Network Working Group                                           L. Yong
Internet Draft                                                L. Dunbar
Category: Informational                                          Huawei
                                                                 M. Toy

                                                               A. Isaac
                                                       Juniper Networks
                                                              V. Manral
                                                         Ionos Networks

Expires: March 2017                                 September 22, 2016

         Use Cases for Data Center Network Virtualization Overlays



   This document describes Data Center (DC) Network Virtualization over
   Layer 3 (NVO3) use cases that can be deployed in various data
   centers and serve different applications.

Status of this Memo

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   This Internet-Draft will expire on March 22, 2017.

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Copyright Notice

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Table of Contents

   1. Introduction...................................................3
      1.1. Terminology...............................................4
   2. Basic Virtual Networks in a Data Center........................5
   3. DC Virtual Network and External Network Interconnection........6
      3.1. DC Virtual Network Access via the Internet................6
      3.2. DC VN and SP WAN VPN Interconnection......................8
   4. DC Applications Using NVO3.....................................9
      4.1. Supporting Multiple Technologies..........................9
      4.2. DC Application with Multiple Virtual Networks.............9
      4.3. Virtual Data Center (vDC)................................10
   5. Summary.......................................................11
   6. Security Considerations.......................................12
   7. IANA Considerations...........................................12
   8. References....................................................12
      8.1. Normative References.....................................12
      8.2. Informative References...................................12
   Authors' Addresses...............................................14

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1. Introduction

   Server Virtualization has changed the Information Technology (IT)
   industry in terms of the efficiency, cost, and speed of providing
   new applications and/or services such as cloud applications. However
   traditional Data Center (DC) networks have some limits in supporting
   cloud applications and multi tenant networks [RFC7364]. The goal of
   Network Virtualization Overlays in the DC is to decouple the
   communication among tenant systems from DC physical infrastructure
   networks and to allow one physical network infrastructure to provide:

   o  Multi-tenant virtual networks and traffic isolation among the
      virtual networks over the same physical network.

   o  Independent address spaces in individual virtual networks such as
      MAC, IP, TCP/UDP etc.

   o  Flexible Virtual Machines (VM) and/or workload placement
      including the ability to move them from one server to another
      without requiring VM address and configuration changes, and the
      ability to perform a "hot move" with no disruption to the live
      application running on VMs.

   These characteristics of NVO3 help address the issues that cloud
   applications face in Data Centers [RFC7364].

   An NVO3 network may interconnect with another NVO3 virtual network,
   or another physical network (i.e., not the physical network that the
   NVO3 network is over), via a gateway. The use case examples for the
   latter are: 1) DCs that migrate toward an NVO3 solution will be done
   in steps, where a portion of tenant systems in a VN is on
   virtualized servers while others exist on a LAN. 2) many DC
   applications serve to Internet users who are on physical networks; 3)
   some applications are CPU bound, such as Big Data analytics, and may
   not run on virtualized resources. Some inter-VN policies can be
   enforced at the gateway.

   This document describes general NVO3 use cases that apply to various
   data centers. The use cases described here represent DC provider's
   interests and vision for their cloud services. The document groups
   the use cases into three categories from simple to advance in term
   of implementation. However the implementations of these use cases
   are outside the scope of this document. These three categories are
   highlighted below:

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   o  Basic NVO3 virtual networks in a DC (Section 2). All Tenant
      Systems (TS) in the virtual network are located within the same
      DC. The individual virtual networks can be either Layer 2 (L2) or
      Layer 3 (L3). The number of NVO3 virtual networks in a DC is much
      higher than what traditional VLAN based virtual networks [IEEE
      802.1Q] can support. This case is often referred as to the DC
      East-West traffic.

   o  Virtual networks that span across multiple Data Centers and/or to
      customer premises, i.e., an NVO3 virtual network where some
      tenant systems in a DC attach to interconnect another virtual or
      physical network outside the data center. An enterprise customer
      may use a traditional carrier VPN or an IPsec tunnel over the
      Internet to communicate with its systems in the DC. This is
      described in Section 3.

   o  DC applications or services require an advanced network that
      contains several NVO3 virtual networks that are interconnected by
      the gateways. Three scenarios are described in Section 4: 1)
      supporting multiple technologies; 2) constructing several virtual
      networks as a tenant network; 3) applying NVO3 to a virtual Data
      Center (vDC).

