Internet Engineering Task Force                           Marc Lasserre
Internet Draft                                             Florin Balus
Intended status: Informational                           Alcatel-Lucent
Expires: September 2012
                                                           Thomas Morin
                                                  France Telecom Orange

                                                          March 5, 2012

                  Framework for DC Network Virtualization

Status of this Memo

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   Copyright (c) 2012 IETF Trust and the persons identified as the
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   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document. Please review these documents

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   carefully, as they describe your rights and restrictions with
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   Several IETF drafts relate to the use of overlay networks to support
   large scale virtual data centers. This draft provides a framework
   for Network Virtualization over L3 (NVO3) and is intended to help
   plan a set of work items in order to provide a complete solution
   set. It defines a logical view of the main components with the
   intention of streamlining the terminology and focusing the solution

Table of Contents

   1. Introduction...................................................3
      1.1. Conventions used in this document.........................4
      1.2. General terminology.......................................4
      1.3. DC network architecture...................................4
      1.4. Tenant networking view....................................6
   2. Reference Models...............................................7
      2.1. Generic Reference Model...................................7
      2.2. NVE Reference Model.......................................9
      2.3. NVE Service Types........................................10
         2.3.1. L2 NVE providing Ethernet LAN-like service..........10
         2.3.2. L3 NVE providing IP/VRF-like service................10
   3. Functional components.........................................10
      3.1. Generic service virtualization components................10
         3.1.1. Virtual Access Points (VAPs)........................11
         3.1.2. Tenant Instance.....................................11
         3.1.3. Overlay Modules and Tenant ID.......................12
         3.1.4. Tunnel Overlays and Encapsulation options...........12
         3.1.5. Use of Control Plane Protocols......................13
      3.2. Service Overlay Topologies...............................13
   4. Key aspects of overlay networks...............................13
      4.1. Pros & Cons..............................................13
      4.2. Overlay issues to consider...............................14
         4.2.1. End System to Overlay Network Mapping...............14
         4.2.2. Address to tunnel mapping...........................15
         4.2.3. Data plane vs Control plane driven..................15
         4.2.4. Coordination between data plane and control plane...16
         4.2.5. Multicast Handling..................................16

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         4.2.6. Path MTU............................................16
         4.2.7. NVE location trade-offs.............................17
         4.2.8. Interaction between network overlays and underlays..18
   5. Security Considerations.......................................18
   6. IANA Considerations...........................................19
   7. References....................................................19
      7.1. Normative References.....................................19
      7.2. Informative References...................................19
   8. Acknowledgments...............................................20

1. Introduction

   This document provides a framework for Data Center Network
   Virtualization over L3 tunnels. This framework is intended to aid in
   standardizing protocols and mechanisms to support large scale
   network virtualization for data centers.

   Several IETF drafts relate to the use of overlay networks for data

   [NVOPS] defines the rationale for using overlay networks in order to
   build large data center networks. The use of virtualization leads to
   a very large number of communication domains and end systems to cope
   with. Existing virtual network models used for data center networks
   have known limitations, specifically in the context of multiple
   tenants, that have also been described in various sections of
   [VXLAN], [NVGRE], and [DCVPN]. These issues can be summarized as:

     o Limited VLAN space

     o FIB explosion due to handling of large number of MACs/IP

     o Spanning Tree limitations

     o Excessive ARP handling

     o Broadcast storms

     o Inefficient Broadcast/Multicast handling

     o Limited mobility/portability support

     o Lack of service auto-discovery

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   [VXLAN], [NVGRE], [STT] and [DCVPN] describe the use of overlay
   techniques that address some of these issues.

   [OVCPREQ] describes the requirements for a control plane protocol
   required by overlay border nodes to exchange overlay mappings.

   This document provides reference models and functional components of
   data center overlay networks as well as a discussion of technical
   issues that have to be addressed in the design of standards and
   mechanisms for large scale data centers.

1.1. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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.

