Anunderlay networkrefers to the physical or logical network infrastructure that provides the foundation for overlay networks in cloud environments. It handles the actual transport of data between devices and serves as the backbone for cloud architectures. Let’s analyze each statement:
A. An underlay network can be built using either Layer 2 or Layer 3 connectivity.
Correct:Underlay networks can operate at both Layer 2 (switching) and Layer 3 (routing). For example:
Layer 2:Uses Ethernet switching to forward traffic within a single broadcast domain.
Layer 3:Uses IP routing to forward traffic across multiple subnets or networks.
B. A Layer 3 underlay network uses routing protocols to provide IP connectivity.
Correct:In a Layer 3 underlay network, routing protocols like OSPF, BGP, or EIGRP are used to exchange routing information and ensure IP connectivity between devices. This is common in large-scale cloud environments where scalability and segmentation are critical.
C. The underlay network is the virtual network used to connect multiple virtual machines (VMs).
Incorrect:The underlay network is the physical or logical infrastructure that supports the overlay network. The overlay network, on the other hand, is the virtual network used to connect VMs, containers, or other endpoints. The underlay provides the foundation, while the overlay adds abstraction and flexibility.
D. The underlay network is built using encapsulations tunnels.
Incorrect:Encapsulation tunnels (e.g., VXLAN, GRE) are used in overlay networks, not underlay networks. The underlay network provides the physical or logical transport layer, while the overlay network uses tunnels to create virtualized network segments.
Why These Answers?
Layer 2 and Layer 3 Flexibility:The underlay network must support both switching and routing to accommodate diverse workloads and topologies.
Routing Protocols in Layer 3:Routing protocols are essential for scalable and efficient IP connectivity in Layer 3 underlay networks.
JNCIA Cloud References:
The JNCIA-Cloud certification covers underlay and overlay networks as part of its discussion on cloud architectures. Understanding the distinction between underlay and overlay networks is crucial for designing and managing cloud environments.
For example, Juniper Contrail uses an underlay network to provide the physical connectivity required for overlay networks. The underlay ensures reliable and scalable transport, while the overlay enables flexible virtualized networking.
[Reference:, Juniper JNCIA-Cloud Study Guide: Underlay and Overlay Networks, Network Virtualization Documentation, ]
