICE traffic is given priority over VIDEO, but VIDEO can use up to 30% of bandwidth only if VOICE is not using its allocation.
Why wrong: Incorrect. The 'priority' command gives strict priority, but VIDEO is guaranteed bandwidth regardless of VOICE usage.
D
The policy-map is invalid because 'priority' and 'bandwidth' cannot be used together in the same policy-map.
Why wrong: Incorrect. 'priority' and 'bandwidth' can be used in different classes within the same policy-map.

Question 20mediummultiple choice

Consider the following configuration on a Cisco router:

class-map match-any CRITICAL_DATA match ip dscp af21 af22 af23

policy-map QOS

class CRITICAL_DATA

bandwidth remaining percent 50

class class-default

fair-queue

interface GigabitEthernet0/0

service-policy output QOS

Which statement about this configuration is true?

Trap 1: Only traffic with DSCP AF21 is matched; AF22 and AF23 are ignored…

Incorrect. 'match-any' means any one of the conditions is sufficient for a match.

Trap 2: The configuration is invalid because 'bandwidth remaining percent'…

Incorrect. They can be used together; 'bandwidth remaining percent' allocates a share, and 'fair-queue' provides fairness within the default class.

Trap 3: The policy-map will only be applied to incoming traffic on…

Incorrect. The 'service-policy output' command applies the policy to outgoing traffic.

A
Traffic matching DSCP AF21, AF22, or AF23 is guaranteed 50% of the interface bandwidth, and all other traffic is subject to fair-queuing.
Correct. 'bandwidth remaining percent' guarantees a percentage of the bandwidth left after priority queues, and the default class uses fair-queue.
B
Only traffic with DSCP AF21 is matched; AF22 and AF23 are ignored because 'match-any' requires all conditions to be true.
Why wrong: Incorrect. 'match-any' means any one of the conditions is sufficient for a match.
C
The configuration is invalid because 'bandwidth remaining percent' cannot be used with 'fair-queue' in the same policy-map.
Why wrong: Incorrect. They can be used together; 'bandwidth remaining percent' allocates a share, and 'fair-queue' provides fairness within the default class.
D
The policy-map will only be applied to incoming traffic on GigabitEthernet0/0.
Why wrong: Incorrect. The 'service-policy output' command applies the policy to outgoing traffic.