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Cisco 300-420 Practice Test 56

Question 550

A campus design requires both distribution uplinks active but the chosen topology uses classic STP on all Layer 2 connections. Which specific risk makes the uncorrected design unacceptable?

  1. Redundancy claims may not match actual hardware or software failover behavior.
  2. Arbitrary VLAN load splitting can overload the surviving device and create asymmetry.
  3. Assuming all STP redundant paths can actively forward leads to incorrect bandwidth capacity planning.
  4. Shared chassis does not automatically imply network-plane isolation without route-policy controls.

Explanation

Correct Answer

C:

The supported design response is to use a supported multi-chassis EtherChannel or routed-access design to make redundancy active without a spanning-tree loop.

Incorrect Answers

A:

That hazard arises in a separate case: A remote campus uses two distribution switches and requires nonstop gateway access during a planned supervisor replacement. It is not the failure mode evidenced here.

B:

That hazard arises in a separate case: A campus with several hundred VLANs uses one active HSRP gateway for all VLANs while another distribution router remains mostly idle. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A public safety campus requires independent operations from a corporate tenant even when both use the same distribution hardware. It is not the failure mode evidenced here.

Question 551

A company wants most return traffic for its public prefix to enter ISP B rather than ISP A. Which specific risk makes the uncorrected design unacceptable?

  1. Assuming every higher-metric neighbor is a feasible successor can lead to unexpected reconvergence.
  2. AS-path prepending never guarantees that every external AS selects the intended ingress.
  3. Unbounded received routes can destabilize the edge router control plane.
  4. Dual stack on one site does not transform a single-stack external client automatically.

Explanation

Correct Answer

B:

The supported design response is to assess supported inbound traffic engineering such as scoped AS-path prepending or provider communities, recognizing remote-AS policy discretion.

Incorrect Answers

A:

That hazard arises in a separate case: A router receives two EIGRP routes for a prefix with different metrics and the design team wants deterministic failover. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A company accepts routes from a newly merged BGP AS without maximum-prefix limits, and the peer mistakenly sends hundreds of thousands of prefixes. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A company wants to expose IPv6 resources to a partner with IPv4-only routing and assumes dual stack at headquarters solves the partner boundary. It is not the failure mode evidenced here.

Question 552

Two DMVPN spokes can reach the hub but never build a direct shortcut after new spoke routes are learned. Which specific risk makes the uncorrected design unacceptable?

  1. Static hub-only GRE tunnels scale poorly for dynamic multi-spoke reachability.
  2. Unrestricted any-to-any reachability can violate inspection and data-flow requirements.
  3. Misassigned segment identifiers can bypass intended enterprise isolation.
  4. Incorrect shortcut or route summarization design can force persistent hairpin traffic.

Explanation

Correct Answer

D:

The supported design response is to align DMVPN phase/design, NHRP mappings and redirect/shortcut behavior with the intended topology.

Incorrect Answers

A:

That hazard arises in a separate case: A retail chain needs many spokes to make dynamic spoke-to-spoke tunnels without permanent full-mesh configuration. It is not the failure mode evidenced here.

B:

That hazard arises in a separate case: A network wants a hub-and-spoke topology for finance traffic but allows any-to-any policy for all service VPNs. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: An SD-WAN fabric routes guest traffic into the production VPN because a new edge reused the corporate service VPN identifier. It is not the failure mode evidenced here.

Question 553

An NOC polls every router with SNMP once every ten minutes and misses 30-second interface utilization spikes. Which specific risk makes the uncorrected design unacceptable?

  1. Incorrect model classification can produce malformed payloads or unsupported paths.
  2. Slow periodic polling can miss short-lived congestion incidents.
  3. Oversampling can consume bandwidth and CPU without improving the use case.
  4. Unbounded telemetry streams can exhaust collectors and impair network control operations.

Explanation

Correct Answer

B:

The supported design response is to use appropriately sampled or on-change model-driven telemetry for the monitored signals, with a scalable receiver architecture.

