July 2018 · Estimated Reading Time: 12 minutes
This is the second part of our deep dive series on SD-WAN. If you missed Part 1, where we covered overlay models, hardware footprints, and operational architectures, you can read it here. In this post, we shift our focus from architecture to implementation.
Routing Strategy and Policy Design
Modern SD-WAN solutions replace static route tables with dynamic, policy-based routing engines. Enterprises define application-driven policies—by DSCP, port, or even packet signatures—allowing real-time steering across underlay links. Some controllers allow nested policies that cascade across edge sites, enabling location-aware routing decisions.
QoS and Traffic Classification
SD-WAN vendors implement built-in QoS engines. They offer packet inspection, flow tracking, and bandwidth shaping. Traffic classification integrates with business policies, identifying mission-critical flows (like VoIP or ERP) and guaranteeing their performance. Marking packets at the edge and preserving DSCP across tunnels ensures end-to-end integrity.
Failover and High Availability Design
Failover mechanisms rely on link probing, jitter analysis, and SLA monitoring. Architectures now default to active-active link usage with seamless failover, using loss/jitter thresholds to trigger flow redirection. Hybrid setups (fiber + LTE) also rise as backup options. Multi-edge redundancy is handled via edge clustering or standby appliances.
Internet Breakout Models
Breakout design is a hot topic. Enterprises balance centralized vs distributed internet access. DIA (Direct Internet Access) at branches reduces latency for SaaS apps, but brings security concerns. Most deployments implement secure DIA using cloud-based SWG (Secure Web Gateway) or firewall-as-a-service (FWaaS) partners.
Security Policy Enforcement
Edge-to-edge tunnels provide encryption, but policy enforcement varies. Integrated NGFWs or service chaining to third-party firewalls (e.g., Palo Alto, Zscaler) helps bridge the security gap. More vendors embed URL filtering, malware protection, and DNS enforcement natively at the edge.
Orchestration and Change Management
SD-WAN orchestration platforms provide centralized push-based configuration, often via GUI or API. Policy rollouts include pre-checks, versioning, and staged rollouts. Some even allow intent-based change validation using digital twins or simulation. This minimizes outage risk during policy updates.
Lessons from Field Deployments
We see common implementation challenges: misaligned SLA thresholds, overzealous application definitions, and controller overload during failovers. Best practices include building test topologies, tuning telemetry thresholds, and incrementally introducing breakout policies with failback options.
Transition to Part 3
In our upcoming Part 3, we’ll dive into monitoring and optimization. Expect coverage on telemetry frameworks, anomaly detection, analytics, and ongoing tuning strategies.