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Internet Engineering Task Force                               L. Kreeger
Internet-Draft                                                     Cisco
Intended status: Informational                                   D. Dutt
Expires: December 16, 2013                              Cumulus Networks
                                                               T. Narten
                                                                D. Black
                                                            M. Sridharan
                                                           June 14, 2013

      Network Virtualization Overlay Control Protocol Requirements


   The document "Problem Statement: Overlays for Network Virtualization"
   discusses the needs for network virtualization using overlay networks
   in highly virtualized data centers.  The problem statement outlines a
   need for control protocols to facilitate running these overlay
   networks.  This document outlines the high level requirements to be
   fulfilled by the control protocols related to building and managing
   the mapping tables and other state information used by the Network
   Virtualization Edge to transmit encapsulated packets across the
   underlying network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on December 16, 2013.

Copyright Notice

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Control Plane Protocol Functionality  . . . . . . . . . . . .   4
     3.1.  Inner to Outer Address Mapping  . . . . . . . . . . . . .   5
     3.2.  Underlying Network Multi-Destination Delivery Address(es)   6
     3.3.  VN Connect/Disconnect Notification  . . . . . . . . . . .   6
     3.4.  VN Name to VN ID Mapping  . . . . . . . . . . . . . . . .   6
   4.  Control Plane Characteristics . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Informative References  . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   "Problem Statement: Overlays for Network Virtualization"
   [I-D.ietf-nvo3-overlay-problem-statement] discusses the needs for
   network virtualization using overlay networks in highly virtualized
   data centers and provides a general motivation for building such
   networks.  "Framework for DC Network Virtualization"
   [I-D.ietf-nvo3-framework] provides a framework for discussing overlay
   networks generally and the various components that must work together
   in building such systems.  The reader is assumed to be familiar with
   both documents.

   Section 4.5 of [I-D.ietf-nvo3-overlay-problem-statement] describes
   three separate work areas that fall under the general category of a
   control protocol for NVO3.  This document focuses entirely on those
   aspects of the control protocol related to the building and
   distributing the mapping tables an NVE uses to tunnel traffic from
   one VM to another.  Specifically, this document focuses on work areas
   1 and 2 given in Section 4.5 of
   [I-D.ietf-nvo3-overlay-problem-statement].  Work areas 1 and 2 cover

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   the interaction between an NVE and the Network Virtualization
   Authority (NVA) (work area 2) or operation of the NVA itself (work
   area 1).  Requirements related to interaction between a hypervisor
   and NVE when the two entities reside on separate physical devices
   (work area 3) are covered in [I-D.kreeger-nvo3-hypervisor-nve-cp-

2.  Terminology

   This document uses the same terminology as found in
   [I-D.ietf-nvo3-framework].  This section defines additional
   terminology used by this document.

   Network Service Appliance:  A stand-alone physical device or a
      virtual device that provides a network service, such as a
      firewall, load balancer, etc.  Such appliances may embed Network
      Virtualization Edge (NVE) functionality within them in order to
      more efficiently operate as part of a virtualized network.

   VN Alias:  A string name for a VN as used by administrators and
      customers to name a specific VN.  A VN Alias is a human-usable
      string that can be listed in contracts, customer forms, email,
      configuration files, etc. and that can be communicated easily
      vocally (e.g., over the phone).  A VN Alias is independent of the
      underlying technology used to implement a VN and will generally
      not be carried in protocol fields of control protocols used in
      virtual networks.  Rather, a VN Alias will be mapped into a VN
      Name where precision is required.

   VN Name:  A globally unique identifier for a VN suitable for use
      within network protocols.  A VN Name will usually be paired with a
      VN Alias, with the VN Alias used by humans as a shorthand way to
      name and identify a specific VN.  A VN Name should have a compact
      representation to minimize protocol overhead where a VN Name is
      carried in a protocol field.  Using a Universally Unique
      Identifier (UUID) as discussed in RFC 4122, may work well because
      it is both compact and a fixed size and can be generated locally
      with a very high likelihood of global uniqueness.

