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Versions: 00 01 02 03 04

Network Working Group                                      M. Sridharan
Internet Draft                                                Microsoft
Intended Category: Informational                                K. Duda
Expires: March 2012                                     Arista Networks
                                                                I. Ganga
                                                                   Intel
                                                            A. Greenberg
                                                               Microsoft
                                                                  G. Lin
                                                                    Dell
                                                              M. Pearson
                                                         Hewlett-Packard
                                                               P. Thaler
                                                                Broadcom
                                                             C. Tumuluri
                                                                  Emulex
                                                        N. Venkataramiah
                                                               Microsoft
                                                                 Y. Wang
                                                               Microsoft


                                                          September 2011




     NVGRE: Network Virtualization using Generic Routing Encapsulation
                draft-sridharan-virtualization-nvgre-00.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) 2011 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   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




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   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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   This Internet-Draft will expire on March 14, 2012.

Abstract

   We describe a framework for policy-based, software controlled
   network virtualization to support multitenancy in public and private
   clouds using Generic Routing Encapsulation (GRE). The framework
   outlined in this document can be used by cloud hosters, enterprise
   data centers and enables seamless migration of workloads between
   public and private clouds. This document is focused on the data
   plane aspects of the NVGRE framework.

Table of Contents


   1. Introduction...................................................3
   2. Conventions used in this document..............................4
   3. Network Virtualization using GRE...............................4
      3.1. NVGRE Endpoint............................................5
      3.2. Network virtualization frame format.......................5
      3.3. Broadcast and Multicast Traffic...........................9
      3.4. Unicast Traffic...........................................9
      3.5. IP Fragmentation.........................................10
      3.6. Address/Policy Management & Routing......................10
      3.7. Cross-subnet, Cross-premise Communication................10
      3.8. Internet Connectivity....................................13


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      3.9. Manageability............................................13
   4. Deployment Considerations.....................................13
      4.1. Network Scalability with GRE.............................14
   5. Security Considerations.......................................15
   6. IANA Considerations...........................................15
   7. References....................................................15
      7.1. Normative References.....................................15
      7.2. Informative References...................................15
   8. Acknowledgments...............................................16



1. Introduction

   Conventional data center network designs cater to largely static
   workloads and cause fragmentation of network and server capacity
   [VL2, COST-CCR]. The key concepts described in this document are
   motivated by earlier work [VL2], although the specific approach
   described here is significantly different from the one outlined in
   the paper. 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 [TRILL].

   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 run 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 (e.g., ARP). 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 workload's addresses. This can be
   achieved today by stretching VLANs however when workloads migrate
   the network needs to be reconfigured which is typically error prone.


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   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 concurrent VLANs,
   c) preserving Layer-2 semantics for services and allowing them to
   retain their addresses as they move within and across data centers,
   and d) providing broadcast isolation as workloads move around
   without burdening the network control plane.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

3. Network Virtualization using GRE

   Network virtualization involves creating virtual Layer 2 and/or
   Layer 3 topologies on top of an arbitrary physical Layer 2/Layer 3
   network. Connectivity in the virtual topology is provided by
   tunneling Ethernet frames in IP over the physical network. Virtual
   broadcast domains are realized as multicast distribution trees. The
   multicast distribution trees are analogous to the VLAN broadcast
   domains. A virtual Layer 2 network can span multiple physical
   subnets. Support for bi-directional IP unicast and multicast
   connectivity is the only expectation from the underlying physical
   network. If the operator chooses to support broadcast and multicast
   traffic in the virtual topology the physical topology must support
   IP multicast. The physical network, for example, can be a
   conventional hierarchical 3-tier network, a full bisection bandwidth
   Clos network or a large Layer 2 network with or without TRILL
   support.

   Every virtual Layer-2 network is associated with a 24 bit Tenant
   Network Identifier (TNI). A 24 bit TNI allows up to 16 million
   logical networks in the same management domain in contrast to only
   4K achievable with VLANs. Each TNI represents a virtual Layer-2
   broadcast domain and routes can be configured for communication


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   between virtual subnets. The TNI can be crafted in such a way that
   it uniquely identifies a specific tenant's subnet. The TNI is
   carried in an outer header allowing unique identification of the
   tenant's virtual subnet to various devices in the network.

   GRE is a proposed IETF standard [RFC 2784, RFC 2890] and provides a
   way for encapsulating an arbitrary protocol over IP. The tunneling
   mechanism itself is designed to be stateless although for this
   specific implementation there may be some soft state to handle
   issues such as IP fragmentation as explained in later sections. The
   GRE header provides space to carry TNI information in each packet.
   The TNI information in each packet can be used to build multi-
   tenancy aware tools for traffic analysis, traffic inspection, and
   monitoring.