   The document uses the architecture reference model defined in
   [RFC7365] to describe the use cases.

1.1.  Terminology

   This document uses the terminologies defined in [RFC7365] and
   [RFC4364]. Some additional terms used in the document are listed

   DMZ: Demilitarized Zone. A computer or small sub-network that sits
   between a trusted internal network, such as a corporate private LAN,
   and an un-trusted external network, such as the public Internet.

   DNS: Domain Name Service [RFC1035]

   DC Operator: A role who is responsible to construct and manage cloud
   service instances in their life-cycle and manage DC infrastructure
   that runs these cloud instances.

   DC Provider: A company that uses its DC infrastructure to offer
   cloud services to its customers.

   NAT: Network Address Translation [RFC3022]

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   vGW: virtual Gateway; a gateway component used for an NVO3 virtual
   network to interconnect with another virtual/physical network.

   Note that a virtual network in this document refers to an NVO3
   virtual network in a DC [RFC7365].

2. Basic Virtual Networks in a Data Center

   A virtual network in a DC enables communications among Tenant
   Systems (TS). A TS can be a physical server/device or a virtual
   machine (VM) on a server, i.e., end-device [RFC7365]. A Network
   Virtual Edge (NVE) can be co-located with a TS, i.e., on the same
   end-device, or reside on a different device, e.g., a top of rack
   switch (ToR). A virtual network has a virtual network identifier
   (can be globally unique or locally significant at NVEs).

   Tenant Systems attached to the same NVE may belong to the same or
   different virtual networks. An NVE provides tenant traffic
   forwarding/encapsulation and obtains tenant systems reachability
   information from a Network Virtualization Authority (NVA)[NVO3ARCH].
   DC operators can construct multiple separate virtual networks, and
   provide each with own address space.

   Network Virtualization Overlay in this context means that a virtual
   network is implemented with an overlay technology, i.e., within a DC
   that has IP infrastructure, tenant traffic is encapsulated at its
   local NVE and carried by a tunnel to another NVE where the packet is
   decapsulated and sent to a target tenant system. This architecture
   decouples tenant system address space and configuration from the
   infrastructure's, which provides great flexibility for VM placement
   and mobility. It also means that the transit nodes in the
   infrastructure are not aware of the existence of the virtual
   networks and tenant systems attached to the virtual networks. The
   tunneled packets are carried as regular IP packets and are sent to
   NVEs. One tunnel may carry the traffic belonging to multiple virtual
   networks; a virtual network identifier is used for traffic
   demultiplexing. A tunnel encapsulation protocol is necessary for NVE
   to encapsulate the packets from Tenant Systems and encode other
   information on the tunneled packets to support NVO3 implementation.

   A virtual network implemented by NVO3 may be an L2 or L3 domain. The
   virtual network can carry unicast traffic and/or multicast,
   broadcast/unknown (for L2 only) traffic from/to tenant systems.
   There are several ways to transport virtual network BUM traffic

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   It is worth mentioning two distinct cases regarding to NVE location.
   The first is where TSs and an NVE are co-located on a single end
   host/device, which means that the NVE can be aware of the TS's state
   at any time via an internal API. The second is where TSs and an NVE
   are not co-located, with the NVE residing on a network device; in
   this case, a protocol is necessary to allow the NVE to be aware of
   the TS's state [NVO3HYVR2NVE].

  One virtual network can provide connectivity to many TSs that attach
  to many different NVEs in a DC. TS dynamic placement and mobility
  results in frequent changes of the binding between a TS and an NVE.
  The TS reachability update mechanisms need be fast enough so that
  the updates do not cause any communication disruption/interruption.
  The capability of supporting many TSs in a virtual network and many
  more virtual networks in a DC is critical for the NVO3 solution.