   VN ID:  A unique and compact identifier for a VN within the scope of
      a specific NVO3 administrative domain.  It will generally be more
      efficient to carry VN IDs as fields in control protocols than VN
      Names or VN Aliases.  There is a one-to-one mapping between a VN
      Name and a VN ID within an NVO3 Administrative Domain.  Depending
      on the technology used to implement an overlay network, the VN ID
      could be used as the VN Context in the data plane, or would need
      to be mapped to a locally-significant context ID.

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3.  Control Plane Protocol Functionality

   The NVO3 problem statement [I-D.ietf-nvo3-overlay-problem-statement],
   discusses the needs for a control plane protocol (or protocols) to
   populate each NVE with the state needed to perform its functions.

   In one common scenario, an NVE provides overlay encapsulation/
   decapsulation packet forwarding services to Tenant Systems that are
   co-resident with the NVE on the same End Device (e.g. when the NVE is
   embedded within a hypervisor or a Network Service Appliance).
   Alternatively, a Tenant System may use an externally connected NVE
   (e.g. an NVE residing on a physical Network Switch connected to the
   hypervisor via an access network).  The latter scenario is not
   discussed in this document, but is covered in [I-D.kreeger-nvo3

   The following figures show examples of scenarios in which the NVE is
   co-resident within the same End Device as the Tenant System connected
   to a given VN.

   | +--+   +-------+---+  |
   | |VM|---|       |   |  |
   | +--+   |Virtual|NVE|----- Underlying
   | +--+   |Switch |   |  |    Network
   | |VM|---|       |   |  |
   | +--+   +-------+---+  |

   Hypervisor with an Embedded NVE.

                                 Figure 1

    Network Service Appliance
   | +------------+   +-----+  |
   | |Net Service |---|     |  |
   | |Instance    |   |     |  |
   | +------------+   | NVE |------ Underlying
   | +------------+   |     |  |    Network
   | |Net Service |---|     |  |
   | |Instance    |   |     |  |
   | +------------+   +-----+  |

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   Network Service Appliance (physical or virtual) with an Embedded NVE.

                                 Figure 2

   To support an NVE, a control plane protocol is necessary to provide
   an NVE with the information it needs to maintain its own internal
   state necessary to carry out its forwarding functions as explained in
   detail below.

   1.  An NVE maintains a per-VN table of mappings from Tenant System
       (inner) addresses to Underlying Network (outer) addresses of
       remote NVEs.

   2.  An NVE maintains per-VN state for delivering tenant multicast and
       broadcast packets to other Tenant Systems.  Such state could
       include a list of multicast addresses and/or unicast addresses on
       the Underlying Network for the NVEs associated with a particular

   3.  End Devices (such as a Hypervisor or Network Service Appliance)
       utilizing an external NVE need to "attach to" and "detach from"
       an NVE.  Specifically, a mechanism is needed to notify an NVE
       when a Tenant System attaches to or detaches from a specific VN.
       Such a mechanism would provide the necessary information to the
       NVE that it needs to provide service to a particular Tenant
       System.  The details of such a mechanism are out-of-scope for
       this document and are covered in [I-D.kreeger-nvo3-hypervisor-

   4.  An NVE needs a mapping from each unique VN name to the VN Context
       value used within encapsulated data packets within the
       administrative domain that the VN is instantiated.

3.1.  Inner to Outer Address Mapping

   When presented with a data packet to forward to a Tenant System
   within a VN, the NVE needs to know the mapping of the Tenant System
   destination (inner) address to the (outer) address on the Underlying
   Network of the remote NVE which can deliver the packet to the
   destination Tenant System.  In addition, the NVE needs to know what
   VN Context to use when sending to a destination Tenant System.

   A protocol is needed to provide this inner to outer mapping and VN
   Context to each NVE that requires it and keep the mapping updated in
   a timely manner.  Timely updates are important for maintaining
   connectivity between Tenant Systems when one Tenant System is a VM.

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   Note that one technique that could be used to create this mapping
   without the need for a control protocol is via data plane learning;
   However, the learning approach requires packets to be flooded to all
   NVEs participating in the VN when no mapping exists.  One goal of
   using a control protocol is to eliminate this flooding.

