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RFC 7348

Informational
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Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks

 


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Independent Submission                                     M. Mahalingam
Request for Comments: 7348                                     Storvisor
Category: Informational                                          D. Dutt
ISSN: 2070-1721                                         Cumulus Networks
                                                                 K. Duda
                                                                  Arista
                                                              P. Agarwal
                                                                Broadcom
                                                              L. Kreeger
                                                                   Cisco
                                                              T. Sridhar
                                                                  VMware
                                                              M. Bursell
                                                                   Intel
                                                               C. Wright
                                                                 Red Hat
                                                             August 2014


       Virtual eXtensible Local Area Network (VXLAN): A Framework
   for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks

Abstract

   This document describes Virtual eXtensible Local Area Network
   (VXLAN), which is used to address the need for overlay networks
   within virtualized data centers accommodating multiple tenants.  The
   scheme and the related protocols can be used in networks for cloud
   service providers and enterprise data centers.  This memo documents
   the deployed VXLAN protocol for the benefit of the Internet
   community.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7348.

Page 2 
Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1. Introduction ....................................................3
      1.1. Acronyms and Definitions ...................................4
   2. Conventions Used in This Document ...............................4
   3. VXLAN Problem Statement .........................................5
      3.1. Limitations Imposed by Spanning Tree and VLAN Ranges .......5
      3.2. Multi-tenant Environments ..................................5
      3.3. Inadequate Table Sizes at ToR Switch .......................6
   4. VXLAN ...........................................................6
      4.1. Unicast VM-to-VM Communication .............................7
      4.2. Broadcast Communication and Mapping to Multicast ...........8
      4.3. Physical Infrastructure Requirements .......................9
   5. VXLAN Frame Format .............................................10
   6. VXLAN Deployment Scenarios .....................................14
      6.1. Inner VLAN Tag Handling ...................................18
   7. Security Considerations ........................................18
   8. IANA Considerations ............................................19
   9. References .....................................................19
      9.1. Normative References ......................................19
      9.2. Informative References ....................................20
   10. Acknowledgments ...............................................21

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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.

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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

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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3.  VXLAN Problem Statement

   This section provides further details on the areas that VXLAN is
   intended to address.  The focus is on the networking infrastructure
   within the data center and the issues related to them.

3.1.  Limitations Imposed by Spanning Tree and VLAN Ranges

   Current Layer 2 networks use the IEEE 802.1D Spanning Tree Protocol
   (STP) [802.1D] to avoid loops in the network due to duplicate paths.
   STP blocks the use of links to avoid the replication and looping of
   frames.  Some data center operators see this as a problem with Layer
   2 networks in general, since with STP they are effectively paying for
   more ports and links than they can really use.  In addition,
   resiliency due to multipathing is not available with the STP model.
   Newer initiatives, such as TRILL [RFC6325] and SPB [802.1aq], have
   been proposed to help with multipathing and surmount some of the
   problems with STP.  STP limitations may also be avoided by
   configuring servers within a rack to be on the same Layer 3 network,
   with switching happening at Layer 3 both within the rack and between
   racks.  However, this is incompatible with a Layer 2 model for inter-
   VM communication.

   A key characteristic of Layer 2 data center networks is their use of
   Virtual LANs (VLANs) to provide broadcast isolation.  A 12-bit VLAN
   ID is used in the Ethernet data frames to divide the larger Layer 2
   network into multiple broadcast domains.  This has served well for
   many data centers that require fewer than 4094 VLANs.  With the
   growing adoption of virtualization, this upper limit is seeing
   pressure.  Moreover, due to STP, several data centers limit the
   number of VLANs that could be used.  In addition, requirements for
   multi-tenant environments accelerate the need for larger VLAN limits,
   as discussed in Section 3.3.

3.2.  Multi-tenant Environments

   Cloud computing involves on-demand elastic provisioning of resources
   for multi-tenant environments.  The most common example of cloud
   computing is the public cloud, where a cloud service provider offers
   these elastic services to multiple customers/tenants over the same
   physical infrastructure.

