Network Working Group                                         L. Dunbar
     Internet Draft                                                Futurewei
     Intended status: Informational                               Andy Malis
     Expires: September 16, 2020                                 Independent
                                                                C. Jacquenet
                                                                      M. Toy
                                                              March 16, 2020
                Dynamic Networks to Hybrid Cloud DCs Problem Statement
        This document describes the problems that enterprises face today
        when interconnecting their branch offices with dynamic workloads in
        third party data centers (a.k.a. Cloud DCs). There can be many
        problems associated with network connecting to or among Clouds, many
        of which probably are out of the IETF scope. The objective of this
        document is to identify some of the problems that need additional
        work in IETF Routing area. Other problems are out of the scope of
        this document.
        It examines some of the approaches interconnecting cloud DCs with
        enterprises  on-premises DCs & branch offices. This document also
        describes some of the network problems that many enterprises face
        when they have workloads & applications & data split among different
        data centers, especially for those enterprises with multiple sites
        that are already interconnected by VPNs (e.g., MPLS L2VPN/L3VPN).
        Current operational problems are examined to determine whether there
        is a need to improve existing protocols or whether a new protocol is
        necessary to solve them.
     Status of this Memo
        This Internet-Draft is submitted in full conformance with the
        provisions of BCP 78 and BCP 79.
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     Internet-Draft        Net2Cloud Problem Statement            March 2020
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     Table of Contents
        1. Introduction...................................................3
           1.1. Key Characteristics of Cloud Services:....................3
           1.2. Connecting to Cloud Services..............................3
           1.3. The role of SD-WAN in connecting to Cloud Services........4
        2. Definition of terms............................................5
        3. High Level Issues of Connecting to Multi-Cloud.................6
           3.1. Security Issues...........................................6
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           3.2. Authorization and Identity Management.....................6
           3.3. API abstraction...........................................7
           3.4. DNS for Cloud Resources...................................8
           3.5. NAT for Cloud Services....................................9
           3.6. Cloud Discovery...........................................9
        4. Interconnecting Enterprise Sites with Cloud DCs...............10
           4.1. Sites to Cloud DC........................................10
           4.2. Inter-Cloud Interconnection..............................12
        5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs...14
        6. Problem with using IPsec tunnels to Cloud DCs.................15
           6.1. Scaling Issues with IPsec Tunnels........................15
           6.2. Poor performance over long distance......................16
        7. Problems of Using SD-WAN to connect to Cloud DCs..............16
           7.1. More Complexity to Edge Nodes............................17
           7.2. Edge WAN Port Management.................................17
           7.3. Forwarding based on Application..........................18
        8. End-to-End Security Concerns for Data Flows...................18
        9. Requirements for Dynamic Cloud Data Center VPNs...............18
        10. Security Considerations......................................19
        11. IANA Considerations..........................................19
        12. References...................................................19
           12.1. Normative References....................................19
           12.2. Informative References..................................19
        13. Acknowledgments..............................................20
     1. Introduction
     1.1. Key Characteristics of Cloud Services:
        Key characteristics of Cloud Services are on-demand, scalable,
        highly available, and usage-based billing. Cloud Services, such as,
        compute, storage, network functions (most likely virtual), third
        party managed applications, etc. are usually hosted and managed by
        third parties Cloud Operators. Here are some examples of Cloud
        network functions: Virtual Firewall services, Virtual private
        network services, Virtual PBX services including voice and video
        conferencing systems, etc. Cloud Data Center (DC) is shared
        infrastructure that hosts the Cloud Services to many customers.
     1.2. Connecting to Cloud Services
        With the advent of widely available third-party cloud DCs and
        services in diverse geographic locations and the advancement of
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        tools for monitoring and predicting application behaviors, it is
        very attractive for enterprises to instantiate applications and
        workloads in locations that are geographically closest to their end-
        users. Such proximity can improve end-to-end latency and overall
        user experience. Conversely, an enterprise can easily shutdown
        applications and workloads whenever end-users are in motion (thereby
        modifying the networking connection of subsequently relocated
        applications and workloads). In addition, enterprises may wish to
        take advantage of more and more business applications offered by
        cloud operators.
