Internet Engineering Task Force
Independent Submission                                     M. Mahalingam
Internet Draft
Request for Comments: 7348                                     Storvisor
Intended Status:
Category: Informational                                          D. Dutt
Expires: October 10, 2014
ISSN: 2070-1721                                         Cumulus Networks
                                                                 K. Duda
                                                                  Arista
                                                              P. Agarwal
                                                                Broadcom
                                                              L. Kreeger
                                                                   Cisco
                                                              T. Sridhar
                                                                  VMware
                                                              M. Bursell
                                                                 Citrix
                                                                   Intel
                                                               C. Wright
                                                                 Red Hat
                                                         April 10,
                                                             August 2014

    VXLAN:

       Virtual eXtensible Local Area Network (VXLAN): A Framework
   for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks
                 draft-mahalingam-dutt-dcops-vxlan-09.txt

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
  provider providers and enterprise data center networks. centers.  This memo documents
   the deployed VXLAN protocol for the benefit of the IETF community.

Status of this This Memo

   This Internet-Draft document is submitted in full conformance with not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents RFC Series, independently of the Internet Engineering
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   The list level of Internet
   Standard; see Section 2 of RFC 5741.

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   http://www.rfc-editor.org/info/rfc7348.

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Table of Contents

   1. Introduction...................................................3 Introduction ....................................................3
      1.1. Acronyms & Definitions....................................4 and Definitions ...................................4
   2. Conventions used Used in this document..............................5 This Document ...............................4
   3. VXLAN Problem Statement........................................5 Statement .........................................5
      3.1. Limitations imposed Imposed by Spanning Tree & and VLAN Ranges........5 Ranges .......5
      3.2. Multitenant Environments..................................6 Multi-tenant Environments ..................................5
      3.3. Inadequate Table Sizes at ToR Switch......................6 Switch .......................6
   4. Virtual eXtensible Local Area Network (VXLAN)..................7 VXLAN ...........................................................6
      4.1. Unicast VM to VM communication............................8 VM-to-VM Communication .............................7
      4.2. Broadcast Communication and Mapping to Multicast..........9 Multicast ...........8
      4.3. Physical Infrastructure Requirements.....................10 Requirements .......................9
   5. VXLAN Frame Format............................................10 Format .............................................10
   6. VXLAN Deployment Scenarios....................................16 Scenarios .....................................14
      6.1. Inner VLAN Tag Handling..................................19 Handling ...................................18
   7. Security Considerations.......................................19 Considerations ........................................18
   8. IANA Considerations...........................................21 Considerations ............................................19
   9. References....................................................21 References .....................................................19
      9.1. Normative References.....................................21 References ......................................19
      9.2. Informative References...................................21 References ....................................20
   10. Acknowledgments..............................................22 Acknowledgments ...............................................20

1.  Introduction

   Server virtualization has placed increased demands on the physical
   network infrastructure.  A physical server now has multiple virtual
   machines Virtual
   Machines (VMs) each with its own MAC 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, (VLAN), one might need thousands of VLANs to
   partition the traffic according to the specific group that to which the VM
   may belong to. 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 network, and storage resources.  In such
   networks, using traditional approaches like the Spanning Tree
   Protocol (STP) for a loop free 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. (e.g., to
   achieve multipath scalability through Equal Cost 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 "Virtual eXtensible Local
   Area Network (VXLAN) which (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 IETF
   community.

1.1.  Acronyms & and Definitions

   ACL  -      Access Control List

   ECMP - Equal Cost     Equal-Cost Multipath

   IGMP -     Internet Group Management Protocol

   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

        VXLAN -

   VLAN     Virtual eXtensible Local Area Network

   VM       Virtual Machine

   VNI      VXLAN Segment - VXLAN Layer 2 overlay network over which VMs

                        communicate

        VXLAN Overlay Network - Identifier (or VXLAN Segment

        VXLAN Gateway - an entity which forwards traffic between VXLAN

                        and non-VXLAN environments ID)

   VTEP -     VXLAN Tunnel End Point - an Point.  An entity which that originates and/or
            terminates VXLAN tunnels

        VLAN -

   VXLAN    Virtual eXtensible Local Area Network
        VM -   Virtual Machine

        VNI -  VXLAN Network Identifier (or

   VXLAN Segment ID)
            VXLAN Layer 2 overlay network over which VMs communicate

   VXLAN Gateway
            an entity that forwards traffic between VXLANs

2.  Conventions used Used in this document 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 RFC 2119 [RFC2119].

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 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 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 initiatives, such as TRILL [RFC6325] and SPB[802.1aq]) SPB [802.1aq], have
   been proposed to help with multipathing and thus 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 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 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
   several
   many data centers which 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
   multitenant
   multi-tenant environments accelerate the need for larger VLAN limits,
   as discussed in Section 3.3.

3.2. Multitenant  Multi-tenant Environments

   Cloud computing involves on demand 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
   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 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 multi-tenancy
   either.  Two tenants might use the same set of Layer 3 addresses
   within their networks 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 Top-of-Rack (ToR) switches which 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 100s hundreds per server).  This is needed because traffic
   from/to
   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 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. Virtual eXtensible Local Area Network (VXLAN)  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 over on a Layer 3 network.  Each overlay is termed a VXLAN
   segment.  Only VMs within the same VXLAN segment can communicate with
   each other.  Each VXLAN segment is identified through a 24 bit 24-bit
   segment ID, hereafter termed the VXLAN "VXLAN Network Identifier (VNI). (VNI)".  This allows
   up to 16M 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
   which 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 termed 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 which that hosts the VM.  Thus, the VNI VNI- and VXLAN
   related tunnel/outer
   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 source-address learning.  Multicast is used for
   carrying unknown destination, broadcast broadcast, and multicast frames.

