PlantUML DiagramCisco SD-WAN Architecture
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MPLS gives you low latency at high cost. Broadband gives you low cost at variable quality. What if you could use both, sending voice traffic over MPLS and bulk backups over broadband, with automatic failover if either path degrades? That's SD-WAN. It's not a new WAN technology — it's a new way of controlling the WAN you already have.
The economic argument is the strongest. Replacing two MPLS circuits per site with one MPLS plus one broadband cuts costs by 30-50% for the same performance. SD-WAN makes this viable by intelligently using both paths and providing the reliability that pure broadband alone can't guarantee.
Cisco's SD-WAN (Viptela) has three controller components. vManage is the web UI — where you configure policy and monitor the fabric. vBond is the orchestrator — the first device each new router contacts to authenticate and learn about the other controllers. vSmart is the brain — it holds routing and policy information and distributes it to the vEdge routers.
The data plane is separate from the control plane. Traffic between sites flows directly between vEdge routers over encrypted tunnels — it doesn't traverse the controllers. The controllers just tell the vEdges how to route and what policy to apply. This architecture scales because the controllers only handle control traffic, not user data.
The killer SD-WAN feature. Instead of routing by destination, SD-WAN routes by application. Voice traffic (identified by DPI or flow characteristics) goes over the path with the lowest jitter. Bulk backup traffic goes over the cheapest path. If a path degrades (packet loss above threshold, latency spikes), SD-WAN automatically re-routes the affected flows to a better path — within seconds.
A retail chain with 300 stores is spending 40% of its IT budget on MPLS. Each store has one MPLS circuit. Bandwidth is limited and adding circuits is expensive. The CFO wants to cut WAN costs without hurting the store experience. What's the SD-WAN pitch?
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SD-WAN isn't magic — it's centralized management plus intelligent path selection over transports you already have. The technical challenges (encryption, routing, failover) were all solvable before SD-WAN. What SD-WAN adds is making them configurable from one dashboard, at scale, with a consistent policy across hundreds of sites. That operational leverage is the real value.
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