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Independent Submission                                      P. Garg, Ed.Request for Comments: 7637                                  Y. Wang, Ed.Category: Informational                                        MicrosoftISSN: 2070-1721                                           September 2015NVGRE: Network Virtualization Using Generic Routing EncapsulationAbstract   This document describes the usage of the Generic Routing   Encapsulation (GRE) header for Network Virtualization (NVGRE) in   multi-tenant data centers.  Network Virtualization decouples virtual   networks and addresses from physical network infrastructure,   providing isolation and concurrency between multiple virtual networks   on the same physical network infrastructure.  This document also   introduces a Network Virtualization framework to illustrate the use   cases, but the focus is on specifying the data-plane aspect of NVGRE.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This is a contribution to the RFC Series, independently of any other   RFC stream.  The RFC Editor has chosen to publish this document at   its discretion and makes no statement about its value for   implementation or deployment.  Documents approved for publication by   the RFC Editor are not a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7637.Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Garg & Wang                   Informational                     [Page 1]

RFC 7637                          NVGRE                   September 2015Table of Contents1. Introduction ....................................................21.1. Terminology ................................................42. Conventions Used in This Document ...............................43. Network Virtualization Using GRE (NVGRE) ........................43.1. NVGRE Endpoint .............................................53.2. NVGRE Frame Format .........................................53.3. Inner Tag as Defined by IEEE 802.1Q ........................83.4. Reserved VSID ..............................................84. NVGRE Deployment Considerations .................................94.1. ECMP Support ...............................................94.2. Broadcast and Multicast Traffic ............................94.3. Unicast Traffic ............................................94.4. IP Fragmentation ..........................................104.5. Address/Policy Management and Routing .....................104.6. Cross-Subnet, Cross-Premise Communication .................104.7. Internet Connectivity .....................................124.8. Management and Control Planes .............................124.9. NVGRE-Aware Devices .......................................124.10. Network Scalability with NVGRE ...........................135. Security Considerations ........................................146. Normative References ...........................................14   Contributors ......................................................16   Authors' Addresses ................................................171.  Introduction   Conventional data center network designs cater to largely static   workloads and cause fragmentation of network and server capacity [6]   [7].  There are several issues that limit dynamic allocation and   consolidation of capacity.  Layer 2 networks use the Rapid Spanning   Tree Protocol (RSTP), which is designed to eliminate loops by   blocking redundant paths.  These eliminated paths translate to wasted   capacity and a highly oversubscribed network.  There are alternative   approaches such as the Transparent Interconnection of Lots of Links   (TRILL) that address this problem [13].   The network utilization inefficiencies are exacerbated by network   fragmentation due to the use of VLANs for broadcast isolation.  VLANs   are used for traffic management and also as the mechanism for   providing security and performance isolation among services belonging   to different tenants.  The Layer 2 network is carved into smaller-   sized subnets (typically, one subnet per VLAN), with VLAN tags   configured on all the Layer 2 switches connected to server racks that   host a given tenant's services.  The current VLAN limits   theoretically allow for 4,000 such subnets to be created.  The sizeGarg & Wang                   Informational                     [Page 2]

RFC 7637                          NVGRE                   September 2015   of the broadcast domain is typically restricted due to the overhead   of broadcast traffic.  The 4,000-subnet limit on VLANs is no longer   sufficient in a shared infrastructure servicing multiple tenants.   Data center operators must be able to achieve high utilization of   server and network capacity.  In order to achieve efficiency, it   should be possible to assign workloads that operate in a single Layer   2 network to any server in any rack in the network.  It should also   be possible to migrate workloads to any server anywhere in the   network while retaining the workloads' addresses.  This can be   achieved today by stretching VLANs; however, when workloads migrate,   the network needs to be reconfigured and that is typically error   prone.  By decoupling the workload's location on the LAN from its   network address, the network administrator configures the network   once, not every time a service migrates.  This decoupling enables any   server to become part of any server resource pool.   The following are key design objectives for next-generation data   centers:      a) location-independent addressing      b) the ability to a scale the number of logical Layer 2 / Layer 3         networks, irrespective of the underlying physical topology or         the number of VLANs      c) preserving Layer 2 semantics for services and allowing them to         retain their addresses as they move within and across data         centers      d) providing broadcast isolation as workloads move around without         burdening the network control plane   This document describes use of the Generic Routing Encapsulation   (GRE) header [3] [4] for network virtualization.  Network   virtualization decouples a virtual network from the underlying   physical network infrastructure by virtualizing network addresses.   Combined with a management and control plane for the virtual-to-   physical mapping, network virtualization can enable flexible virtual   machine placement and movement and provide network isolation for a   multi-tenant data center.   Network virtualization enables customers to bring their own address   spaces into a multi-tenant data center, while the data center   administrators can place the customer virtual machines anywhere in   the data center without reconfiguring their network switches or   routers, irrespective of the customer address spaces.Garg & Wang                   Informational                     [Page 3]

