Examkin

Question

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

A network operations team is reviewing the architectural layers of a newly deployed software-defined campus fabric. They need to ensure that the physical infrastructure properly supports endpoint encapsulation and tunneled communication across the fabric. Which of the following best describes the primary function of the underlay network in this software-defined architecture?

  1. Providing underlying physical IP connectivity and routing between fabric nodes using protocols like OSPF or IS-IS to transport overlay packetsAnswer
  2. B
    Encapsulating Layer 2 ethernet frames inside UDP datagrams to stretch subnets across Layer 3 boundaries
  3. C
    Maintaining the Endpoint Identifier (EID) to Routing Locator (RLOC) mapping database for fabric control plane lookups
  4. D
    Executing centralized data-plane forwarding decisions for all real-time user traffic traversing fabric switches

Answer

Providing underlying physical IP connectivity and routing between fabric nodes using protocols like OSPF or IS-IS to transport overlay packets
The correct option accurately identifies the underlay network's role: establishing baseline physical layer IP reachability and routing across switches using traditional routing protocols (e.g., OSPF, IS-IS), allowing overlay encapsulated packets to be transported between nodes.

Step-by-Step Solution

1
Identify the role of the Underlay layer in an SDN fabric
The underlay consists of physical switches, routers, cabling, and routing protocols responsible purely for point-to-point IP connectivity between nodes.
Without reliable IP reachability provided by the underlay, overlay tunneling protocols (such as VXLAN) cannot form tunnels between endpoints (VTEPs).
2
Distinguish Underlay responsibilities from Overlay responsibilities
The overlay handles network virtualization, encapsulation (e.g., VXLAN), and mapping (e.g., LISP), running on top of the underlay infrastructure.
Clear separation between underlay transport and overlay service delivery allows overlay networks to scale independently of the physical topology.

Key Concept

Underlay vs. Overlay in Software-Defined Architectures
Rate this question

Topics

Software-Defined Architectures: Overlay, Underlay, and Fabric

More questions from this topic