        The networks that interconnect hybrid cloud DCs must address the
        following requirements:
          - High availability to access all workloads in the desired cloud
             Many enterprises include cloud in their disaster recovery
             strategy, such as enforcing periodic backup policies within the
             cloud, or running backup applications in the Cloud.
          - Global reachability from different geographical zones, thereby
             facilitating the proximity of applications as a function of the
             end users  location, to improve latency.
          - Elasticity: prompt connection to newly instantiated
             applications at Cloud DCs when usages increase and prompt
             release of connection after applications at locations being
             removed when demands change.
          - Scalable security management.
     1.3. The role of SD-WAN in connecting to Cloud Services
        Some of the characteristics of SD-WAN [SDWAN-BGP-USAGE], such as
        network augmentation and forwarding based on application IDs instead
        of based on destination IP addresses, are very essential for
        connecting to on-demand Cloud services.
        Issues associated with using SD-WAN for connecting to Cloud services
        are also discussed in this document.
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     2. Definition of terms
        Cloud DC:   Third party Data Centers that usually host applications
                    and workload owned by different organizations or
        Controller: Used interchangeably with SD-WAN controller to manage
                    SD-WAN overlay path creation/deletion and monitoring the
                    path conditions between two or more sites.
        DSVPN:      Dynamic Smart Virtual Private Network. DSVPN is a secure
                    network that exchanges data between sites without
                    needing to pass traffic through an organization's
                    headquarter virtual private network (VPN) server or
        Heterogeneous Cloud: applications and workloads split among Cloud
                    DCs owned or managed by different operators.
        Hybrid Clouds: Hybrid Clouds refers to an enterprise using its own
                    on-premises DCs in addition to Cloud services provided
                    by one or more cloud operators. (e.g. AWS, Azure,
                    Google, Salesforces, SAP, etc).
        SD-WAN:     Software Defined Wide Area Network. In this document,
                     SD-WAN  refers to the solutions of pooling WAN
                    bandwidth from multiple underlay networks to get better
                    WAN bandwidth management, visibility & control. When the
                    underlay networks are private networks, traffic can
                    traverse without additional encryption; when the
                    underlay networks are public, such as Internet, some
                    traffic needs to be encrypted when traversing through
                    (depending on user provided policies).
        VPC:        Virtual Private Cloud is a virtual network dedicated to
                    one client account. It is logically isolated from other
                    virtual networks in a Cloud DC. Each client can launch
                    his/her desired resources, such as compute, storage, or
                    network functions into his/her VPC. Most Cloud
                    operators  VPCs only support private addresses, some
                    support IPv4 only, others support IPv4/IPv6 dual stack.
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     3. High Level Issues of Connecting to Multi-Cloud
        There are many problems associated with connecting to hybrid Cloud
        Services, many of which are out of the IETF scope. This section is
        to identify some of the high level problems that can be addressed by
        IETF, especially by Routing area. Other problems are out of the
        scope of this document. By no means has this section covered all
        problems for connecting to Hybrid Cloud Services, e.g. difficulty in
        managing cloud spending is not discussed here.
     3.1. Security Issues
        Cloud Services is built upon shared infrastructure, therefore not
        secure by nature. Security has been a primary, and valid, concern
        from the start of cloud computing: you are unable to see the exact
        location where your data is stored or being processed. Headlines
        highlighting data breaches, compromised credentials, and broken
        authentication, hacked interfaces and APIs, account hijacking
        haven t helped alleviate concerns.
        Secure user identity management, authentication, and access control
        mechanisms are important. Developing appropriate security
        measurements can enhance the confidence needed by enterprises to
        fully take advantage of Cloud Services.