   In addition to a learning based 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
   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 models, respectively.  This draft document will focus on the data
   plane learning scheme as the control plane for VXLAN.

4.1.  Unicast VM to VM communication 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
   is a mapping of the destination MAC address to the remote VTEP.  If
   so, an outer header comprising an outer MAC, outer IP header 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 if 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 Inner Source mapping from inner source MAC to outer Source source
   IP address
   mapping. 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 ARP Address Resolution Protocol (ARP)
   broadcast frame.  In the non-
   VXLAN 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
   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
   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 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 PIM-bidir (see 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 which 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 - 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 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.

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 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 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):

    O

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

     o

      - Flags (8 bits)- 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 transmit transmission and
        ignored on
     receive.

     o receipt.

      - VXLAN Segment ID/VXLAN Network Identifier (VNI) - (VNI): this is a 24
     bit
        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.

     o

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

   O 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 well-known
      UDP port.  IANA has assigned the value 4789 for the VXLAN UDP
   port
      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.  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 frame's headers.  This
      is to enable a level of entropy for ECMP/load balancing 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].

      The UDP checksum field 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 endpoint 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 header, and encapsulated MAC frame.  When a
      decapsulating endpoint end point receives a packet with a non-zero checksum
      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.

   O

   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.

   O

   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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   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 = xxxx 4789      |       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 1 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               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Outer UDP Header:
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Source Port = xxxx 4789      |       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 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.

   Consider Figure 3 below depicting 3, which depicts two virtualized servers attached to
   a Layer 3 infrastructure.  The servers could be on the same rack,
   or on
   different racks racks, or potentially across data centers within the same
   administrative domain.  There are 4 four VXLAN overlay networks
   identified by the VNIs 22, 34, 74 74, and 98.  Consider the case of
   VM1-1 in Server 1 and VM2-4 on Server 2 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: are VM1-2 on
   Server 1 and VM2-1 on Server 2 2, both on VNI 34, 34; VM1-3 on Server 1 and
   VM2-2 on Server 2 on VNI 74, 74; and finally VM1-4 on Server 1 and VM2-3
   on Server 2 on VNI 98.

   +------------+-------------+
   |        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 3: VXLAN Deployment - VTEPs across a Layer 3 Network
   One deployment scenario is where the tunnel termination point is a
   physical server which that understands VXLAN.  An alternate scenario is
   where nodes on a VXLAN overlay network need to communicate with nodes
   on legacy networks which 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) which 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 which that provide VXLAN tunnel termination functions could
   be ToR/access switches or switches higher up in the data center
   network topology -  e.g. -- e.g., core or even WAN edge devices.  The last
   case (WAN edge) could involve a Provider Edge (PE) router which that
   terminates VXLAN tunnels in a hybrid cloud environment. Note that in  In all these
   instances, note that the gateway functionality could be implemented
   in software or hardware.

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

           Figure 4 4: VXLAN Deployment - VXLAN Gateway

6.1.  Inner VLAN Tag Handling

   Inner VLAN Tag Handling in VTEP and VXLAN Gateway 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 Layer 2 networks can only be attacked from 'within' by
   rogue endpoints - end points -- either by having inappropriate access to a LAN
   and snooping on traffic or traffic, by injecting spoofed packets to 'take over'
   another MAC address 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.

   This document does not, at this time, 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 for
   admission control of individual end points.   Also, the use of the
   UDP based
   UDP-based encapsulation of VXLAN enables configuration and use of the 5 tuple based ACLs
   5-tuple-based ACL (Access Control Lists) 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 endpoints 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.

9.2.  Informative References

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

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

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

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

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

   [802.1aq] IEEE, "Standard for Local and Metropolitan Area Networks / metropolitan area networks --
             Media Access Control (MAC) Bridges and Virtual Bridged
             Local Area Networks / Amendment20: -- Amendment 20: Shortest Path Bridging,
             Bridging", IEEE P802.1aq-2012". P802.1aq-2012, 2012.

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

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

   [RFC6335] Cotton, M, M., Eggert, L., Touch, J., Westerlund, M., and S.
             Cheshire, S., "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.

10.  Acknowledgments

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

Authors' Addresses

   Mallik Mahalingam
   Storvisor
   333 W.El W. El Camino Real
   Sunnyvale, CA 94087

   Email:
   USA

   EMail: mallik_mahalingam@yahoo.com

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

   Email:
   USA

   EMail: ddutt.ietf@hobbesdutt.com

   Kenneth Duda
   Arista Networks
   5470 Great America Parkway
   Santa Clara, CA 95054

   Email:
   USA

   EMail: kduda@aristanetworks.com

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

   Email:
   USA

   EMail: pagarwal@broadcom.com

   Lawrence Kreeger
   Cisco Systems, Inc.
   170 W. Tasman Avenue
   San Jose, CA 95134

   Email:
   USA

   EMail: kreeger@cisco.com
   T. Sridhar
   VMware
   VMware, Inc.
   3401 Hillview
   Palo Alto, CA 94304

   Email:
   USA

   EMail: tsridhar@vmware.com

   Mike Bursell
   Citrix Systems Research & Development Ltd.
   Building 101
   Cambridge Science Park
   Milton
   Intel
   Bowyer's, North Road
   Cambridge CB4 0FY
   United Kingdom

   Email: mike.bursell@citrix.com
   Great Yeldham
   Halstead
   Essex. C09 4QD
   UK

   EMail: mike.bursell@intel.com

   Chris Wright
   Red Hat Hat, Inc.
   1801 Varsity Drive
   Raleigh, NC 27606

   Email:
   USA

   EMail: chrisw@redhat.com