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     Network Working Group                                      M.Mahalingam
     Internet Draft                                                   VMware
     Intended Status: Experimental                                    D.Dutt
     Expires: February 2012                                            Cisco
                                                                      K.Duda
                                                                      Arista
                                                                   P.Agarwal
                                                                    Broadcom
                                                                  L. Kreeger
                                                                       Cisco
                                                                  T. Sridhar
                                                                      VMware
                                                                   M.Bursell
                                                                      Citrix
                                                                    C.Wright
                                                                     Red Hat
                                                             August 26, 2011
     
     
     
         VXLAN: A Framework for Overlaying Virtualized Layer 2 Networks over
                                  Layer 3 Networks
                      draft-mahalingam-dutt-dcops-vxlan-00.txt
     
     
     Status of this Memo
     
        This  Internet-Draft  is  submitted  in  full  conformance  with  the
        provisions of BCP 78 and BCP 79.
     
        Internet-Drafts are working documents of the Internet Engineering
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        This Internet-Draft will expire on February 26, 2012.
     
     
     
     
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     Copyright Notice
     
        Copyright (c) 2011 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.
     
     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 cloud service
       provider and enterprise data center networks.
     
     
     
     Table of Contents
     
     
        1. Introduction...................................................3
           1.1. Acronyms & Definitions....................................3
        2. Conventions used in this document..............................4
        3. VXLAN Problem Statement........................................5
           3.1. Limitations imposed by Spanning Tree & VLAN Spaces........5
           3.2. Multitenant Environments..................................5
           3.3. Inadequate Table Sizes at ToR Switch......................6
        4. Virtual eXtensible Local Area Network (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.............................................9
        6. VXLAN Deployment Scenarios....................................12
           6.1. Inner VLAN Tag Handling..................................16
        7. Security Considerations.......................................16
        8. IANA Considerations...........................................17
        9. Conclusions...................................................18
        10. References...................................................18
           10.1. Normative References....................................18
           10.2. Informative References..................................18
        11. Acknowledgments..............................................18
     
     
     
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     1. Introduction
     
        Server virtualization has placed increased demands on the physical
        network infrastructure. At a minimum, there is a need for more MAC
        address table entries throughout the switched Ethernet network due
        to potential attachment of hundreds of thousands of Virtual Machines
        (VMs), each with its own MAC address.
     
     
        Second, the VMs may be grouped according to their Virtual LAN
        (VLAN). In a data center one might need thousands of VLANs to
        partition the traffic according to the specific group that the VM
        may belong to. The current VLAN limit of 4094 is inadequate in such
        situations. A related requirement for virtualized environments 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. Using traditional approaches like
        Spanning Tree Protocol (STP) for a loop free topology can result in
        a large number of disabled links in such environments.
     
        Another type of demand that is being placed on data centers is the
        need to host multiple tenants, each with their own isolated network
        domain.  This  is  not  economical  to  realize  with  dedicated
        infrastructure, so network administrators opt to implement this over
        a shared network. A concomitant problem is that each tenant may
        independently assign MAC addresses and VLAN IDs leading to potential
        duplication of these on the physical network.
     
        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])
        while still preserving the Layer 2 model for inter-VM communication.
     
        The scenarios described above lead to a requirement for an overlay
        network. This overlay would be 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) which provides such an encapsulation scheme to
        address the  various requirements specified above.
     
     1.1. Acronyms & Definitions
     
              ACL -  Access Control List
     
             ECMP - Equal Cost Multipath
     
     
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             IGMP - Internet Group Management Protocol
     
             PIM -  Protocol Independent Multicast
     
             STP -  Spanning Tree Protocol
     
             ToR -  Top of Rack
     
             TRILL - Transparent Interconnection of Lots of Links
     
             VXLAN -   Virtual eXtensible Local Area Network
     
             VXLAN Segment - VXLAN Layer 2 overlay network over which VMs
     
                             communicate
     
             VXLAN Overlay Network - another term for VXLAN Segment
     
             VXLAN Gateway - an entity which forwards traffic between VXLAN
     
                            and non-VXLAN environments
     
             VTEP - VXLAN Tunnel End Point - an entity which originates or
     
                                            terminates VXLAN tunnels
     
             VLAN - Virtual Local Area Network
     
             VM -   Virtual Machine
     
             VNI -  VXLAN Network Identifier (or VXLAN Segment ID)
     
     
     
     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].
     
