What is the characteristic benefit of a routed ToR design?

• A. Top‑of‑Rack switches perform L3 routing to aggregation; reduces L2 fault domain.
• B. All switches operate at L2, with no routing at ToR.
• C. ToR has no direct connection to aggregation.
• D. Routing happens only at the core, not at ToR.

Answer: (A)

In a routed ToR design, the edge switches at the rack carry Layer 3 routing for traffic leaving the rack. Servers connect to the ToR using L2, but the ToR forwards inter-rack and outbound traffic through L3 routing toward the aggregation layer. This confines the L2 domain to the rack level, rather than letting L2 span across the entire data center.

That containment of the L2 domain is the key benefit: smaller L2 fault domains make failures easier to isolate, reduce broadcast and flood traffic, and improve scalability as you add racks. Routing at the ToR also supports better multi-tenant segmentation and more predictable performance since routing decisions are made at the edge rather than across a large flat L2 network.

Choosing this approach aligns with the idea that ToR switches perform L3 routing to aggregation, which directly leads to the reduced size of the L2 fault domain. If all switches operated at L2, the fault domain would be larger and more susceptible to broadcast-related issues. If the ToR had no direct connection to aggregation, there’d be no path beyond the rack. If routing happened only at the core, edge routing advantages would be lost.