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Zorluk: OrtaSoftware-Defined Architectures: Overlay, Underlay, and Fabric

An network operations team is verifying traffic delivery across a Cisco Software-Defined Access (SD-Access) fabric infrastructure. The physical underlay network is configured using an Interior Gateway Protocol (IGP) to ensure full IP reachability between all switch loopback interfaces. Which statement accurately describes the primary function of the fabric control plane when an ingress fabric edge switch needs to forward overlay traffic to a remote host?

  1. It uses Locator/ID Separation Protocol (LISP) mapping database lookups to correlate destination host Endpoint Identifiers (EIDs) with egress switch Routing Locators (RLOCs).Cevap
  2. B
    It relies on intermediate underlay routers running OSPF to inspect VXLAN inner headers and dynamically recalculate physical forwarding paths for every host IP address.
  3. C
    It issues synchronous REST API calls to the centralized controller for every data packet to retrieve real-time data-plane forwarding decisions.
  4. D
    It utilizes RADIUS authentication messages encapsulated within GRE tunnels to dynamically rebuild Layer 2 VLAN trunking links across underlay switches.

Cevap

The fabric control plane uses Locator/ID Separation Protocol (LISP) mapping database lookups to correlate destination host Endpoint Identifiers (EIDs) with egress switch Routing Locators (RLOCs).
In a Cisco SD-Access fabric architecture, the control plane relies on Locator/ID Separation Protocol (LISP). LISP separates device identity (Endpoint Identifier or EID) from physical location (Routing Locator or RLOC). When an ingress fabric edge switch receives a frame destined for an overlay endpoint, it queries the LISP mapping database to locate the destination host's RLOC (the IP address of the egress fabric edge device), allowing VXLAN encapsulation to transport the payload across the underlay.

Adım Adım Çözüm

1
Identify the separation of roles between underlay and overlay in Software-Defined Access (SD-Access).
The underlay provides basic IP reachability between network nodes (RLOCs), while the overlay manages host traffic (EIDs) encapsulated in VXLAN.
SD-Access separates host identity from host location to enable mobility and fabric scale.
2
Determine the control plane protocol responsible for host location mapping.
LISP serves as the control plane protocol operating on the Control Plane node (Map-Server/Map-Resolver).
When a fabric edge switch receives traffic for a destination host EID, it queries the LISP map-server to discover the IP address of the egress fabric edge switch (RLOC).
3
Select the option that correctly describes the LISP EID-to-RLOC mapping function.
The statement describing LISP mapping destination host EIDs to egress switch RLOCs is correct.
This process enables the ingress edge switch to encapsulate the packet in VXLAN addressed to the correct destination RLOC.

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Software-Defined Architectures: Fabric Control Plane LISP EID-to-RLOC Mapping
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Software-Defined Architectures: Overlay, Underlay, and Fabric

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