CCNP QoS Architecture Practice Test 2 — 15 Questions

Question 1

An enterprise is designing a QoS architecture for its WAN edge routers connecting to multiple service providers. The design must support traffic shaping to avoid packet drops due to provider policers, while also prioritizing real-time traffic. Which approach should the architect use to shape traffic to the contracted CIR while still allowing bursts?

Accepted Answer

Apply a shape average policy on the egress interface of the WAN edge router, setting the CIR and burst parameters to match the provider contract.. Option A is correct because 'shape average' on the egress interface allows the router to buffer excess traffic and transmit it at the contracted CIR, while the burst parameters (Bc and Be) enable short-term bursts above CIR to accommodate real-time traffic spikes without drops. This prevents the provider's policer from discarding packets, as the shaper ensures the outbound traffic rate stays within the agreed contract limits.

Answer

Use a policer on the ingress interface to drop traffic exceeding the CIR.

Answer

Configure a shaper on the provider's device instead of the customer router.

Answer

Set the interface bandwidth to the CIR and rely on FIFO queuing.

Question 2

A network architect is designing QoS for a Cisco SD-WAN deployment that uses a mix of MPLS and broadband Internet transports. The design must ensure that interactive video traffic is not delayed by large file transfers, even when the Internet link experiences congestion. Which SD-WAN policy type should the architect use to enforce this behavior?

Accepted Answer

Configure a localized QoS policy on the WAN edge routers that matches video traffic and applies a priority queue.. Option A is correct because a localized QoS policy on the WAN edge router can classify interactive video traffic and place it into a priority queue, ensuring low-latency treatment even when the Internet link is congested. This policy operates locally on the router, directly controlling queuing and scheduling behavior on the specific interface, which is essential for protecting real-time traffic from bulk file transfers.

Answer

Use a centralized data policy to steer video traffic to the MPLS link only.

Answer

Implement a centralized application-aware routing policy to prefer the MPLS link for video.

Answer

Configure a VPN membership policy to isolate video traffic in a separate VPN.

Question 3

A company is deploying a new campus network with a hierarchical design (core, distribution, access). The QoS design must ensure that voice traffic is prioritized end-to-end, and that marking is trusted only on access ports connected to IP phones. Which architectural approach should the architect take for classification and marking?

Accepted Answer

Configure the access switches to trust DSCP on ports connected to IP phones, and apply queuing policies on distribution and core switches that match the trusted markings.. Option A is correct because it aligns with the Cisco QoS trust boundary model for campus networks. IP phones are trusted endpoints that mark voice traffic with the correct DSCP values (e.g., EF for voice, AF41 for video). By configuring the access switch port to trust DSCP from the IP phone, the marking is preserved end-to-end. Distribution and core switches then apply queuing policies (e.g., LLQ) based on these trusted markings, ensuring voice traffic receives priority treatment across the entire network.

Answer

Remark all traffic to a single DSCP value at the access layer and apply priority queuing at the core.

Answer

Apply QoS policies only at the core layer, ignoring markings from the access layer.

Answer

Use the distribution layer to reclassify traffic based on source MAC addresses of IP phones.

Question 4

Consider the following configuration snippet:

policy-map QOS_POLICY
 class VOICE
  priority percent 30
 class VIDEO
  bandwidth percent 20
  queue-limit 50 packets
 class class-default
  fair-queue
  queue-limit 100 packets

What is the effect of this configuration?

Accepted Answer

The VOICE class traffic is always sent before other classes, but if it exceeds 30% of the interface bandwidth, excess traffic is dropped.. The 'priority percent 30' command under the VOICE class enables strict priority queuing, meaning VOICE traffic is always transmitted before any other class. However, the priority queue is policed at 30% of the interface bandwidth; any traffic exceeding this rate is dropped, not queued. This is a fundamental behavior of the priority command in Cisco IOS — excess priority traffic is dropped to prevent starvation of other queues.

Answer

The VOICE class traffic is always sent before other classes, and excess traffic beyond 30% is queued in the default class.

Answer

The VIDEO class traffic is treated with strict priority after the VOICE class.