   If a virtual network spans across multiple DC sites, one design is
   to allow the network to seamlessly span across the sites without DC
   gateway routers' termination. In this case, the tunnel between a
   pair of NVEs can be carried within other intermediate tunnels over
   the Internet or other WANs, or the intra DC and inter DC tunnels can
   be stitched together to form a tunnel between the pair of NVEs that
   are in different DC sites. Both cases will form one virtual network
   across multiple DC sites.

3. DC Virtual Network and External Network Interconnection

   Many customers (an enterprise or individuals) who utilize a DC
   provider's compute and storage resources to run their applications
   need to access their systems hosted in a DC through Internet or
   Service Providers' Wide Area Networks (WAN). A DC provider can
   construct a virtual network that provides connectivity to all the
   resources designated for a customer and allows the customer to
   access the resources via a virtual gateway (vGW). This, in turn,
   becomes the case of interconnecting a DC virtual network and the
   network at customer site(s) via the Internet or WANs. Two use cases
   are described here.

3.1. DC Virtual Network Access via the Internet

   A customer can connect to a DC virtual network via the Internet in a
   secure way. Figure 1 illustrates this case. The DC virtual network
   has an instance at NVE1 and NVE2 and the two NVEs are connected via
   an IP tunnel in the Data Center. A set of tenant systems are
   attached to NVE1 on a server. NVE2 resides on a DC Gateway device.
   NVE2 terminates the tunnel and uses the VNID on the packet to pass
   the packet to the corresponding vGW entity on the DC GW (the vGW is

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   the default gateway for the virtual network). A customer can access
   their systems, i.e., TS1 or TSn, in the DC via the Internet by using
   an IPsec tunnel [RFC4301]. The IPsec tunnel is configured between
   the vGW and the customer gateway at the customer site. Either a
   static route or iBGP may be used for prefix advertisement. The vGW
   provides IPsec functionality such as authentication scheme and
   encryption; iBGP protocol traffic is carried within the IPsec tunnel.
   Some vGW features are listed below:

   o  The vGW maintains the TS/NVE mappings and advertises the TS
      prefix to the customer via static route or iBGP.

   o  Some vGW functions such as firewall and load balancer can be
      performed by locally attached network appliance devices.

   o  If the virtual network in the DC uses different address space
      than external users, then the vGW needs to provide the NAT

   o  More than one IPsec tunnel can be configured for redundancy.

   o  The vGW can be implemented on a server or VM. In this case, IP
      tunnels or IPsec tunnels can be used over the DC infrastructure.

   o  DC operators need to construct a vGW for each customer.

         |   TS1 TSn     |
         |    |...|      |
         |  +-+---+-+    |             Customer Site
         |  |  NVE1 |    |               +-----+
         |  +---+---+    |               | CGW |
         +------+--------+               +--+--+
                |                           *
            L3 Tunnel                       *
                |                           *
   DC GW +------+---------+            .--.  .--.
         |  +---+---+     |           (    '*   '.--.
         |  |  NVE2 |     |        .-.'   *          )
         |  +---+---+     |       (    *  Internet    )
         |  +---+---+.    |        ( *               /
         |  |  vGW  | * * * * * * * * '-'          '-'
         |  +-------+ |   | IPsec       \../ \.--/'
         |   +--------+   | Tunnel