Incorrect Answers

A:

That hazard arises in a separate case: A standards group needs an interoperable interface model but mistakenly calls every IETF YANG module an OpenConfig model. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A global WAN telemetry system publishes a complete 10,000-interface snapshot every 100 ms although the target is only five-minute capacity planning. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A fleet telemetry design streams all available operational leaves every second over a constrained management link. It is not the failure mode evidenced here.

Question 554

A campus QoS policy gives low priority to routing keepalives and network monitoring, and routing adjacencies flap during congestion. Which specific risk makes the uncorrected design unacceptable?

  1. Oversized strict priority can starve lower-priority traffic and still harm voice.
  2. Treating network control messages as ordinary bulk data can cause false path failures.
  3. Equal queue bandwidth does not reflect differing application tolerance to loss and delay.
  4. QoS on one hop cannot undo queueing loss caused at a later bottleneck.

Explanation

Correct Answer

B:

The supported design response is to protect essential routing/control traffic within bounded QoS classes at actual bottlenecks.

Incorrect Answers

A:

That hazard arises in a separate case: Video and voice both use one strict-priority queue, causing voice jitter when video surges. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A branch policy gives every queue an equal share although its database synchronization is delaying emergency call signaling. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A campus designs priority queues only on the access switch but ignores a congested upstream WAN edge. It is not the failure mode evidenced here.

Question 555

A fabric site needs a guest wireless SSID without extending the guest Layer 2 domain across the whole enterprise. Which specific risk makes the uncorrected design unacceptable?

  1. Stretching a broad guest broadcast domain enlarges the fault and attack surface.
  2. An IP transit that removes fabric encapsulation may not automatically extend fabric segmentation end to end.
  3. Unicast fabric reachability does not prove multicast distribution or replication.
  4. Undersized PoE causes reduced AP capabilities or unstable power negotiation.

Explanation

Correct Answer

A:

The supported design response is to design supported fabric wireless segmentation with dedicated VNs/SGTs and appropriate wireless control integration.

Incorrect Answers

B:

That hazard arises in a separate case: An organization needs consistent segmentation across two SD-Access fabric sites connected by a routed MPLS service. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A financial application needs multicast delivery across SDA sites, but all validation has covered unicast endpoint maps only. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A wireless access-point refresh increases PoE needs above the available 802.3at class on older switches. It is not the failure mode evidenced here.

Question 556

A network with 80 iBGP routers becomes difficult to operate because every router forms a full mesh of peer sessions. Which specific risk makes the uncorrected design unacceptable?

  1. Allowing a nontransit branch to act as a query/transit path increases instability and query scope.
  2. Unbounded import can consume resources and expose unexpected paths.
  3. Poor reflector placement or single-reflector dependency can hide routes and amplify outages.
  4. Misdesigned confederation boundaries can leak internal member-AS details or break route propagation.

Explanation

Correct Answer

C:

The supported design response is to design redundant BGP route reflectors with consistent cluster IDs and reflector-client relationships.

Incorrect Answers

A:

That hazard arises in a separate case: A branch EIGRP router advertises remote routes back into its hub and occasionally becomes a transit path between hubs. It is not the failure mode evidenced here.

B:

That hazard arises in a separate case: An edge router receives a full BGP table where the security policy allows only the provider's approved default. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A merger requires two administrative BGP regions to appear as one external AS while reducing iBGP mesh size internally. It is not the failure mode evidenced here.

Question 557

A retail design directs all cloud SaaS traffic through headquarters even though local internet breakout is allowed and latency is poor. Which specific risk makes the uncorrected design unacceptable?

  1. Centralized hairpin routing can add avoidable delay and overload headquarters links.
  2. Best-effort internet access may not meet the required deterministic metro transport SLA.
  3. Cost-only transport selection can violate real-time service SLAs.
  4. Hand-configuring every edge pair undermines scalable centralized policy and error control.

Explanation

Correct Answer

A:

The supported design response is to evaluate policy-controlled local internet breakout with appropriate security inspection and application path measurement.

