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ENSLD Question Bank, Part 1 (Domains 1 and 2)

55 original questions covering ENSLD 300-420 v1.1 domains 1.0 Advanced Addressing and Routing Solutions (28 questions) and 2.0 Advanced Enterprise Campus Networks (27 questions). Part 2 continues with questions 56 to 105 for domains 3.0, 4.0 and 5.0.

ENSLD is a design exam. Almost every question gives you a set of requirements and constraints and asks you to choose the design that fits best, so read for the constraint first (scale, failure behavior, operational cost, vendor neutrality) and only then compare the options. Answer each question before you open its explanation, and log every miss by the blueprint number shown under the question. Target: 44 of 55 (80%).

1.0 Advanced Addressing and Routing Solutions

1. Blueprint 1.1

A company has four campuses. Each campus has about 600 hosts today and is expected to grow to 1,500 within five years. The WAN edge router at each campus should advertise exactly one IPv4 prefix to the core, and no campus may need to renumber during that period. Which addressing plan meets the requirement?

  • A. Reserve a /21 for each campus from one aligned /19 (for example 10.16.0.0/21, 10.16.8.0/21, 10.16.16.0/21 and 10.16.24.0/21) and allocate subnets inside each block as needed
  • B. Allocate /24 subnets sequentially from 10.16.0.0/16 to whichever campus requests the next one
  • C. Allocate a /22 to each campus now and add a second /22 from unused space when it runs out
  • D. Assign each campus a different RFC 1918 range so the prefixes never overlap
Answer: A

A /21 holds 2,046 hosts, which covers the 1,500-host growth target, and four aligned /21 blocks collapse into one /19 for summarization at the core. Sequential allocation (B) scatters each campus across the address space and defeats summarization. A /22 holds only 1,022 hosts, and a second, non-adjacent /22 (C) means two prefixes per campus and eventually renumbering. Using a different RFC 1918 range per campus (D) gives unique prefixes but wastes space and offers no summary boundary at the core.

2. Blueprint 1.1

An enterprise receives a /48 IPv6 prefix from its provider for a headquarters site with 12 buildings. Each building has up to 200 VLANs plus routed point-to-point links. The design team wants a plan that is hierarchical, summarizable per building and compatible with SLAAC. Which plan fits?

  • A. Use /112 subnets for user VLANs to conserve address space
  • B. Use /64 for server VLANs only and /120 for user VLANs
  • C. Assign each building a /52 on a nibble boundary, use a /64 for every VLAN, and use /127 for point-to-point links
  • D. Assign each building a /60 and subnet it into /64s
Answer: C

A /48 split into /52 blocks gives 16 building blocks of 4,096 /64 subnets each, which covers 12 buildings with spare blocks and 200 VLANs per building with plenty of room. Each building summarizes to one /52, and /52 sits on a hexadecimal digit boundary so the plan is easy to read. A /64 per VLAN is required for SLAAC. A /127 on point-to-point links is allowed and reduces neighbor-cache exhaustion attacks. Subnets longer than /64 on user VLANs (A, B) break SLAAC and many IPv6 features. A /60 per building (D) holds only 16 subnets, far short of 200 VLANs.

3. Blueprint 1.1

A design team is writing the IPv4 addressing standard for a new WAN with 40 sites that will be added over several years. Which two practices support route summarization as sites are added? (Choose two.)

  • A. Allocate subnets to sites in the order the sites are commissioned, from any free space
  • B. Assign each site a block aligned on a power-of-two boundary and sized for its expected growth
  • C. Use a different prefix length for every site so no two sites can be confused
  • D. Reserve unallocated space at each summarization level so that regions can grow without breaking their summary
  • E. Number WAN links from the same block as user LANs so there are fewer prefixes to track
Answer: B, D

A summary only works when the component subnets form one contiguous, aligned block. Aligned blocks sized for growth (B) plus reserved space at each level (D) let a region or site expand without being split into a second summary. Allocating in commissioning order (A) scatters sites, and mixing WAN links with user LANs (E) pollutes the summary block. Varying prefix lengths for their own sake (C) has no summarization benefit.

4. Blueprint 1.1

An enterprise is dual-homed to two ISPs with BGP. It wants to keep the same public IPv6 addresses if it changes either provider, and wants to advertise them to both providers. Which addressing choice meets this requirement?

  • A. Use a provider-assigned prefix from ISP 1 and advertise it to ISP 2
  • B. Number the network with provider-assigned space from each ISP and use NAT between them
  • C. Use unique local addresses (fd00::/8) and advertise them to both providers
  • D. Obtain provider-independent address space and an AS number from the regional registry and advertise the prefix to both providers
Answer: D

Provider-independent space belongs to the enterprise, so it can be advertised through any provider and survives a change of ISP. Provider-assigned space from ISP 1 (A) is part of ISP 1's aggregate, and ISP 2 or upstream networks may filter a more specific route they do not expect, and the enterprise must renumber if ISP 1 is dropped. Using PA space from each ISP with translation (B) adds NAT complexity and renumbering. Unique local addresses (C) are not globally routable and are filtered on the Internet.

5. Blueprint 1.2

A service-provider-style enterprise runs a single flat Level 2 IS-IS domain with 600 routers. SPF runs and LSP flooding are consuming too much CPU after every change. The team must keep IS-IS and reduce the scope of flooding. Which redesign is most appropriate?

  • A. Put every router in the same Level 1 area so the LSDB is shared
  • B. Split the network into regional Level 1 areas, make the border routers Level 1-2, and keep the Level 2 routers contiguous as the backbone
  • C. Keep Level 2 on the regional leaf routers only and leave the core routers in Level 1
  • D. Set every router to Level 1-2 so each area boundary is bypassed
Answer: B

Level 1 areas confine LSP flooding and SPF to the area. Level 1-2 routers at the boundary connect each area to the Level 2 backbone, and they set the attached bit so Level 1 routers can use a default route to reach other areas. The Level 2 routers must form a contiguous path. One large Level 1 area (A) makes flooding worse. A Level 2 domain built only from leaf routers with Level 1 core routers (C) breaks backbone continuity. Making every router Level 1-2 (D) keeps a single large Level 2 LSDB and gains nothing.

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