350-501 Automation and Quality of Service — All Questions With Answers

A service provider has deployed a new MPLS L3VPN service for a customer with multiple sites. The customer reports intermittent voice quality issues during peak hours. The provider uses a DiffServ QoS model with MPLS EXP markings. The PE routers apply the following policy on the customer-facing interfaces:

policy-map CUSTOMER-OUT

class VOICE

priority percent 10 set mpls experimental topmost 5

class VIDEO

bandwidth remaining percent 30 set mpls experimental topmost 4

class DATA

bandwidth remaining percent 70 set mpls experimental topmost 0

The core network has a simple policy that maps EXP 5 to PQ, EXP 4 to a low-latency queue, and EXP 0 to best effort. The provider monitors the network and finds that the PE-CE interfaces are not congested (average utilization is 40%), but the voice packets are experiencing jitter. The customer's voice traffic is about 5% of the link capacity. Which action is most likely to reduce the jitter?

Question 3mediumdrag order

Drag and drop the steps to configure MPLS LDP on a Cisco router into the correct order.

Drag or tap steps into the slots.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 4mediummatching

Read the full Automation and Quality of Service explanation →

Match each BGP attribute to its category or purpose.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Well-known mandatory attribute for loop prevention

Well-known mandatory attribute indicating next-hop IP

Well-known discretionary attribute for best path selection

Optional non-transitive attribute to influence inbound traffic

Optional transitive attribute for route tagging and policy

Question 5mediummatching

Match each network automation tool to its primary use.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Network configuration protocol using XML-based data encoding

Data modeling language for network device configuration and state

HTTP-based API for NETCONF data stores

Automation tool for configuration management and orchestration

High-performance RPC framework for telemetry and streaming

Question 6hardmultiple choice

An SP uses BGP FlowSpec to mitigate DDoS attacks. They also want to rate-limit the traffic per FlowSpec rule. Which configuration is required to enable policing within a FlowSpec action?

Question 7mediummultiple choice

An SP's core router experiences excessive packet drops on a congested link. The QoS policy uses CBWFQ with 4 queues. The drops occur only in the queue for a premium business class. Which is the most likely cause?

Question 8mediummultiple choice

Study the full ACL explanation →

An SP uses model-driven telemetry to monitor queue depths on core interfaces. They observe periodic spikes in the queue depth for EF traffic, causing increased latency. Which automation technique could dynamically adjust the QoS policy to mitigate the spikes?

Question 9easymultiple choice

An SP engineer configures a QoS policy on an IOS XR router to re-mark DSCP from AF11 to AF22 for traffic matching a specific ACL. The policy compiles successfully but traffic is not re-marked. What is a likely reason?

Question 10hardmultiple choice

While troubleshooting a customer complaint about slow data transfers, you notice that traffic from a specific site is being dropped. The QoS policy on the PE router includes a police command for the customer's traffic. The observed drop rate is exactly half of the configured police rate. What is the most probable reason?

Question 11mediummulti select

Review the full routing breakdown →

A network engineer is implementing QoS on a Cisco ASR 1000 for a customer with multiple service classes. The customer requires that mission-critical data not be starved when voice traffic bursts. Which two actions should the engineer take? (Choose two.)

Question 12mediummultiple choice

Refer to the exhibit. The policy above is applied on a PE router. The customer complains that voice quality is poor. Based on the exhibit, what is the most likely cause?

Exhibit

router# show policy-map interface GigabitEthernet0/0/0
 GigabitEthernet0/0/0

  Service-policy input: QOS_INPUT

    Class-map: VOICE (match-any)
      9286 packets, 12345678 bytes
      5 minute offered rate 100000 bps, drop rate 0 bps
      Match: ip dscp ef (46)
      police:
        cir 64000 bps, bc 8000 bytes
        conformed 5000 packets, 6400000 bytes; actions:
          set-dscp-transmit ef
        exceeded 4286 packets, 5934578 bytes; actions:
          drop
        conformed 60000 bps, exceed 40000 bps

    Class-map: DATA (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: ip dscp af31 (26)

    Class-map: class-default
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps

Question 13easymultiple choice

Read the full Automation and Quality of Service explanation →

Refer to the exhibit. An engineer checks the policy and notices that the policing is not working as expected—traffic is not being dropped even when exceeding 1 Mbps. What could be the issue?

