Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2VirtualizationMedium
A network architect is designing a virtualized data center environment where virtual machines (VMs) on different hypervisors need to communicate over a shared Layer 2 segment, but the underlying physical network is routed at Layer 3. Which data path virtualization technology is commonly used to extend Layer 2 domains over a Layer 3 underlay?
- AGRE
- BMPLS
- CVXLAN
- DOpenFlow
Show answer & explanationAnswer & explanation
Correct answer: C. VXLAN
VXLAN (Virtual eXtensible LAN) is a network virtualization encapsulation protocol that extends Layer 2 segments over an underlying Layer 3 network. It encapsulates Layer 2 Ethernet frames within UDP packets, allowing VMs on different hypervisors, even across different IP subnets, to communicate as if they were on the same Layer 2 segment.
Why the other options are wrong
- A. GRE is a general-purpose tunneling protocol but lacks the specific optimizations and control plane integrations of VXLAN for data center Layer 2 extension.
- B. MPLS is a forwarding mechanism that can be used for various services (like VPNs) but is not primarily designed for extending Layer 2 domains over a Layer 3 underlay for data center virtualization in the same way VXLAN is.
- D. OpenFlow is a protocol for SDN controllers to program network devices, not a data path encapsulation technology for Layer 2 extension.
VXLAN (Virtual eXtensible LAN)
A network virtualization encapsulation protocol that extends Layer 2 network segments over a Layer 3 IP network.
- Encapsulates Ethernet frames in UDP, typically on port 4789.
- Uses a 24-bit VXLAN Network Identifier (VNI) for scalability (up to 16 million segments).
- Enables large-scale multi-tenancy and VM mobility across Layer 3 boundaries.
Memory trick: VXLAN: Virtual eXtensible LANs bridge Layer 2 over Layer 3.