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

An enterprise network engineer is designing a software-defined fabric infrastructure using Cisco SD-Access concepts. The design requires establishing IP reachability between physical switches, encapsulating tenant traffic across the fabric, and maintaining a dynamic endpoint location database. Which two statements accurately describe the operational responsibilities of the underlay and overlay network components in this architecture?

  1. The underlay network relies on interior gateway protocols such as IS-IS or OSPF to provide IP connectivity between fabric node loopback addresses (RLOCs).Cevap
  2. The overlay data plane uses VXLAN encapsulation to transport Layer 2 Ethernet frames and Layer 3 IP packets over the Layer 3 underlay infrastructure.Cevap
  3. C
    The overlay network is responsible for configuring physical port speed, duplex, and MTU settings across intermediate transport switches.
  4. D
    The underlay control plane uses LISP mapping tables to map endpoint IDs (EIDs) directly to MAC address tables on access layer switches.
  5. E
    The overlay control plane directly terminates physical 802.1Q VLAN trunks between core and distribution switches to eliminate Spanning Tree Protocol dependency.

Cevap

The underlay network relies on interior gateway protocols such as IS-IS or OSPF to provide IP connectivity between fabric node loopback addresses, and the overlay data plane uses VXLAN encapsulation to transport Layer 2 Ethernet frames and Layer 3 IP packets over the Layer 3 underlay infrastructure.
In software-defined campus fabric architectures like Cisco SD-Access, the underlay consists of physical switches and routers configured with a Layer 3 routing protocol (such as IS-IS or OSPF) to ensure complete IP reachability between fabric nodes (Routing Locators / RLOCs). The overlay network abstracts virtual networks above this underlay; specifically, the overlay data plane utilizes Virtual Extensible LAN (VXLAN) encapsulation to encapsulate Layer 2 Ethernet frames and Layer 3 IP packets inside UDP packets, forwarding them across the Layer 3 underlay.

Adım Adım Çözüm

1
Analyze the underlay network responsibilities.
Identified that the underlay provides physical Layer 3 IP reachability between fabric nodes (RLOCs) using standard routing protocols like IS-IS or OSPF.
Overlay encapsulation (VXLAN) requires underlying IP connectivity between tunnel endpoints.
2
Analyze the overlay network data plane responsibilities.
Identified that VXLAN encapsulates original host frames with a UDP outer header to carry Layer 2/3 traffic across the routed underlay.
Overlay encapsulation decouples host connectivity and virtual networks from the underlying physical topology.
3
Evaluate and eliminate incorrect distractor options.
Disqualified options that misattribute physical port attributes to the overlay, confuse LISP control plane functionality with underlay routing, or misidentify trunking mechanics.
Clear functional separation exists: underlay manages physical reachability, overlay manages virtual encapsulation and endpoint mapping.

Anahtar Kavram

Software-Defined Architecture Component Separation (Underlay vs. Overlay)
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Software-Defined Architectures: Overlay, Underlay, and Fabric

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