   Isolation of network traffic by a tenant could be done via Layer 2 or
   Layer 3 networks.  For Layer 2 networks, VLANs are often used to
   segregate traffic -- so a tenant could be identified by its own VLAN,
   for example.  Due to the large number of tenants that a cloud

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   provider might service, the 4094 VLAN limit is often inadequate.  In
   addition, there is often a need for multiple VLANs per tenant, which
   exacerbates the issue.

   A related use case is cross-pod expansion.  A pod typically consists
   of one or more racks of servers with associated network and storage
   connectivity.  Tenants may start off on a pod and, due to expansion,
   require servers/VMs on other pods, especially in the case when
   tenants on the other pods are not fully utilizing all their
   resources.  This use case requires a "stretched" Layer 2 environment
   connecting the individual servers/VMs.

   Layer 3 networks are not a comprehensive solution for multi-tenancy
   either.  Two tenants might use the same set of Layer 3 addresses
   within their networks, which requires the cloud provider to provide
   isolation in some other form.  Further, requiring all tenants to use
   IP excludes customers relying on direct Layer 2 or non-IP Layer 3
   protocols for inter VM communication.

3.3.  Inadequate Table Sizes at ToR Switch

   Today's virtualized environments place additional demands on the MAC
   address tables of Top-of-Rack (ToR) switches that connect to the
   servers.  Instead of just one MAC address per server link, the ToR
   now has to learn the MAC addresses of the individual VMs (which could
   range in the hundreds per server).  This is needed because traffic
   to/from the VMs to the rest of the physical network will traverse the
   link between the server and the switch.  A typical ToR switch could
   connect to 24 or 48 servers depending upon the number of its server-
   facing ports.  A data center might consist of several racks, so each
   ToR switch would need to maintain an address table for the
   communicating VMs across the various physical servers.  This places a
   much larger demand on the table capacity compared to non-virtualized
   environments.

   If the table overflows, the switch may stop learning new addresses
   until idle entries age out, leading to significant flooding of
   subsequent unknown destination frames.

4.  VXLAN

   VXLAN (Virtual eXtensible Local Area Network) addresses the above
   requirements of the Layer 2 and Layer 3 data center network
   infrastructure in the presence of VMs in a multi-tenant environment.
   It runs over the existing networking infrastructure and provides a
   means to "stretch" a Layer 2 network.  In short, VXLAN is a Layer 2
   overlay scheme on a Layer 3 network.  Each overlay is termed a VXLAN
   segment.  Only VMs within the same VXLAN segment can communicate with

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   each other.  Each VXLAN segment is identified through a 24-bit
   segment ID, termed the "VXLAN Network Identifier (VNI)".  This allows
   up to 16 M VXLAN segments to coexist within the same administrative
   domain.

   The VNI identifies the scope of the inner MAC frame originated by the
   individual VM.  Thus, you could have overlapping MAC addresses across
   segments but never have traffic "cross over" since the traffic is
   isolated using the VNI.  The VNI is in an outer header that
   encapsulates the inner MAC frame originated by the VM.  In the
   following sections, the term "VXLAN segment" is used interchangeably
   with the term "VXLAN overlay network".

   Due to this encapsulation, VXLAN could also be called a tunneling
   scheme to overlay Layer 2 networks on top of Layer 3 networks.  The
   tunnels are stateless, so each frame is encapsulated according to a
   set of rules.  The end point of the tunnel (VXLAN Tunnel End Point or
   VTEP) discussed in the following sections is located within the
   hypervisor on the server that hosts the VM.  Thus, the VNI- and
   VXLAN-related tunnel / outer header encapsulation are known only to
   the VTEP -- the VM never sees it (see Figure 1).  Note that it is
   possible that VTEPs could also be on a physical switch or physical
   server and could be implemented in software or hardware.  One use
   case where the VTEP is a physical switch is discussed in Section 6 on
   VXLAN deployment scenarios.

