In a 3-tier network design consisting of core, aggregation, and access layers, the implementation of Virtual Switching Extension (VSX) at the core is considered a best practice when the aggregation layer functions primarily at Layer 3 with routing protocols like OSPF facilitating traffic forwarding between the core and aggregation layers. This design choice, as verified by Aruba Campus Access documents, leverages the high availability and redundancy features of VSX technology while maintaining efficient and scalable routing at the aggregation layer. Implementing VSX at the core in such a scenario ensures seamless failover and redundancy, minimizing the risk of downtime and ensuring consistent performance across the network. The core layer, equipped with VSX, provides a robust and resilient backbone for the network, facilitating efficient traffic management and routing decisions, which is critical for large-scale enterprise networks.