Blog Post

What is VX-LAN (Virtual Extensible LAN)?

VX-LAN is an encapsulation protocol that provides data center connectivity using tunnelling to stretch Layer 2 connections over an underlying Layer 3 network.

How does VX-LAN work in DATA CENTER?

VXLAN is an overlay technology It allows Layer-2 connection or Layer-2 traffic flow over the Layer-3 network by encapsulating an L-2 Ethernet frame in the VXLAN packet that includes IP Address and Mac Address

The devices who support VXLAN we call them as a VTEP’s (virtual tunnel end points) and these VTEP’s are responsible to encapsulate and decapsulate the VXLAN traffic. this encapsulation starts when the traffic flows from one end tunnel to another end tunnel. This VTEP’s create a tunnel in between the sender and receiver.

To encapsulate the original ethernet frame it adds some of the fields like:

• Outer MAC address [Destination media access control address of the tunnel endpoint VTEP]
• Outer source Mac address [Source MAC address of the tunnel VTEP]
• Outer destination IP address [Destination IP address of the tunnel endpoint VTEP]
• Outer source IP address [Source IP address of the tunnel VTEP]
• Outer UDP header [UDP Port no.4789]

A VXLAN header that is having a 24-bit field called the VXLAN network Identifier (VNI) that is used to uniquely identify the VXLAN. The VNI is the same as a VLAN ID but having 24 bits allows you to produce 16 million VXLANs over the 4096 VLANs.

VX-LAN Encapsulation Packet Header

The Main things we need to learn to understand the VX-LAX concept:

• VTEP (Virtual Tunnel End Points)
• VNI (VX-LAN Network Identifier)

VXLAN Tunnel Endpoint

• VXLAN uses the VXLAN tunnel endpoint (VTEP) to map tenant’s end devices to VXLAN segments and to perform VXLAN encapsulation and decapsulation. Each VTEP function has two interfaces: 1 is a switch interface on the local LAN segment to support local endpoint communication, and 2 is an IP interface to the transport IP network.
• The Infrastructure VLAN is a unique IP address that identifies the VTEP devices on the transport IP network. The VTEP device uses this IP address to encapsulate the Ethernet frames and transmits the encapsulated packets to the transport network through the IP Interface.
• A VTEP device also discovers the remote VTEP’s for its VX-LAN segments and learns remote MAC Addresses to VTEP mappings through its IP interfaces.

• The VX-LAN segments are independent of the underlying network topology, on the other hand, the underlying IP network between VTEP’s is independent of the VXLAN overlay. It directs the encapsulated packets based on the outer IP address, which has the starting VTEP as the source IP address and the terminating VTEP as the destination IP address.

Virtual Network Identifier

A virtual network identifier [VNI] is a field in the VX-Lan header that Identifies a specific virtual network in a data plane. It is typically a 24–bit value part of the VX-LAN header, which can support up to 16 million individual network segments. [Valid VNI values are starting from 4096 to 16,777,215].

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Author
D. Madhukar
Associate Consultant