Cisco Nexus vPC, VXLAN Overlay & BGP EVPN Flow

What is Cisco Nexus vPC, VXLAN & BGP EVPN?

Modern Cisco Data Center architectures combine Virtual Port Channel (vPC) for physical link redundancy at the Leaf layer with VXLAN (Virtual Extensible LAN) and BGP EVPN (Ethernet VPN) to build scalable, multi-tenant overlay networks over a Layer 3 Spine-Leaf IP fabric.

Core Fabric Components & Architecture

• Virtual Port Channel (vPC): Allows links connected to two distinct Cisco Nexus switches to appear as a single Port Channel to a downstream server or switch, eliminating Spanning Tree Protocol (STP) blocked ports.
• vPC Peer-Keepalive & Peer-Link: Out-of-band link tracks peer health to prevent split-brain scenarios, while the Peer-Link synchronizes control state (CFSo), MAC tables, and IGMP snooping.
• VXLAN Overlay (NVE Interface): Encapsulates Layer 2 Ethernet frames into Layer 3 UDP packets (Port 4789), allowing L2 networks to extend across L3 boundaries using 24-bit VXLAN Network Identifiers (VNIs).
• BGP EVPN Control Plane: Distributes MAC and IP host reachability information using MP-BGP (Type-2 MAC/IP routes and Type-5 IP Prefix routes), removing the need for flood-and-learn data-plane replication.

Key NX-OS Terminology

• VTEP (VXLAN Tunnel End Point): Nexus switch entity that performs VXLAN encapsulation and decapsulation.
• Anycast Gateway: Identical default gateway IP/MAC configured across all Leaf VTEPs using SVI with Distributed Anycast Gateway for seamless VM mobility.
• Orphan Ports: Single-homed devices attached to only one vPC peer switch.