        In this document, these words will appear with that interpretation
        only when in ALL CAPS. Lower case uses of these words are not to be
        interpreted as carrying RFC-2119 significance.
     
     
     
     
     
     
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     3. VXLAN Problem Statement
     
        This section details the problems 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 & VLAN Spaces
     
        Current Layer 2 networks use the Spanning Tree Protocol (STP) to
        avoid loops in the network due to duplicate paths. STP will turn off
        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  use.  In  addition,  resiliency  due  to
        multipathing is not available with the STP model.  Newer initiatives
        like TRILL are being proposed to help with multipathing and thus
        surmount some of the problems with STP.  STP limitations may 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.
     
        Another 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 several data centers which are limited to less 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 environments accelerate the need for larger VLAN
        limits, as discussed in Section 3.3.
     
     3.2. Multitenant Environments
     
        Cloud computing involves on demand elastic provisioning of resources
        for multitenant environments. The most common example of cloud
        computing is the public cloud, where a cloud service provider offers
        these  elastic  services  to  multiple  customers  over  the  same
        infrastructure.
     
        Isolation of network traffic by 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
     
     
     
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        addition, there is often a need for multiple VLANs per tenant, which
        exacerbates the issue.
     
        Another use case is cross pod expansion. A pod typically consists of
        one or more racks of servers with its associated network and storage
        connectivity. Tenants may start off on a pod and, due to expansion,
        require servers/VMs on other pods, especially 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 complete 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 which 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 per server). This is a requirement since
        traffic from/to the VMs to the rest of the physical network will
        traverse the link to 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
        unknown destination frames.
     
     4. Virtual eXtensible Local Area Network (VXLAN)
     
        VXLAN  (Virtual  eXtensible  Local  Area  Network)  addresses  the
        requirements  of  Layer  2  and  Layer  3  data  center  network
        infrastructure in the presence of VMs in a multitenant 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 a Layer 3 network. Each overlay is termed a
     
     
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        VXLAN  segment.  Only  VMs  within  the  same  VXLAN  segment  can
        communicate with each other. Each VXLAN segment is scoped through a
        24 bit segment ID, hereafter termed the VXLAN Network Identifier
        (VNI). This allows up to 16M VXLAN segments to coexist within the
        same administrative domain.
     
        The VNI scopes 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 qualifier.  This qualifier is in an outer header envelope
        over 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 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 (VTEP) discussed in the
        following sections is located within the hypervisor on the server
        which houses 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  VXLAN  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  is
        discovered via source learning. Multicast is used for carrying
        unknown destination, broadcast and multicast frames.  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 before. 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. If so, an
        outer header comprising an outer MAC, outer IP address and VXLAN
        header (see Figure 1 in Section 5 for frame format) are inserted in
        front of the original MAC frame. The final packet is transmitted out
        to the destination, which is the IP address of the remote VTEP
        connecting the destination VM addressed by the inner MAC destination
        address.
     
     
     
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        Upon reception, the remote VTEP verifies that the VNI is a valid one
        and is used by the destination VM. If so, the packet is stripped of
        its  outer  header  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 MAC to outer Source IP address
        mapping. 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 VM is performed as with non-VXLAN environments
        except  as  described  below.  Broadcast  frames  are  used  but  are
        encapsulated within a multicast packet, as detailed in the next
        section.
     
