1. Introduction
Server virtualization has placed increased demands on the physical network infrastructure. A physical server now has multiple Virtual Machines (VMs) each with its own Media Access Control (MAC) address. This requires larger MAC address tables in the switched Ethernet network due to potential attachment of and communication among hundreds of thousands of VMs.
In the case when the VMs in a data center are grouped according to their Virtual LAN (VLAN), one might need thousands of VLANs to partition the traffic according to the specific group to which the VM may belong. The current VLAN limit of 4094 is inadequate in such situations.
Data centers are often required to host multiple tenants, each with their own isolated network domain. Since it is not economical to realize this with dedicated infrastructure, network administrators opt to implement isolation over a shared network. In such scenarios, a common problem is that each tenant may independently assign MAC addresses and VLAN IDs leading to potential duplication of these on the physical network.
An important requirement for virtualized environments using a Layer 2 physical infrastructure is having the Layer 2 network scale across the entire data center or even between data centers for efficient allocation of compute, network, and storage resources. In such networks, using traditional approaches like the Spanning Tree Protocol (STP) for a loop-free topology can result in a large number of disabled links.
The last scenario is the case where the network operator prefers to use IP for interconnection of the physical infrastructure (e.g., to achieve multipath scalability through Equal-Cost Multipath (ECMP), thus avoiding disabled links). Even in such environments, there is a need to preserve the Layer 2 model for inter-VM communication.
The scenarios described above lead to a requirement for an overlay network. This overlay is used to carry the MAC traffic from the individual VMs in an encapsulated format over a logical "tunnel".
This document details a framework termed "Virtual eXtensible Local Area Network (VXLAN)" that provides such an encapsulation scheme to address the various requirements specified above. This memo documents the deployed VXLAN protocol for the benefit of the Internet community.
1.1. Acronyms and Definitions
ACL - Access Control List
ECMP - Equal-Cost Multipath
IGMP - Internet Group Management Protocol
IHL - Internet Header Length
MTU - Maximum Transmission Unit
PIM - Protocol Independent Multicast
SPB - Shortest Path Bridging
STP - Spanning Tree Protocol
ToR - Top of Rack
TRILL - Transparent Interconnection of Lots of Links
VLAN - Virtual Local Area Network
VM - Virtual Machine
VNI - VXLAN Network Identifier (or VXLAN Segment ID)
VTEP - VXLAN Tunnel End Point. An entity that originates and/or terminates VXLAN tunnels
VXLAN - Virtual eXtensible Local Area Network
VXLAN Segment - VXLAN Layer 2 overlay network over which VMs communicate
VXLAN Gateway - an entity that forwards traffic between VXLANs