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           DC Provider Site

          Figure 1 - DC Virtual Network Access via the Internet

3.2. DC VN and SP WAN VPN Interconnection

   In this case, an Enterprise customer wants to use a Service Provider
   (SP) WAN VPN [RFC4364] [RFC7432] to interconnect its sites with a
   virtual network in a DC site. The Service Provider constructs a VPN
   for the enterprise customer. Each enterprise site peers with an SP
   PE. The DC Provider and VPN Service Provider can build a DC virtual
   network (VN) and VPN independently, and then interconnect them via a
   local link, or a tunnel between the DC GW and WAN PE devices. The
   control plane interconnection options between the DC and WAN are
   described in RFC4364 [RFC4364]. Using Option A with VRF-LITE [VRF-
   LITE], both ASBRs, i.e., DC GW and SP PE, maintain a
   routing/forwarding table (VRF). Using Option B, the DC ASBR and SP
   ASBR do not maintain the VRF table; they only maintain the VN and
   VPN identifier mappings, i.e., label mapping, and swap the label on
   the packets in the forwarding process. Both option A and B allow VN
   and VPN using own identifier and two identifiers are mapped at DC GW.
   With option C, the VN and VPN use the same identifier and both ASBRs
   perform the tunnel stitching, i.e., tunnel segment mapping. Each
   option has pros/cons [RFC4364] and has been deployed in SP networks
   depending on the applications in use. BGP is used with these options
   for route distribution between DCs and SP WANs. Note that if the DC
   is the SP's Data Center, the DC GW and SP PE in this case can be
   merged into one device that performs the interworking of the VN and
   VPN within an AS.

   The configurations above allow the enterprise networks to
   communicate with the tenant systems attached to the VN in a DC
   without interfering with the DC provider's underlying physical
   networks and other virtual networks. The enterprise can use its own
   address space in the VN. The DC provider can manage which VM and
   storage elements attach to the VN. The enterprise customer manages
   which applications run on the VMs in the VN without knowing the
   location of the VMs in the DC. (See Section 4 for more)

   Furthermore, in this use case, the DC operator can move the VMs
   assigned to the enterprise from one sever to another in the DC
   without the enterprise customer being aware, i.e., with no impact on
   the enterprise's 'live' applications. Such advanced technologies
   bring DC providers great benefits in offering cloud services, but
   add some requirements for NVO3 [RFC7364] as well.

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4. DC Applications Using NVO3

   NVO3 technology provides DC operators with the flexibility in
   designing and deploying different applications in an end-to-end
   virtualization overlay environment. The operators no longer need to
   worry about the constraints of the DC physical network configuration
   when creating VMs and configuring a virtual network. A DC provider
   may use NVO3 in various ways, in conjunction with other physical
   networks and/or virtual networks in the DC for a reason. This
   section highlights some use cases for this goal.

4.1. Supporting Multiple Technologies

   Servers deployed in a large data center are often installed at
   different times, and may have different capabilities/features. Some
   servers may be virtualized, while others may not; some may be
   equipped with virtual switches, while others may not. For the
   servers equipped with Hypervisor-based virtual switches, some may
   support VxLAN [RFC7348] encapsulation, some may support NVGRE
   encapsulation [RFC7637], and some may not support any encapsulation.
   To construct a tenant network among these servers and the ToR
   switches, operators can construct one traditional VLAN network and
   two virtual networks where one uses VxLAN encapsulation and the
   other uses NVGRE, and interconnect these three networks via a
   gateway or virtual GW. The GW performs packet
   encapsulation/decapsulation translation between the networks.

   Another case is that some software of a tenant is high CPU and
   memory consumption, which only makes a sense to run on metal servers;
   other software of the tenant may be good to run on VMs. However
   provider DC infrastructure is configured to use NVO3 to connect to
   VMs and VLAN [IEEE802.1Q] connect to metal services. The tenant
   network requires interworking between NVO3 and traditional VLAN.