   The following sections discuss typical traffic flow scenarios in a
   VXLAN environment using one type of control scheme -- data plane
   learning.  Here, the association of VM's MAC to VTEP's IP address is
   discovered via source-address learning.  Multicast is used for
   carrying unknown destination, broadcast, and multicast frames.

   In addition to a learning-based control plane, there are other
   schemes possible for the distribution of the VTEP IP to VM MAC
   mapping information.  Options could include a central
   authority-/directory-based lookup by the individual VTEPs,
   distribution of this mapping information to the VTEPs by the central
   authority, and so on.  These are sometimes characterized as push and
   pull models, respectively.  This document will focus on the data
   plane learning scheme as the control plane for VXLAN.

4.1.  Unicast VM-to-VM Communication

   Consider a VM within a VXLAN overlay network.  This VM is unaware of
   VXLAN.  To communicate with a VM on a different host, it sends a MAC
   frame destined to the target as normal.  The VTEP on the physical
   host looks up the VNI to which this VM is associated.  It then
   determines if the destination MAC is on the same segment and if there

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   is a mapping of the destination MAC address to the remote VTEP.  If
   so, an outer header comprising an outer MAC, outer IP header, and
   VXLAN header (see Figure 1 in Section 5 for frame format) are
   prepended to the original MAC frame.  The encapsulated packet is
   forwarded towards the remote VTEP.  Upon reception, the remote VTEP
   verifies the validity of the VNI and whether or not there is a VM on
   that VNI using a MAC address that matches the inner destination MAC
   address.  If so, the packet is stripped of its encapsulating headers
   and passed on to the destination VM.  The destination VM never knows
   about the VNI or that the frame was transported with a VXLAN
   encapsulation.

   In addition to forwarding the packet to the destination VM, the
   remote VTEP learns the mapping from inner source MAC to outer source
   IP address.  It stores this mapping in a table so that when the
   destination VM sends a response packet, there is no need for an
   "unknown destination" flooding of the response packet.

   Determining the MAC address of the destination VM prior to the
   transmission by the source VM is performed as with non-VXLAN
   environments except as described in Section 4.2.  Broadcast frames
   are used but are encapsulated within a multicast packet, as detailed
   in the Section 4.2.

4.2.  Broadcast Communication and Mapping to Multicast

   Consider the VM on the source host attempting to communicate with the
   destination VM using IP.  Assuming that they are both on the same
   subnet, the VM sends out an Address Resolution Protocol (ARP)
   broadcast frame.  In the non-VXLAN environment, this frame would be
   sent out using MAC broadcast across all switches carrying that VLAN.

   With VXLAN, a header including the VXLAN VNI is inserted at the
   beginning of the packet along with the IP header and UDP header.
   However, this broadcast packet is sent out to the IP multicast group
   on which that VXLAN overlay network is realized.

   To effect this, we need to have a mapping between the VXLAN VNI and
   the IP multicast group that it will use.  This mapping is done at the
   management layer and provided to the individual VTEPs through a
   management channel.  Using this mapping, the VTEP can provide IGMP
   membership reports to the upstream switch/router to join/leave the
   VXLAN-related IP multicast groups as needed.  This will enable
   pruning of the leaf nodes for specific multicast traffic addresses
   based on whether a member is available on this host using the
   specific multicast address (see [RFC4541]).  In addition, use of

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   multicast routing protocols like Protocol Independent Multicast -
   Sparse Mode (PIM-SM see [RFC4601]) will provide efficient multicast
   trees within the Layer 3 network.

   The VTEP will use (*,G) joins.  This is needed as the set of VXLAN
   tunnel sources is unknown and may change often, as the VMs come up /
   go down across different hosts.  A side note here is that since each
   VTEP can act as both the source and destination for multicast
   packets, a protocol like bidirectional PIM (BIDIR-PIM -- see
   [RFC5015]) would be more efficient.