3.2.  Underlying Network Multi-Destination Delivery Address(es)

   Each NVE needs a way to deliver multi-destination packets (i.e.
   tenant broadcast/multicast) within a given VN to each remote NVE
   which has a destination Tenant System for these packets.  Three
   possible ways of accomplishing this are:

   o  Use the multicast capabilities of the Underlying Network.

   o  Have each NVE replicate the packets and send a copy across the
      Underlying Network to each remote NVE currently participating in
      the VN.

   o  Use one or more distribution servers that replicate the packets on
      the behalf of the NVEs.

   Whichever method is used, a protocol is needed to provide on a per VN
   basis, one or more multicast addresses (assuming the Underlying
   Network supports multicast), and/or one or more unicast addresses of
   either the remote NVEs which are not multicast reachable, or of one
   or more distribution servers for the VN.

   The protocol must also keep the list of addresses up to date in a
   timely manner as the set of NVEs for a given VN changes over time.
   For example, the set of NVEs for a VN could change as VMs power on/
   off or migrate to different hypervisors.

3.3.  VN Connect/Disconnect Notification

   For the purposes of this document, it is assumed that an NVE receives
   appropriate notifications when a Tenant System attaches to or
   detaches from a specific VN.  The details of how that is done are
   orthogonal to the NVE-to-NVA control plane, so long as such
   notification provides the necessary information needed by the control
   plane.  As one example, the attach/detach notification would
   presumably include a VN Name that identifies the specific VN to which
   the attach/detach operation applies to.

3.4.  VN Name to VN ID Mapping

   Once an NVE (embedded or external) receives a VN connect indication
   with a specified VN Name, the NVE must determine what VN Context

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   value and other necessary information to use to forward Tenant System
   traffic to remote NVEs.  In one approach, the NVE-to-NVA protocol
   uses VN Names directly when interacting, with the NVA providing such
   information as the VN Context (or VN ID) along with egress NVE's
   address.  Alternatively, it may be desirable for the NVE-to-NVA
   protocol to use a more compact representation of the VN name, that
   is, a VN ID.  In such a case, a specific NVE-to-NVA operation might
   be needed to first map the VN Name into a VN ID, with subsequent NVE-
   to-NVA operations utilizing the VN ID directly.  Thus, it may be
   useful for the NVE-to-NVA protocol to support an operation that maps
   VN Names into VN IDs.

4.  Control Plane Characteristics

   NVEs are expected to be implemented within both hypervisors (or
   Network Service Appliances) and within access switches.  Any
   resources used by these protocols (e.g. processing or memory) takes
   away resources that could be better used by these devices to perform
   their intended functions (e.g. providing resources for hosted VMs).

   A large scale data center may contain hundreds of thousands of these
   NVEs (which may be several independent implementations); Therefore,
   any savings in per-NVE resources can be multiplied hundreds of
   thousands of times.

   Given this, the control plane protocol(s) implemented by NVEs to
   provide the functionality discussed above should have the below

   1.   Minimize the amount of state needed to be stored on each NVE.
        The NVE should only be required to cache state that it is
        actively using, and be able to discard any cached state when it
        is no longer required.  For example, an NVE should only need to
        maintain an inner-to-outer address mapping for destinations to
        which it is actively sending traffic as opposed to maintaining
        mappings for all possible destinations.

   2.   Fast acquisition of needed state.  For example, when a Tenant
        System emits a packet destined to an inner address that the NVE
        does not have a mapping for, the NVE should be able to acquire
        the needed mapping quickly.

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   3.   Fast detection/update of stale cached state information.  This
        only applies if the cached state is actually being used.  For
        example, when a VM moves such that it is connected to a
        different NVE, the inner to outer mapping for this VM's address
        that is cached on other NVEs must be updated in a timely manner
        (if they are actively in use).  If the update is not timely, the
        NVEs will forward data to the wrong NVE until it is updated.

   4.   Minimize processing overhead.  This means that an NVE should
        only be required to perform protocol processing directly related
        to maintaining state for the Tenant Systems it is actively
        communicating with.  This requirement is for the NVE
        functionality only.  The network node that contains the NVE may
        be involved in other functionality for the underlying network
        that maintains connectivity that the NVE is not actively using
        (e.g., routing and multicast distribution protocols for the
        underlying network).

