Overlay Networking withVXLAN
Frankie Lim @ Arista.com

Needs for an Overlay Networks
Logical Network (aka “Overlay” Network)
§ NetworkVirtualization (SDN)
§ Abstracts the virtualized environment form
the physical topology
§ Constructs Layer 2 tunnels across the physical
infrastructure
§ Tunnels provide connectivity between physical
and virtual end-points
Physical Network (aka “Underlay” Network)
§ Transparent to the overlay technology
§ Allows the building of L3 infrastructure – No L2
§ Physical provide the bandwidth and scale for the
communication
§ Removes the scaling constraints of the physical
from the virtual
Physical Infrastructure
Overlay
Networks

Introducing VXLAN (RFC 7348)
Virtual eXtensible LAN (VXLAN RFC 7348)
§ IETF framework proposal, co-authored by Arista, Broadcom,
Cisco, Citrix Red Hat &VMware
Provides Layer 2 “Overlay Networks” on top of a Layer 3
network
§ “MAC in IP” Encapsulation
§ Layer 2 multi-point tunneling over IP UDP
Tunnel End-Points (VTEPs) perform encapsulation/decapsulation
§ In Software e.g. Hypervisor vSwitch
§ In Hardware e.g. Leaf Switches
Enables Layer 2 interconnection across Layer 3 boundaries
§ Transparent to the physical IP network
§ Provides Layer 2 scale across the Layer 3 IP fabric
§ Abstracts theVirtual connectivity from the physical IP
infrastructure
§ e.g. EnablesVMotion, L2 clusters etc. across standards based
IP fabrics
VM-1
10.10.10.1/24
VM-2
20.20.20.1/24
VM-3
10.10.10.2/24
VM-4
20.20.20.2/24
ESX host
ESX host
Subnet A
Layer 2 (e.g. forVM mobility,
storage access, clustering etc.)
Across Layer 3 subnets
NAS
20.20.20.324
Load Balancer
10.10.10.3/24
Subnet B

VXLAN Terminology
Virtual Tunnel End-point (VTEP)
§ Performs for VXLAN encapsulation & decapsulation of the
native frame
§ Adds the the appropriate VXLAN header.
§ Can be implemented on software virtual switch or a physical
switch.
Virtual Tunnel Identifier (VTI)
§ An IP interface used as the Source IP address for the
encapsulatedVXLAN traffic
§ The destination IP address forVXLAN encapsulated traffic
Virtual Network Identifier (VNI)
§ A 24-bit field added within theVXLAN header.
§ Identifies the Layer 2 segment of the encapsulated Ethernet
frame
VXLAN Header
§ The IP/UDP VXLAN header added by theVTEP
§ Uses a UDP source port based on a hash of the inner frame
to create entropy for ECMP
Software
VTEP
Hardware