   The destination VM sends a standard ARP response using IP unicast.
   This frame will be encapsulated back to the VTEP connecting the
   originating VM using IP unicast VXLAN encapsulation.  This is
   possible since the mapping of the ARP response's destination MAC to
   the VXLAN tunnel end point IP was learned earlier through the ARP
   request.

   Note that multicast frames and "unknown MAC destination" frames are
   also sent using the multicast tree, similar to the broadcast frames.

4.3.  Physical Infrastructure Requirements

   When IP multicast is used within the network infrastructure, a
   multicast routing protocol like PIM-SM can be used by the individual
   Layer 3 IP routers/switches within the network.  This is used to
   build efficient multicast forwarding trees so that multicast frames
   are only sent to those hosts that have requested to receive them.

   Similarly, there is no requirement that the actual network connecting
   the source VM and destination VM should be a Layer 3 network: VXLAN
   can also work over Layer 2 networks.  In either case, efficient
   multicast replication within the Layer 2 network can be achieved
   using IGMP snooping.

   VTEPs MUST NOT fragment VXLAN packets.  Intermediate routers may
   fragment encapsulated VXLAN packets due to the larger frame size.
   The destination VTEP MAY silently discard such VXLAN fragments.  To
   ensure end-to-end traffic delivery without fragmentation, it is
   RECOMMENDED that the MTUs (Maximum Transmission Units) across the
   physical network infrastructure be set to a value that accommodates
   the larger frame size due to the encapsulation.  Other techniques
   like Path MTU discovery (see [RFC1191] and [RFC1981]) MAY be used to
   address this requirement as well.

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5.  VXLAN Frame Format

   The VXLAN frame format is shown below.  Parsing this from the bottom
   of the frame -- above the outer Frame Check Sequence (FCS), there is
   an inner MAC frame with its own Ethernet header with source,
   destination MAC addresses along with the Ethernet type, plus an
   optional VLAN.  See Section 6 for further details of inner VLAN tag
   handling.

   The inner MAC frame is encapsulated with the following four headers
   (starting from the innermost header):

   VXLAN Header:  This is an 8-byte field that has:

      - Flags (8 bits): where the I flag MUST be set to 1 for a valid
        VXLAN Network ID (VNI).  The other 7 bits (designated "R") are
        reserved fields and MUST be set to zero on transmission and
        ignored on receipt.

      - VXLAN Segment ID/VXLAN Network Identifier (VNI): this is a
        24-bit value used to designate the individual VXLAN overlay
        network on which the communicating VMs are situated.  VMs in
        different VXLAN overlay networks cannot communicate with each
        other.

      - Reserved fields (24 bits and 8 bits): MUST be set to zero on
        transmission and ignored on receipt.

   Outer UDP Header:  This is the outer UDP header with a source port
      provided by the VTEP and the destination port being a well-known
      UDP port.

      -  Destination Port: IANA has assigned the value 4789 for the
         VXLAN UDP port, and this value SHOULD be used by default as the
         destination UDP port.  Some early implementations of VXLAN have
         used other values for the destination port.  To enable
         interoperability with these implementations, the destination
         port SHOULD be configurable.

      -  Source Port:  It is recommended that the UDP source port number
         be calculated using a hash of fields from the inner packet --
         one example being a hash of the inner Ethernet frame's headers.
         This is to enable a level of entropy for the ECMP/load-
         balancing of the VM-to-VM traffic across the VXLAN overlay.
         When calculating the UDP source port number in this manner, it
         is RECOMMENDED that the value be in the dynamic/private port
         range 49152-65535 [RFC6335].