1.2. General terminology

   Some general terminology is defined here. Terminology specific to
   this memo is introduced as needed in later sections.

   DC: Data Center

   ELAN: MEF ELAN, multipoint to multipoint Ethernet service

   EVPN: Ethernet VPN as defined in [EVPN]

1.3. DC network architecture

   A generic architecture for Data Centers is depicted in Figure 1:

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                              ,'           `.
                             (  IP/MPLS WAN )
                              `.           ,'
                             +--+--+   +-+---+
                             |DC GW|+-+|DC GW|
                             +-+---+   +-----+
                                 |       /
                                 .--. .--.
                               (    '    '.--.
                            .-.' Intra-DC     '
                           (     network      )
                            (             .'-'
                             '--'._.'.    )\ \
                              / /     '--'  \ \
                             / /      | |    \ \
                      +---+--+   +-`.+--+  +--+----+
                      | ToR  |   | ToR  |  |  ToR  |
                      +-+--`.+   +-+-`.-+  +-+--+--+
                       .'     \   .'    \   .'    `.
                    __/_      _i./       i./_      _\__
                   '----'    '----'    '----'    '----'
                   : ED :    : ED :    : ED :    : ED :
                   '----'    '----'    '----'    '----'

            Figure 1 : A Generic Architecture for Data Centers

   An example of multi-tier DC network architecture is presented in
   this figure. A cloud network is composed of intra-Data Center (DC)
   networks and network services, and, inter-DC network and network
   connectivity services. Depending upon the scale, DC distribution,
   operations model, Capex and Opex aspects, DC networking elements can
   act as strict L2 switches and/or provide IP routing capabilities,
   including also service virtualization.

   In some DC architectures, it is possible that some tier layers
   provide L2 and/or L3 services, are collapsed, and that Internet
   connectivity, inter-DC connectivity and VPN support are handled by a
   smaller number of nodes. Nevertheless, one can assume that the
   functional blocks fit with the architecture above.

   The following components can be present in a DC:

     o End Device (ED): a DC resource to which the networking service
        is provided. ED may be a compute resource (server or server

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        blade), storage component or a network appliance (firewall,
        load-balancer, IPsec gateway). Alternatively, the End Device
        may include software based networking functions used to
        interconnect multiple IP hosts. An example of soft networking
        is the virtual switch in the server blades, used to
        interconnect multiple virtual machines (VMs). ED may be single
        or multi-homed to the Top of Rack switches (ToRs).

     o Top of Rack (ToR): Hardware-based Ethernet switch aggregating
        all Ethernet links from the End Devices in a rack representing
        the entry point in the physical DC network for the hosts. ToRs
        may also provide routing functionality, virtual IP network
        connectivity, or Layer2 tunneling over IP for instance. ToRs
        are usually multi-homed to switches in the Intra-DC network.
        Other deployment scenarios may use an EoR (End of Row) switch
        to provide similar function as a ToR.

     o Intra-DC Network: High capacity network composed of core
        switches aggregating multiple ToRs. Core switches are usually
        Ethernet switches but can also support routing capabilities.

     o DC GW: Gateway to the outside world providing DC Interconnect
        and connectivity to Internet and VPN customers. In the current
        DC network model, this may be simply a Router connected to the
        Internet and/or an IPVPN/L2VPN PE. Some network implementations
        may dedicate DC GWs for different connectivity types (e.g., a
        DC GW for Internet, and another for VPN).

   We use throughout this document the term "End System" to define an
   end system of a particular tenant, which can be for instance a
   virtual machine (VM), a non-virtualized server, or a non-virtualized
   network appliance. One or more End Systems can be part of an ED.