   The following sections detail the packet format for network
   virtualization, 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 gateways between the virtual and the physical
   networks. Any physical server or network device can be a 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 TNI. The endpoint can optionally participate in routing and
   function as a gateway in the virtual subnet space. To encapsulate an
   Ethernet frame, the endpoint needs to know location information for
   the destination address in the frame. The way to obtain this
   information is not covered in this document and will be covered in a
   different draft. Any number of techniques can be used in the control
   plane to configure, discover and distribute the policy information.
   For the rest of this document we assume that the location
   information including TNI is readily available to the NVGRE
   endpoint.



3.2. Network virtualization frame format

   GRE encapsulation as specified in RFC 2784 and RFC 2890 is used for
   communication between NVGRE endpoints. The Key extension to GRE



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   specified in RFC 2890 is used to carry the TNI. The packet format
   for Layer-2 encapsulation in GRE is shown in Figure 1.















































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   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        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Tenant Network ID (TNI)|   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Inner Ethernet Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                (Inner) Destination MAC Address                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |(Inner)Destination MAC Address |  (Inner)Source MAC Address    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  (Inner) Source MAC Address                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Optional Ethertype=C-Tag 802.1Q| PCP |0| VID set to 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Ethertype 0x0800        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Inner IPv4 Header:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version|  IHL  |Type of Service|          Total Length         |


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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         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

   O The inner Ethernet frame comprises of an inner Ethernet header
   followed by the 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.

   0 Traffic may go through multiple NV-GRE gateways and no assumptions
   can be made about the VLAN ID space. NVGRE endpoint MUST set the VID
   in 802.1Q VLAN tags, if present, to zero before encapsulating the
   frame in a GRE header. If a VLAN-tagged frame arrives encapsulated
   in NV-GRE with VID not set to zero, then the decapsulating device
   SHOULD drop the frame.

   0 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).

   O The Key field in the GRE header is used to carry the Tenant
   Network Identifier. Key field is 32 bits long of which the lower 24
   bits are used for TNI. The Key Present (bit 2 in the GRE header) is
   always set to 1.

   0 The upper 8 bits of the Key field are reserved for use by NVGRE
   endpoints and are not part of the TNI space. NVGRE endpoints MUST
   set this value to zero.

   0 NVGRE endpoint MUST set C and S bits in the GRE header to zero.




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   O The protocol type field in the GRE header is set to 0x6558
   (transparent Ethernet bridging) [ETHTYPES].

   O 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 the NVGRE endpoint, with policy controlling the
   choice of PA to use for a given CA.

   O The source Ethernet address in the outer frame is set to the MAC
   address associated with the NVGRE endpoint. The destination Ethernet
   address is set to the MAC address of the nexthop IP address for the
   destination PA. The destination endpoint may or may not be on the
   same physical subnet. The outer VLAN tag information is optional and
   can be used for traffic management and broadcast scalability.

3.3. Broadcast and Multicast Traffic

   The following discussion applies if the network operator chooses to
   support broadcast and multicast traffic. Each virtual subnet is
   assigned an administratively scoped multicast address to carry
   broadcast and multicast traffic. All traffic originating from within
   a TNI is encapsulated and sent to the assigned multicast address. As
   an example, the addresses can be derived from a administratively
   scoped multicast address as specified in RFC 2365 for IPv4
   (organization Local Scope 239.192.0.0/14), or an Organization-Local
   scope multicast address for IPv6 as specified in RFC 4291. This
   provides a wide range of address choices. Purely from an efficiency
   standpoint for every multicast address that a tenant uses the
   network operator may configure a corresponding multicast address in
   the PA space. To support broadcast and multicast traffic in the
   virtual topology the physical topology must support IP multicast.
   Depending on the hardware capabilities of the physical network
   devices multiple virtual broadcast domains may be assigned the same
   physical IP multicast address. For interoperability reasons, a
   future version of this draft will specify a standard way to map TNI
   to IP multicast address.

3.4. 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


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   normally by the physical network to the destination. Bridging uses
   the outer Ethernet encapsulation for scope on the LAN. The only
   assumption 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.

3.5. 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 future version of this draft will clarify the details around
   setting the DF bit on the outer IP header as well as maintaining per
   destination NVGRE endpoint MTU soft state so that ICMP Datagram Too
   Big messages can be exploited. Fragmentation behavior when tunneling
   non-IP Ethernet frames in GRE will also be specified in a future
   version.

