This low level design document proposes migrating A CUSTOMER's core network infrastructure to new Cisco Catalyst 4500-X and Nexus 5000 series switches. The design involves a two-phased approach, beginning with replacing the existing Catalyst 6509 core switches with a Virtual Switching System (VSS) using two Catalyst 4500-X switches. In phase two, two Nexus 5548-UP switches will be configured as a virtual Port Channel (vPC) pair and connected to the new core and existing FlexPod server infrastructure. Standard practices for layer 2 and 3 protocols are also defined to maintain consistency across the new network design.