   5.   Highly scalable.  This means scaling to hundreds of thousands of
        NVEs and several million VNs within a single administrative
        domain.  As the number of NVEs and/or VNs within a data center
        grows, the protocol overhead at any one NVE should not increase

   6.   Minimize the complexity of the implementation.  This argues for
        using the least number of protocols to achieve all the
        functionality listed above.  Ideally a single protocol should be
        able to be used.  The less complex the protocol is on the NVE,
        the more likely interoperable implementations will be created in
        a timely manner.

   7.   Extensible.  The protocol should easily accommodate extension to
        meet related future requirements.  For example, access control
        or QoS policies, or new address families for either inner or
        outer addresses should be easy to add while maintaining
        interoperability with NVEs running older versions.

   8.   Simple protocol configuration.  A minimal amount of
        configuration should be required for a new NVE to be
        provisioned.  Existing NVEs should not require any configuration
        changes when a new NVE is provisioned.  Ideally NVEs should be
        able to auto configure themselves.

   9.   Do not rely on IP Multicast in the Underlying Network.  Many
        data centers do not have IP multicast routing enabled.  If the
        Underlying Network is an IP network, the protocol should allow
        for, but not require the presence of IP multicast services
        within the data center.

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   10.  Flexible mapping sources.  It should be possible for either NVEs
        themselves, or other third party entities (e.g.  data center
        management or orchestration systems) to create inner to outer
        address mappings in the NVA.  The protocol should allow for
        mappings created by an NVE to be automatically removed from all
        other NVEs if it fails or is brought down unexpectedly.

   11.  Secure.  See the Security Considerations section below.

5.  Security Considerations

   Editor's Note: This is an initial start on the security
   considerations section; it will need to be expanded, and suggestions
   for material to add are welcome.

   The protocol(s) should protect the integrity of the mapping against
   both off-path and on-path attacks.  It should authenticate the
   systems that are creating mappings, and rely on light weight security
   mechanisms to minimize the impact on scalability and allow for simple

   Use of an overlay exposes virtual networks to attacks on the
   underlying network beyond attacks on the control protocol that is the
   subject of this draft.  In addition to the directly applicable
   security considerations for the networks involved, the use of an
   overlay enables attacks on encapsulated virtual networks via the
   underlying network.  Examples of such attacks include traffic
   injection into a virtual network via injection of encapsulated
   traffic into the underlying network and modifying underlying network
   traffic to forward traffic among virtual networks that should have no
   connectivity.  The control protocol should provide functionality to
   help counter some of these attacks, e.g., distribution of NVE access
   control lists for each virtual network to enable packets from non-
   participating NVEs to be discarded, but the primary security measures
   for the underlying network need to be applied to the underlying
   network.  For example, if the underlying network includes
   connectivity across the public Internet, use of secure gateways
   (e.g., based on IPsec [RFC4301]) may be appropriate.

   The inner to outer address mappings used for forwarding data towards
   a remote NVE could also be used to filter incoming traffic to ensure
   the inner address sourced packet came from the correct NVE source
   address, allowing access control to discard traffic that does not
   originate from the correct NVE.  This destination filtering
   functionality should be optional to use.

6.  Acknowledgements

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   Thanks to the following people for reviewing and providing feedback:
   Fabio Maino, Victor Moreno, Ajit Sanzgiri, Chris Wright.

7.  Informative References

              Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
              Rekhter, "Framework for DC Network Virtualization", draft-
              ietf-nvo3-framework-02 (work in progress), February 2013.

              Narten, T., Gray, E., Black, D., Fang, L., Kreeger, L.,
              and M. Napierala, "Problem Statement: Overlays for Network
              Virtualization", draft-ietf-nvo3-overlay-problem-
              statement-03 (work in progress), May 2013.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

Authors' Addresses

   Lawrence Kreeger

   Email: kreeger@cisco.com

   Dinesh Dutt
   Cumulus Networks

   Email: ddutt@cumulusnetworks.com

   Thomas Narten

   Email: narten@us.ibm.com

   David Black

   Email: david.black@emc.com

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   Murari Sridharan

   Email: muraris@microsoft.com

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