Virtual Extensible LAN (VXLAN):

  • VXLAN is the base of network virtualization which provides network overlay.
  • VXLAN encapsulates Ethernet frames on a UDP routable packet.
  • VXLAN provides extending a single L2 segment across L3 boundaries.
  • VXLAN also overcomes the VLAN limits.The 802.1q standard has a maximum of 4094 VLANs.
  • VXLAN overcomes this by maximum of 2^24 VNIs (VXLAN Network Identifier).

Overlay Architecture: NSX

  • The term “Overlay” refers to any virtual networks over any “underlay” network.  (Underlay refers to the physical network)
  • Virtual networks are created with a MAC-over-IP encapsulation with VXLAN.
  • The encapsulation allows two VMs on the same network to talk to each other even if the path between the VMs needs to be routed.
  • VXLAN modules operate in ESXi Hypervisor.
  • VTEPs encapsulate & de-capsulate network packets.
  • VTEP’s terminate VXLAN tunnels
  • Wrap UDP Packet Header around L2 packet
  • VXLAN Packet header includes VNI (VXLAN Network Identifier)
  • Manage by NSX Controllers
                  – ARP,VTEP,MAC tables
  • Encapsulated packets are forwarded between VTEPS over physical network like any other IP traffic.
  • VTEP is a host interface which forwards Ethernet frames from a virtual network via VXLAN or vice-versa.
  • ll hosts with the same VNI configured must be able to retrieve and synchronize data (ARP & MAC tables).

MTU Considerations:
VXLAN is an overlay technology which uses encapsulation; the MTU needs to be adjusted.
VXLAN adds 50 bytes of overhaed to the header.
The entire underlay path needs to be configured to support the MTU requirment of the VXLAN.

  • IPv4 Header – 20 bytes
  • UDP Header – 8 bytes
  • VXLAN Header – 8 bytes
  • Original Ethernet Header with VLAN – 18 bytes
  • Original Ethernet Payload – 1500 bytes

Total = 1554 bytes

  • VMware recommends having the MTU value to be set as 1600 bytes.