Answer

The class-default uses Weighted Fair Queuing with a maximum queue size of 100 packets, and all classes share the remaining bandwidth equally.

Question 5

Given the following configuration:

interface GigabitEthernet0/1
 service-policy output QOS_POLICY

Which statement is true about applying a service-policy in the output direction?

Accepted Answer

The policy-map is applied to traffic exiting the interface, allowing queuing and scheduling decisions.. When a service-policy is applied in the output direction, the policy-map inspects and acts on packets as they leave the interface. This allows the policy to perform queuing and scheduling decisions (e.g., CBWFQ, LLQ, shaping) on outbound traffic, which is the correct behavior for managing bandwidth and latency on egress.

Answer

The policy-map is applied to traffic entering the interface, performing classification and marking.

Answer

The policy-map can only be applied if the interface is in a shutdown state.

Answer

The policy-map must contain a class-default with a shape command to be valid.

Question 6

Consider the following configuration:

class-map match-any VOICE
 match ip dscp ef
class-map match-any VIDEO
 match ip dscp af41
 match ip dscp af42

What is the effect of the match-any keyword in these class-maps?

Accepted Answer

A packet matching any one of the specified DSCP values is classified into that class.. The `match-any` keyword in a Cisco class-map means that a packet needs to match only one of the listed match criteria to be classified into that class. In the VIDEO class-map, a packet matching either DSCP AF41 or AF42 will be classified as VIDEO. This is the default behavior for class-maps when no keyword is specified, but explicitly using `match-any` reinforces that logical OR operation is applied.

Answer

A packet must match all specified DSCP values to be classified into the class.

Answer

A packet matching either DSCP EF or AF41 will be classified into both classes.

Answer

The match-any keyword is invalid for DSCP matching; only match-all is supported.

Question 7

Examine the following configuration:

policy-map SHAPE_POLICY
 class class-default
  shape average 10000000
  service-policy INNER_POLICY

What is the purpose of the nested service-policy (service-policy INNER_POLICY) under the shape command?

Accepted Answer

It applies the INNER_POLICY to traffic after shaping, allowing per-class queuing within the shaped rate.. The correct answer is A because the nested service-policy under the shape command applies the INNER_POLICY to traffic after it has been shaped to 10 Mbps. This allows per-class queuing and scheduling within the shaped rate, enabling finer QoS control such as bandwidth allocation or priority queuing for specific traffic classes while ensuring the overall output does not exceed the shaped rate.

Answer

It applies the INNER_POLICY to traffic before shaping, which is not supported.

Answer

It is used to shape traffic twice, first at 10 Mbps and then again based on INNER_POLICY.

Answer

This configuration is invalid because service-policy cannot be nested under shape.

Question 8

Given the following configuration:

policy-map MARKING_POLICY
 class CRITICAL_DATA
  set dscp af31
 class BULK_DATA
  set dscp af11
 class class-default
  set dscp default

What is the effect of the set dscp default command in the class-default?

Accepted Answer

It sets the DSCP value to 0, which is the default best-effort marking.. The 'set dscp default' command explicitly sets the DSCP field to a value of 0, which corresponds to the default best-effort per-hop behavior (PHB) as defined in RFC 2474. This ensures that any traffic not matching the user-defined classes (CRITICAL_DATA or BULK_DATA) is marked with the lowest priority, which is the standard behavior for class-default in a marking policy.

Answer

It sets the DSCP value to the original value of the packet, effectively not changing it.

Answer

It sets the DSCP value to 46, which is the default for voice.

Answer

It is invalid because class-default cannot have a set action.

Question 9

Consider the following configuration:

policy-map QUEUE_POLICY
 class VOICE
  priority level 1
  police cir 1000000
 class VIDEO
  priority level 2
  police cir 2000000
 class class-default
  fair-queue

What is the effect of using priority level 1 and priority level 2?