3.6. 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, CA can be
   IPv4 while PA is IPv6 and vice versa. The isolation policies MUST be
   explicitly configured in the NVGRE endpoint. A typical policy table
   entry consists of CA, MAC address, TNI and optionally, the specific
   PA if more than one PA is associated with the NVGRE endpoint. If
   there are multiple virtual subnets, explicit routing information
   MUST be configured along with a default gateway for cross-subnet
   communication. Routing between virtual subnets can be optionally
   handled by the NVGRE endpoint acting as a gateway. If
   broadcast/multicast support is required the NVGRE endpoints MUST
   participate in IGMP/MLD for all subscribed multicast groups.

3.7. 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.


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   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.









































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   +-----------------------+        +-----------------------+
   |       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 VMe | | Corp VM2 | |
                                   | |          | |          | |
                                   | |  IP=CAe  | | IP=CAE2  | |
                                   | +----------+ +----------+ |
                                   |         Hypervisor        |
                                   +---------------------------+
            Figure 2 Cross-Subnet, Cross-Premise Communication



   The flow here is similar to the unicast traffic flow between VMs,
   the key difference in this case the packet needs to be sent to a VPN


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   gateway before it gets forwarded to the destination. As part of
   routing configuration in the CA space, a VPN gateway is provisioned
   per-tenant for communication back to the enterprise. The example
   illustrates an outbound connection between VM1 inside the datacenter
   and VMe inside the enterprise network. The outbound packet from CA1
   to CAe when it hits the hypervisor on Server 1 matches the default
   gateway rule as CAe is not part of the tenant virtual network in the
   datacenter. The packet is 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
   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 decapsulates the packet and sends
   it inside the enterprise where the CAe is routable on the network.
   The reverse path is similar once the packet hits the enterprise VPN
   gateway.

3.8. 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 performs translation between the
   virtualized world and the Internet, for example, the NVGRE endpoint
   can be part of a load balancer or a NAT. Section 4 has more
   discussions around building GRE gateways.

3.9. Manageability

   There are several protocols that can manage and distribute policy;
   however this document does not recommend any one mechanism.
   Implementations SHOULD choose a mechanism that meets their scale
   requirements.

4. Deployment Considerations

   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 GRE, 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 TNI can provide rich multi-tenancy aware services inside the


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   data center. As outlined earlier it is imperative to exploit
   multiple paths inside the network through techniques such as Equal
   Cost Multipath (ECMP). The Key field may provide additional entropy
   to the switches to exploit path diversity inside the network. One
   such example could be to use the upper 8 bits of the Key field to
   add flow based entropy and tag all the packets from a flow with an
   entropy label. A diverse ecosystem play is expected to emerge as
   more and more devices become multitenancy 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
   GRE 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.

4.1. Network Scalability with GRE

   One of the key benefits of using GRE 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


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   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
   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.

6. IANA Considerations

   None.



7. References

7.1. Normative References

     [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.

     [ETHTYPES] ftp://ftp.isi.edu/in-notes/iana/assignments/ethernet-
numbers


7.2. Informative References

   [VL2] A. Greenberg et al, "VL2: A Scalable and Flexible Data Center
         Network", Proc. SIGCOMM 2009.

   [COST-CCR] A. Greenberg et al, "The Cost of a Cloud: Research
               Problems in the Data Center", ACM SIGCOMM Computer
               Communication Review.


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8. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.












































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Authors' Addresses

   Murari Sridharan
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA 98052
   Email: muraris@microsoft.com

   Kenneth Duda
   Arista Networks, Inc.
   5470 Great America Pkwy
   Santa Clara, CA 95054
   kduda@aristanetworks.com

   Ilango Ganga
   Intel Corporation
   2200 Mission College Blvd.
   M/S: SC12-325
   Santa Clara, CA - 95054
   Email: ilango.s.ganga@intel.com

   Albert Greenberg
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA 98052
   Email: albert@microsoft.com

   Geng Lin
   Dell
   One Dell Way
   Round Rock, TX 78682
   Email: geng_lin@dell.com

   Mark Pearson
   Hewlett-Packard Co.
   8000 Foothills Blvd.
   Roseville, CA 95747
   Email: mark.pearson@hp.com


   Patricia Thaler
   Broadcom Corporation


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   3151 Zanker Road
   San Jose, CA 95134
   Email: pthaler@broadcom.com

   Chait Tumuluri
   Emulex Corporation
   3333 Susan Street
   Costa Mesa, CA 92626
   Email: chait@emulex.com

   Narasimhan Venkataramiah
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA 98052
   Email: narave@microsoft.com

   Yu-Shun Wang
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA 98052
   Email: yushwang@microsoft.com


























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