RFC 7637                          NVGRE                   September 20151.1.  Terminology   Please refer to RFCs 7364 [10] and 7365 [11] for more formal   definitions of terminology.  The following terms are used in this   document.   Customer Address (CA): This is the virtual IP address assigned and   configured on the virtual Network Interface Controller (NIC) within   each VM.  This is the only address visible to VMs and applications   running within VMs.   Network Virtualization Edge (NVE): This is an entity that performs   the network virtualization encapsulation and decapsulation.   Provider Address (PA): This is the IP address used in the physical   network.  PAs are associated with VM CAs through the network   virtualization mapping policy.   Virtual Machine (VM): This is an instance of an OS running on top of   the hypervisor over a physical machine or server.  Multiple VMs can   share the same physical server via the hypervisor, yet are completely   isolated from each other in terms of CPU usage, storage, and other OS   resources.   Virtual Subnet Identifier (VSID): This is a 24-bit ID that uniquely   identifies a virtual subnet or virtual Layer 2 broadcast domain.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 inRFC 2119 [1].   In this document, these words will appear with that interpretation   only when in ALL CAPS.  Lowercase uses of these words are not to be   interpreted as carrying the significance defined inRFC 2119.3.  Network Virtualization Using GRE (NVGRE)   This section describes Network Virtualization using GRE (NVGRE).   Network virtualization involves creating virtual Layer 2 topologies   on top of a physical Layer 3 network.  Connectivity in the virtual   topology is provided by tunneling Ethernet frames in GRE over IP over   the physical network.   In NVGRE, every virtual Layer 2 network is associated with a 24-bit   identifier, called a Virtual Subnet Identifier (VSID).  A VSID is   carried in an outer header as defined inSection 3.2.  This allowsGarg & Wang                   Informational                     [Page 4]

RFC 7637                          NVGRE                   September 2015   unique identification of a tenant's virtual subnet to various devices   in the network.  A 24-bit VSID supports up to 16 million virtual   subnets in the same management domain, in contrast to only 4,000 that   is achievable with VLANs.  Each VSID represents a virtual Layer 2   broadcast domain, which can be used to identify a virtual subnet of a   given tenant.  To support multi-subnet virtual topology, data center   administrators can configure routes to facilitate communication   between virtual subnets of the same tenant.   GRE is a Proposed Standard from the IETF [3] [4] and provides a way   for encapsulating an arbitrary protocol over IP.  NVGRE leverages the   GRE header to carry VSID information in each packet.  The VSID   information in each packet can be used to build multi-tenant-aware   tools for traffic analysis, traffic inspection, and monitoring.   The following sections detail the packet format for NVGRE; describe   the functions of an NVGRE endpoint; illustrate typical traffic flow   both within and across data centers; and discuss address/policy   management, and deployment considerations.3.1.  NVGRE Endpoint   NVGRE endpoints are the ingress/egress points between the virtual and   the physical networks.  The NVGRE endpoints are the NVEs as defined   in the Network Virtualization over Layer 3 (NVO3) Framework document   [11].  Any physical server or network device can be an NVGRE   endpoint.  One common deployment is for the endpoint to be part of a   hypervisor.  The primary function of this endpoint is to   encapsulate/decapsulate Ethernet data frames to and from the GRE   tunnel, ensure Layer 2 semantics, and apply isolation policy scoped   on VSID.  The endpoint can optionally participate in routing and   function as a gateway in the virtual topology.  To encapsulate an   Ethernet frame, the endpoint needs to know the location information   for the destination address in the frame.  This information can be   provisioned via a management plane or obtained via a combination of   control-plane distribution or data-plane learning approaches.  This   document assumes that the location information, including VSID, is   available to the NVGRE endpoint.3.2.  NVGRE Frame Format   The GRE header format as specified in RFCs 2784 [3] and 2890 [4] is   used for communication between NVGRE endpoints.  NVGRE leverages the   Key extension specified inRFC 2890 [4] to carry the VSID.  The   packet format for Layer 2 encapsulation in GRE is shown in Figure 1.Garg & Wang                   Informational                     [Page 5]

