350-401 · topic practice
Practise ENCOR 350-401 Qos practice questions — original exam-style scenarios with answer choices, explanations, and analysis of common mistakes.
Courseiva uses original exam-style practice questions designed for learning and revision. The goal is to understand the concepts, recognise exam patterns, and improve through explanations — not memorise copied exam dumps.
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20 questions · select your answer, then reveal the explanation
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Uses RSVP to signal per-flow reservations; Requires per-flow state in every router
Classifies traffic using DSCP markings; Scales well for large enterprise networks
No guarantees for delivery or delay
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Expedited Forwarding
Assured Forwarding class 4, low drop probability
Class Selector 3
Assured Forwarding class 2, medium drop probability
Best-effort
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No classification, single queue, packets served in order of arrival
Automatically classifies flows and provides fair queuing per flow
Allows creation of custom traffic classes with guaranteed bandwidth
Adds a strict priority queue within CBWFQ for delay-sensitive traffic
Multiple queues with strict priority servicing, lower queues starve if higher queues are non-empty
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Single queue, no differentiation
Per-flow flow-based fair queuing
User-defined traffic classes with guaranteed bandwidth
Strict priority queue with rate limiting
Always serves highest-priority queue first
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Drag steps to the numbered slots on the right, or tap a step then tap a slot.
Drag steps to the numbered slots on the right, or tap a step then tap a slot.
Trap 1: Application-aware routing policies are a type of localized control…
Incorrect because app-route policies are centralized data policies, not localized control policies.
Trap 2: Centralized data policies are applied on the edge devices to…
Incorrect because centralized data policies are applied on vSmart, not on edge devices.
Trap 3: vManage is the primary device where all SD-WAN policies are…
Incorrect because vManage is the management plane for configuration and monitoring, not for policy enforcement.
Centralized control policies are configured on the vSmart controller and affect route advertisement and path selection.
Correct because control policies on vSmart manipulate OMP routes and TLOCs to influence routing decisions.
Localized data policies, such as QoS and ACL, are configured on vEdge or cEdge routers and affect traffic forwarding.
Correct because localized policies are applied directly on the edge devices for per-packet actions.
Application-aware routing policies are a type of localized control policy that steers traffic based on application performance.
Why wrong: Incorrect because app-route policies are centralized data policies, not localized control policies.
Centralized data policies are applied on the edge devices to enforce per-tunnel QoS and ACL rules.
Why wrong: Incorrect because centralized data policies are applied on vSmart, not on edge devices.
vManage is the primary device where all SD-WAN policies are enforced and processed in real time.
Why wrong: Incorrect because vManage is the management plane for configuration and monitoring, not for policy enforcement.
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Trap 1: Marking can only be applied to Layer 2 frames using CoS bits.
Incorrect because marking can be applied at Layer 3 using DSCP or IP precedence, not just Layer 2 CoS.
Trap 2: Marking is a congestion avoidance mechanism that uses tail drop.
Incorrect because marking is a classification tool, not a congestion avoidance mechanism; tail drop is used in queuing.
Trap 3: A class map is used to apply marking actions to classified traffic.
Incorrect because class maps only define match criteria; policy maps apply actions like marking.
A class map can match traffic based on DSCP, CoS, IP precedence, or ACL.
Correct because class maps support multiple match criteria including DSCP, CoS, IP precedence, and ACLs.
Marking should be performed as close to the source as possible, typically at the access layer.
Correct because marking at the access layer ensures consistent treatment throughout the network.
Marking can only be applied to Layer 2 frames using CoS bits.
Why wrong: Incorrect because marking can be applied at Layer 3 using DSCP or IP precedence, not just Layer 2 CoS.
Marking is a congestion avoidance mechanism that uses tail drop.
Why wrong: Incorrect because marking is a classification tool, not a congestion avoidance mechanism; tail drop is used in queuing.
A class map is used to apply marking actions to classified traffic.
Why wrong: Incorrect because class maps only define match criteria; policy maps apply actions like marking.
Trap 1: Policing buffers traffic that exceeds the rate to reduce packet…
Incorrect because policing does not buffer; it drops or re-marks excess traffic immediately.
Trap 2: Shaping is typically applied on the ingress interface to control…
Incorrect because shaping is applied on egress to control outgoing traffic rate.
Policing can re-mark traffic that exceeds the configured rate to a lower priority.
Correct because policing can set a new DSCP or CoS value for out-of-profile traffic.
Shaping buffers excess traffic and transmits it later to avoid drops.
Correct because shaping uses a buffer to hold packets that exceed the rate, sending them at a later time.
Both policing and shaping use a token bucket algorithm to measure traffic rates.
Correct because both mechanisms use token buckets to determine if traffic conforms to the configured rate.
Policing buffers traffic that exceeds the rate to reduce packet loss.
Why wrong: Incorrect because policing does not buffer; it drops or re-marks excess traffic immediately.
