NVGRE: Network Virtualization Using Generic Routing Encapsulation
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 7637.
|Authors||Pankaj Garg , Yu-Shun Wang|
|Last updated||2015-10-14 (Latest revision 2015-04-13)|
|RFC stream||Independent Submission|
|IETF conflict review||conflict-review-sridharan-virtualization-nvgre, conflict-review-sridharan-virtualization-nvgre, conflict-review-sridharan-virtualization-nvgre, conflict-review-sridharan-virtualization-nvgre, conflict-review-sridharan-virtualization-nvgre, conflict-review-sridharan-virtualization-nvgre|
|Stream||ISE state||Published RFC|
|Document shepherd||Eliot Lear|
|Shepherd write-up||Show Last changed 2015-04-21|
|IESG||IESG state||RFC 7637 (Informational)|
|Send notices to||(None)|
|IANA||IANA review state||IANA OK - No Actions Needed|
|IANA action state||No IANA Actions|
Network Working Group P. Garg Ed. Internet Draft Y. Wang Ed. Intended Category: Informational Microsoft Expires: October 12, 2015 April 13, 2015 NVGRE: Network Virtualization using Generic Routing Encapsulation draft-sridharan-virtualization-nvgre-08.txt Status of this Memo This memo provides information for the Internet Community. It does not specify an Internet standard of any kind; instead it relies on a proposed standard. Distribution of this memo is unlimited. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. 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 Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html 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. This Internet-Draft will expire on October 12, 2015. Sridharan et al Informational [Page 1] Internet-Draft NVGRE April 2015 Abstract This document describes the usage of Generic Routing Encapsulation (GRE) header for Network Virtualization (NVGRE) in multi-tenant datacenters. 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. Table of Contents 1. Introduction...................................................2 1.1. Terminology...............................................4 2. Conventions used in this document..............................4 3. NVGRE: Network Virtualization using GRE........................5 3.1. NVGRE Endpoint............................................5 3.2. NVGRE frame format........................................6 3.3. Inner 802.1Q Tag..........................................9 3.4. Reserved VSID.............................................9 4. NVGRE Deployment Consideration................................10 4.1. ECMP Support.............................................10 4.2. Broadcast and Multicast Traffic..........................10 4.3. Unicast Traffic..........................................10 4.4. IP Fragmentation.........................................11 4.5. Address/Policy Management & Routing......................11 4.6. Cross-subnet, Cross-premise Communication................11 4.7. Internet Connectivity....................................13 4.8. Management and Control Planes............................13 4.9. NVGRE-Aware Devices......................................13 4.10. Network Scalability with NVGRE..........................14 5. Security Considerations.......................................15 6. IANA Considerations...........................................15 7. References....................................................15 7.1. Normative References.....................................15 7.2. Informative References...................................16 8. Authors and Contributors......................................16 9. Acknowledgments...............................................17 1. Introduction Conventional data center network designs cater to largely static workloads and cause fragmentation of network and server capacity Sridharan et al Informational [Page 2] Internet-Draft NVGRE April 2015 . There are several issues that limit dynamic allocation and consolidation of capacity. Layer 2 networks use 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 TRILL that address this problem . 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 4K such subnets to be created. The size of the broadcast domain is typically restricted due to the overhead of broadcast traffic. The 4K VLAN limit 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 which is typically error prone. By decoupling the workload's location on the LAN from its network address, the network administrator configures the network once and 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 Sridharan et al Informational [Page 3] Internet-Draft NVGRE April 2015 This document describes use of the Generic Routing Encapsulation (GRE, ) header 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 datacenter. Network virtualization enables customers to bring their own address spaces into a multi-tenant datacenter while the datacenter administrators can place the customer virtual machines anywhere in the datacenter without reconfiguring their network switches or routers, irrespective of the customer address spaces. 