A data center network supports a facility or dedicated space that centralizes servers, storage systems, and the network infrastructure connecting them. Large data centers may contain thousands of servers, storage devices, and network devices. section 15.3
Traditional data center networks use a three-tier design: access, aggregation, and core. A server group with its access and aggregation switches forms a pod. Virtual servers and distributed applications increased east–west traffic between servers, while north–south traffic enters or exits through the WAN or internet. Multiple-layer paths can create bottlenecks and unpredictable server-to-server latency. section 15.3.1
Figure 15.8 A three-tier data center LAN consisting of an access layer, aggregation layer, and core layer
Use the three-tier topology to identify access, aggregation, and core layers and understand how server traffic traverses the design. section 15.3.1
Spine-leaf architecture addresses modern east–west traffic with two layers: servers connect to leaf switches, every leaf connects to every spine, and leaf-to-leaf and spine-to-spine connections are absent. Leaf switches serving external networks may be called border leaves. section 15.5