     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 broadcast frame. In the non-
        VXLAN environment, this frame would be sent out using MAC broadcast
        which 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. VXLAN
     
        To realize 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 that
        specific multicast address. In addition, use of multicast routing
        protocols like PIM 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
     
     
     
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        each VTEP can act as both the source and destination for multicast
        packets, a protocol like PIM-bidir 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.
     
        Another point to note is 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  Protocol  Independent  Multicast
        Sparse  Mode  (PIM-SM)  is  used  by  the  individual  Layer  3  IP
        routers/switches within the network. This is used to build efficient
        multicast forwarding trees so that multicast trees are only sent to
        those hosts which 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.
     
     5. VXLAN Frame Format
     
        The VXLAN frame format is shown below. Parsing this from the bottom,
        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 tag (see Section 6 for further details of inner
        VLAN tag handling).
     
        The inner MAC frame is encapsulated with the following three headers
        starting from the innermost header.
     
         O VXLAN Header:  This is an 8 byte field which has:
     
     
     
     
     
     
     
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           o Flags (8 bits) where the I flag MUST be set  to 1 for a valid
          VXLAN Network ID (VNI).  The remaining 7 bits (designated "R") are
          reserved fields and MUST be set to zero.
     
          o 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.
     
          o Reserved fields (24 bits and 8 bits) - MUST be set to zero.
     
        O 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 to be obtained by IANA assignment. It is recommended
        that the source port be a hash of the inner Ethernet frame's headers
        to obtain a level of entropy for ECMP/load balancing of the VM to VM
        traffic across the VXLAN overlay.
     
        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 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 endpoint 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.
     
        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 depicted by the inner source MAC address) is
        running.  The destination IP address is the IP address of the VTEP
        connecting the communicating VM as depicted by the inner destination
        MAC address.
     
        O Outer Ethernet Header (example):  Figure 1 shows an example of a
        common encapsulation of the entire IP packet with the VXLAN
        encapsulation inside an outer Ethernet header. The destination MAC
     
     
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        address in this frame may be the address of the target VTEP or 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                       |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       Optional Ethertype = C-Tag 802.1Q   | Outer.VLAN Tag Information    |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           | Ethertype 0x0800              |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        Outer IP Header:
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |Version|  IHL  |Type of Service|          Total Length         |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |         Identification        |Flags|      Fragment Offset    |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |  Time to Live |    Protocol   |         Header Checksum       |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                       Outer Source Address                    |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                   Outer Destination Address                   |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Outer UDP Header:
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |       Source Port = xxxx      |       Dest Port = VXLAN Port  |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |           UDP Length          |        UDP Checksum           |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         VXLAN Header:
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |R|R|R|R|I|R|R|R|            Reserved                           |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                VXLAN Network Identifier (VNI) |   Reserved    |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
     
     
     
     
     
     
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             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
     
      Inner Ethernet Header:             |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Inner Destination MAC Address                     |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            | Inner Destination MAC Address | Inner Source MAC Address      |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |                Inner Source MAC Address                       |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Optional Ethertype = 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 VXLAN Frame Format
     
        The frame format above shows tunneling of Ethernet frames using IPv4
        for transport.  Use of VXLAN with IPv6 transport will be addressed
        in a future version of this draft.
     
     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 one
        Layer 2 network. The VXLAN segments/overlay networks are overlaid on
        top of these Layer 2 or Layer 3 networks.
     
        Consider Figure 2 below depicting two virtualized servers attached
        to a Layer 3 infrastructure. The servers could be on the same rack,
        or on different racks or potentially across data centers within the
        same administrative domain. There are 4 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
     
     
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        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.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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          +------------+-------------+
          |        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 2   VXLAN Deployment - VTEPs across a Layer 3 Network
     
     
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        One deployment scenario is where the tunnel termination point is a
        physical server which understands VXLAN. Another scenario is where
        nodes on a VXLAN overlay network need to communicate with nodes on
        legacy networks which 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 3 below with a switch
        acting as a VXLAN gateway) which forward traffic between VXLAN and
        non-VXLAN environments.
     
