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VXLAN: A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks
draft-mahalingam-dutt-dcops-vxlan-09

Internet Engineering Task Force                           M. Mahalingam 
Internet Draft                                                Storvisor 
Intended Status: Informational                                  D. Dutt 
Expires: October 10, 2014                              Cumulus Networks 
                                                                K. Duda 
                                                                 Arista 
                                                             P. Agarwal  
                                                               Broadcom 
                                                             L. Kreeger 
                                                                  Cisco 
                                                             T. Sridhar 
                                                                 VMware 
                                                             M. Bursell 
                                                                 Citrix 
                                                              C. Wright 
                                                                Red Hat 
                                                         April 10, 2014 
                                                                        
                                                                  
 
                                      
    VXLAN: A Framework for Overlaying Virtualized Layer 2 Networks over 
                             Layer 3 Networks 
                 draft-mahalingam-dutt-dcops-vxlan-09.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 October 10, 2014. 

 
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Copyright Notice 

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

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

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. This memo documents the 
  deployed VXLAN protocol for the benefit of the IETF community.  

    

Table of Contents 

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

 
 
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      9.1. Normative References.....................................21 
      9.2. Informative References...................................21 
   10. Acknowledgments..............................................22 
 
1. Introduction 

   Server virtualization has placed increased demands on the physical 
   network infrastructure. A physical server now has multiple virtual 
   machines (VMs) each with its own MAC address.  This requires larger 
   MAC address tables in the switched Ethernet network due to potential 
   attachment of and communication among hundreds of thousands of VMs. 
    
   In the case when the VMs in a data center are grouped according to 
   their Virtual LAN (VLAN, one might need thousands of VLANs to 
   partition the traffic according to the specific group that the VM 
   may belong to. The current VLAN limit of 4094 is inadequate in such 
   situations.  

   Data centers are often required to host multiple tenants, each with 
   their own isolated network domain. Since it is not economical to 
   realize this with dedicated infrastructure, network administrators 
   opt to implement isolation over a shared network. In such scenarios, 
   a common problem is that each tenant may independently assign MAC 
   addresses and VLAN IDs leading to potential duplication of these on 
   the physical network.  

   An important requirement for virtualized environments using a Layer 
   2 physical infrastructure is having the Layer 2 network scale across 
   the entire data center or even between data centers for efficient 
   allocation of compute, network and storage resources. In such 
   networks, using traditional approaches like the Spanning Tree 
   Protocol (STP) for a loop free topology can result in a large number 
   of disabled links. 

   The last scenario is the case where the network operator prefers to 
   use IP for interconnection of the physical infrastructure (e.g. to 
   achieve multipath scalability through Equal Cost Multipath (ECMP), 
   thus avoiding disabled links). Even in such environments, there is a 
   need to preserve the Layer 2 model for inter-VM communication.       

   The scenarios described above lead to a requirement for an overlay 
   network. This overlay is used to carry the MAC traffic from the 
   individual VMs in an encapsulated format over a logical "tunnel".  
 
 
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   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. This memo 
   documents the deployed VXLAN protocol for the benefit of the IETF 
   community.  

1.1. Acronyms & Definitions 

         ACL  - Access Control List 

        ECMP - 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 - Virtual eXtensible Local Area Network 

        VXLAN Segment - VXLAN Layer 2 overlay network over which VMs 

                        communicate 

        VXLAN Overlay Network -  VXLAN Segment 

        VXLAN Gateway - an entity which forwards traffic between VXLAN 

                        and non-VXLAN environments 

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

        VLAN - Virtual Local Area Network 

 
 
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        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].  