RFC 7637                          NVGRE                   September 2015   Outer Ethernet Header:    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) 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 IPv4 Header:   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |Version|  HL   |Type of Service|          Total Length         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |         Identification        |Flags|      Fragment Offset    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Time to Live | Protocol 0x2F |         Header Checksum       |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                      (Outer) Source Address                   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                  (Outer) Destination Address                  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   GRE Header:   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |0| |1|0|   Reserved0     | Ver |   Protocol Type 0x6558        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |               Virtual Subnet ID (VSID)        |    FlowID     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Inner Ethernet Header   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                (Inner) Destination MAC Address                |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |(Inner)Destination MAC Address |  (Inner)Source MAC Address    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                  (Inner) Source MAC Address                   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |       Ethertype 0x0800        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Garg & Wang                   Informational                     [Page 6]

RFC 7637                          NVGRE                   September 2015   Inner IPv4 Header:   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |Version|  HL   |Type of Service|          Total Length         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |         Identification        |Flags|      Fragment Offset    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Time to Live |    Protocol   |         Header Checksum       |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                       Source Address                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                    Destination Address                        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                    Options                    |    Padding    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                      Original IP Payload                      |   |                                                               |   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               Figure 1: GRE Encapsulation Frame Format   Note: HL stands for Header Length.   The outer/delivery headers include the outer Ethernet header and the   outer IP header:   o  The outer Ethernet header: The source Ethernet address in the      outer frame is set to the MAC address associated with the NVGRE      endpoint.  The destination endpoint may or may not be on the same      physical subnet.  The destination Ethernet address is set to the      MAC address of the next-hop IP address for the destination NVE.      The outer VLAN tag information is optional and can be used for      traffic management and broadcast scalability on the physical      network.   o  The outer IP header: Both IPv4 and IPv6 can be used as the      delivery protocol for GRE.  The IPv4 header is shown for      illustrative purposes.  Henceforth, the IP address in the outer      frame is referred to as the Provider Address (PA).  There can be      one or more PA associated with an NVGRE endpoint, with policy      controlling the choice of which PA to use for a given Customer      Address (CA) for a customer VM.   In the GRE header:   o  The C (Checksum Present) and S (Sequence Number Present) bits in      the GRE header MUST be zero.Garg & Wang                   Informational                     [Page 7]

RFC 7637                          NVGRE                   September 2015   o  The K (Key Present) bit in the GRE header MUST be set to one.  The      32-bit Key field in the GRE header is used to carry the Virtual      Subnet ID (VSID) and the FlowID:      -  Virtual Subnet ID (VSID): This is a 24-bit value that is used         to identify the NVGRE-based Virtual Layer 2 Network.      -  FlowID: This is an 8-bit value that is used to provide per-flow         entropy for flows in the same VSID.  The FlowID MUST NOT be         modified by transit devices.  The encapsulating NVE SHOULD         provide as much entropy as possible in the FlowID.  If a FlowID         is not generated, it MUST be set to all zeros.   o  The Protocol Type field in the GRE header is set to 0x6558      (Transparent Ethernet Bridging) [2].   In the inner headers (headers of the GRE payload):   o  The inner Ethernet frame comprises an inner Ethernet header      followed by optional inner IP header, followed by the IP payload.      The inner frame could be any Ethernet data frame not just IP.      Note that the inner Ethernet frame's Frame Check Sequence (FCS) is      not encapsulated.   o  For illustrative purposes, IPv4 headers are shown as the inner IP      headers, but IPv6 headers may be used.  Henceforth, the IP address      contained in the inner frame is referred to as the Customer      Address (CA).3.3.  Inner Tag as Defined by IEEE 802.1Q   The inner Ethernet header of NVGRE MUST NOT contain the tag as   defined by IEEE 802.1Q [5].  The encapsulating NVE MUST remove any   existing IEEE 802.1Q tag before encapsulation of the frame in NVGRE.   A decapsulating NVE MUST drop the frame if the inner Ethernet frame   contains an IEEE 802.1Q tag.3.4.  Reserved VSID   The VSID range from 0-0xFFF is reserved for future use.   The VSID 0xFFFFFF is reserved for vendor-specific NVE-to-NVE   communication.  The sender NVE SHOULD verify the receiver NVE's   vendor before sending a packet using this VSID; however, such a   verification mechanism is out of scope of this document.   Implementations SHOULD choose a mechanism that meets their   requirements.Garg & Wang                   Informational                     [Page 8]

