What is vni in vxlan

Overview

VNI (VXLAN Network Identifier) is a crucial component of VXLAN (Virtual Extensible LAN) technology that enables network virtualization and overlay networking. The VNI is a 24-bit numerical identifier embedded in VXLAN packet headers that defines which virtual network a data frame belongs to. This mechanism allows administrators to create multiple isolated virtual networks that exist independently across physical network infrastructure, enabling flexible network topology management and large-scale network virtualization without modifying underlying hardware.

How VNI Works

When a packet is transmitted in a VXLAN environment, the source VXLAN tunnel endpoint (VTEP) encapsulates the original Ethernet frame within a VXLAN header. This header includes the VNI field that identifies which virtual network the traffic belongs to. The encapsulated packet is then sent over the physical network to the destination VTEP. At the destination, the VTEP decapsulates the packet and forwards it to the appropriate virtual network segment based on the VNI. The VNI essentially acts as a virtual network membership identifier.

VNI vs. VLAN Comparison

Scalability: VNI supports 16 million identifiers versus VLAN's 4,096. Scope: VLANs are limited to local network segments, while VNI-based networks span across wide area networks and cloud infrastructures. Encapsulation: VNI operates at Layer 3, allowing it to traverse IP networks without modification, while VLANs operate at Layer 2. Flexibility: VNI enables network architects to design more complex multi-tenant and cloud-ready architectures without physical network constraints.

Multi-Tenancy and Network Isolation

VNI is fundamental to multi-tenant cloud environments. Different tenants or business units can be assigned unique VNIs, ensuring complete network isolation. A tenant's traffic carrying one VNI will never be mixed with traffic from another tenant's VNI, even if both traverse the same physical network infrastructure. This architectural model enables cloud providers to support thousands of isolated customer networks on shared data center hardware.

Implementation in Modern Infrastructure

VXLAN with VNI is widely implemented in cloud platforms, container orchestration systems like Kubernetes, and modern data center networks. Software-defined networking controllers assign and manage VNI allocation, while network virtualization hardware accelerates VXLAN processing. Major infrastructure vendors including Cisco, Arista, Juniper, and open-source projects support VXLAN VNI-based networking as a core virtualization technology.