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Difficulty: EasySoftware-Defined Architectures: Overlay, Underlay, and Fabric

In a Cisco Software-Defined Access (SD-Access) architecture, which function is strictly the responsibility of the physical underlay network?

  1. Providing underlying IP connectivity to ensure reachability between fabric nodes.Answer
  2. B
    Encapsulating user data packets inside VXLAN headers for virtual network transport.
  3. C
    Maintaining the mapping database between Endpoint Identifiers (EIDs) and Routing Locators (RLOCs).
  4. D
    Enforcing role-based access control policies using Scalable Group Tags (SGTs).

Answer

Providing underlying IP connectivity to ensure reachability between fabric nodes.
The underlay network provides basic, robust Layer 3 unicast IP reachability between all fabric nodes (such as fabric edge switches and control plane nodes) using traditional routing protocols.

Step-by-Step Solution

1
Identify the primary definition of the underlay in software-defined network architectures.
The underlay is the physical infrastructure (switches, routers, links) and IGP routing protocols.
The underlay exists to establish basic Layer 3 IP reachability across all physical network devices.
2
Differentiate underlay transport from overlay fabric services.
Encapsulation (VXLAN), control plane mapping (LISP), and policy enforcement (Cisco TrustSec/SGTs) operate in the overlay built on top of the underlay.
Keeping transport functions in the underlay decouples physical topology from virtual fabric services.

Key Concept

SDN Underlay vs. Overlay Functionality
Estimated Time:45s
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Topics

Software-Defined Architectures: Overlay, Underlay, and Fabric

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