     3.2. Authorization and Identity Management
        One of the more prominent challenges for Cloud Services is Identity
        Management and Authorization. The Authorization not only includes
        user authorization, but also the authorization of API calls by
        applications from different Cloud DCs managed by different Cloud
        Operators. In addition, there are authorization for Workload
        Migration, Data Migration, and Workload Management.
        There are many types of users in cloud environments, e.g. end users
        for accessing applications hosted in Cloud DCs, Cloud-resource users
        who are responsible for setting permissions for the resources based
        on roles, access lists, IP addresses, domains, etc.
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        There are many types of Cloud authorizations: including MAC
        (Mandatory Access Control)   where each app owns individual access
        permissions, DAC (Discretionary Access Control)   where each app
        requests permissions from an external permissions app, RBAC (Role-
        based Access Control)   where the authorization service owns roles
        with different privileges on the cloud service, and ABAC (Attribute-
        based Access Control)   where access is based on request attributes
        and policies.
        IETF hasn t yet developed comprehensive specification for Identity
        management and data models for Cloud Authorizations.
     3.3. API abstraction
        Different Cloud Operators have different APIs to access their Cloud
        resources, security functions, the NAT, etc.
        It is difficult to move applications built by one Cloud operator s
        APIs to another. However, it is highly desirable to have a single
        and consistent way to manage the networks and respective security
        policies for interconnecting applications hosted in different Cloud
        The desired property would be having a single network fabric to
        which different Cloud DCs and enterprise s multiple sites can be
        attached or detached, with a common interface for setting desired
        The difficulty of connecting applications in different Clouds might
        be stemmed from the fact that they are direct competitors. Usually
        traffic flow out of Cloud DCs incur charges. Therefore, direct
        communications between applications in different Cloud DCs can be
        more expensive than intra Cloud communications.
        It is desirable to have a common API shim layer or abstraction for
        different Cloud providers to make it easier to move applications
        from one Cloud DC to another.
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     3.4. DNS for Cloud Resources
        DNS name resolution is essential for on-premises and cloud-based
        resources. For customers with hybrid workloads, which include on-
        premises and cloud-based resources, extra steps are necessary to
        configure DNS to work seamlessly across both environments.
        Cloud operators have their own DNS to resolve resources within their
        Cloud DCs and to well-known public domains. Cloud s DNS can be
        configured to forward queries to customer managed authoritative DNS
        servers hosted on-premises, and to respond to DNS queries forwarded
        by on-premises DNS servers.
        For enterprises utilizing Cloud services by different cloud
        operators, it is necessary to establish policies and rules on
        how/where to forward DNS queries to. When applications in one Cloud
        need to communication with applications hosted in another Cloud,
        there could be DNS queries from one Cloud DC being forwarded to the
        enterprise s on premise DNS, which in turn be forwarded to the DNS
        service in another Cloud. Needless to say, configuration can be
        complex depending on the application communication patterns.
        However, even with carefully managed policies and configurations,
        collisions can still occur. If you use an internal name like .cloud
        and then want your services to be available via or within some other
        cloud provider which also uses .cloud, then it can't work.
        Therefore, it is better to use the global domain name even when an
        organization does not make all its namespace globally resolvable. An
        organization's globally unique DNS can include subdomains that
        cannot be resolved at all outside certain restricted paths, zones
        that resolve differently based on the origin of the query, and zones
        that resolve the same globally for all queries from any source.
        Globally unique names do not equate to globally resolvable names or
        even global names that resolve the same way from every perspective.
        Globally unique names do prevent any possibility of collision at the
        present or in the future and they make DNSSEC trust manageable.
        Consider using a registered and fully qualified domain name (FQDN)
        from global DNS as the root for enterprise and other internal
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     3.5. NAT for Cloud Services
        Cloud resources, such as VM instances, are usually assigned with
        private IP addresses. By configuration, some private subnets can
        have the NAT function to reach out to external network and some
        private subnets are internal to Cloud only.