        Consider Figure 3 for the following discussion. For incoming frames
        on the VXLAN connected interface, the gateway strips out the VXLAN
        header and forwards 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 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 which
        terminates VXLAN tunnels in a hybrid cloud environment. Note that in
        all these instances, the gateway functionality could be implemented
        in software or hardware.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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           +---+-----+---+                                    +---+-----+---+
           |    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 3   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 endpoints - either by having inappropriate access to a LAN
        and  snooping on traffic or 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
     
     
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        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 proposal does not, at this time, 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 encapsulation of VXLAN enables exploiting the 5 tuple
        based  ACLs  (Access  Control  Lists)  functionality  in  physical
        switches.
     
        Tunneled traffic over the IP network can be secured with traditional
        IPSEC mechanisms that authenticate and optionally encrypt VXLAN
        traffic.  This  will,  of  course,  need  to  be  coupled  with  an
        authentication infrastructure for authorized endpoints 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
     
        An IANA port will be requested for the VXLAN destination UDP port.
     
     
     
     
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     9. Conclusions
     
        This  document  has  introduced  VXLAN,  an  overlay  framework  for
        transporting  MAC  frames  generated  by  VMs  in  isolated  Layer  2
        networks over an IP network. Through this scheme, it is possible to
        stretch Layer 2 networks across Layer 3 networks. This finds use in
        virtualized data center environments where Layer 2 networks may need
        to span across the entire data center, or even between data centers.
     
     10. References
     
     10.1. Normative References
     
         [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.
     
     10.2. Informative References
     
        [RFC4601] Fenner, B., Handley, M., Holbrook, H., and Kouvelas, I.,
        "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol
        Specification", RFC 4601, August 2006.
     
        [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and Vicisano, L.,
        "Bidirectional  Protocol  Independent  Multicast  (BIDIR-PIM)",  RFC
        5015, October 2007.
     
        [RFC4541]  Christensen,  M.,  Kimball,  K.,  and  Solensky,  F.,
        "Considerations  for  Internet  Group  Management  Protocol  (IGMP)
        and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541,
        May 2006.
     
     11. Acknowledgments
     
        The authors wish to thank Ajit Sanzgiri for contributions to the
        Security Considerations section and editorial inputs, Joseph Cheng,
        Margaret Petrus and Milin Desai for their editorial reviews, inputs
        and comments.
     
     
     
     
     
     
     
     
     
     
     
     
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     Authors' Addresses
     
        Mallik Mahalingam
        VMware Inc.
        3401 Hillview
        Palo Alto, CA 94304
     
        Email: mallik@vmware.com
     
        Dinesh G. Dutt
        Cisco Systems, Inc.
        170 W. Tasman Avenue
        Palo Alto, CA 94304
     
        Email: ddutt@cisco.com
     
        Kenneth Duda
        Arista Networks
        5470 Great America Parkway
        Santa Clara, CA 95054
     
        Email: kduda@aristanetworks.com
     
        Puneet Agarwal
        Broadcom Corporation
        3151 Zanker Road
        San Jose, CA 95134
     
        Email: pagarwal@broadcom.com
     
        Lawrence Kreeger
        Cisco Systems, Inc.
        170 W. Tasman Avenue
        Palo Alto, CA 94304
     
        Email: kreeger@cisco.com
     
        T. Sridhar
        VMware Inc.
        3401 Hillview
        Palo Alto, CA 94304
     
        Email: tsridhar@vmware.com
     
     
     
     
     
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        Mike Bursell
        Citrix Systems Research & Development Ltd.
        Building 101
        Cambridge Science Park
        Milton Road
        Cambridge CB4 0FY
        United Kingdom
     
        Email: mike.bursell@citrix.com
     
        Chris Wright
        Red Hat Inc.
        1801 Varsity Drive
        Raleigh, NC 27606
     
        Email: chrisw@redhat.com
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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