3. VXLAN Problem Statement 

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

3.1. Limitations imposed by Spanning Tree & VLAN Ranges 

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

   A key characteristic of Layer 2 data center networks is their use of 
   Virtual LANs (VLANs) to provide broadcast isolation.  A 12 bit VLAN 
   ID is used in the Ethernet data frames to divide the larger Layer 2 
   network into multiple broadcast domains.  This has served well for 
   several data centers which 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 

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

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

   Today's virtualized environments place additional demands on the MAC 
   address tables of Top of Rack (ToR) switches 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 needed because traffic 
   from/to the VMs to the rest of the physical network will traverse 

 
 
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   the link between the server and the switch. A typical ToR switch 
   could connect to 24 or 48 servers depending upon the number of its 
   server facing ports. A data center might consist of several racks, 
   so each ToR switch would need to maintain an address table for the 
   communicating VMs across the various physical servers. This places a 
   much larger demand on the table capacity compared to non-virtualized 
   environments.  

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

4. Virtual eXtensible Local Area Network (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 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 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 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 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 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 hosts the VM. Thus, the VNI and VXLAN 
   related tunnel/outer header encapsulation are known only to the VTEP 
   - the VM never sees it (see Figure 1). Note that it is possible that 
   VTEPs could also be on a physical switch or physical server and 

 
 
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   could be implemented in software or hardware.  One use case where 
   the VTEP is a physical switch is discussed in Section 6 on VXLAN 
   deployment scenarios. 

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

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

4.1. Unicast VM to VM communication  

   Consider a VM within a VXLAN overlay network. This VM is unaware of 
   VXLAN. To communicate with a VM on a different host, it sends a MAC 
   frame destined to the target as normal. The VTEP on the physical 
   host looks up the VNI to which this VM is associated.  It then 
   determines if the destination MAC is on the same segment and if 
   there is a mapping of the destination MAC address to  
   the remote VTEP. If so, an outer header comprising an outer MAC, 
   outer IP header and VXLAN header (see Figure 1 in Section 5 for 
   frame format) are prepended to the original MAC frame. The 
   encapsulated packet is forwarded towards the remote VTEP. Upon 
   reception, the remote VTEP verifies the validity of the VNI and if 
   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 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.  

 
 
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   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 broadcast frame. In the non-
   VXLAN environment, this frame would be sent out using MAC broadcast 
   across all switches carrying that VLAN.  

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

   To effect this, we need to have a mapping between the VXLAN VNI and 
   the IP multicast group that it will use. This mapping is done at the 
   management layer and provided to the individual VTEPs through a 
   management channel. Using this mapping, the VTEP can provide IGMP 
   membership reports to the upstream switch/router to join/leave the 
   VXLAN related IP multicast groups as needed. This will enable 
   pruning of the leaf nodes for specific multicast traffic addresses 
   based on whether a member is available on this host using the 
   specific multicast address (see [RFC4541]). In addition, use of 
   multicast routing protocols like Protocol Independent Multicast - 
   Sparse Mode (PIM-SM see [RFC4601]) will provide efficient multicast 
   trees within the Layer 3 network.  

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

 
 
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   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 have requested to receive them.  

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

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

    

5. VXLAN Frame Format 

   The VXLAN frame format is shown below. Parsing this from the bottom 
   of the frame - above the outer frame check sequence (FCS), there is 
   an inner MAC frame with its own Ethernet header with source, 
   destination MAC addresses along with the Ethernet type plus an 
   optional VLAN. See Section 6 for further details of inner VLAN tag 
   handling. 
    
   The inner MAC frame is encapsulated with the following four headers 
   (starting from the innermost header):  
 
 
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    O VXLAN Header:  This is an 8 byte field which has:  
       

     o Flags (8 bits)-  where the I flag MUST be set to 1 for a valid 
     VXLAN Network ID (VNI).  The other 7  bits (designated "R") are 
     reserved fields and MUST be set to zero on transmit and ignored on 
     receive.  
      
     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 with each other.  
  
     o Reserved fields (24 bits and 8 bits) - MUST be set to zero on 
   transmit and ignored on receive. 
  
