VXLAN – Overlay protocol


In my last blogpost, I elaborated on EVPN as the next-generation datacenter interconnect. Within datacenter interconnect, VXLAN works as an overlay protocol. What is VXLAN and what application areas are there?  In this blog, I will give you the answers to those questions.

VXLAN stands for Virtual Extensible LAN. VXLAN is an encapsulation technique in which layer 2 ethernet frames are encapsulated in UDP packets. VXLAN is a network virtualization technology. When devices communicate within a Software Defined Datacenter, a VXLAN tunnel is set up between those devices. Those tunnels can be set up on both physical and virtual switches. The switch ports are known as VXLAN Tunnel EndPoints (VTEPs) and are responsible for the encapsulation and de-encapsulation of VXLAN packets. Devices without VXLAN support are connected to a switch with VTEP functionality. The switch will provide the conversion from and to VXLAN.

The different VXLAN networks are provided with a VXLAN Network Identifier. This VNI number is similar to a VLAN ID. The VNI identifies the layer 2 Ethernet frame segment. Virtual machines that are linked to each other by the VNI are able to communicate with each other on layer 2.

Underlay Network

In a Software Defined Data Center we use an underlay- and overlay network. VXLAN is a technique that is used in an overlay network. So, there is also an underlay network next to the overlay network. The various components are connected with each other in a Software Defined Data Center in an underlay network. This underlay network may be a L2 or L3 network and it is used to connect the various components to each other. The VXLAN tunnels are set up on top of the underlay network. Modern data centers are also often equipped with a reliable and scalable L3 clos architecture on which the VXLAN tunnels can be transported.

Since the current L2 Ethernet frames are encapsulated in a UDP frame, and thus overhead is added, it is of great importance that the MTU of the underlay is adjusted to 1600 instead of the standard MTU. Without this adjustment VXLAN cannot function.

Which problem does VXLAN solve?

VXLAN is a technique that occurs in two application areas. The technique is used within the Software Defined Data Center and within data center interconnects. VXLAN has several important advantages:

  • VXLAN uses 24-bit VNIs. Thus, it is possible to define 16 million different VNIs. This ensures that the technique is more scalable compared to 802.1q with a maximum number of 4096 VLANs;
  • The solution is ideal for a multi-tenant environment. Through the use of VXLAN, the same IP-series can be used in various VNIs;
  • By using network virtualization and an underlay network, it is possible to carry out all network adaptations quickly from the software without having to adjust all physical network components;
  • With VXLAN, layer 2 networks can be stretched across L3 underlay networks

By using network virtualization in combination with VXLAN, scalable, multi-tenant networks can be built which makes VXLAN a vital link in the Software Defined Data Center.