4.2. DC Application with Multiple Virtual Networks

   A DC application may necessarily be constructed with multi-tier
   zones, where each zone has different access permissions and runs
   different applications. For example, a three-tier zone design has a
   front zone (Web tier) with Web applications, a mid zone (application
   tier) where service applications such as credit payment or ticket
   booking run, and a back zone (database tier) with Data. External
   users are only able to communicate with the Web application in the
   front zone; the back zone can only receive traffic from the
   application zone. In this case, communications between the zones
   must pass through a GW/firewall. Each zone can be implemented by one
   virtual network and a GW/firewall can be used to between two virtual

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   networks, i.e., two zones. A tunnel carrying virtual network traffic
   has to be terminated at the GW/firewall where overlay traffic is

4.3. Virtual Data Center (vDC)

   An Enterprise Data Center today may deploy routers, switches, and
   network appliance devices to construct its internal network, DMZ,
   and external network access; it may have many servers and storage
   running various applications. With NVO3 technology, a DC Provider
   can construct a virtual Data Center (vDC) over its physical DC
   infrastructure and offer a virtual Data Center service to enterprise
   customers. A vDC at the DC Provider site provides the same
   capability as the physical DC at a customer site. A customer manages
   its own applications running in its vDC. A DC Provider can further
   offer different network service functions to the customer. The
   network service functions may include firewall, DNS, load balancer,
   gateway, etc.

   Figure 2 below illustrates one such scenario at service abstraction
   level. In this example, the vDC contains several L2 VNs (L2VNx,
   L2VNy, L2VNz) to group the tenant systems together on a per-
   application basis, and one L3 VN (L3VNa) for the internal routing. A
   network firewall and gateway runs on a VM or server that connects to
   L3VNa and is used for inbound and outbound traffic processing. A
   load balancer (LB) is used in L2VNx. A VPN is also built between the
   gateway and enterprise router. An Enterprise customer runs
   Web/Mail/Voice applications on VMs within the vDC. The users at the
   Enterprise site access the applications running in the vDC via the
   VPN; Internet users access these applications via the
   gateway/firewall at the provider DC site.

   The Enterprise customer decides which applications should be
   accessible only via the intranet and which should be assessable via
   both the intranet and Internet, and configures the proper security
   policy and gateway function at the firewall/gateway. Furthermore, an
   enterprise customer may want multi-zones in a vDC (See section 4.2)
   for the security and/or the ability to set different QoS levels for
   the different applications.

   The vDC use case requires an NVO3 solution to provide DC operators
   with an easy and quick way to create a VN and NVEs for any vDC
   design, to allocate TSs and assign TSs to the corresponding VN, and
   to illustrate vDC topology and manage/configure individual elements
   in the vDC in a secure way.

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                           Internet                    ^ Internet
                              ^                     +--+---+
                              |                     |  GW  |
                              |                     +--+---+
                              |                        |
                      +-------+--------+            +--+---+
                      |Firewall/Gateway+--- VPN-----+router|
                      +-------+--------+            +-+--+-+
                              |                       |  |
                           ...+....                   |..|
                  +-------: L3 VNa :---------+        LANs
                +-+-+      ........          |
                |LB |          |             |     Enterprise Site
                +-+-+          |             |
               ...+...      ...+...       ...+...
              : L2VNx :    : L2VNy :     : L2VNz :
               .......      .......       .......
                 |..|         |..|          |..|
                 |  |         |  |          |  |
               Web App.     Mail App.      VoIP App.

                        Provider DC Site

             Figure 2 - Virtual Data Center Abstraction View

5. Summary

   This document describes some general and potential NVO3 use cases in
   DCs. The combination of these cases will give operators the
   flexibility and capability to design more sophisticated cases for
   various cloud applications.

   DC services may vary, from infrastructure as a service (IaaS), to
   platform as a service (PaaS), to software as a service (SaaS).
   In these services, NVO3 virtual networks are just a portion of such

   NVO3 uses tunnel techniques to deliver VN traffic over an IP network.
   A tunnel encapsulation protocol is necessary. An NVO3 tunnel may in

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   turn be tunneled over other intermediate tunnels over the Internet
   or other WANs.

   An NVO3 virtual network in a DC may be accessed by external users in
   a secure way. Many existing technologies can help achieve this.

