What is a characteristic of the overlay network in Cisco SD-Access?

Cisco SD-Access Architecture

What is a characteristic of the overlay network in the Cisco SD-Access architecture?

  1. It provides multicast support to enable Layer 2 flooding capability in the underlay network.
  2. It provides isolation among the virtual networks and independence from the physical network. Source Reference Answer
  3. It uses a traditional routed access design to provide performance and high availability to the network.
  4. It consists of a group of physical routers and switches that are used to maintain the network.

Community Votes

B
100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

The exam tests understanding that the SD-Access overlay abstracts the physical underlay; the common trap is confusing overlay characteristics with underlay functions such as multicast routing or physical device roles.

In Cisco SD-Access, the overlay network uses LISP to create a virtualized, logical layer that is independent of the physical underlay, enabling segmentation and policy enforcement. Community consensus confirms that the overlay provides isolation among virtual networks without relying on the physical topology.

Option D is often chosen because candidates mistakenly describe the underlay (physical routers and switches) rather than the overlay, which is a logical, virtualized construct.

Community Discussion (3 comments)

Mizuchan 👍 6 Selected: B
In Cisco SD-Access, the overlay network is designed to abstract and provide independence from the underlying physical network. It enables segmentation, policy enforcement, and logical network isolation without direct dependence on the physical network topology. This characteristic contributes to the flexibility and programmability of SD-Access.
chiacche 👍 2
Overlay network in SD-Access: 1. Create a virtual layer from the underlying physical network topology. 2. Can be modified, expanded, or updated without impacting the physical network. 3. Support network segmentation and policy enforcement. 4. Provide logical isolation of network traffic
nj1999 👍 1
https://study-ccnp.com/cisco-sd-access-architecture-network-layer/#:~:text=The%20overlay%20network%20is%20fully,the%20SD%2DAccess%20fabric%20operation.

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Expert Analysis

Why the Answer Is Correct

Option B correctly states that the overlay provides isolation among virtual networks (VN/SGT-based segmentation) and is independent of the physical underlay. The overlay is built using LISP tunnels between fabric nodes, creating a logical topology that can be modified without altering physical cabling or device roles. This abstraction is a foundational principle of Cisco SD-Access, enabling multi-tenancy and micro-segmentation.

Why the Other Options Are Wrong

Option A is incorrect because multicast in the underlay is used to optimize LISP control-plane and data-plane replication, not to provide Layer 2 flooding—Layer 2 flooding is explicitly avoided in SD-Access. Option C describes a traditional routed access design, which is an underlay characteristic, not an overlay function. Option D describes the physical underlay infrastructure (routers and switches), whereas the overlay is a logical, virtualized layer running over that infrastructure.

Community Comment Notes

Comment [1] emphasizes that the overlay abstracts the physical network to enable segmentation and policy enforcement, reinforcing Option B. Comment [2] provides a concise four-point summary of overlay traits: virtual layer creation, independence from physical changes, segmentation support, and logical traffic isolation. Comment [3] links to study material confirming that the overlay is fully virtualized and decoupled from underlay operation.

Official Reference

Exam Strategy

When an SD-Access question mentions 'overlay,' immediately think LISP, virtualization, segmentation, and independence from the physical topology. Eliminate any option that describes physical devices, traditional routing, or Layer 2 flooding, as those belong to the underlay or legacy designs.

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