Incorrect Answers

B:

That hazard arises in a separate case: A city campus needs a 10-Gbps local metro interconnect with SLA and carrier demarcation, but the proposed design assumes standard broadband internet guarantees. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A voice application has a 120-ms latency budget, but SD-WAN traffic follows the cheapest internet path despite BFD reporting 220-ms delay. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A network team manually builds static IPsec tunnels between every SD-WAN edge even though centralized overlay policy is available. It is not the failure mode evidenced here.

Question 558

A regional WAN prioritizes voice using a DiffServ marking but provides no scheduler preference on its congested egress link. Which specific risk makes the uncorrected design unacceptable?

  1. A primary-link shaper on a much smaller backup can trigger major provider drops.
  2. Oversized strict priority can starve lower-priority traffic and still harm voice.
  3. Impossible aggregate guarantees lead to unexpected arbitration or configuration rejection.
  4. Marking packets alone does not guarantee queue service under oversubscription.

Explanation

Correct Answer

D:

The supported design response is to combine trusted traffic classification and marking with a suitable egress priority queue and bandwidth admission design.

Incorrect Answers

A:

That hazard arises in a separate case: A 20-Mbps backup link replaces a 200-Mbps primary WAN but the shaper keeps its 200-Mbps limit after failover. It is not the failure mode evidenced here.

B:

That hazard arises in a separate case: Video and voice both use one strict-priority queue, causing voice jitter when video surges. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A switch QoS scheduler guarantees 30% to backup traffic and 80% to voice under full congestion, exceeding possible link capacity. It is not the failure mode evidenced here.

Question 559

The IS-IS backbone has a router in overload state after reboot and operators mistake it for an ordinary forwarding transit. Which specific risk makes the uncorrected design unacceptable?

  1. Ignoring overload can select a router that has not populated a usable forwarding table.
  2. Logical redundancy on the same physical uplink does not remove the single point of failure.
  3. Assuming parallel sessions alone implies BGP load sharing hides the default single-best-path behavior.
  4. Allowing a nontransit branch to act as a query/transit path increases instability and query scope.

Explanation

Correct Answer

A:

The supported design response is to honor the IS-IS overload-bit signaling and restore normal transit eligibility only when routing readiness is confirmed.

Incorrect Answers

B:

That hazard arises in a separate case: An EIGRP deployment relies on a single aggregation router and an outage cuts off all downstream branches. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A campus border is configured with two equal-cost external BGP paths but only one is installed for traffic forwarding. It is not the failure mode evidenced here.

D:

That hazard arises in a separate case: A branch EIGRP router advertises remote routes back into its hub and occasionally becomes a transit path between hubs. It is not the failure mode evidenced here.

Question 560

A port used only for workstations undergoes lengthy spanning-tree transitions whenever a client reconnects. Which specific risk makes the uncorrected design unacceptable?

  1. Oversubscribed PoE can shut off critical phones or cameras during high load.
  2. A missing or overbroad MAC limit creates unauthorized layer-2 expansion.
  3. All-trusted DHCP snooping provides no protection against rogue lease servers.
  4. Broad edge designation on switch-to-switch trunks can create loops during topology changes.

Explanation

Correct Answer

D:

The supported design response is to apply a supported edge/PortFast designation only to validated endpoint-facing interfaces.

Incorrect Answers

A:

That hazard arises in a separate case: IP phones and cameras are scheduled for a new closet, but PoE budget is calculated only from the switch's total port count. It is not the failure mode evidenced here.

B:

That hazard arises in a separate case: A guest workstation port can learn hundreds of source MAC addresses because an unmanaged mini-switch is connected behind it. It is not the failure mode evidenced here.

C:

That hazard arises in a separate case: A routed campus uses DHCP snooping on access switches but marks every endpoint port trusted for convenience. It is not the failure mode evidenced here.

Designing Cisco Enterprise Networks (ENSLD) (300-420) Practice Tests

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