What is North-South traffic in networking?
Traffic flowing between clients/users and servers (into/out of the data center).
What is East-West traffic in networking?
Traffic flowing laterally between servers inside the data center.
Why has East-West traffic grown in modern networks?
Because of virtualization, clustering, and microservices where servers/VMs communicate heavily with each other.
What problem does East-West traffic create in traditional 3-tier networks?
Oversubscription: traffic must go up to the core and back down, wasting bandwidth and adding latency.
How does Spanning Tree impact East-West traffic in legacy designs?
STP blocks redundant paths, preventing full use of available bandwidth for server-to-server flows.
What modern design solves East-West traffic bottlenecks?
Leaf-Spine architecture with ECMP, which provides predictable 1–2 hop latency and all links active.
Exam key point: North-South vs East-West?
North-South = client-to-server, East-West = server-to-server; modern DCs use Leaf-Spine and ECMP for East-West scalability.
What are the three tiers in a traditional enterprise campus design?
Access, Distribution, Core.
What is the function of the access layer in a 3-tier design?
Provides user/device connectivity, implements edge security, and QoS trust boundaries.
What is the function of the distribution layer in a 3-tier design?
Provides policy enforcement, route summarization, and redundancy between access and core.
What is the function of the core layer in a 3-tier design?
Provides fast, reliable backbone switching with minimal policy enforcement.
What is the difference between a 2-tier (collapsed core) and 3-tier design?
2-tier collapses distribution and core into one layer; used in smaller networks for simplicity.
What is the advantage of leaf-spine architecture in data centers?
Predictable latency (1–2 hops), equal-cost multipath (ECMP), and high East-West bandwidth.
What is the Cisco Enterprise Architecture model?
It divides the enterprise into Campus, WAN, Branch, Data Center, Cloud, and Remote Worker modules.
What is the benefit of modular network design?
Scalability, ease of troubleshooting, and isolation of failures.
What are common high availability design principles?
Redundancy, fast convergence, resiliency, and load balancing.
What is controller-based networking?
A centralized control plane (e.g., Cisco DNA Center, SD-WAN) manages distributed data plane devices.
What is the difference between traditional and SDN architecture?
Traditional = distributed control plane; SDN = centralized control plane with APIs and programmability.
What is the role of overlays in network design?
Provide logical networks (e.g., VXLAN, GRE) on top of physical underlay, enabling flexibility and segmentation.
What is the difference between underlay and overlay?
Underlay = physical network providing connectivity; Overlay = logical network built on top.
What is the purpose of a WAN edge in enterprise design?
Connects the campus/branch to the WAN, Internet, or cloud with redundancy and security.
What is the benefit of hybrid cloud architecture?
Allows workloads to run across on-prem and public cloud, increasing flexibility and scalability.
What is the advantage of virtualization in network architecture?
Increases resource utilization, enables multi-tenancy, and allows rapid workload mobility.