   NVO3 implementations may vary. Some DC operators prefer to use a
   centralized controller to manage tenant system reachability in a
   virtual network, while other operators prefer to use distribution
   protocols to advertise the tenant system location, i.e., NVE
   location. When a tenant network spans across multiple DCs and WANs,
   each network administration domain may use different methods to
   distribute the tenant system locations. Both control plane and data
   plane interworking are necessary.

6. Security Considerations

   Security is a concern. DC operators need to provide a tenant with a
   secured virtual network, which means one tenant's traffic is
   isolated from other tenants' traffic as well as from underlay
   networks. DC operators also need to prevent against a tenant
   application attacking their underlay DC network; further, they need
   to protect against a tenant application attacking another tenant
   application via the DC infrastructure network. For example, a tenant
   application attempts to generate a large volume of traffic to
   overload the DC's underlying network. An NVO3 solution has to
   address these issues.

7. IANA Considerations

   This document does not request any action from IANA.

8. References

8.1. Normative References

   [RFC7364] Narten, T., et al "Problem Statement: Overlays for Network
             Virtualization", RFC7364, October 2014.

   [RFC7365] Lasserre, M., Motin, T., and et al, "Framework for DC
             Network Virtualization", RFC7365, October 2014.

8.2. Informative References

   [IEEE802.1Q]  IEEE, "IEEE Standard for Local and metropolitan area
             networks -- Media Access Control (MAC) Bridges and Virtual
             Bridged Local Area", IEEE Std 802.1Q, 2011.

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   [NVO3HYVR2NVE] Li, Y., et al, "Hypervisor to NVE Control Plane
             Requirements", draft-ietf-nvo3-hpvr2nve-cp-req-05, work in

   [NVO3ARCH] Black, D., et al, "An Architecture for Overlay Networks
             (NVO3)", draft-ietf-nvo3-arch-08, work in progress.

   [NVO3MCAST] Ghanwani, A., "Framework of Supporting Applications
             Specific Multicast in NVO3", draft-ghanwani-nvo3-app-
             mcast-framework-02, work in progress.

   [RFC1035] Mockapetris, P., "DOMAIN NAMES - Implementation and
             Specification", RFC1035, November 1987.

   [RFC3022] Srisuresh, P. and Egevang, K., "Traditional IP Network
             Address Translator (Traditional NAT)", RFC3022, January

   [RFC4301] Kent, S., "Security Architecture for the Internet
             Protocol", rfc4301, December 2005

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

   [RFC7348]  Mahalingam,M., Dutt, D., ific Multicast in etc "VXLAN: A
             Framework for Overlaying Virtualized Layer 2 Networks over
             Layer 3 Networks", RFC7348 August 2014.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A. and
             J. Uttaro, "BGP MPLS Based Ethernet VPN", RFC7432,
             February 2015

   [RFC7637] Garg, P., and Wang, Y., "NVGRE: Network Virtualization
             using Generic Routing Encapsulation", RFC7637, Sept. 2015.

   [VRF-LITE] Cisco, "Configuring VRF-lite",


      Vinay Bannai
      2211 N. First St,
      San Jose, CA 95131
      Phone: +1-408-967-7784

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      Ram Krishnan
      Brocade Communications
      San Jose, CA 95134
      Phone: +1-408-406-7890

      Kieran Milne
      Juniper Networks
      1133 Innovation Way
      Sunnyvale, CA 94089
      Phone: +1-408-745-2000


   Authors like to thank Sue Hares, Young Lee, David Black, Pedro
   Marques, Mike McBride, David McDysan, Randy Bush, Uma Chunduri, Eric
   Gray, David Allan, Joe Touch, and Olufemi Komolafe for the review,
   comments, and suggestions.

 Authors' Addresses

   Lucy Yong
   Huawei Technologies

   Phone: +1-918-808-1918

   Linda Dunbar
   Huawei Technologies,
   5340 Legacy Dr.
   Plano, TX 75025 US

   Phone: +1-469-277-5840

   Mehmet Toy

   Phone : +1-856-792-2801
   E-mail :

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   Aldrin Isaac
   Juniper Networks

   Vishwas Manral


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