1.4. Tenant networking view

   The DC network architecture is used to provide L2 and/or L3 service
   connectivity to each tenant. An example is depicted in Figure 2:

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                         +----- L3 Infrastructure ----+
                         |                            |
                      ,--+-'.                      ;--+--.
                 .....  Rtr1 )......              .  Rtr2 )
                 |    '-----'      |               '-----'
                 |     Tenant1     |LAN12      Tenant1|
                 |LAN11        ....|........          |LAN13
             '':'''''''':'       |        |     '':'''''''':'
              ,'.      ,'.      ,+.      ,+.     ,'.      ,'.
             (VM )....(VM )    (VM )... (VM )   (VM )....(VM )
              `-'      `-'      `-'      `-'     `-'      `-'

        Figure 2 : Logical Service connectivity for a single tenant

   In this example one or more L3 contexts and one or more LANs (e.g.,
   one per Application) running on DC switches are assigned for DC
   tenant 1.

   For a multi-tenant DC, a virtualized version of this type of service
   connectivity needs to be provided for each tenant by the Network
   Virtualization solution.

2. Reference Models

2.1. Generic Reference Model

   The following diagram shows a DC reference model for network
   virtualization using Layer3 overlays where edge devices provide a
   logical interconnect between end systems that belong to specific
   tenant network.

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         +--------+                                  +--------+
         +  End   +--+                           +---|  End   |
         + System +  |                           |   | System |
         +--------+  |    ...................    |   +--------+
                     |  +-+--+           +--+-+  |
                     |  | NV |           | NV |  |
                     +--|Edge|           |Edge|--+
                        +-+--+           +--+-+
                       /  .    L3 Overlay   .  \
         +--------+   /   .     Network     .   \     +--------+
         +  End   +--+    .                 .    +----|  End   |
         + System +       .    +----+       .         | System |
         +--------+       .....| NV |........         +--------+
                              |  End   |
                              | System |

     Figure 3 : Generic reference model for DC network virtualization
                       over a Layer3 infrastructure

   An End System attaches to a Network Virtualization Edge (NVE) node,
   either directly or via a switched network (typically Ethernet).
   Examples of DC End Systems are host machines, including Virtual
   Machines, Network Appliances or Storage Systems.

   The NVE implements network virtualization functions that allow for
   L2 and/or L3 tenant separation and for hiding tenant addressing
   information (MAC and IP addresses), tenant-related control plane
   activity and service contexts from the Routed Backbone nodes.

   Core nodes utilize L3 techniques to interconnect NVE nodes in
   support of the overlay network. These devices perform forwarding
   based on outer L3 tunnel header, and generally do not maintain per
   tenant-service state albeit some applications (e.g., multicast) may
   require control plane or forwarding plane information that pertain
   to a tenant, group of tenants, tenant service or a set of services
   that belong to one or more tunnels. When such tenant or tenant-

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   service related information is maintained in the core, overlay
   virtualization provides knobs to control the magnitude of that

2.2. NVE Reference Model

   The NVE is composed of a tenant service instance that end systems
   interface with and an overlay module that provides tunneling overlay
   functions (e.g. encapsulation/decapsulation of tenant traffic
   from/to the tenant forwarding instance, tenant identification and
   mapping, etc), as described in figure 4:

                      +------- L3 Network ------+
                      |                         |
                      |                         |
         +------------+--------+       +--------+------------+
         | +----------+------+ |       | +------+----------+ |
         | | Overlay Module  | |       | | Overlay Module  | |
         | +--------+--------+ |       | +--------+--------+ |
         |          |          |       |          |          |
         |   NVE1   |          |        |         |   NVE2   |
         |  +-------+-------+  |       |  +-------+-------+  |
         |  |Tenant Instance|  |       |  |Tenant Instance|  |
         |  +-+-----------+-+  |       |  +-+-----------+-+  |
         |    |           |    |       |    |           |    |
         +----+-----------+----+       +----+-----------+----+
              |           |                 |           |
              |           |     Tenant      |           |
              |           |   Service IF    |           |
               End Systems                   End Systems

              Figure 4 : Generic reference model for NV Edge

   Note that some NVE functions (e.g. data plane and control plane
   functions) may reside in one device or they may be distributed
   between multiple devices.