Accepted Answer

VOICE traffic (level 1) is always sent before VIDEO traffic (level 2), and both are policed.. The 'priority level' command under a class in a policy-map allows multiple priority queues with different levels. Level 1 is the highest priority, so VOICE traffic (level 1) is always scheduled before VIDEO traffic (level 2). Both classes are also subject to policing, which enforces a maximum rate (CIR) and drops or remarks excess traffic. This ensures low-latency treatment for VOICE while still providing priority queuing for VIDEO, but with a lower scheduling preference.

Answer

VOICE and VIDEO traffic are treated equally and share the priority bandwidth.

Answer

VIDEO traffic (level 2) is sent before VOICE traffic (level 1) because it has a higher police rate.

Answer

This configuration is invalid because only one priority level is allowed.

Question 10

What is the default CoS-to-queue mapping on a Cisco switch that supports QoS?

Accepted Answer

CoS 0-1 to queue 1, CoS 2-3 to queue 2, CoS 4-5 to queue 3, CoS 6-7 to queue 4. On Cisco switches that support QoS, the default Class of Service (CoS) to queue mapping distributes CoS values across four egress queues. CoS 0 and 1 are mapped to queue 1 (best effort), CoS 2 and 3 to queue 2, CoS 4 and 5 to queue 3, and CoS 6 and 7 to queue 4 (highest priority). This mapping is defined by the default trust state and is used to prioritize traffic based on the 802.1p priority bits in the VLAN tag.

Answer

CoS 0-2 to queue 1, CoS 3-5 to queue 2, CoS 6-7 to queue 3

Answer

CoS 0 to queue 1, CoS 1 to queue 2, CoS 2 to queue 3, CoS 3 to queue 4

Answer

All CoS values are mapped to a single queue by default.

Question 11

Which QoS mechanism is used to prevent congestion by dropping packets before a queue becomes full?

Accepted Answer

Weighted Random Early Detection (WRED). Weighted Random Early Detection (WRED) is a congestion avoidance mechanism that proactively drops packets before a queue becomes full. By monitoring the average queue depth and dropping packets with a probability that increases as the queue depth grows, WRED signals TCP senders to reduce their transmission rate, thereby preventing tail drop and global synchronization. This differs from congestion management mechanisms like PQ or CBWFQ, which only act on packets after the queue is full.

Answer

Priority Queuing (PQ)

Answer

Class-Based Weighted Fair Queuing (CBWFQ)

Answer

Tail Drop

Question 12

What is the purpose of the 'police' command in a QoS policy-map?

Accepted Answer

To limit the rate of traffic and take action (drop or remark) on packets that exceed the rate.. The 'police' command in a Cisco QoS policy-map implements traffic policing, which enforces a rate limit by measuring traffic flow and taking immediate action—typically dropping or remarking packets—when the traffic exceeds the configured rate. Unlike shaping, policing does not buffer excess traffic; it acts on packets in real time, making it ideal for marking down or discarding non-compliant traffic at the ingress or egress of an interface.

Answer

To shape traffic to a specific rate by buffering excess packets.

Answer

To prioritize traffic by assigning it to a strict priority queue.

Answer

To classify traffic based on IP precedence or DSCP values.

Question 13

Drag and drop the steps of the DiffServ traffic classification and marking pipeline into the correct order, from first to last.

Accepted Answer

Create a class map to match traffic. In the DiffServ QoS pipeline, traffic must first be classified using class maps, then marked with a policy map, and finally applied to an interface using a service policy. The order ensures that packets are identified, marked, and then enforced on the egress interface.

Question 14

Drag and drop the steps of the QoS trust boundary configuration process into the correct order, from first to last.

Accepted Answer

Enable trust on the interface (e.g., trust cos). The trust boundary process starts by enabling trust on the interface, then optionally setting a default CoS/DSCP for untrusted traffic, and finally applying a service policy to enforce policing or marking. Verification ensures the trust boundary is correctly applied.

Question 15

Drag and drop the steps of the QoS shaping and policing configuration sequence into the correct order, from first to last.

Accepted Answer

Define traffic classes using class maps. Shaping and policing require first defining traffic classes, then configuring the shaping/policing actions in a policy map, applying the policy to an interface, and finally adjusting parameters based on monitoring. This order ensures proper traffic control.