RFC 7637                          NVGRE                   September 20154.  NVGRE Deployment Considerations4.1.  ECMP Support   Equal-Cost Multipath (ECMP) may be used to provide load balancing.   If ECMP is used, it is RECOMMENDED that the ECMP hash is calculated   either using the outer IP frame fields and entire Key field (32 bits)   or the inner IP and transport frame fields.4.2.  Broadcast and Multicast Traffic   To support broadcast and multicast traffic inside a virtual subnet,   one or more administratively scoped multicast addresses [8] [9] can   be assigned for the VSID.  All multicast or broadcast traffic   originating from within a VSID is encapsulated and sent to the   assigned multicast address.  From an administrative standpoint, it is   possible for network operators to configure a PA multicast address   for each multicast address that is used inside a VSID; this   facilitates optimal multicast handling.  Depending on the hardware   capabilities of the physical network devices and the physical network   architecture, multiple virtual subnets may use the same physical IP   multicast address.   Alternatively, based upon the configuration at the NVE, broadcast and   multicast in the virtual subnet can be supported using N-way unicast.   In N-way unicast, the sender NVE would send one encapsulated packet   to every NVE in the virtual subnet.  The sender NVE can encapsulate   and send the packet as described inSection 4.3 ("Unicast Traffic").   This alleviates the need for multicast support in the physical   network.4.3.  Unicast Traffic   The NVGRE endpoint encapsulates a Layer 2 packet in GRE using the   source PA associated with the endpoint with the destination PA   corresponding to the location of the destination endpoint.  As   outlined earlier, there can be one or more PAs associated with an   endpoint and policy will control which ones get used for   communication.  The encapsulated GRE packet is bridged and routed   normally by the physical network to the destination PA.  Bridging   uses the outer Ethernet encapsulation for scope on the LAN.  The only   requirement is bidirectional IP connectivity from the underlying   physical network.  On the destination, the NVGRE endpoint   decapsulates the GRE packet to recover the original Layer 2 frame.   Traffic flows similarly on the reverse path.Garg & Wang                   Informational                     [Page 9]

RFC 7637                          NVGRE                   September 20154.4.  IP FragmentationSection 5.1 of RFC 2003 [12] specifies mechanisms for handling   fragmentation when encapsulating IP within IP.  The subset of   mechanisms NVGRE selects are intended to ensure that NVGRE-   encapsulated frames are not fragmented after encapsulation en route   to the destination NVGRE endpoint and that traffic sources can   leverage Path MTU discovery.   A sender NVE MUST NOT fragment NVGRE packets.  A receiver NVE MAY   discard fragmented NVGRE packets.  It is RECOMMENDED that the MTU of   the physical network accommodates the larger frame size due to   encapsulation.  Path MTU or configuration via control plane can be   used to meet this requirement.4.5.  Address/Policy Management and Routing   Address acquisition is beyond the scope of this document and can be   obtained statically, dynamically, or using stateless address   autoconfiguration.  CA and PA space can be either IPv4 or IPv6.  In   fact, the address families don't have to match; for example, a CA can   be IPv4 while the PA is IPv6, and vice versa.4.6.  Cross-Subnet, Cross-Premise Communication   One application of this framework is that it provides a seamless path   for enterprises looking to expand their virtual machine hosting   capabilities into public clouds.  Enterprises can bring their entire   IP subnet(s) and isolation policies, thus making the transition to or   from the cloud simpler.  It is possible to move portions of an IP   subnet to the cloud; however, that requires additional configuration   on the enterprise network and is not discussed in this document.   Enterprises can continue to use existing communications models like   site-to-site VPN to secure their traffic.   A VPN gateway is used to establish a secure site-to-site tunnel over   the Internet, and all the enterprise services running in virtual   machines in the cloud use the VPN gateway to communicate back to the   enterprise.  For simplicity, we use a VPN gateway configured as a VM   (shown in Figure 2) to illustrate cross-subnet, cross-premise   communication.Garg & Wang                   Informational                    [Page 10]