Exhibit

interface GigabitEthernet0/0/0
 service-policy input POLICE_IN
 service-policy output SHAPE_OUT
!
policy-map POLICE_IN
 class VOICE
  police cir 1000000
!
policy-map SHAPE_OUT
 class class-default
  shape average 10000000

Question 14mediummultiple choice

Review the full routing breakdown →

A customer has a 100 Mbps access link and wants to limit traffic to 95 Mbps with burst allowance up to 100 Mbps. Which QoS action should be applied on the egress interface?

Question 15easymulti select

Which TWO conditions cause a router to drop packets when a police action is configured?

Question 16mediummulti select

Which THREE QoS mechanisms can be used for traffic policing?

Question 17hardmultiple choice

A service provider operates a large MPLS network with hundreds of PE routers. They have deployed QoS policies to ensure real-time traffic (voice and video) receives priority. The policy uses LLQ with a strict priority queue for voice (DSCP EF) and another for video (DSCP AF41). Each priority queue has a policer to prevent starvation of other classes. Recently, a customer reports that their video calls are experiencing jitter and packet loss. The engineer examines the PE router connected to this customer. The interface is GigabitEthernet0/0/1 with the policy applied in the output direction. Show commands indicate that the video priority queue is frequently dropping packets, while the voice queue has no drops. The police for the video queue is set to 10 Mbps. The customer's contract guarantees 20 Mbps for video traffic. However, the actual video traffic is averaging 15 Mbps with bursts to 18 Mbps. The engineer notes that the video class also has a bandwidth command of 10 Mbps under the priority statement. What is the most likely cause of the video packet loss?

Question 18mediummultiple choice

A large enterprise recently implemented centralized QoS policies using Cisco DNA Center. The policies are pushed via RESTCONF to the branch routers. After the deployment, the branch office reports that critical business applications (like ERP) are being delayed. The network team verifies that the QoS policy is applied correctly on the WAN interface (Serial0/0/0) with a shape of 10 Mbps. The policy-map has a class for 'critical-data' with bandwidth 5 Mbps and another class for 'transactional-data' with bandwidth 3 Mbps. The remaining traffic is in class-default with fair-queue. The branch router's CPU utilization is normal. The interface output shows that the queue for critical-data is rarely full, but packets are experiencing high latency. The engineer pings from the branch server to the central site and sees 200 ms RTT normally, but up to 500 ms during peak hours. What is the most likely cause of the high latency for critical-data?

Question 19mediummultiple choice

A network engineer is troubleshooting QoS on a Cisco ASR 1000 router. The router has a service-policy applied on the ingress interface GigabitEthernet0/0/0. The policy uses a class-map to match traffic based on NBAR protocol discovery for 'cisco-jabber'. The goal is to mark the traffic with DSCP AF41. However, when the engineer checks the policy statistics, the class 'jabber' shows zero matches, even though the users are actively using Cisco Jabber. The NBAR protocol discovery is enabled globally and on the interface. The engineer verifies that the NBAR protocol pack is up-to-date. What is the most likely reason for the class-map not matching?

Question 20easymulti select

Which TWO actions are required to implement QoS trust boundaries correctly in a service provider network?

Question 21mediummultiple choice

Based on the exhibit, which statement is true about the applied QoS policy?

Exhibit

Refer to the exhibit.
Router# show policy-map interface GigabitEthernet0/0/0 input

GigabitEthernet0/0/0

Service-policy input: QOS-POLICY

  Class-map: VOICE (match-all)
    1151375 packets, 108215153 bytes
    5 minute offered rate 13000 bps, drop rate 0000 bps
    Match: ip dscp ef (46)
    police:
        cir 10000 bps, bc 1500 bytes
      conformed 1151375 packets, 108215153 bytes; actions:
        transmit
      exceeded 0 packets, 0 bytes; actions:
        drop
      conformed 13000 bps, exceed 0000 bps

  Class-map: VIDEO (match-all)
    250000 packets, 35000000 bytes
    5 minute offered rate 25000 bps, drop rate 5000 bps
    Match: ip dscp af41 (34)
    police:
        cir 20000 bps, bc 1500 bytes
      conformed 200000 packets, 28000000 bytes; actions:
        transmit
      exceeded 50000 packets, 7000000 bytes; actions:
        drop
      conformed 20000 bps, exceed 5000 bps

