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Network Working Group                                         L. Dunbar
Internet Draft                                                Futurewei
Intended status: Informational                               Andy Malis
Expires: August 19, 2020                                    Independent
                                                           C. Jacquenet
                                                                 Orange
                                                                 M. Toy
                                                                Verizon
                                                      February 19, 2020



           Dynamic Networks to Hybrid Cloud DCs Problem Statement
              draft-ietf-rtgwg-net2cloud-problem-statement-08

Abstract

   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-Drafts are working documents of the Internet Engineering
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   This document is subject to BCP 78 and the IETF Trust's Legal
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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
        DCs.
        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
               tenants.

   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
               router.

   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
   DCs.

   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
   policies.

   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. It's
   not as if there is or even could be some sort of shortage in
   available names that can be used, especially when subdomains and the
   ability to delegate administrative boundaries are considered.








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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
   Peering. https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-
   nat-gateway.html#nat-gateway-other-services. AWS Direct
   Connect/VPN/VPC Peering does not currently support any NAT
   functionality.

   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
   NAT.

   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
   belong.

   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
   infrastructure.


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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:

     a)            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).
     b)            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.
     c)            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-
   SDWAN].



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
   because:

     - 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
   requirements:

     - 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
        guarantees.
     - 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
   contributions.























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Authors' Addresses


   Linda Dunbar
   Futurewei
   Email: Linda.Dunbar@futurewei.com

   Andrew G. Malis
   Independent
   Email: agmalis@gmail.com

   Christian Jacquenet
   Orange
   Rennes, 35000
   France
   Email: Christian.jacquenet@orange.com

   Mehmet Toy
   Verizon
   One Verizon Way
   Basking Ridge, NJ 07920
   Email: mehmet.toy@verizon.com























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