PlantUML DiagramSD-Access Architecture
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That's the traditional way — configuring each port, each switch, individually. Multiply by 500 switches and 20,000 ports, and you have a configuration management problem that no team can scale. SDN changes the model: instead of configuring devices, you describe intent, and a controller translates that intent into device configurations.
| Plane | What it does | Where it lives traditionally |
|---|---|---|
| Management plane | Configuration, monitoring, policy input | CLI on each device |
| Control plane | Route computation, topology awareness | CPU on each device |
| Data plane | Packet forwarding | ASIC on each device |
Traditional networking runs all three planes on every device. SDN centralizes the control plane (and often the management plane) in a controller. The data plane stays distributed on devices — they still forward packets — but they no longer compute routes or topologies. The controller does that.
Cisco SD-Access uses a fabric architecture with three underlay/overlay components. The underlay is IS-IS routing between switches. The overlay is VXLAN — user traffic is encapsulated in VXLAN tunnels between edge nodes. The control plane is LISP — endpoints register with the control plane node, which maintains a mapping of 'where is 10.10.10.5'.
The magic of SD-Access: an endpoint's location becomes decoupled from its IP address. A user can move from one floor to another, plug into a different switch, and keep the same IP — the fabric routes their traffic to wherever they are. This eliminates the traditional VLAN-everywhere problem and enables true mobility.
Security Group Tags (SGTs) are the SD-Access answer to ACL complexity. Instead of maintaining ACLs per device, you classify traffic with tags (e.g. 'Employee', 'Guest', 'IoT') and define policy once at the DNA Center level. The fabric enforces it everywhere. Move a device between floors — its tag follows it, so its policy follows it.
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