  Class-map: class-default (match-any)
    500000 packets, 60000000 bytes
    5 minute offered rate 50000 bps, drop rate 0000 bps
    Match: any

Question 22hardmultiple choice

A service provider is experiencing congestion on a core link connecting two P routers. The customer traffic is classified into three classes: voice (low latency), video (low loss), and data (best effort). The current configuration uses DSCP-based classification at the PE ingress, but many customers are remarking DSCP values to gain better service, bypassing the provider's QoS policy. The provider wants to enforce a strict trust boundary at the PE and re-mark all traffic according to a per-customer contract. Additionally, the provider must offer per-customer bandwidth guarantees, ensuring that one customer's traffic does not starve another customer's traffic on the congested core link. The solution must be scalable to hundreds of customers. What should the designer recommend?

Question 23hardmulti select

A service provider runs a Cisco IOS XR core where QoS policies are deployed through an automation pipeline using NETCONF over SSH. The pipeline retrieves the running configuration and commits new policy-map definitions. During an audit, the team observes that some commits succeed even though the candidate configuration contains a class-map that does not exist. Which two NETCONF operations, when used together, allow the pipeline to validate the full candidate configuration before committing? (Choose two.)

Question 24easymultiple choice

A network automation team wants to use a model-driven telemetry solution on Cisco IOS XR routers to stream QoS statistics to a collector. The team needs to subscribe to interface-level policy-map statistics and ensure the stream is pushed only when values change beyond a threshold. Which telemetry subscription mode should be configured to meet this requirement?

Question 25easymultiple choice

A service provider is implementing QoS on an MPLS network to support voice, video, and data traffic. Which queuing mechanism provides the lowest latency for real-time traffic?

Question 26mediummultiple choice

An engineer is troubleshooting a QoS policy on a Cisco router. The policy is intended to mark voice traffic with DSCP EF and video traffic with DSCP AF41. After applying the policy, voice traffic is correctly marked, but video traffic is marked as DSCP 0. What is the most likely cause?

Question 27hardmultiple choice

A service provider uses an MPLS-TE tunnel to carry voice and data traffic. The tunnel is experiencing packet loss during congestion. The engineer wants to ensure that voice traffic receives guaranteed bandwidth and low latency while data traffic uses remaining bandwidth. Which QoS configuration should be applied on the tunnel interface?

Question 28easymultiple choice

An engineer is configuring MPLS VPN and needs to ensure that customer traffic is automatically marked with a specific QoS policy based on the VPN. Which method should be used to propagate QoS markings across the MPLS network?

Question 29mediummultiple choice

A network administrator configures a class map to match VoIP traffic using 'match ip dscp ef' on a Cisco router. However, the QoS policy is not applying the expected marking to VoIP packets. What is a possible reason?

Question 30mediummulti select

Which TWO QoS mechanisms are used to provide congestion avoidance? (Choose two.)

Question 31hardmulti select

Which THREE statements about implementing QoS in an MPLS VPN environment are correct? (Choose three.)

Question 32mediummultiple choice

Based on the exhibit, which statement is true about the QoS policy?

Exhibit

Refer to the exhibit.

class-map match-any VIDEO
 match ip dscp af41 af42 af43
!
class-map match-all VOICE
 match ip dscp ef
!
policy-map QOS-POLICY
 class VOICE
  priority percent 10
 class VIDEO
  bandwidth remaining percent 30
 class class-default
  fair-queue
!
interface GigabitEthernet0/0
 service-policy output QOS-POLICY

Question 33hardmultiple choice

A service provider is designing a QoS policy for a multi-service MPLS VPN network that carries voice, video, and data traffic. The network uses DiffServ and MPLS EXP markings. The design must ensure that voice traffic is given priority over video and data, while video traffic should have better treatment than data but not at the expense of voice. The provider plans to use a hierarchical QoS (HQoS) policy at the PE-CE interfaces. Which configuration approach best meets these requirements?

Question 34mediummulti select

Study the full ACL explanation →

Which TWO statements accurately describe the behavior of the QoS policy shown in the exhibit?

