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Addressing and Routing Practice Questions

15 original scenario questions covering ENSLD 1.1 to 1.6. Answer every one before opening any explanation. Target: 12 of 15 (80%).

1. Blueprint 1.1. A company has 6 regions. Each region has up to 20 sites, and each site needs at most 6 subnets of /24 size. The plan must allow one summary per site and one per region from 10.0.0.0/8. Which allocation fits?

  • A. A /22 per site and a /16 per region
  • B. A /24 per site and a /20 per region
  • C. A /21 per site and a /16 per region
  • D. A /23 per site and a /18 per region
Answer: C

Six /24s need eight aligned /24s, which is a /21. Twenty /21 sites need 32 aligned /21s (the next power of two), which is a /16. A /22 holds only four /24s. A /23 holds two, and a /24 holds one, so D and B cannot fit six subnets per site.

2. Blueprint 1.1. A network engineer plans the IPv6 LAN subnets for a new site and proposes /112 prefixes so that only 65,536 addresses exist per VLAN. What is the main problem?

  • A. IPv6 does not allow prefixes longer than /64
  • B. SLAAC and several neighbour discovery based features require a /64
  • C. The summary at the site border becomes impossible
  • D. Unique local addresses cannot be used with /112
Answer: B

SLAAC builds a 64-bit interface identifier, so the subnet must be a /64. Longer prefixes are allowed on point-to-point links and loopbacks (A is wrong). Summarization depends on the allocation hierarchy, not the subnet length (C), and ULA works with any valid prefix length (D).

3. Blueprint 1.2. In an IS-IS domain, an L1 access router chooses suboptimal exits toward two L1/L2 border routers, and the team wants L1 routers to pick the best exit per destination. What should the designer do?

  • A. Add a virtual link between the areas
  • B. Change the metric style to narrow
  • C. Clear the attached bit on both border routers
  • D. Leak selected L2 routes into L1 (or use a single-level L2 design)
Answer: D

L1 routers send unknown destinations to the nearest attached L1/L2 router, so they lack information for optimal exit choice. Route leaking from L2 to L1 gives them specifics, and a flat L2 design removes the issue. IS-IS has no virtual link (A). Clearing ATT would remove the default route and break reachability (C). Narrow metrics reduce metric range and do not help (B).

4. Blueprint 1.2. A designer must reduce LSP size and SPF work in a large IS-IS core and wants to limit the attack surface from transit link addresses. Which option achieves this?

  • A. metric-style narrow
  • B. Advertise only passive interface prefixes such as loopbacks
  • C. Disable hello authentication
  • D. Set every interface to level-1
Answer: B

advertise passive-only (IS-IS prefix suppression) keeps transit link prefixes out of the LSPs. Narrow metrics reduce range and do not reduce LSP content meaningfully (A). Moving to level-1 changes hierarchy, not LSP content (D). Disabling authentication reduces security (C).

5. Blueprint 1.3. 60 branch routers connect to an EIGRP hub over DMVPN. A branch link flap sometimes causes stuck-in-active events at the hub. Which change contains the problem with the least disruption?

  • A. Configure branch routers as EIGRP stubs and summarize from the hub
  • B. Increase the hello interval on the tunnel
  • C. Place each branch in a separate EIGRP autonomous system
  • D. Change K values to use reliability
Answer: A

A stub is not queried, so its failure cannot spread an active query, and hub summaries keep tables small. Longer hellos slow detection and do not stop queries (B). Separate autonomous systems force redistribution and risk loops (C). K values must match on every neighbour and do not control query scope (D).

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