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Network Services Practice Questions

15 original scenario-style questions covering ENSLD 4.1 to 4.5. Answer every one before opening any explanation. Target: 12 of 15 (80%).

1. Blueprint 4.1

A company wants a hard guarantee that a new video conference is refused when the WAN cannot carry it, but it also has thousands of other flows. Which approach fits best?

  • A. Full IntServ with RSVP reservations for every flow
  • B. DiffServ for all traffic plus admission control for the video flows
  • C. Policing all video at ingress
  • D. DiffServ only, with a larger priority queue
Answer: B

DiffServ scales to thousands of flows, and admission control (such as RSVP for the video flows only) refuses a call that would overload the priority queue. A needs per-flow state on every router. D does not refuse calls, it only delays the overload. C drops packets of calls that are already running.

2. Blueprint 4.1

A small branch has IP phones, a point-of-sale application and web browsing. The WAN team is small. Which class model is the best fit?

  • A. A 12-class model so every application has its own class
  • B. One class per application, created in Catalyst Center
  • C. A single class with fair queuing
  • D. A model of four or five classes that separates voice, signalling, transactional data and best effort
Answer: D

Use the smallest model that separates what the business cares about. Twelve classes add operational cost with no benefit at this branch, one class cannot protect voice, and one class per application does not scale.

3. Blueprint 4.1

An administrator notices that PCs on a user VLAN are sending traffic marked EF and receiving priority. What is the correct design fix?

  • A. Increase the priority queue size
  • B. Trust DSCP on all access ports
  • C. Re-mark or reset PC traffic at the access port and use conditional trust for phones
  • D. Move the priority queue to the distribution layer
Answer: C

The trust boundary must sit where the network stops believing the marks. Conditional trust accepts phone marks only when a phone is detected, and everything else is classified or reset. A and D leave the abuse in place, and B makes it worse.

4. Blueprint 4.1

A provider sells three QoS classes, and the enterprise uses eight internally. What is the correct handling at the WAN edge?

  • A. Send all eight markings unchanged and let the provider decide
  • B. Map the enterprise classes to the provider's three markings on egress and back on ingress
  • C. Use only the enterprise's top three classes
  • D. Mark everything EF so the provider gives it priority
Answer: B

The provider polices or re-marks anything outside its sold classes. Mapping on the way out and back on the way in preserves intent. A risks being re-marked to best effort. C discards classes the business needs. D overruns the real-time class and is policed.

5. Blueprint 4.2

A router has a 1 Gbps Ethernet port connected to a Metro Ethernet service contracted at 200 Mbps. A queuing policy with a priority class for voice is attached to the port, yet voice is dropped during busy periods. What is missing?

  • A. WRED on the voice class
  • B. A larger bandwidth percentage for the default class
  • C. A parent shaper at 200 Mbps with the queuing policy as the child
  • D. An ingress policer at 1 Gbps
Answer: C

The port never congests at 1 Gbps, so the queues do not act, and the provider's policer drops at 200 Mbps without regard for markings. A shaper creates the congestion point at the contracted rate. WRED on voice (A) makes loss worse.

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