Exhibit

Refer to the exhibit.

class-map match-any VOICE
 match ip dscp ef
class-map match-any VIDEO
 match ip dscp af41 af42
class-map match-any DATA
 match ip dscp default
!
policy-map QOS_POLICY
 class VOICE
  priority level 1
  set mpls experimental topmost 5
 class VIDEO
  bandwidth remaining percent 30
  set mpls experimental topmost 4
 class DATA
  bandwidth remaining percent 70
  set mpls experimental topmost 0
!
interface GigabitEthernet0/0/0
 service-policy output QOS_POLICY

Question 35mediumdrag order

Drag and drop the steps to configure a standard ACL on a Cisco router into the correct order.

Drag or tap steps into the slots.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 36mediummultiple choice

A service provider needs to prioritize voice traffic over best-effort data in an MPLS VPN. The PE router uses a QoS policy applied to the ingress interface. Which action ensures that voice packets are marked with the correct DSCP value before entering the MPLS core?

Question 37easymultiple choice

A network operator deploys a QoS policy on a route reflector to classify traffic based on BGP community values. However, the policy is not matching the intended traffic. Which is the most likely cause?

Question 38hardmultiple choice

Read the full Automation and Quality of Service explanation →

A SP wants to automate the deployment of QoS policies on numerous PE routers using NETCONF. Which YANG module is most appropriate for modeling the QoS policy-map configuration?

Question 39easymultiple choice

An SP engineer implements LLQ for VoIP traffic on a DS3 link. The policy-map calls for a priority queue of 500 kbps. The actual VoIP traffic averages 400 kbps with bursts to 600 kbps. What is the expected behavior during bursts?

Question 40hardmultiple choice

Read the full network assurance explanation →

An SP router is configured with a hierarchical QoS policy (parent policy shaper, child policy with CBWFQ). When applying this policy to an interface, the router reports 'Policy map not found' error. What is the most likely cause?

Question 41mediummulti select

Which TWO statements about model-driven telemetry compared to SNMP are correct? (Choose two.)

Question 42hardmulti select

Which THREE YANG data nodes are part of the Cisco-IOS-XR-qos-ma-cfg module for defining a QoS policy-map? (Choose three.)

Question 43easymulti select

Which TWO are valid benefits of automating QoS policy management in a large SP network? (Choose two.)

Question 44mediummulti select

Read the full Automation and Quality of Service explanation →

Which THREE are common causes of QoS misconfiguration on PE routers? (Choose three.)

Question 45mediummultiple choice

Refer to the exhibit. An engineer applies two service policies to the same subinterface in the outbound direction. Which statement describes the expected behavior?

Exhibit

Refer to the exhibit.

policy-map SHAPE-1M
 class class-default
  shape average 1000000
!
policy-map CHILD-QOS
 class VOICE
  priority level 1
  police cir 256000
 class DATA
  bandwidth remaining ratio 50
 class MANAGEMENT
  bandwidth remaining ratio 10
!
interface GigabitEthernet0/0/0/0.100
 service-policy output SHAPE-1M
 service-policy output CHILD-QOS

Question 46hardmultiple choice

Read the full Automation and Quality of Service explanation →

Refer to the exhibit. A network automation engineer uses NETCONF to retrieve the QoS policy 'POLICE-CUSTOMER'. Based on the response, what is the effect of this policy?

Exhibit

Refer to the exhibit.

<rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
 <get>
  <filter type="subtree">
   <policy-maps xmlns="http://cisco.com/ns/yang/Cisco-IOS-XR-qos-ma-cfg">
    <policy-map>
     <type>qos</type>
     <name>POLICE-CUSTOMER</name>
    </policy-map>
   </policy-maps>
  </filter>
 </get>
</rpc>

Response:
<data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
 <policy-maps xmlns="http://cisco.com/ns/yang/Cisco-IOS-XR-qos-ma-cfg">
  <policy-map>
   <type>qos</type>
   <name>POLICE-CUSTOMER</name>
   <class>
    <name>class-default</name>
    <police>
     <cir>256000</cir>
     <conform-action>transmit</conform-action>
     <exceed-action>drop</exceed-action>
    </police>
   </class>
  </policy-map>
 </policy-maps>
</data>

Question 47easymultiple choice

Refer to the exhibit. An engineer monitors the queue depths on a core interface. Which class is experiencing the most congestion?

Exhibit

Refer to the exhibit.

