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

A network engineer is auditing a campus software-defined fabric infrastructure. During a traffic flow trace between two endpoints residing in different subnets, the engineer notes that the ingress fabric edge switch must resolve the location of a remote Endpoint Identifier (EID) to a destination Routing Locator (RLOC) IP address before encapsulating the frame. Which protocol and architectural layer are directly responsible for maintaining and querying this mapping database?

  1. Locator/ID Separation Protocol (LISP) operating at the fabric control plane layerAnswer
  2. B
    Virtual Extensible LAN (VXLAN) operating at the underlay data plane layer
  3. C
    Open Shortest Path First (OSPF) operating at the overlay control plane layer
  4. D
    Border Gateway Protocol (BGP) EVPN operating at the physical underlay transport layer

Answer

Locator/ID Separation Protocol (LISP) operating at the fabric control plane layer
The correct answer identifies LISP at the fabric control plane layer. In Cisco SD-Access fabric architectures, LISP acts as the control plane tracking system. It maintains a database mapping host addresses (Endpoint Identifiers or EIDs) to the IP addresses of the edge switches to which they are attached (Routing Locators or RLOCs).

Step-by-Step Solution

1
Identify the requirement in the scenario
The scenario describes looking up an Endpoint Identifier (EID) to find its corresponding Routing Locator (RLOC) IP address.
Before an ingress fabric edge switch can encapsulate customer traffic into VXLAN headers, it must query the mapping database to identify the remote edge node where the target destination host is currently registered.
2
Map the operation to the SDN architectural component
LISP serves as the control plane protocol that manages the map-server/map-resolver database in SD-Access fabrics.
LISP separates endpoint identity (EID) from network location (RLOC), allowing efficient lookup and tracking of host mobility across the fabric overlay.
3
Differentiate control plane, overlay data plane, and underlay transport
The control plane handles EID-to-RLOC mappings (LISP), the overlay data plane handles packet encapsulation (VXLAN), and the underlay transport handles physical IP routing (OSPF/IS-IS).
Understanding the distinct separation of duties prevents misattributing control database functions to data plane encapsulation or underlay routing protocols.

Key Concept

Separation of Underlay Routing, Overlay Encapsulation, and Fabric Control Plane Mapping in Software-Defined Architectures
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Topics

Software-Defined Architectures: Overlay, Underlay, and Fabric

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