Replacing legacy Spanning Tree Protocol (STP) three-tier architectures with 2-tier Clos leaf-spine fabrics enables horizontal scalability, non-blocking East-West throughput, and multi-tenant virtualization.
1. Core Tenets of Clos Leaf-Spine Architecture
- Equal-Cost Multi-Path (ECMP): Layer 3 IP routing between every Leaf and Spine switch allows traffic to load-balance across all uplinks simultaneously without blocked ports.
- VXLAN Encapsulation (RFC 7348): Encapsulating Layer 2 Ethernet frames into Layer 3 UDP packets (port 4789) expands VLAN limitations from 4,096 to 16 million Virtual Network Identifiers (VNIs).
- BGP-EVPN (RFC 7432): Serves as the standardized control plane, eliminating data plane flood-and-learn mechanisms through distributed MAC/IP route advertisements.