        Different Cloud operators support different levels of NAT functions.
        For example, AWS NAT Gateway does not currently support connections
        towards, or from VPC Endpoints, VPN, AWS Direct Connect, or VPC
        nat-gateway.html#nat-gateway-other-services. AWS Direct
        Connect/VPN/VPC Peering does not currently support any NAT
        Google s Cloud NAT allows Google Cloud virtual machine (VM)
        instances without external IP addresses and private Google
        Kubernetes Engine (GKE) clusters to connect to the Internet. Cloud
        NAT implements outbound NAT in conjunction with a default route to
        allow instances to reach the Internet. It does not implement inbound
        NAT. Hosts outside of VPC network can only respond to established
        connections initiated by instances inside the Google Cloud; they
        cannot initiate their own, new connections to Cloud instances via
        For enterprises with applications running in different Cloud DCs,
        proper configuration of NAT have to be performed in Cloud DC and in
        their own on-premise DC.
     3.6. Cloud Discovery
        One of the concerns of using Cloud services is not aware where the
        resource is actually located, especially Cloud operators can move
        application instances from one place to another. When applications
        in Cloud communicate with on-premise applications, it may not be
        clear where the Cloud applications are located or to which VPCs they
        It is highly desirable to have tools to discover cloud services in
        much the same way as you would discover your on-premises
        infrastructure. A significant difference is that cloud discovery
        uses the cloud vendor's API to extract data on your cloud services,
        rather than the direct access used in scanning your on-premises
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        Standard data models, APIs or tools can alleviate concerns of
        enterprise utilizing Cloud Resources, e.g. having a Cloud service
        scan that connects to the API of the cloud provider and collects
        information directly.
     4. Interconnecting Enterprise Sites with Cloud DCs
        Considering that many enterprises already have existing VPNs (e.g.
        MPLS based L2VPN or L3VPN) interconnecting branch offices & on-
        premises data centers, connecting to Cloud services will be mixed of
        different types of networks. When an enterprise s existing VPN
        service providers do not have direct connections to the
        corresponding cloud DCs that the enterprise prefers to use, the
        enterprise has to face additional infrastructure and operational
        costs to utilize Cloud services.
     4.1. Sites to Cloud DC
        Most Cloud operators offer some type of network gateway through
        which an enterprise can reach their workloads hosted in the Cloud
        DCs. AWS (Amazon Web Services) offers the following options to reach
        workloads in AWS Cloud DCs:
          - AWS Internet gateway allows communication between instances in
             AWS VPC and the internet.
          - AWS Virtual gateway (vGW) where IPsec tunnels [RFC6071] are
             established between an enterprise s own gateway and AWS vGW, so
             that the communications between those gateways can be secured
             from the underlay (which might be the public Internet).
          - AWS Direct Connect, which allows enterprises to purchase direct
             connect from network service providers to get a private leased
             line interconnecting the enterprises gateway(s) and the AWS
             Direct Connect routers. In addition, an AWS Transit Gateway can
             be used to interconnect multiple VPCs in different Availability
             Zones. AWS Transit Gateway acts as a hub that controls how
             traffic is forwarded among all the connected networks which act
             like spokes.
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        Microsoft s ExpressRoute allows extension of a private network to
        any of the Microsoft cloud services, including Azure and Office365.
        ExpressRoute is configured using Layer 3 routing. Customers can opt
        for redundancy by provisioning dual links from their location to two
        Microsoft Enterprise edge routers (MSEEs) located within a third-
        party ExpressRoute peering location. The BGP routing protocol is
        then setup over WAN links to provide redundancy to the cloud. This
        redundancy is maintained from the peering data center into
        Microsoft's cloud network.
        Google s Cloud Dedicated Interconnect offers similar network
        connectivity options as AWS and Microsoft. One distinct difference,
        however, is that Google s service allows customers access to the
        entire global cloud network by default. It does this by connecting
        your on-premises network with the Google Cloud using BGP and Google
        Cloud Routers to provide optimal paths to the different regions of
        the global cloud infrastructure.