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      -  UDP Checksum: It SHOULD be transmitted as zero.  When a packet
         is received with a UDP checksum of zero, it MUST be accepted
         for decapsulation.  Optionally, if the encapsulating end point
         includes a non-zero UDP checksum, it MUST be correctly
         calculated across the entire packet including the IP header,
         UDP header, VXLAN header, and encapsulated MAC frame.  When a
         decapsulating end point receives a packet with a non-zero
         checksum, it MAY choose to verify the checksum value.  If it
         chooses to perform such verification, and the verification
         fails, the packet MUST be dropped.  If the decapsulating
         destination chooses not to perform the verification, or
         performs it successfully, the packet MUST be accepted for
         decapsulation.

   Outer IP Header:  This is the outer IP header with the source IP
      address indicating the IP address of the VTEP over which the
      communicating VM (as represented by the inner source MAC address)
      is running.  The destination IP address can be a unicast or
      multicast IP address (see Sections 4.1 and 4.2).  When it is a
      unicast IP address, it represents the IP address of the VTEP
      connecting the communicating VM as represented by the inner
      destination MAC address.  For multicast destination IP addresses,
      please refer to the scenarios detailed in Section 4.2.

   Outer Ethernet Header (example):  Figure 1 is an example of an inner
      Ethernet frame encapsulated within an outer Ethernet + IP + UDP +
      VXLAN header.  The outer destination MAC address in this frame may
      be the address of the target VTEP or of an intermediate Layer 3
      router.  The outer VLAN tag is optional.  If present, it may be
      used for delineating VXLAN traffic on the LAN.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

   Outer Ethernet Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Outer Destination MAC Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Outer Destination MAC Address | Outer Source MAC Address      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Outer Source MAC Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |OptnlEthtype = C-Tag 802.1Q    | Outer.VLAN Tag Information    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ethertype = 0x0800            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   Outer IPv4 Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version|  IHL  |Type of Service|          Total Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Identification        |Flags|      Fragment Offset    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Time to Live |Protocl=17(UDP)|   Header Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Outer Source IPv4 Address               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Outer Destination IPv4 Address              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Outer UDP Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Source Port         |       Dest Port = VXLAN Port  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           UDP Length          |        UDP Checksum           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   VXLAN Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R|R|R|R|I|R|R|R|            Reserved                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                VXLAN Network Identifier (VNI) |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Inner Ethernet Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Inner Destination MAC Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Inner Destination MAC Address | Inner Source MAC Address      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Inner Source MAC Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |OptnlEthtype = C-Tag 802.1Q    | Inner.VLAN Tag Information    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Payload:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ethertype of Original Payload |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                  Original Ethernet Payload    |
   |                                                               |
   |(Note that the original Ethernet Frame's FCS is not included)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   Frame Check Sequence:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   New FCS (Frame Check Sequence) for Outer Ethernet Frame     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 1: VXLAN Frame Format with IPv4 Outer Header

   The frame format above shows tunneling of Ethernet frames using IPv4
   for transport.  Use of VXLAN with IPv6 transport is detailed below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

   Outer Ethernet Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Outer Destination MAC Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Outer Destination MAC Address | Outer Source MAC Address      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Outer Source MAC Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |OptnlEthtype = C-Tag 802.1Q    | Outer.VLAN Tag Information    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ethertype = 0x86DD            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Outer IPv6 Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version| Traffic Class |           Flow Label                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Payload Length        | NxtHdr=17(UDP)|   Hop Limit   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                     Outer Source IPv6 Address                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                  Outer Destination IPv6 Address               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   Outer UDP Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Source Port         |       Dest Port = VXLAN Port  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           UDP Length          |        UDP Checksum           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   VXLAN Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R|R|R|R|I|R|R|R|            Reserved                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                VXLAN Network Identifier (VNI) |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Inner Ethernet Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Inner Destination MAC Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Inner Destination MAC Address | Inner Source MAC Address      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Inner Source MAC Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |OptnlEthtype = C-Tag 802.1Q    | Inner.VLAN Tag Information    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Payload:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ethertype of Original Payload |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                  Original Ethernet Payload    |
   |                                                               |
   |(Note that the original Ethernet Frame's FCS is not included)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Frame Check Sequence:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   New FCS (Frame Check Sequence) for Outer Ethernet Frame     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 2: VXLAN Frame Format with IPv6 Outer Header

6.  VXLAN Deployment Scenarios

   VXLAN is typically deployed in data centers on virtualized hosts,
   which may be spread across multiple racks.  The individual racks may
   be parts of a different Layer 3 network or they could be in a single
   Layer 2 network.  The VXLAN segments/overlay networks are overlaid on
   top of these Layer 2 or Layer 3 networks.