RFC 7637                          NVGRE                   September 2015   +-----------------------+        +-----------------------+   |       Server 1        |        |       Server 2        |   | +--------+ +--------+ |        | +-------------------+ |   | | VM1    | | VM2    | |        | |    VPN Gateway    | |   | | IP=CA1 | | IP=CA2 | |        | | Internal  External| |   | |        | |        | |        | |  IP=CAg   IP=GAdc | |   | +--------+ +--------+ |        | +-------------------+ |   |       Hypervisor      |        |     | Hypervisor| ^   |   +-----------------------+        +-------------------:---+               | IP=PA1                   | IP=PA4    | :               |                          |           | :               |     +-------------------------+      | : VPN               +-----|     Layer 3 Network     |------+ : Tunnel                     +-------------------------+        :                                  |                     :        +-----------------------------------------------:--+        |                                               :  |        |                     Internet                  :  |        |                                               :  |        +-----------------------------------------------:--+                                  |                     v                                  |   +-------------------+                                  |   |    VPN Gateway    |                                  |---|                   |                             IP=GAcorp| External IP=GAcorp|                                      +-------------------+                                                |                                    +-----------------------+                                    |  Corp Layer 3 Network |                                    |      (In CA Space)    |                                    +-----------------------+                                                |                                   +---------------------------+                                   |       Server X            |                                   | +----------+ +----------+ |                                   | | Corp VMe1| | Corp VMe2| |                                   | |  IP=CAe1 | |  IP=CAe2 | |                                   | +----------+ +----------+ |                                   |         Hypervisor        |                                   +---------------------------+            Figure 2: Cross-Subnet, Cross-Premise Communication   The packet flow is similar to the unicast traffic flow between VMs;   the key difference in this case is that the packet needs to be sent   to a VPN gateway before it gets forwarded to the destination.  As   part of routing configuration in the CA space, a per-tenant VPN   gateway is provisioned for communication back to the enterprise.  TheGarg & Wang                   Informational                    [Page 11]

RFC 7637                          NVGRE                   September 2015   example illustrates an outbound connection between VM1 inside the   data center and VMe1 inside the enterprise network.  When the   outbound packet from CA1 to CAe1 reaches the hypervisor on Server 1,   the NVE in Server 1 can perform the equivalent of a route lookup on   the packet.  The cross-premise packet will match the default gateway   rule, as CAe1 is not part of the tenant virtual network in the data   center.  The virtualization policy will indicate the packet to be   encapsulated and sent to the PA of the tenant VPN gateway (PA4)   running as a VM on Server 2.  The packet is decapsulated on Server 2   and delivered to the VM gateway.  The gateway in turn validates and   sends the packet on the site-to-site VPN tunnel back to the   enterprise network.  As the communication here is external to the   data center, the PA address for the VPN tunnel is globally routable.   The outer header of this packet is sourced from GAdc destined to   GAcorp.  This packet is routed through the Internet to the enterprise   VPN gateway, which is the other end of the site-to-site tunnel; at   that point, the VPN gateway decapsulates the packet and sends it   inside the enterprise where the CAe1 is routable on the network.  The   reverse path is similar once the packet reaches the enterprise VPN   gateway.4.7.  Internet Connectivity   To enable connectivity to the Internet, an Internet gateway is needed   that bridges the virtualized CA space to the public Internet address   space.  The gateway needs to perform translation between the   virtualized world and the Internet.  For example, the NVGRE endpoint   can be part of a load balancer or a NAT that replaces the VPN Gateway   on Server 2 shown in Figure 2.4.8.  Management and Control Planes   There are several protocols that can manage and distribute policy;   however, it is outside the scope of this document.  Implementations   SHOULD choose a mechanism that meets their scale requirements.4.9.  NVGRE-Aware Devices   One example of a typical deployment consists of virtualized servers   deployed across multiple racks connected by one or more layers of   Layer 2 switches, which in turn may be connected to a Layer 3 routing   domain.  Even though routing in the physical infrastructure will work   without any modification with NVGRE, devices that perform specialized   processing in the network need to be able to parse GRE to get access   to tenant-specific information.  Devices that understand and parse   the VSID can provide rich multi-tenant-aware services inside the data   center.  As outlined earlier, it is imperative to exploit multiple   paths inside the network through techniques such as ECMP.  The KeyGarg & Wang                   Informational                    [Page 12]