        Figure below shows an example of some of a tenant s workloads are
        accessible via a virtual router connected by AWS Internet Gateway;
        some are accessible via AWS vGW, and others are accessible via AWS
        Direct Connect.
        Different types of access require different level of security
        functions. Sometimes it is not visible to end customers which type
        of network access is used for a specific application instance.  To
        get better visibility, separate virtual routers (e.g. vR1 & vR2) can
        be deployed to differentiate traffic to/from different cloud GWs. It
        is important for some enterprises to be able to observe the specific
        behaviors when connected by different connections.
        Customer Gateway can be customer owned router or ports physically
        connected to AWS Direct Connect GW.
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          |    ,---.         ,---. |
          |   (TN-1 )       ( TN-2)|
          |    `-+-'  +---+  `-+-' |
          |      +----|vR1|----+   |
          |           ++--+        |
          |            |         +-+----+
          |            |        /Internet\ For External
          |            +-------+ Gateway  +----------------------
          |                     \        / to reach via Internet
          |                      +-+----+
          |                        |
          |    ,---.         ,---. |
          |   (TN-1 )       ( TN-2)|
          |    `-+-'  +---+  `-+-' |
          |      +----|vR2|----+   |
          |           ++--+        |
          |            |         +-+----+
          |            |        / virtual\ For IPsec Tunnel
          |            +-------+ Gateway  +----------------------
          |            |        \        /  termination
          |            |         +-+----+
          |            |           |
          |            |         +-+----+              +------+
          |            |        /        \ For Direct /customer\
          |            +-------+ Gateway  +----------+ gateway  |
          |                     \        /  Connect   \        /
          |                      +-+----+              +------+
          |                        |
          Figure 1: Examples of Multiple Cloud DC connections.
     4.2. Inter-Cloud Interconnection
        The connectivity options to Cloud DCs described in the previous
        section are for reaching Cloud providers  DCs, but not between cloud
        DCs. When applications in AWS Cloud need to communicate with
        applications in Azure, today s practice requires a third-party
        gateway (physical or virtual) to interconnect the AWS s Layer 2
        DirectConnect path with Azure s Layer 3 ExpressRoute.
        Enterprises can also instantiate their own virtual routers in
        different Cloud DCs and administer IPsec tunnels among them, which
        by itself is not a trivial task. Or by leveraging open source VPN
        software such as strongSwan, you create an IPSec connection to the
        Azure gateway using a shared key. The StrongSwan instance within AWS
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        not only can connect to Azure but can also be used to facilitate
        traffic to other nodes within the AWS VPC by configuring forwarding
        and using appropriate routing rules for the VPC.
        Most Cloud operators, such as AWS VPC or Azure VNET, use non-
        globally routable CIDR from private IPv4 address ranges as specified
        by RFC1918. To establish IPsec tunnel between two Cloud DCs, it is
        necessary to exchange Public routable addresses for applications in
        different Cloud DCs. [BGP-SDWAN] describes one method. Other methods
        are worth exploring.
        In summary, here are some approaches, available now (which might
        change in the future), to interconnect workloads among different
        Cloud DCs:
            Utilize Cloud DC provided inter/intra-cloud connectivity
             services (e.g., AWS Transit Gateway) to connect workloads
             instantiated in multiple VPCs. Such services are provided with
             the cloud gateway to connect to external networks (e.g., AWS
             DirectConnect Gateway).
            Hairpin all traffic through the customer gateway, meaning all
             workloads are directly connected to the customer gateway, so
             that communications among workloads within one Cloud DC must
             traverse through the customer gateway.
            Establish direct tunnels among different VPCs (AWS  Virtual
             Private Clouds) and VNET (Azure s Virtual Networks) via
             client s own virtual routers instantiated within Cloud DCs.
