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WAN Practice Questions

15 original scenario-style questions covering ENSLD 3.1 to 3.5. Answer every one before opening any explanation. Target: 12 of 15 (80%).

1. A company wants to run its own OSPF between its two data centres across a provider network. The provider must not take part in the customer's routing. Which service fits best? Blueprint 3.1.a

  • A. MPLS Layer 3 VPN with eBGP PE-CE
  • B. Layer 2 VPN (VPWS)
  • C. Internet DIA with no overlay
  • D. Cellular 5G
Answer: B

A Layer 2 VPN carries Ethernet frames and the customer routers peer directly across it. In an MPLS L3VPN (A) the CE peers with the provider PE, so the provider is part of the routing. Cellular (D) and plain Internet (C) are not private and give no routing transparency.

2. Two data centres 80 km apart need high-bandwidth replication of Ethernet and Fibre Channel traffic with fixed low latency. The company can lease wavelengths. Which option is best? Blueprint 3.1.d

  • A. MPLS L3VPN
  • B. 5G with dual SIM
  • C. Site-to-site IPsec over the Internet
  • D. DWDM
Answer: D

DWDM is a Layer 1 service that is protocol transparent, so it can carry both Ethernet and Fibre Channel with predictable latency and large capacity. L3VPN and Internet IPsec add routing, jitter and throughput limits. Cellular cannot meet the bandwidth.

3. A branch buys 100 Mbps of Metro Ethernet on a 1 Gbps handoff. Voice is delayed when the link is busy even though the router has an LLQ policy on the interface. What is the most likely design flaw? Blueprint 3.1.c

  • A. The policy needs a larger priority queue
  • B. Metro Ethernet cannot carry voice
  • C. There is no parent shaper at 100 Mbps, so the router never sees congestion
  • D. The interface needs a lower MTU
Answer: C

The port is faster than the service rate, so the provider drops excess traffic and the router never queues. A parent shaper at 100 Mbps with the LLQ as child policy fixes it. A larger priority queue does not help if there is no local congestion. Metro Ethernet carries voice well, and MTU is unrelated.

4. A remote construction site needs connectivity in three days. No wired circuit can be installed for three months. Staff need outbound access to the head office only. Which is the best interim design? Blueprint 3.1.e

  • A. Wait for a leased line
  • B. Layer 2 VPN over satellite
  • C. 5G router with the head office initiating inbound connections to the site
  • D. 5G router with an IPsec tunnel initiated to the head office
Answer: D

Cellular is fast to deploy. Many carriers use carrier-grade NAT, so the site cannot accept inbound connections, and the tunnel must be started from the site. Option C fails for that reason. Option A misses the deadline and B is not a realistic quick option.

5. A company has an MPLS L3VPN between 150 sites. The audit now requires encryption. Provider QoS classes by DSCP and multicast must keep working, and no tunnel mesh is acceptable. Which solution fits? Blueprint 3.2.f

  • A. A full mesh of GRE over IPsec tunnels
  • B. GET VPN
  • C. SSL VPN clients on every host
  • D. DMVPN phase 3 over MPLS
Answer: B

GET VPN encrypts any-to-any traffic with a shared group key and keeps the original IP header, so provider QoS and multicast still work and no tunnels are created. A and D add tunnels and a new outer header. C is a remote-access approach.

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