Shaping is typically applied on the ingress interface to control incoming traffic.
Why wrong: Incorrect because shaping is applied on egress to control outgoing traffic rate.
Trap 1: VRF can be used to replace VLANs for Layer 2 isolation.
Incorrect because VRF is a Layer 3 concept, while VLANs operate at Layer 2.
Trap 2: In VRF-lite, path isolation is achieved using MPLS labels.
Incorrect because VRF-lite does not use MPLS; it relies on separate routing tables.
VRFs allow multiple customers to share the same physical infrastructure while keeping their traffic isolated.
Correct because each VRF maintains separate forwarding tables, providing Layer 3 isolation.
In MPLS VPN, VRFs are combined with route targets to control route distribution between PE routers.
Correct because route targets (import/export) determine which VRFs receive which routes.
VRF-aware features such as NAT, QoS, and ACLs can be applied per VRF to enforce path isolation policies.
Correct because Cisco IOS supports VRF-aware services for granular control.
VRF can be used to replace VLANs for Layer 2 isolation.
Why wrong: Incorrect because VRF is a Layer 3 concept, while VLANs operate at Layer 2.
In VRF-lite, path isolation is achieved using MPLS labels.
Why wrong: Incorrect because VRF-lite does not use MPLS; it relies on separate routing tables.
Trap 1: The 'set dscp' command in a policy map can be used to mark packets…
Incorrect. The 'set dscp' command can be used on both ingress and egress policy maps, depending on the platform.
Trap 2: MPLS EXP bits are a 3-bit field used for QoS in MPLS networks and…
Incorrect. MPLS EXP bits are 3 bits, but they are not automatically mapped; mapping can be configured using the 'mpls qos' commands.
The trust boundary can be configured using the 'mls qos trust' command on a switch port to trust the CoS or DSCP value received from an attached device.
Correct. The trust boundary is set with 'mls qos trust' to honor incoming markings.
NBAR (Network-Based Application Recognition) can classify traffic based on application signatures, including HTTP URLs and SSL certificate fields.
Correct. NBAR performs deep packet inspection and can match on many application attributes.
Layer 2 CoS marking uses a 3-bit field in the 802.1Q tag, providing 8 possible values, while DSCP uses 6 bits for 64 values.
Correct. CoS is 3 bits (0–7), DSCP is 6 bits (0–63).
The 'set dscp' command in a policy map can be used to mark packets with a DSCP value, but only on egress interfaces.
Why wrong: Incorrect. The 'set dscp' command can be used on both ingress and egress policy maps, depending on the platform.
MPLS EXP bits are a 3-bit field used for QoS in MPLS networks and are always directly mapped from the IP DSCP value without any configuration.
Why wrong: Incorrect. MPLS EXP bits are 3 bits, but they are not automatically mapped; mapping can be configured using the 'mpls qos' commands.
Drag a concept onto its matching description — or click a concept then click the description.
Expedited forwarding, strict priority queuing, low delay and jitter
Assured forwarding, four classes with three drop probabilities per class
Class selector, backward compatible with IP precedence, simple priority queuing
Best-effort, default queue, no guarantees
Default forwarding, same as best-effort (DSCP 0)
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Strict priority queuing for delay-sensitive traffic
Guarantees minimum bandwidth per class; Used for data traffic classes requiring bandwidth assurance
Strict priority queue with bandwidth guarantees for other classes
Fair queuing based on flow weights
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Trap 1: Weighted Fair Queuing (WFQ) is the default queuing mechanism on all…
Incorrect because WFQ is the default only on low-speed interfaces (below 2.048 Mbps); high-speed interfaces use FIFO by default.
Trap 2: Tail drop is the only drop policy available for CBWFQ queues.
Incorrect because CBWFQ can also use WRED (Weighted Random Early Detection) as a drop policy to avoid tail drop.
Trap 3: FIFO queuing provides per-class bandwidth guarantees.
Incorrect because FIFO is a single queue without any bandwidth differentiation or guarantees.
CBWFQ allows you to define multiple classes and assign each a guaranteed minimum bandwidth.
Correct because CBWFQ allocates bandwidth to each class based on the 'bandwidth' command.
LLQ combines a strict priority queue with CBWFQ classes to support real-time traffic.
Correct because LLQ uses the 'priority' command to create a strict priority queue alongside CBWFQ.
Weighted Fair Queuing (WFQ) is the default queuing mechanism on all Cisco router interfaces.
Why wrong: Incorrect because WFQ is the default only on low-speed interfaces (below 2.048 Mbps); high-speed interfaces use FIFO by default.
Tail drop is the only drop policy available for CBWFQ queues.
Why wrong: Incorrect because CBWFQ can also use WRED (Weighted Random Early Detection) as a drop policy to avoid tail drop.
FIFO queuing provides per-class bandwidth guarantees.
Why wrong: Incorrect because FIFO is a single queue without any bandwidth differentiation or guarantees.
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