             DMVPN (Dynamic Multipoint Virtual Private Network) or DSVPN
             (Dynamic Smart VPN) techniques can be used to establish direct
             Multi-point-to-Point or multi-point-to multi-point tunnels
             among those client s own virtual routers.
        Approach a) usually does not work if Cloud DCs are owned and managed
        by different Cloud providers.
        Approach b) creates additional transmission delay plus incurring
        cost when exiting Cloud DCs.
        For the Approach c), DMVPN or DSVPN use NHRP (Next Hop Resolution
        Protocol) [RFC2735] so that spoke nodes can register their IP
        addresses & WAN ports with the hub node. The IETF ION
        (Internetworking over NBMA (non-broadcast multiple access) WG
        standardized NHRP for connection-oriented NBMA network (such as ATM)
        network address resolution more than two decades ago.
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        There are many differences between virtual routers in Public Cloud
        DCs and the nodes in an NBMA network. NHRP cannot be used for
        registering virtual routers in Cloud DCs unless an extension of such
        protocols is developed for that purpose, e.g. taking NAT or dynamic
        addresses into consideration. Therefore, DMVPN and/or DSVPN cannot
        be used directly for connecting workloads in hybrid Cloud DCs.
        Other protocols such as BGP can be used, as described in [BGP-
     5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs
        Traditional MPLS-based VPNs have been widely deployed as an
        effective way to support businesses and organizations that require
        network performance and reliability. MPLS shifted the burden of
        managing a VPN service from enterprises to service providers. The
        CPEs attached to MPLS VPNs are also simpler and less expensive,
        because they do not need to manage routes to remote sites; they
        simply pass all outbound traffic to the MPLS VPN PEs to which the
        CPEs are attached (albeit multi-homing scenarios require more
        processing logic on CPEs).  MPLS has addressed the problems of
        scale, availability, and fast recovery from network faults, and
        incorporated traffic-engineering capabilities.
        However, traditional MPLS-based VPN solutions are sub-optimized for
        connecting end-users to dynamic workloads/applications in cloud DCs
          - The Provider Edge (PE) nodes of the enterprise s VPNs might not
             have direct connections to third party cloud DCs that are used
             for hosting workloads with the goal of providing an easy access
             to enterprises  end-users.
          - It takes some time to deploy provider edge (PE) routers at new
             locations. When enterprise s workloads are changed from one
             cloud DC to another (i.e., removed from one DC and re-
             instantiated to another location when demand changes), the
             enterprise branch offices need to be connected to the new cloud
             DC, but the network service provider might not have PEs located
             at the new location.
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             One of the main drivers for moving workloads into the cloud is
             the widely available cloud DCs at geographically diverse
             locations, where apps can be instantiated so that they can be
             as close to their end-users as possible. When the user base
             changes, the applications may be migrated to a new cloud DC
             location closest to the new user base.
          - Most of the cloud DCs do not expose their internal networks. An
             enterprise with a hybrid cloud deployment can use an MPLS-VPN
             to connect to a Cloud provider at multiple locations.  The
             connection locations often correspond to gateways of different
             Cloud DC locations from the Cloud provider.  The different
             Cloud DCs are interconnected by the Cloud provider's own
             internal network.  At each connection location (gateway), the
             Cloud provider uses BGP to advertise all of the prefixes in the
             enterprise's VPC, regardless of which Cloud DC a given prefix
             is actually in. This can result in inefficient routing for the
             end-to-end data path.
        Another roadblock is the lack of a standard way to express and
        enforce consistent security policies for workloads that not only use
        virtual addresses, but in which are also very likely hosted in
        different locations within the Cloud DC [RFC8192]. The current VPN
        path computation and bandwidth allocation schemes may not be
        flexible enough to address the need for enterprises to rapidly
        connect to dynamically instantiated (or removed) workloads and
        applications regardless of their location/nature (i.e., third party
        cloud DCs).
