A network engineer receives a new router to use for WAN connectivity. Which of the following best describes the layer the network engineer should…

In the widely adopted three-tier hierarchical network model, the Core layer acts as the high-speed backbone, responsible for transporting large amounts of traffic quickly and reliably between different parts of the network. The WAN router, which serves as the gateway to external networks (like the internet or a private WAN), is a critical component of the network edge. This edge infrastructure connects directly to the Core layer. This design ensures that all devices on the network have a fast, centralized, and resilient path to the WAN, leveraging the high-speed switching capacity of the core.

A. Access: The access layer is the lowest tier in the hierarchy, designed to connect end-user devices (e.g., PCs, printers, IP phones) to the network.

C. Leaf: The leaf layer is specific to a spine-leaf data center architecture. While a WAN router connects to a "border leaf" in that design, it is not a layer in the more general three-tier campus model.

D. Spine: In a spine-leaf architecture, spine switches function as the fabric's backbone and exclusively connect to leaf switches, never directly to external routers or other devices.

1. Cisco Systems

Inc.

"Enterprise Campus 3.0 Architecture: Overview and Framework

" Nov 2008. In the section "Enterprise Campus Functional Areas

" Figure 1-3 explicitly shows the "Enterprise Edge" module

which contains WAN and Internet routers

connecting directly to the "Campus Core" module. This illustrates the standard design principle of connecting the WAN edge to the core backbone.

2. Juniper Networks

"Hierarchical Network Design

" TechLibrary. The document states

"The core layer is the backbone of the network and is responsible for high-speed packet switching... This layer is the interconnection point for the distribution layer and also for connecting to key resources such as the data center and the network edge for Internet or WAN connectivity."

3. Arista Networks

"Arista Design Guide: L3LS for the Data Center

" Section 2.1 "Spine-Leaf Overview." This document clarifies the roles in a spine-leaf topology

stating

"The spine layer serves as the backbone of the network... The leaf layer connects to all the spine switches... External L3 connectivity is achieved by connecting one or more routers or firewalls to the leaf switches." This confirms that 'Leaf' and 'Spine' are specific to this data center architecture and that spines do not connect to external routers.