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2.3. NVE Service Types

   NVE components may be used to provide different types of virtualized
   service connectivity. This section defines the service types and
   associated attributes

2.3.1. L2 NVE providing Ethernet LAN-like service

   L2 NVE implements Ethernet LAN emulation (ELAN), an Ethernet based
   multipoint service where the End Systems appear to be interconnected
   by a LAN environment over a set of L3 tunnels. It provides per
   tenant virtual switching instance with MAC addressing isolation and
   L3 tunnel encapsulation across the core.

2.3.2. L3 NVE providing IP/VRF-like service

   Virtualized IP routing and forwarding is similar from a service
   definition perspective with IETF IP VPN (e.g., BGP/MPLS IPVPN and
   IPsec VPNs). It provides per tenant routing instance with addressing
   isolation and L3 tunnel encapsulation across the core.

3. Functional components

   This section breaks down the Network Virtualization architecture
   into functional components to make it easier to discuss solution
   options for different modules.

   This version of the document gives an overview of generic functional
   components that are shared between L2 and L3 service types. Details
   specific for each service type will be added in future revisions.

3.1. Generic service virtualization components

   A Network Virtualization solution is built around a number of
   functional components as depicted in Figure 5:

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                      +------- L3 Network ------+
                      |                         |
                      |       Tunnel Overlay    |
         +------------+--------+       +--------+------------+
         | +----------+------+ |       | +------+----------+ |
         | | Overlay Module  | |       | | Overlay Module  | |
         | +--------+--------+ |       | +--------+--------+ |
         |          |Tenant ID |       |          |Tenant ID |
         |          | (TNI)    |       |          | (TNI)    |
         |  +-------+-------+  |       |  +-------+-------+  |
         |  |Tenant Instance|  |       |  |Tenant Instance|  |
    NVE2 |  +-+-----------+-+  |       |  +-+-----------+-+  | NVE1
         |    |   VAPs    |    |       |    |   VAPs    |    |
         +----+-----------+----+       +----+-----------+----+
              |           |                 |           |
              |           |     Tenant      |           |
              |           |   Service IF    |           |
               End Systems                   End Systems

              Figure 5 : Generic reference model for NV Edge

3.1.1. Virtual Access Points (VAPs)

   End Systems are connected to the Tenant Instance through Virtual
   Access Points (VAPs). The VAPs can be in reality physical ports on a
   ToR or virtual ports identified through logical interface
   identifiers (VLANs, internal VSwitch Interface ID leading to a VM).

3.1.2. Tenant Instance

   The Tenant Instance represents a set of configuration attributes
   defining access and tunnel policies and (L2 and/or L3) forwarding

   Per tenant FIB tables and control plane protocol instances are used
   to maintain separate private contexts between tenants. Hence tenants
   are free to use their own addressing schemes without concerns about
   address overlapping with other tenants.

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3.1.3. Overlay Modules and Tenant ID

   The Overlay module provides tunneling overlay functions: tunnel
   initiation/termination, encapsulation/decapsulation of frames from
   VAPs/L3 Backbone and may provide for transit forwarding of IP
   traffic (e.g., transparent tunnel forwarding).

   In a multi-tenant context, the tunnel aggregates frames from/to
   different Tenant Instances. Tenant identification and traffic
   demultiplexing are based on the Tenant Identifier (TNI).

   At least two possible approaches for TNI should be considered:

     o One ID per Tenant: A globally unique (on a per-DC
        administrative domain) Tenant ID is used to identify the
        related Tenant instances. An example of this approach is the
        use of IEEE VLAN or ISID tags to provide virtual L2 domains.

     o One ID per Tenant Instance (TNI): A per-tenant local ID is
        automatically generated by the egress NVE and usually
        distributed by a control plane protocol to all the related
        NVEs. An example of this approach is the use of per VRF MPLS
        labels in IP VPN [RFC4364].

     o One ID per VAP: A per-VAP local ID is assigned and usually
        distributed by a control plane protocol. An example of this
        approach is the use of per CE-PE MPLS labels in IP VPN

     Note that when using one ID per TNI or VAP, an additional global
     identifier may be used by the control plane to identify the Tenant

3.1.4. Tunnel Overlays and Encapsulation options

   Once the TNI is added to the frame an IP Tunnel encapsulation is
   used to transport the frame to the destination NVE. The backbone
   devices do not usually keep any per service state, simply forwarding
   the frames based on the outer tunnel header.