     6. Problem with using IPsec tunnels to Cloud DCs
        As described in the previous section, many Cloud operators expose
        their gateways for external entities (which can be enterprises
        themselves) to directly establish IPsec tunnels. Enterprises can
        also instantiate virtual routers within Cloud DCs to connect to
        their on-premises devices via IPsec tunnels.
     6.1. Scaling Issues with IPsec Tunnels
        If there is only one enterprise location that needs to reach the
        Cloud DC, an IPsec tunnel is a very convenient solution.
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        However, many medium-to-large enterprises have multiple sites and
        multiple data centers. For multiple sites to communicate with
        workloads and apps hosted in cloud DCs, Cloud DC gateways have to
        maintain many IPsec tunnels to all those locations. In addition,
        each of those IPsec Tunnels requires pair-wise periodic key
        refreshment. For a company with hundreds or thousands of locations,
        there could be hundreds (or even thousands) of IPsec tunnels
        terminating at the cloud DC gateway, which is very processing
        intensive. That is why many cloud operators only allow a limited
        number of (IPsec) tunnels & bandwidth to each customer.
        Alternatively, you could use a solution like group encryption where
        a single IPsec SA is necessary at the GW but the drawback is key
        distribution and maintenance of a key server, etc.
     6.2. Poor performance over long distance
        When enterprise CPEs or gateways are far away from cloud DC gateways
        or across country/continent boundaries, performance of IPsec tunnels
        over the public Internet can be problematic and unpredictable. Even
        though there are many monitoring tools available to measure delay
        and various performance characteristics of the network, the
        measurement for paths over the Internet is passive and past
        measurements may not represent future performance.
        Many cloud providers can replicate workloads in different available
        zones. An App instantiated in a cloud DC closest to clients may have
        to cooperate with another App (or its mirror image) in another
        region or database server(s) in the on-premises DC. This kind of
        coordination requires predicable networking behavior/performance
        among those locations.
     7. Problems of Using SD-WAN to connect to Cloud DCs
        SD-WAN lets enterprises augment their current VPN network with cost-
        effective, readily available Broadband Internet connectivity,
        enabling some traffic offloading to paths over the Internet
        according to differentiated, possibly application-based traffic
        forwarding policies, or when the MPLS VPN connection between the two
        locations is congested, or otherwise undesirable or unavailable.
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     7.1. More Complexity to Edge Nodes
        Augmenting transport path is not as simple as it appears. For an
        enterprise with multiple sites, CPE managed overlay paths among
        sites requires each CPE to manage all the addresses that local hosts
        have potential to reach, i.e., map internal VPN addresses to
        appropriate Overlay paths. This is similar to the complexity of
        Frame Relay based VPNs, where each CPE needed to maintain mesh
        routing for all destinations if they were to avoid an extra hop
        through a hub router. Even with the  assistance from a central
        controller (instead of running a routing protocol) to resolve the
        mapping between destinations and SD-WAN paths, SD-WAN CPEs are still
        responsible for routing table maintenance as remote destinations
        change their attachments, e.g., the dynamic workload in other DCs
        are de-commissioned or added.
        In addition, overlay path for interconnecting branch offices are
        different from connecting to Cloud DCs:
          - Overlay path interconnecting branch offices usually have two
             end-points (e.g. CPEs) controlled by one entity (e.g.
             controllers or management systems operated by the enterprise).
          - Connecting to Cloud DC may consists of CPEs owned or managed by
             the enterprise, and the remote end-points being managed or
             controlled by Cloud DCs.
     7.2. Edge WAN Port Management
             An SDWAN edge node can have WAN ports connected to different
             networks or public internet managed by different operators.
             There is therefore a need to propagate WAN port property to
             remote authorized peers in third party network domains in
             addition to route propagation. Such an exchange cannot happen
             before communication between peers is properly secured.
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     7.3. Forwarding based on Application
          Forwarding based on application IDs instead of based on
          destination IP addresses is often referred to as Application based
          Segmentation. If the Applications have unique IP addresses, then
          the Application Based Segmentation can be achieved by propagating
          different BGP UPDATE messages to different nodes, as described in
          [BGP-SDWAN-USAGE]. If the Application cannot be uniquely
          identified by the IP addresses, more work is needed.