   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.  IANA has assigned the value 4789 for the VXLAN UDP 
   port and this value SHOULD be used by default as the destination UDP 
   port.  Some early implementations of VXLAN have used other values 
   for the destination port.  To enable interoperability with these 
   implementations, the destination port SHOULD be configurable.  It is 
   recommended that the UDP source port number be calculated using a 
   hash of fields from the inner packet - one example being a hash of 
   the inner Ethernet frame`s headers. This is to enable a level of 
   entropy for 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 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 

 
 
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   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.  
                     

 
 
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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  
    
  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      |       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:              
 
 
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       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       |             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 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            |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     
 
 
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  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      |       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                       | 
 
 
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       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       |OptnlEthtype = C-Tag 802.1Q    | Inner.VLAN Tag Information    | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 
  Payload: 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       | Ethertype of Original Payload |                               | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               | 
       |                                  Original Ethernet Payload    | 
       |                                                               | 
       |(Note that the original Ethernet Frame's FCS is not included)  |                               
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
  
  Frame Check Sequence: 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       |   New FCS (Frame Check Sequence) for Outer Ethernet Frame     | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
      
           Figure 2 VXLAN Frame Format with IPv6 Outer Header 

6. VXLAN Deployment Scenarios 

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

   Consider Figure 3 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 
   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 3   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. An alternate 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 4 below with a 
   switch acting as a VXLAN gateway) which 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 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 4   VXLAN Deployment - VXLAN Gateway 

    

6.1. Inner VLAN Tag Handling 

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

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

7. Security Considerations 

   Traditionally, layer 2 networks can only be attacked from 'within' 
   by rogue endpoints - either by having inappropriate access to a LAN 
   and snooping on traffic or by injecting spoofed packets to 'take 

 
 
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   over' another MAC address or by flooding and causing denial of 
   service. A   MAC-over-IP mechanism for delivering Layer 2 traffic 
   significantly extends this attack surface. This can happen by rogues 
   injecting themselves into the network by subscribing to one or more 
   multicast groups that carry broadcast traffic for VXLAN segments and 
   also by sourcing MAC-over-UDP frames into the transport network to 
   inject spurious traffic, possibly to hijack MAC addresses. 
    
   This document 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 configuration and use of 
   the 5 tuple based ACLs (Access Control Lists) 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 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.  

 
 
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8. IANA Considerations 

   A well-known UDP port (4789) has been assigned by the IANA 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 for Local and Metropolitan Area Networks/              
   Media Access Control (MAC) Bridges, IEEE P802.1D-2004". 

   [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. 

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

   [802.1aq] "Standard for Local and Metropolitan Area Networks /              
   Virtual Bridged Local Area Networks / Amendment20: Shortest             
   Path Bridging, IEEE P802.1aq-2012". 

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

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

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

 
 
10. Acknowledgments 

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

Authors' Addresses 

   Mallik Mahalingam 
   Storvisor  
   333 W.El Camino Real 
   Sunnyvale, CA 94087 
       
   Email: mallik_mahalingam@yahoo.com 
    
   Dinesh G. Dutt 
   Cumulus Networks 
   140C S.Whisman Road 
   Mountain View, CA 94041  
                         
   Email: ddutt.ietf@hobbesdutt.com 
    
   Kenneth Duda 
   Arista Networks 
   5470 Great America Parkway 
   Santa Clara, CA 95054 
    
   Email: kduda@aristanetworks.com 
    
   Puneet Agarwal 
   Broadcom Corporation 
   3151 Zanker Road 
 
 
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   San Jose, CA 95134 
 
   Email: pagarwal@broadcom.com 
 
   Lawrence Kreeger 
   Cisco Systems, Inc. 
   170 W. Tasman Avenue 
   San Jose, CA 95134 
       
   Email: kreeger@cisco.com 
    
   T. Sridhar 
   VMware Inc. 
   3401 Hillview  
   Palo Alto, CA 94304 
       
   Email: tsridhar@vmware.com 
    
   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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