   Different IP tunneling options (GRE/L2TP/IPSec) are already
   available for both Ethernet and IP formats. A UDP/IP option is
   described in [VXLAN].

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3.1.5. Use of Control Plane Protocols

   A set of control plane components may be used to provide certain
   functions related to auto-provisioning, route advertisement,
   efficient BUM handling, or ARP reduction for instance, as discussed
   in section 4.2.

   Further details will be provided in a subsequent revision of this

3.2. Service Overlay Topologies

   A number of service topologies may be used to optimize the service
   connectivity and to address NVE performance limitations.

   The topology described in Figure 3 suggests the use of a tunnel mesh
   between the NVEs where each tenant instance is one hop away from a
   service processing perspective. Partial mesh topologies and an NVE
   hierarchy may be used where certain NVEs may act as service transit

4. Key aspects of overlay networks

4.1. Pros & Cons

   An overlay network is a layer of virtual network topology on top of
   the physical network.

   Overlay networks offer the following key advantages:

     o Tunnel state management is handled at the edge of the network.
        Intermediate transport nodes are unaware of such state,
        provided that flood containment or multicast capabilities on a
        per-tenant basis are not required from the core network

     o Tunnels are used to aggregate traffic and hence offer the
        advantage of minimizing the amount of forwarding state required
        within the underlay network

     o Decoupling of the overlay addresses (MAC and IP) used by VMs
        from the underlay network. This offers a clear separation
        between addresses used within the overlay and the underlay
        networks and it enables the use of overlapping addresses spaces
        by end systems

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     o Support of a large number of virtual network identifiers

   Overlay networks also create several challenges:

     o Overlay networks have no controls of underlay networks and lack
        critical network information

          o Overlays typically probe the network to measure link
             properties, such as available bandwidth or packet loss
             rate. It is difficult to accurately evaluate network
             properties. It might be preferable for the underlay
             network to expose usage and performance information.

     o Miscommunication between overlay and underlay networks can lead
        to an inefficient usage of network resources.

     o Fairness of resource sharing and collaboration among end-nodes
        in overlay networks are two critical issues

     o When multiple overlays co-exist on top of a common underlay
        network, the lack of communication between overlays can lead to
        performance issues.

     o Overlaid traffic may not traverse firewalls and NAT devices.

     o Multicast service scalability. Multicast support may be
        required in the overlay network to address for each tenant
        flood containment or efficient multicast handling.

4.2. Overlay issues to consider

4.2.1. End System to Overlay Network Mapping

   NVEs must be able to select the appropriate Tenant Instance for each
   End System. This is based on state information that is often
   distributed from external entities. For example, in a VM
   environment, this information is provided by compute management
   systems, since these are the only entities that have visibility on
   which VM belongs to which tenant.

   A standard mechanism for communicating this information between End
   Systems and the network is required. Note, that depending on the
   implementation this control interface can be between compute
   management and a virtual switch or between compute management and/or
   End Systems and a ToR switch.

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   In either case the protocol must provide appropriate security and
   authentication mechanisms to verify that End System information is
   not spoofed or altered. This is one of the most critical aspects for
   providing integrity and tenant isolation in the system.

4.2.2. Address to tunnel mapping

   As traffic reaches an ingress NVE, a lookup is performed to
   determine which tunnel the packet needs to be sent to. It is then
   encapsulated with a tunnel header containing the destination address
   of the egress overlay node. Intermediate nodes (between the ingress
   and egress NVEs) switch or route traffic based upon the outer
   destination address.

   One key step in this process consists of mapping a final destination
   address to the proper tunnel. NVEs are responsible for maintaining
   such mappings in their lookup tables.