1.1. Terminology Please refer to  for more formal definition of terminology. The following terms were used in this document. Customer Address (CA): These are the virtual IP addresses assigned and configured on the virtual NIC within each VM. These are the only addresses visible to VMs and applications running within VMs. Network Virtualization Edge (NVE): An entity that performs the network virtualization encapsulation and decapsulation. Provider Address (PA): These are the IP addresses used in the physical network. PA's are associated with VM CA's through the network virtualization mapping policy. Virtual Machine (VM): These are instances of OS's running on top of 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 compute, storage, and other OS resources. Virtual Subnet Identifier (VSID): 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 in RFC-2119 [RFC2119]. Sridharan et al Informational [Page 4] Internet-Draft NVGRE April 2015 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. 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 in Section 3.2. , allowing 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 4K 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, datacenter administrators can configure routes to facilitate communication between virtual subnets of the same tenant. GRE is a proposed IETF standard  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 a 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 NVO Framework document . 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 Sridharan et al Informational [Page 5] Internet-Draft NVGRE April 2015 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 RFC 2784 and RFC 2890  is used for communication between NVGRE endpoints. NVGRE leverages the Key extension specified in RFC 2890  to carry the VSID. The packet format for Layer 2 encapsulation in GRE is shown in Figure 1. Sridharan et al Informational [Page 6] Internet-Draft NVGRE April 2015 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 IPv4 Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL |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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (Continued on the next page) Sridharan et al Informational [Page 7] Internet-Draft NVGRE April 2015 Inner IPv4 Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL |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 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 nexthop 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 address associated with an NVGRE endpoint, with policy controlling the choice of PA to use for a given Customer Address (CA) for a customer VM. The GRE header: o The C (Checksum Present) and S (Sequence Number Present) bits in the GRE header MUST be zero. Sridharan et al Informational [Page 8] Internet-Draft NVGRE April 2015 o The K bit (Key Present) 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 zero. o The protocol type field in the GRE header is set to 0x6558 (transparent Ethernet bridging). The inner headers (headers of the GRE payload): o The inner Ethernet frame comprises of 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 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 802.1Q Tag The inner Ethernet header of NVGRE MUST NOT contain 802.1Q tag. The encapsulating NVE MUST remove any existing 802.1Q Tag before encapsulation of the frame in NVGRE. A decapsulating NVE MUST drop the frame if the inner Ethernet frame contains an 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-NVE communication. The sender NVE SHOULD verify receiver NVE's vendor before sending a packet using this VSID, however such verification mechanism is out of scope of this document. Implementations SHOULD choose a mechanism that meets their requirements. Sridharan et al Informational [Page 9] Internet-Draft NVGRE April 2015 4. NVGRE Deployment Considerations 4.1. ECMP Support ECMP may be used to provide load balancing. If ECMP is used, it is RECOMMENDED that ECMP hash is calculated either using the outer IP frame fields and entire Key field (32-bit) or 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  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, to facilitate optimal multicast handling. Depending on the hardware capabilities of the physical network devices and the physical network architecture, multiple virtual subnet may re-use the same physical IP multicast address. Alternatively, based upon the configuration at NVE, the 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 in the Unicast Traffic Section 4.3. 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 bi-directional 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. Sridharan et al Informational [Page 10] Internet-Draft NVGRE April 2015 4.4. IP Fragmentation RFC 2003  Section 5.1 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 MTU of 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 & Routing Address acquisition is beyond the scope of this document and can be obtained statically, dynamically or using stateless address auto- configuration. 