RFC 7637                          NVGRE                   September 2015   field (a 32-bit field, including both the VSID and the optional   FlowID) can provide additional entropy to the switches to exploit   path diversity inside the network.  A diverse ecosystem is expected   to emerge as more and more devices become multi-tenant aware.  In the   interim, without requiring any hardware upgrades, there are   alternatives to exploit path diversity with GRE by associating   multiple PAs with NVGRE endpoints with policy controlling the choice   of which PA to use.   It is expected that communication can span multiple data centers and   also cross the virtual/physical boundary.  Typical scenarios that   require virtual-to-physical communication include access to storage   and databases.  Scenarios demanding lossless Ethernet functionality   may not be amenable to NVGRE, as traffic is carried over an IP   network.  NVGRE endpoints mediate between the network-virtualized and   non-network-virtualized environments.  This functionality can be   incorporated into Top-of-Rack switches, storage appliances, load   balancers, routers, etc., or built as a stand-alone appliance.   It is imperative to consider the impact of any solution on host   performance.  Today's server operating systems employ sophisticated   acceleration techniques such as checksum offload, Large Send Offload   (LSO), Receive Segment Coalescing (RSC), Receive Side Scaling (RSS),   Virtual Machine Queue (VMQ), etc.  These technologies should become   NVGRE aware.  IPsec Security Associations (SAs) can be offloaded to   the NIC so that computationally expensive cryptographic operations   are performed at line rate in the NIC hardware.  These SAs are based   on the IP addresses of the endpoints.  As each packet on the wire   gets translated, the NVGRE endpoint SHOULD intercept the offload   requests and do the appropriate address translation.  This will   ensure that IPsec continues to be usable with network virtualization   while taking advantage of hardware offload capabilities for improved   performance.4.10.  Network Scalability with NVGRE   One of the key benefits of using NVGRE is the IP address scalability   and in turn MAC address table scalability that can be achieved.  An   NVGRE endpoint can use one PA to represent multiple CAs.  This lowers   the burden on the MAC address table sizes at the Top-of-Rack   switches.  One obvious benefit is in the context of server   virtualization, which has increased the demands on the network   infrastructure.  By embedding an NVGRE endpoint in a hypervisor, it   is possible to scale significantly.  This framework enables location   information to be preconfigured inside an NVGRE endpoint, thus   allowing broadcast ARP traffic to be proxied locally.  This approach   can scale to large-sized virtual subnets.  These virtual subnets can   be spread across multiple Layer 3 physical subnets.  It allowsGarg & Wang                   Informational                    [Page 13]

RFC 7637                          NVGRE                   September 2015   workloads to be moved around without imposing a huge burden on the   network control plane.  By eliminating most broadcast traffic and   converting others to multicast, the routers and switches can function   more optimally by building efficient multicast trees.  By using   server and network capacity efficiently, it is possible to drive down   the cost of building and managing data centers.5.  Security Considerations   This proposal extends the Layer 2 subnet across the data center and   increases the scope for spoofing attacks.  Mitigations of such   attacks are possible with authentication/encryption using IPsec or   any other IP-based mechanism.  The control plane for policy   distribution is expected to be secured by using any of the existing   security protocols.  Further management traffic can be isolated in a   separate subnet/VLAN.   The checksum in the GRE header is not supported.  The mitigation of   this is to deploy an NVGRE-based solution in a network that provides   error detection along the NVGRE packet path, for example, using   Ethernet Cyclic Redundancy Check (CRC) or IPsec or any other error   detection mechanism.6.  Normative References   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, DOI 10.17487/RFC2119, March 1997,        <http://www.rfc-editor.org/info/rfc2119>.   [2]  IANA, "IEEE 802 Numbers",        <http://www.iana.org/assignments/ieee-802-numbers>.   [3]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,        "Generic Routing Encapsulation (GRE)",RFC 2784,        DOI 10.17487/RFC2784, March 2000,        <http://www.rfc-editor.org/info/rfc2784>.   [4]  Dommety, G., "Key and Sequence Number Extensions to GRE",RFC 2890, DOI 10.17487/RFC2890, September 2000,        <http://www.rfc-editor.org/info/rfc2890>.   [5]  IEEE, "IEEE Standard for Local and metropolitan area        networks--Media Access Control (MAC) Bridges and Virtual Bridged        Local Area Networks", IEEE Std 802.1Q.   [6]  Greenberg, A., et al., "VL2: A Scalable and Flexible Data Center        Network", Communications of the ACM,        DOI 10.1145/1897852.1897877, 2011.Garg & Wang                   Informational                    [Page 14]

