Traditional data centers use a -tier architecture: core, aggregation, and access layers.
Access layer. Top-of-rack switches connect servers at or Gbps.
Aggregation layer. Aggregates traffic from access switches. Handles VLANs and routing.
Core layer. Routes traffic between aggregation blocks and external networks.
Problems:
- Spanning tree blocks redundant links
- Server-to-server traffic takes inefficient paths
- Adding capacity means upgrading core switches
- East-west traffic must traverse multiple layers