Top      ToC       Page 15 
   Consider Figure 3, which depicts two virtualized servers attached to
   a Layer 3 infrastructure.  The servers could be on the same rack, on
   different racks, or potentially across data centers within the same
   administrative domain.  There are four VXLAN overlay networks
   identified by the VNIs 22, 34, 74, and 98.  Consider the case of
   VM1-1 in Server 1 and VM2-4 on Server 2, which are on the same VXLAN
   overlay network identified by VNI 22.  The VMs do not know about the
   overlay networks and transport method since the encapsulation and
   decapsulation happen transparently at the VTEPs on Servers 1 and 2.
   The other overlay networks and the corresponding VMs are VM1-2 on
   Server 1 and VM2-1 on Server 2, both on VNI 34; VM1-3 on Server 1 and
   VM2-2 on Server 2 on VNI 74; and finally VM1-4 on Server 1 and VM2-3
   on Server 2 on VNI 98.

Top      ToC       Page 16 
   +------------+-------------+
   |        Server 1          |
   | +----+----+  +----+----+ |
   | |VM1-1    |  |VM1-2    | |
   | |VNI 22   |  |VNI 34   | |
   | |         |  |         | |
   | +---------+  +---------+ |
   |                          |
   | +----+----+  +----+----+ |
   | |VM1-3    |  |VM1-4    | |
   | |VNI 74   |  |VNI 98   | |
   | |         |  |         | |
   | +---------+  +---------+ |
   | Hypervisor VTEP (IP1)    |
   +--------------------------+
                         |
                         |
                         |
                         |   +-------------+
                         |   |   Layer 3   |
                         |---|   Network   |
                             |             |
                             +-------------+
                                 |
                                 |
                                 +-----------+
                                             |
                                             |
                                      +------------+-------------+
                                      |        Server 2          |
                                      | +----+----+  +----+----+ |
                                      | |VM2-1    |  |VM2-2    | |
                                      | |VNI 34   |  |VNI 74   | |
                                      | |         |  |         | |
                                      | +---------+  +---------+ |
                                      |                          |
                                      | +----+----+  +----+----+ |
                                      | |VM2-3    |  |VM2-4    | |
                                      | |VNI 98   |  |VNI 22   | |
                                      | |         |  |         | |
                                      | +---------+  +---------+ |
                                      | Hypervisor VTEP (IP2)    |
                                      +--------------------------+

    Figure 3: VXLAN Deployment - VTEPs across a Layer 3 Network

Top      ToC       Page 17 
   One deployment scenario is where the tunnel termination point is a
   physical server that understands VXLAN.  An alternate scenario is
   where nodes on a VXLAN overlay network need to communicate with nodes
   on legacy networks that could be VLAN based.  These nodes may be
   physical nodes or virtual machines.  To enable this communication, a
   network can include VXLAN gateways (see Figure 4 below with a switch
   acting as a VXLAN gateway) that forward traffic between VXLAN and
   non-VXLAN environments.

   Consider Figure 4 for the following discussion.  For incoming frames
   on the VXLAN connected interface, the gateway strips out the VXLAN
   header and forwards it to a physical port based on the destination
   MAC address of the inner Ethernet frame.  Decapsulated frames with
   the inner VLAN ID SHOULD be discarded unless configured explicitly to
   be passed on to the non-VXLAN interface.  In the reverse direction,
   incoming frames for the non-VXLAN interfaces are mapped to a specific
   VXLAN overlay network based on the VLAN ID in the frame.  Unless
   configured explicitly to be passed on in the encapsulated VXLAN
   frame, this VLAN ID is removed before the frame is encapsulated for
   VXLAN.