RFC 7637                          NVGRE                   September 2015   [7]  Greenberg, A., et al., "The Cost of a Cloud: Research Problems        in Data Center Networks", ACM SIGCOMM Computer Communication        Review, DOI 10.1145/1496091.1496103, 2009.   [8]  Hinden, R. and S. Deering, "IP Version 6 Addressing        Architecture",RFC 4291, DOI 10.17487/RFC4291, February 2006,        <http://www.rfc-editor.org/info/rfc4291>.   [9]  Meyer, D., "Administratively Scoped IP Multicast",BCP 23,RFC 2365, DOI 10.17487/RFC2365, July 1998,        <http://www.rfc-editor.org/info/rfc2365>.   [10] Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L., Kreeger,        L., and M. Napierala, "Problem Statement: Overlays for Network        Virtualization",RFC 7364, DOI 10.17487/RFC7364, October 2014,        <http://www.rfc-editor.org/info/rfc7364>.   [11] Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y. Rekhter,        "Framework for Data Center (DC) Network Virtualization",RFC 7365, DOI 10.17487/RFC7365, October 2014,        <http://www.rfc-editor.org/info/rfc7365>.   [12] Perkins, C., "IP Encapsulation within IP",RFC 2003,        DOI 10.17487/RFC2003, October 1996,        <http://www.rfc-editor.org/info/rfc2003>.   [13] Touch, J. and R. Perlman, "Transparent Interconnection of Lots        of Links (TRILL): Problem and Applicability Statement",RFC 5556, DOI 10.17487/RFC5556, May 2009,        <http://www.rfc-editor.org/info/rfc5556>.Garg & Wang                   Informational                    [Page 15]

RFC 7637                          NVGRE                   September 2015Contributors   Murari Sridharan   Microsoft Corporation   1 Microsoft Way   Redmond, WA 98052   United States   Email: muraris@microsoft.com   Albert Greenberg   Microsoft Corporation   1 Microsoft Way   Redmond, WA 98052   United States   Email: albert@microsoft.com   Narasimhan Venkataramiah   Microsoft Corporation   1 Microsoft Way   Redmond, WA 98052   United States   Email: navenkat@microsoft.com   Kenneth Duda   Arista Networks, Inc.   5470 Great America Pkwy   Santa Clara, CA 95054   United States   Email: kduda@aristanetworks.com   Ilango Ganga   Intel Corporation   2200 Mission College Blvd.   M/S: SC12-325   Santa Clara, CA 95054   United States   Email: ilango.s.ganga@intel.com   Geng Lin   Google   1600 Amphitheatre Parkway   Mountain View, CA 94043   United States   Email: genglin@google.comGarg & Wang                   Informational                    [Page 16]

RFC 7637                          NVGRE                   September 2015   Mark Pearson   Hewlett-Packard Co.   8000 Foothills Blvd.   Roseville, CA 95747   United States   Email: mark.pearson@hp.com   Patricia Thaler   Broadcom Corporation   3151 Zanker Road   San Jose, CA 95134   United States   Email: pthaler@broadcom.com   Chait Tumuluri   Emulex Corporation   3333 Susan Street   Costa Mesa, CA 92626   United States   Email: chait@emulex.comAuthors' Addresses   Pankaj Garg (editor)   Microsoft Corporation   1 Microsoft Way   Redmond, WA 98052   United States   Email: pankajg@microsoft.com   Yu-Shun Wang (editor)   Microsoft Corporation   1 Microsoft Way   Redmond, WA 98052   United States   Email: yushwang@microsoft.comGarg & Wang                   Informational                    [Page 17]