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

Match each Cisco Software-Defined Access (SD-Access) architectural component or protocol on the left with its primary function on the right.

  • Underlay NetworkProvides physical IP reachability and unicast transport between fabric nodes using an Interior Gateway Protocol (IGP).
  • Overlay NetworkEstablishes a virtualized logical topology over physical infrastructure to transport encapsulated user traffic.
  • Fabric Control Plane (LISP)Maintains the fabric mapping database that resolves Endpoint Identifiers (EIDs) to Routing Locators (RLOCs).
  • Fabric Data Plane (VXLAN)Encapsulates Layer 2 Ethernet frames into outer IP/UDP packets for transport across the physical infrastructure.

Answer

Underlay Network matches physical IP reachability using an IGP; Overlay Network matches establishing a virtualized logical topology; Fabric Control Plane (LISP) matches maintaining the EID-to-RLOC mapping database; Fabric Data Plane (VXLAN) matches encapsulating frames into IP/UDP packets.
In Cisco SD-Access fabric architecture, the underlay network handles physical IP routing via an IGP. The overlay network creates the virtualized logical topology on top of the underlay. LISP operates as the control plane mapping protocol (matching EIDs to RLOCs), and VXLAN functions as the data plane protocol (encapsulating Ethernet frames in UDP packets).

Step-by-Step Solution

1
Identify the foundation layer responsible for physical interconnectivity.
The underlay network provides basic unicast IP routing between fabric nodes using traditional protocols like IS-IS or OSPF.
Physical IP reachability is required before any tunneled overlay transport can occur.
2
Identify the logical transport layer created on top of physical infrastructure.
The overlay network represents the virtualized logical fabric carrying user endpoints.
Overlays decouple endpoint addressing and policies from physical network location.
3
Differentiate between control plane mapping and data plane encapsulation functions in SD-Access.
LISP tracks location mapping (EID to RLOC), while VXLAN encapsulates user frames inside UDP packets.
LISP provides lightweight control plane lookups, whereas VXLAN enables flexible Layer 2 and Layer 3 overlay encapsulation over a Layer 3 underlay.

Key Concept

Software-Defined Access Fabric Architecture (Underlay, Overlay, LISP Control Plane, VXLAN Data Plane)
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Topics

Software-Defined Architectures: Overlay, Underlay, and Fabric

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