Which Layers Are Collapsed in a Collapsed Core Design?

Describe characteristics of network topology architectures

Answer Correct answer: A — In a collapsed core architecture, the core and distribution layers are merged into one combined layer.

What is the collapsed layer in collapsed core architectures?

Core and distribution Correct Answer
access and WAN
distribution and access
core and WAN

Community Insight

The question tests whether you know which two hierarchical layers are merged in a collapsed core design; the trap is confusing the layers that are merged with the layers that still remain separate (core and access).

Collapsed core architecture is a two-tier Cisco hierarchical topology in which the core layer and the distribution layer are combined into a single switched layer. This page establishes that the collapsed (merged) layers are the core and distribution, making option A the correct answer.

Option C (distribution and access) is the tempting wrong pick, because learners read 'collapsed core' as the core sitting directly on top of access — but the merge happens between core and distribution, and the access layer stays a distinct tier.

Community Discussion (5 comments)

LordEu79 👍 1 Selected: A

In collapsed core design the layers core and distribution are combined.

PazUK 👍 1 Selected: A

Whoever wrote the question has Primary-school-level proficiency in English. The question asks what is the single LAYER that has been collapsed (which would be the distribution layer). But, what they meant to ask is: "which LAYERS are present in the collapsed core architecture?" (which would be the core and the access layers). Another misleading question.

sjogos 👍 1

All are Wrong. In fact, in colapsed core there are no "distribution". Only core and acess layer

Net1918 👍 2

The question asked what the 'collapsed layer' is and not the components of the collapsed core architecture. In comparison to the 3 tier architecture,the collapsed layer consists of the core and distribution layers combined. I hope this helps.

Vlad_Is_Love_ua 👍 4 Selected: A

If you choose a hierarchical tiered architecture, the exact number of tiers that you would implement in a network depends on the characteristics of the deployment site. For example, a site that occupies a single building might only require two layers while a larger campus of multiple buildings will most likely require three layers. In smaller networks, core and distribution layers are combined and the resulting architecture is called a collapsed core architecture.

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Expert Analysis

Why the Answer Is Correct

In the Cisco three-layer hierarchical model (core, distribution, access), a collapsed core design simply removes one physical tier by combining the functions of the core layer and the distribution layer onto the same devices. Those merged layers are exactly what 'the collapsed layer' refers to, so the collapsed layer is core and distribution — option A. The combined layer performs both high-speed backbone transport and policy/routing boundaries, while the access layer continues to exist as its own tier feeding into it. This design is standard for small sites such as a single building, where a full three-tier build-out would be wasteful. Cisco's own curriculum describes small networks as requiring only two layers because 'core and distribution layers are combined.'

Why the Other Options Are Wrong

Option B (access and WAN) and option D (core and WAN) both introduce the WAN as a hierarchical layer, which is not part of the core/distribution/access model at all — the WAN is an external connectivity concern, not a collapsible tier. Option C (distribution and access) describes merging the bottom two tiers, which would leave a core layer with nothing beneath it and is not a recognized hierarchical variant. Note also that the access layer is never collapsed away in this design; it remains a separate tier connecting end devices. Confusing 'which layers are merged' with 'which layers remain present' is the real source of disagreement here.

Community Comment Notes

Several commenters converged on A: LordEu79 wrote verbatim, "In collapsed core design the layers core and distribution are combined.", and Vlad_Is_Love_ua explained that small sites are built with two layers because 'core and distribution layers are combined'. Net1918 sharpened the wording by insisting 'the collapsed layer consists of the core and distribution layers combined.' PazUK raised a legitimate objection that the phrasing is ambiguous — the question asks what is collapsed rather than what layers remain — but even his reading of the intended meaning points to the core/distribution merge. One dissenting voice claimed 'Only core and acess layer' exist, which misstates the design: the merged tier still performs distribution duties, so distribution is not eliminated.

Exam Strategy

Anchor yourself in the three-layer model first: core, distribution, access. Whenever you see 'collapsed' or 'two-tier,' ask which adjacent pair was merged — it is always core with distribution — and never let the word 'WAN' pull you toward hierarchical-layer options.

Frequently Asked Questions

Why isn't distribution and access (C) the collapsed layer in a collapsed core?

The merge is between the core and distribution layers; the access layer remains a separate tier connecting end devices to the combined layer.

Does a collapsed core design remove the distribution layer entirely?

No. Its functions are not removed — they are performed by the combined core/distribution devices, so routing policy and distribution duties still occur.

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