   These gateways that provide VXLAN tunnel termination functions could
   be ToR/access switches or switches higher up in the data center
   network topology -- e.g., core or even WAN edge devices.  The last
   case (WAN edge) could involve a Provider Edge (PE) router that
   terminates VXLAN tunnels in a hybrid cloud environment.  In all these
   instances, note that the gateway functionality could be implemented
   in software or hardware.

Top      ToC       Page 18 
   +---+-----+---+                                    +---+-----+---+
   |    Server 1 |                                    |  Non-VXLAN  |
   (VXLAN enabled)<-----+                       +---->|  server     |
   +-------------+      |                       |     +-------------+
                        |                       |
   +---+-----+---+      |                       |     +---+-----+---+
   |Server 2     |      |                       |     |  Non-VXLAN  |
   (VXLAN enabled)<-----+   +---+-----+---+     +---->|    server   |
   +-------------+      |   |Switch acting|     |     +-------------+
                        |---|  as VXLAN   |-----|
   +---+-----+---+      |   |   Gateway   |
   | Server 3    |      |   +-------------+
   (VXLAN enabled)<-----+
   +-------------+      |
                        |
   +---+-----+---+      |
   | Server 4    |      |
   (VXLAN enabled)<-----+
   +-------------+

           Figure 4: VXLAN Deployment - VXLAN Gateway

6.1.  Inner VLAN Tag Handling

   Inner VLAN Tag Handling in VTEP and VXLAN gateway should conform to
   the following:

   Decapsulated VXLAN frames with the inner VLAN tag SHOULD be discarded
   unless configured otherwise.  On the encapsulation side, a VTEP
   SHOULD NOT include an inner VLAN tag on tunnel packets unless
   configured otherwise.  When a VLAN-tagged packet is a candidate for
   VXLAN tunneling, the encapsulating VTEP SHOULD strip the VLAN tag
   unless configured otherwise.

7.  Security Considerations

   Traditionally, Layer 2 networks can only be attacked from 'within' by
   rogue end points -- either by having inappropriate access to a LAN
   and snooping on traffic, by injecting spoofed packets to 'take over'
   another MAC address, or by flooding and causing denial of service.  A
   MAC-over-IP mechanism for delivering Layer 2 traffic significantly
   extends this attack surface.  This can happen by rogues injecting
   themselves into the network by subscribing to one or more multicast
   groups that carry broadcast traffic for VXLAN segments and also by
   sourcing MAC-over-UDP frames into the transport network to inject
   spurious traffic, possibly to hijack MAC addresses.

Top      ToC       Page 19 
   This document does not incorporate specific measures against such
   attacks, relying instead on other traditional mechanisms layered on
   top of IP.  This section, instead, sketches out some possible
   approaches to security in the VXLAN environment.

   Traditional Layer 2 attacks by rogue end points can be mitigated by
   limiting the management and administrative scope of who deploys and
   manages VMs/gateways in a VXLAN environment.  In addition, such
   administrative measures may be augmented by schemes like 802.1X
   [802.1X] for admission control of individual end points.  Also, the
   use of the UDP-based encapsulation of VXLAN enables configuration and
   use of the 5-tuple-based ACL (Access Control List) functionality in
   physical switches.

   Tunneled traffic over the IP network can be secured with traditional
   security mechanisms like IPsec that authenticate and optionally
   encrypt VXLAN traffic.  This will, of course, need to be coupled with
   an authentication infrastructure for authorized end points to obtain
   and distribute credentials.

   VXLAN overlay networks are designated and operated over the existing
   LAN infrastructure.  To ensure that VXLAN end points and their VTEPs
   are authorized on the LAN, it is recommended that a VLAN be
   designated for VXLAN traffic and the servers/VTEPs send VXLAN traffic
   over this VLAN to provide a measure of security.

