VNIs

VNIs most commonly refer to VXLAN Network Identifiers, a key concept in network virtualization. In this context, a VNI is a 24-bit value used to label a logical overlay network within a VXLAN (Virtual Extensible LAN) that tunnels Layer 2 traffic over an IP network. Each VNI represents a separate virtual network segment, allowing many isolated networks to coexist on the same underlay infrastructure. The term VNIs can also appear in other contexts, such as referring to virtual network interfaces in virtualization platforms, but in contemporary data centers it is most often connected to VXLAN.

In VXLAN, traffic between virtual machines on different hosts is encapsulated in UDP packets and sent to VXLAN Tunnel Endpoints (VTEPs). The VXLAN header carries the VNI, which identifies the overlay segment to which the inner Ethernet frame belongs. A typical VXLAN deployment uses UDP port 4789, with the VNI enabling scalable segmentation beyond traditional VLAN limits. Control planes for VNIs, such as EVPN-based approaches, advertise MAC and IP reachability across VTEPs, enabling seamless host mobility and multi-tenant isolation.

Practical considerations include MTU management due to encapsulation overhead, ensuring sufficient path MTU, and planning VNI allocation to avoid overlap across tenants or applications. VNIs are commonly configured in data centers to support large-scale virtualization, cloud services, and multi-tenant environments, enabling flexible network provisioning while maintaining isolation and consistent addressing across the underlay network.