     8. End-to-End Security Concerns for Data Flows
          When IPsec tunnels established from enterprise on-premises CPEs
          are terminated at the Cloud DC gateway where the workloads or
          applications are hosted, some enterprises have concerns regarding
          traffic to/from their workload being exposed to others behind the
          data center gateway (e.g., exposed to other organizations that
          have workloads in the same data center).
          To ensure that traffic to/from workloads is not exposed to
          unwanted entities, IPsec tunnels may go all the way to the
          workload (servers, or VMs) within the DC.
     9. Requirements for Dynamic Cloud Data Center VPNs
        In order to address the aforementioned issues, any solution for
        enterprise VPNs that includes connectivity to dynamic workloads or
        applications in cloud data centers should satisfy a set of
          - The solution should allow enterprises to take advantage of the
             current state-of-the-art in VPN technology, in both traditional
             MPLS-based VPNs and IPsec-based VPNs (or any combination
             thereof) that run over the public Internet.
          - The solution should not require an enterprise to upgrade all
             their existing CPEs.
          - The solution should support scalable IPsec key management among
             all nodes involved in DC interconnect schemes.
          - The solution needs to support easy and fast, on-the-fly, VPN
             connections to dynamic workloads and applications in third
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             party data centers, and easily allow these workloads to migrate
             both within a data center and between data centers.
          - Allow VPNs to provide bandwidth and other performance
          - Be a cost-effective solution for enterprises to incorporate
             dynamic cloud-based applications and workloads into their
             existing VPN environment.
     10. Security Considerations
        The draft discusses security requirements as a part of the problem
        space, particularly in sections 4, 5, and 8.
        Solution drafts resulting from this work will address security
        concerns inherent to the solution(s), including both protocol
        aspects and the importance (for example) of securing workloads in
        cloud DCs and the use of secure interconnection mechanisms.
     11. IANA Considerations
        This document requires no IANA actions. RFC Editor: Please remove
        this section before publication.
     12. References
     12.1. Normative References
     12.2. Informative References
        [RFC2735]   B. Fox, et al  NHRP Support for Virtual Private
        networks . Dec. 1999.
        [RFC8192] S. Hares, et al  Interface to Network Security Functions
                  (I2NSF) Problem Statement and Use Cases , July 2017
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         [ITU-T-X1036] ITU-T Recommendation X.1036,  Framework for creation,
                  storage, distribution and enforcement of policies for
                  network security , Nov 2007.
         [RFC6071] S. Frankel and S. Krishnan,  IP Security (IPsec) and
                  Internet Key Exchange (IKE) Document Roadmap , Feb 2011.
        [RFC4364] E. Rosen and Y. Rekhter,  BGP/MPLS IP Virtual Private
                  Networks (VPNs) , Feb 2006
        [RFC4664] L. Andersson and E. Rosen,  Framework for Layer 2 Virtual
                  Private Networks (L2VPNs) , Sept 2006.
        [BGP-SDWAN] L. Dunbar, et al.  BGP Extension for SDWAN Overlay
                  Networks , draft-dunbar-idr-bgp-sdwan-overlay-ext-03,
                  work-in-progress, Nov 2018.
     13. Acknowledgments
        Many thanks to Alia Atlas, Chris Bowers, Paul Vixie, Paul Ebersman,
        Timothy Morizot, Ignas Bagdonas, Michael Huang, Liu Yuan Jiao,
        Katherine Zhao, and Jim Guichard for the discussion and
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     Authors  Addresses
        Linda Dunbar
        Andrew G. Malis
        Christian Jacquenet
        Rennes, 35000
        Mehmet Toy
        One Verizon Way
        Basking Ridge, NJ 07920
     Dunbar, et al.                                                [Page 21]