   In addition, VXLAN requires proper mapping of VNIs and VM membership
   in these overlay networks.  It is expected that this mapping be done
   and communicated to the management entity on the VTEP and the
   gateways using existing secure methods.

8.  IANA Considerations

   A well-known UDP port (4789) has been assigned by the IANA in the
   Service Name and Transport Protocol Port Number Registry for VXLAN.
   See Section 5 for discussion of the port number.

9.  References

9.1.  Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

Top      ToC       Page 20 
9.2.  Informative References

   [802.1aq] IEEE, "Standard for Local and metropolitan area networks --
             Media Access Control (MAC) Bridges and Virtual Bridged
             Local Area Networks -- Amendment 20: Shortest Path
             Bridging", IEEE P802.1aq-2012, 2012.

   [802.1D]  IEEE, "Draft Standard for Local and Metropolitan Area
             Networks/ Media Access Control (MAC) Bridges", IEEE
             P802.1D-2004, 2004.

   [802.1X]  IEEE, "IEEE Standard for Local and metropolitan area
             networks -- Port-Based Network Acces Control", IEEE Std
             802.1X-2010, February 2010.

   [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
             November 1990.

   [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
             for IP version 6", RFC 1981, August 1996.

   [RFC4541] Christensen, M., Kimball, K., and F. Solensky,
             "Considerations for Internet Group Management Protocol
             (IGMP) and Multicast Listener Discovery (MLD) Snooping
             Switches", RFC 4541, May 2006.

   [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
             "Protocol Independent Multicast - Sparse Mode (PIM-SM):
             Protocol Specification (Revised)", RFC 4601, August 2006.

   [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
             "Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
             RFC 5015, October 2007.

   [RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
             Ghanwani, "Routing Bridges (RBridges): Base Protocol
             Specification", RFC 6325, July 2011.

   [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
             Cheshire, "Internet Assigned Numbers Authority (IANA)
             Procedures for the Management of the Service Name and
             Transport Protocol Port Number Registry", BCP 165, RFC
             6335, August 2011.

Top      ToC       Page 21 
10.  Acknowledgments

   The authors wish to thank: Ajit Sanzgiri for contributions to the
   Security Considerations section and editorial inputs; Joseph Cheng,
   Margaret Petrus, Milin Desai, Nial de Barra, Jeff Mandin, and Siva
   Kollipara for their editorial reviews, inputs, and comments.

Authors' Addresses

   Mallik Mahalingam
   Storvisor, Inc.
   640 W. California Ave, Suite #110
   Sunnyvale, CA 94086.
   USA

   EMail: mallik_mahalingam@yahoo.com


   Dinesh G. Dutt
   Cumulus Networks
   140C S. Whisman Road
   Mountain View, CA 94041
   USA

   EMail: ddutt.ietf@hobbesdutt.com


   Kenneth Duda
   Arista Networks
   5453 Great America Parkway
   Santa Clara, CA 95054
   USA

   EMail: kduda@arista.com


   Puneet Agarwal
   Broadcom Corporation
   3151 Zanker Road
   San Jose, CA 95134
   USA

   EMail: pagarwal@broadcom.com

Top      ToC       Page 22 
   Lawrence Kreeger
   Cisco Systems, Inc.
   170 W. Tasman Avenue
   San Jose, CA 95134
   USA

   EMail: kreeger@cisco.com


   T. Sridhar
   VMware, Inc.
   3401 Hillview
   Palo Alto, CA 94304
   USA

   EMail: tsridhar@vmware.com


   Mike Bursell
   Intel
   Bowyer's, North Road
   Great Yeldham
   Halstead
   Essex. C09 4QD
   UK

   EMail: mike.bursell@intel.com


   Chris Wright
   Red Hat, Inc.
   100 East Davie Street
   Raleigh, NC 27601
   USA

   EMail: chrisw@redhat.com