   Several ways of populating these lookup tables are possible: data
   plane driven, control plane driven or management plane driven.
   Destination addresses can be dynamically learned as would occur in
   standard bridges, or they can be populated by a control plane
   protocol or a network management system.

4.2.3. Data plane vs Control plane driven

   Dynamic (data plane) learning implies that flooding of unknown
   destinations be supported and hence implies that broadcast and/or
   multicast be supported. Multicasting in the core network for dynamic
   learning can lead to significant scalability limitations. Specific
   forwarding rules must be enforced to prevent loops from happening.
   This can be achieved using a spanning tree protocol or a shortest
   path tree, or using a split-horizon mesh.

   A control plane protocol can distribute this information instead. As
   an example, [EVPN] describes a procedure to distribute the VM MACs
   and build forwarding entries in each Tenant Instance. Alternative
   control plane protocols and/or options are applicable.

   It should be noted that the amount of state to be distributed is a
   function of the number of virtual machines. Different forms of
   caching can also be utilized to minimize state distribution between
   the various elements.

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4.2.4. Coordination between data plane and control plane

   Often a combination of data plane and control based learning is
   necessary. Learning is applied towards end-user facing ports whereas
   distribution is used on the tunnel ports. Coordination between the
   learning engine and the control protocol is needed such that when a
   new address gets learned or an old address is removed, it triggers
   the local control plane to distribute this information to its peers.

4.2.5. Handling Broadcast, Unknown Unicast and Multicast (BUM) traffic

   There are two techniques to support packet replication needed for
   broadcast, unknown unicast and multicast:

     o Ingress replication

     o Use of core multicast trees

   There is a bandwidth vs state trade-off between the two approaches.
   Depending upon the degree of replication required (i.e. the number
   of hosts per group) and the amount of multicast state to maintain,
   trading bandwidth for state is of consideration.

   When the number of hosts per group is large, the use of core
   multicast trees may be more appropriate. When the number of hosts is
   small (e.g. 2-3), ingress replication may not be an issue.

   Depending upon the size of the data center network and hence the
   number of (S,G) entries, but also the duration of multicast flows,
   the use of core multicast trees can be a challenge.

   When flows are well known, it is possible to pre-provision such
   multicast trees. However, it is often difficult to predict
   application flows ahead of time, and hence programming of (S,G)
   entries for short-lived flows could be impractical.

   A possible trade-off is to use in the core shared multicast trees as
   opposed to dedicated multicast trees.

4.2.6. Path MTU

   When using overlay tunneling, an outer header is added to the
   original frame. This can cause the MTU of the path to the egress
   tunnel endpoint to be exceeded.

   In this section, we will only consider the case of an IP overlay.

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   It is usually not desirable to rely on IP fragmentation for
   performance reasons. Ideally, the interface MTU as seen by an end
   system is adjusted such that no fragmentation is needed. TCP will
   adjust its maximum segment size accordingly.

   It is possible for the MTU to be configured manually or to be
   discovered dynamically. Various Path MTU discovery techniques exist
   in order to determine the proper MTU size to use:

     o Classical ICMP-based MTU Path Discovery [RFC1191] [RFC1981]

          o End systems rely on ICMP messages to discover the MTU of
             the end-to-end path to its destination. This method is not
             always possible, such as when traversing middle boxes
             (e.g. firewalls) which disable ICMP for security reasons

     o Extended MTU Path Discovery techniques such as defined in

   It is also possible to rely on the overlay layer to perform
   segmentation and reassembly operations without relying on the end
   systems to know about the end-to-end MTU. The assumption is that
   some hardware assist is available on the NVE node to perform such
   SAR operations. Such a mechanism is described in [STT]. However,
   fragmentation by the overlay layer can lead to performance and
   congestion issues due to TCP dynamics and might require new
   congestion avoidance mechanisms from then underlay network [FLOYD].

   Finally, the underlay network may be designed in such a way that the
   MTU can accommodate the extra tunnel overhead.