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 a 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 GW configured as a VM shown in Figure 2 to illustrate cross-subnet, cross-premise communication. Sridharan et al Informational [Page 11] Internet-Draft NVGRE April 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 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. The example Sridharan et al Informational [Page 12] Internet-Draft NVGRE April 2015 illustrates an outbound connection between VM1 inside the datacenter 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 an 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 datacenter. The virtualization policy will indicate the packet to be encapsulated and sent to the PA of 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 datacenter 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 which 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 need 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, which 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 out of 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-tenancy aware services inside the data center. As outlined earlier it is imperative to exploit multiple paths inside the network through Sridharan et al Informational [Page 13] Internet-Draft NVGRE April 2015 techniques such as Equal Cost Multipath (ECMP). The Key field (32- bit field, including both 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 PA to be used. It is expected that communication can span multiple data centers and also cross the virtual to physical boundary. Typical scenarios that require virtual-to-physical communication includes 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 (SA) 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. 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 a NVGRE endpoint in a hypervisor it is possible to scale significantly. This framework allows for location information to be preconfigured inside a NVGRE endpoint allowing broadcast ARP traffic to be proxied locally. This approach can scale to large sized virtual subnets. These virtual subnets can be spread Sridharan et al Informational [Page 14] Internet-Draft NVGRE April 2015 across multiple layer 3 physical subnets. It allows 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 efficiently 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 NVGRE based solution in a network that provides error detection along the NVGRE packet path, for example, using Ethernet CRC or IPsec or any other error detection mechanism. 6. IANA Considerations This document has no IANA actions. 7. References 7.1. Normative References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Ethertypes, ftp://ftp.isi.edu/in- notes/iana/assignments/ethernet-numbers  D. Farinacci et al, "Generic Routing Encapsulation (GRE)", RFC 2784, March, 2000.  G. Dommety, "Key and Sequence Number Extensions to GRE", RFC 2890, September 2000.  Institute of Electrical and Electronics Engineers, "Virtual Bridged Local Area Networks", IEEE Standard 802.1Q, 2005 Edition, May 2006. Sridharan et al Informational [Page 15] Internet-Draft NVGRE April 2015 7.2. Informative References  A. Greenberg et al, "VL2: A Scalable and Flexible Data Center Network", Proc. SIGCOMM 2009.  A. Greenberg et al, "The Cost of a Cloud: Research Problems in the Data Center", ACM SIGCOMM Computer Communication Review.  B. Hinden, S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.  M. Lasserre et al, "Framework for DC Network Virtualization", RFC 7365, October 2014.  D. Meyer, "Administratively Scoped IP Multicast", BCP 23, RFC 2365, July 1998.  T. Narten et al, "Problem Statement: Overlays for Network Virtualization", RFC 7364, October 2014.  C. Perkins, "IP Encapsulation within IP", RFC 2003, October 1996.  J. Touch, R. Perlman, "Transparent Interconnection of Lots of Links (TRILL): Problem and Applicability Statement", RFC 5556, May 2009. 8. Authors and Contributors M. Sridharan A. Greenberg Y. Wang P. Garg N. Venkataramiah Microsoft K. Duda Arista Networks I. Ganga Intel G. Lin Google Sridharan et al Informational [Page 16] Internet-Draft NVGRE April 2015 M. Pearson Hewlett-Packard P. Thaler Broadcom C. Tumuluri Emulex 9. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Sridharan et al Informational [Page 17] Internet-Draft NVGRE April 2015 Authors' Addresses Murari Sridharan Microsoft Corporation 1 Microsoft Way Redmond, WA 98052 Email: firstname.lastname@example.org Yu-Shun Wang Microsoft Corporation 1 Microsoft Way Redmond, WA 98052 Email: email@example.com Albert Greenberg Microsoft Corporation 1 Microsoft Way Redmond, WA 98052 Email: firstname.lastname@example.org Pankaj Garg Microsoft Corporation 1 Microsoft Way Redmond, WA 98052 Email: email@example.com Narasimhan Venkataramiah Facebook Inc 1730 Minor Ave. Seattle, WA 98101 Email: firstname.lastname@example.org Kenneth Duda Arista Networks, Inc. 5470 Great America Pkwy Santa Clara, CA 95054 email@example.com Ilango Ganga Intel Corporation 2200 Mission College Blvd. Sridharan et al Informational [Page 18] Internet-Draft NVGRE April 2015 M/S: SC12-325 Santa Clara, CA - 95054 Email: firstname.lastname@example.org Geng Lin Google 1600 Amphitheatre Parkway Mountain View, California 94043 Email: email@example.com Mark Pearson Hewlett-Packard Co. 8000 Foothills Blvd. Roseville, CA 95747 Email: firstname.lastname@example.org Patricia Thaler Broadcom Corporation 3151 Zanker Road San Jose, CA 95134 Email: email@example.com Chait Tumuluri Emulex Corporation 3333 Susan Street Costa Mesa, CA 92626 Email: firstname.lastname@example.org Sridharan et al Informational [Page 19]