Data Center Networks
Data center networks cover the fabric that connects servers, storage, and network functions in cloud infrastructure. The exam tests leaf-spine design, EVPN-VXLAN overlays, Nokia 7250 IXR and SR Linux, and Nokia EDA automation, with attention to oversubscription and lossless traffic.
Fabric architecture
A Clos leaf-spine fabric provides predictable east-west capacity and ECMP paths. The underlay uses IP routing; the overlay uses EVPN for control-plane learning and VXLAN for data-plane encapsulation. SR Linux runs on Nokia data center switches and supports modern operational models. EDA provides event-driven automation for fabric lifecycle and intent. Lossless design for RoCE requires priority flow control, careful buffer tuning, and avoidance of PFC storms.
Rules to apply
- Oversubscription is a design choice; calculate it from downlink and uplink capacity.
- EVPN is the control plane; VXLAN is the data plane. Do not conflate them.
- ECMP requires entropy in the flow hash; otherwise traffic polarizes.
- RoCE needs lossless treatment, but PFC storms can spread congestion.
- Automation must validate fabric state before and after changes.
Worked example
A leaf has 48 × 25G server ports and 8 × 100G uplinks. Downlink capacity is 1.2 Tbps; uplink capacity is 800 Gbps; oversubscription is 1.5:1. For a storage fabric carrying RoCE, a 1.5:1 ratio may be acceptable if traffic is balanced, but a separate storage leaf-spine or a 1:1 design reduces congestion risk. The reasoning: oversubscription is a capacity ratio, while lossless behavior depends on buffering and flow control.
Traps that cost marks
Treating EVPN and VXLAN as the same thing; ignoring hash entropy; designing RoCE without PFC safeguards; and assuming automation removes the need for validation.