Overview
This lecture covers the core concepts of software-defined networking (SDN) with a focus on Cisco's SD-Access architecture, including key terms such as underlay, overlay, fabric, DNA Center, and how SD-Access compares to traditional network management.
SDN Fundamentals
- SDN centralizes the control plane in a controller, unlike traditional networks where control is distributed across devices.
- SDN controllers use southbound APIs to interact with network devices and northbound APIs for application integration.
- SDN architecture consists of three layers: application (apps/scripts), control (the controller), and infrastructure (network devices).
Cisco SD-Access Overview
- SD-Access automates campus LANs using SDN principles, with DNA Center as the main controller.
- The SD-Access fabric includes both physical (underlay) and virtual (overlay) network layers.
- Underlay provides IP connectivity using protocols (e.g., IS-IS), while overlay uses VXLAN tunnels for virtual networking.
Terms: Underlay, Overlay, and Fabric
- Underlay: The physical network of devices and connections that provide base connectivity.
- Overlay: The virtual network built on top of the underlay, enabling features like VXLAN tunnels.
- Fabric: The combination of underlay and overlay, forming the complete SD-Access environment.
SD-Access Device Roles and Protocols
- Edge nodes connect to end hosts.
- Border nodes connect the SD-Access domain to external networks.
- Control nodes manage the control plane, often using LISP (Locator ID Separation Protocol).
- VXLAN is used for data-plane tunneling; LISP is used for control-plane mapping (EID to RLOC).
- Cisco TrustSec (CTS) provides policy and security controls in the overlay.
SD-Access Deployment Types
- Greenfield deployment: New networks built for SD-Access, fully managed by DNA Center.
- Brownfield deployment: SD-Access added to existing networks; DNA Center may not manage underlay to avoid disruption.
DNA Center Features in SD-Access
- DNA Center provides central policy management, device provisioning, network assurance, and compliance monitoring.
- Intent-based networking allows specifying network policies and behaviors without manual per-device configuration.
- Policies can be group-based, with explanations for each rule to clarify network intent.
- Software and device compliance can be centrally monitored and enforced.
DNA Center vs. Traditional Network Management
- Traditional: Devices configured individually via SSH/console; no central policy or software management; higher risk of errors and longer deployment times.
- DNA Center: Central configuration and monitoring; automatic policy and software updates; reduced manual errors and faster deployments.
Key Terms & Definitions
- SDN (Software-Defined Networking) — Networking with a centralized control plane managed by a controller.
- DNA Center — Cisco’s SDN controller and management platform for SD-Access.
- Underlay — The physical network layer providing basic connectivity.
- Overlay — The virtual network layer built on top of the underlay, often using VXLAN.
- Fabric — The combined underlay and overlay network in SD-Access.
- Edge Node — Switch connecting to end hosts.
- Border Node — Switch connecting to external networks.
- Control Node — Switch handling control-plane functions (LISP).
- LISP (Locator ID Separation Protocol) — Protocol for mapping host addresses to switch locations.
- VXLAN (Virtual Extensible LAN) — Protocol for overlay tunneling in SD-Access.
- Cisco TrustSec (CTS) — Provides policy and security in the SD-Access overlay.
- Intent-Based Networking — Defining network behavior by intent rather than manual configuration.
Action Items / Next Steps
- Review differences between underlay, overlay, and fabric concepts.
- Ensure understanding of edge, border, and control node roles.
- Explore DNA Center features and practice configuring policies if possible (e.g., via DevNet sandbox).
- Compare traditional vs. DNA Center-enabled network management for exam prep.