RP/0/0/CPU0:router# show qos interface gigabitEthernet 0/0/0/0

Interface: GigabitEthernet0/0/0/0
Bandwidth configured: 1000000 kbps
Policy: QOS_BUSINESS
Class: VOICE
Queue ID: 1
Taildrop thresholds: 50 packets
Average queue depth: 12 packets
Maximum queue depth: 48 packets
Class: BEST_EFFORT
Queue ID: 2
Taildrop thresholds: 600 packets
Average queue depth: 580 packets
Maximum queue depth: 650 packets

Question 48easymultiple choice

A network engineer notices that voice traffic is being dropped during congestion. The traffic is marked with DSCP EF. After reviewing the QoS policy, it is discovered that the voice traffic is not being placed into a priority queue. Which configuration change would ensure voice traffic receives priority treatment?

Question 49mediummultiple choice

A service provider uses a centralized automation system to manage QoS policies via NETCONF and YANG. When attempting to push a new policy-map, the device returns an error indicating that the policy-map type is not supported in the specified location. What is the most likely cause?

Question 50easymultiple choice

A network administrator needs to automate the deployment of a new QoS policy on dozens of provider edge routers. Which Cisco tool is best suited for this purpose?

Question 51mediummultiple choice

An engineer is using NETCONF to retrieve the operational QoS statistics from a router. The response contains XML data but does not include the queueing statistics. What is the most likely reason?

Question 52hardmultiple choice

During a maintenance window, an automation script pushed a QoS policy that inadvertently changed the marking for all inbound traffic on a core interface. The change was rolled back, but performance reports show that some traffic is still being marked incorrectly. What is the most logical explanation?

Question 53easymultiple choice

An SP engineer is configuring QoS on a router and needs to drop traffic that exceeds a certain rate while allowing bursts up to a specified amount. Which QoS feature should be used?

Question 54mediummultiple choice

A customer is using a Cisco ASR 9000 router with hierarchical QoS (HQoS) on a subscriber interface. The parent policy sets a shape rate of 10 Mbps, but the observed traffic rate is only 8 Mbps. What is a common misconfiguration that would cause this?

Question 55hardmultiple choice

An automation engineer is writing a Python script using Cisco's pyATS library to validate QoS configurations across a fleet of routers. The script runs without errors but reports that all routers are compliant even though some are not. What is the most likely issue?

Question 56hardmulti select

A service provider is automating QoS policy deployment using Cisco NSO and YANG. During validation, the engineer discovers that the pushed policy is not taking effect. Which three possible causes should be investigated? (Choose three.)

Question 57easymulti select

Read the full REST/YANG explanation →

During QoS troubleshooting, you capture traffic and see that DSCP markings are not being applied as configured. Which two common misconfigurations could cause this? (Choose two.)

Question 58hardmultiple choice

Refer to the exhibit. An engineer pushes this XML configuration via NETCONF, but the device rejects it with an error stating 'invalid policy-map structure'. What is the problem?

Exhibit

<config xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
  <native xmlns="http://cisco.com/ns/yang/Cisco-IOS-XE-native">
    <policy>
      <policy-map>
        <name>QOS-POLICY</name>
        <class>
          <name>VOICE</name>
          <priority>
            <level>1</level>
          </priority>
          <police>
            <cir>64000</cir>
            <bc>8000</bc>
            <conform-action>
              <transmit/>
            </conform-action>
            <exceed-action>
              <drop/>
            </exceed-action>
          </police>
        </class>
      </policy-map>
    </policy>
  </native>
</config>

Question 59easymultiple choice

An engineer is configuring QoS for voice traffic on a Cisco router. Which marking should be applied to voice packets to ensure proper end-to-end prioritization?

Question 60hardmultiple choice

An enterprise uses IPsec VPN to connect branch offices. They apply QoS policies on the tunnel interface but notice that original DSCP markings are not preserved after encryption. Which feature should be enabled to maintain end-to-end QoS?

Question 61mediummultiple choice

In an MPLS network, which field in the MPLS label header is used to carry QoS information between LSRs?

Question 62hardmultiple choice

Read the full Automation and Quality of Service explanation →

A network automation engineer needs to retrieve QoS policy statistics from a Cisco IOS XE device using RESTCONF. Which YANG module should be targeted?

Question 63easymultiple choice

Which congestion avoidance technique drops packets probabilistically before the queue becomes full?

Question 64mediummultiple choice