4.2.7. NVE location trade-offs

   In the case of DC traffic, traffic originated from a VM is native
   Ethernet traffic. This traffic can be switched by a local VM switch
   or ToR switch and then by a DC gateway. The NVE function can be
   embedded within any of these elements.

   There are several criteria to consider when deciding where the NVE
   processing boundary happens:

     o Processing and memory requirements

          o Datapath (e.g. lookups, filtering,

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          o Control plane processing (e.g. routing, signaling, OAM)

     o FIB/RIB size

     o Multicast support

          o Routing protocols

          o Packet replication capability

     o Fragmentation support

     o QoS transparency

     o Resiliency

4.2.8. Interaction between network overlays and underlays

   When multiple overlays co-exist on top of a common underlay network,
   this can cause some performance issues. These overlays have
   partially overlapping paths and nodes.

   Each overlay is selfish by nature in that it sends traffic so as to
   optimize its own performance without considering the impact on other
   overlays, unless the underlay tunnels are traffic engineered on a
   per overlay basis so as to avoid sharing underlay resources.

   Better visibility between overlays and underlays can be achieved by
   providing mechanisms to exchange information about:

     o Performance metrics (throughput, delay, loss, jitter)

     o Cost metrics

5. Security Considerations

   The tenant to overlay mapping function can introduce significant
   security risks if appropriate protocols are not used that can
   support mutual authentication.

   No other new security issues are introduced beyond those described
   already in the related L2VPN and L3VPN RFCs.

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6. IANA Considerations

   IANA does not need to take any action for this draft.

7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

7.2. Informative References

   [NVOPS]  Narten, T. et al, "Problem Statement : Overlays for Network
             Virtualization", draft-narten-nvo3-overlay-problem-
             statement (work in progress)

   [OVCPREQ] Kreeger, L. et al, "Network Virtualization Overlay Control
             Protocol Requirements", draft-kreeger-nvo3-overlay-cp
             (work in progress)

   [DCVPN] Bitar, N. et al, "Cloud Networking: Framework and VPN
             Applicability", draft-bitar-datacenter-vpn-applicability
             (work in progress)

   [EVPN]   Raggarwa, R. et al. "BGP MPLS based Ethernet VPN", draft-
             ietf-l2vpn-evpn (work in progress)

   [NVGRE]  Sridhavan, M. et al, "NVGRE: Network Virtualization using
             Generic Routing Encapsulation", draft-sridharan-
             virtualization-nvgre (work in progress)

   [STT]    Davie, B., "A Stateless Transport Tunneling Protocol for
             Network Virtualization", draft-davie-stt (work in

   [VXLAN]  Mahalingam, M. et al, "VXLAN: A Framework for Overlaying
             Virtualized Layer 2 Networks over Layer 3 Networks",
             draft-mahalingam-dutt-dcops-vxlan (work in progress)

   [FLOYD]  Sally Floyd, Allyn Romanow, "Dynamics of TCP Traffic over
             ATM Networks", IEEE JSAC, V. 13 N. 4, May 1995

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Internet-Draft  Framework for DC Network Virtualization  March 2012

   [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
             Networks (VPNs)", RFC 4364, February 2006.

   [RFC1191] Mogul, J. "Path MTU Discovery", RFC1191, November 1990

   [RFC1981] McCann, J. et al, "Path MTU Discovery for IPv6", RFC1981,
             August 1996

   [RFC4821] Mathis, M. et al, "Packetization Layer Path MTU
             Discovery", RFC4821, March 2007

8. Acknowledgments

   In addition to the authors the following people have contributed to
   this document:

   Nabil Bitar, Verizon

   Dimitrios Stiliadis, Rotem Salomonovitch, Alcatel-Lucent

   This document was prepared using

Authors' Addresses

   Marc Lasserre

   Florin Balus
   777 E. Middlefield Road
   Mountain View, CA, USA 94043

   Thomas Morin
   France Telecom Orange

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