Network Working Group                                         L. Dunbar
Internet Draft                                                 A. Malis
Intended status: Informational                                   Huawei
Expires: January 2018                                      C. Jacquenet
                                                          March 2, 2018

     Seamless Interconnect Underlay to Cloud Overlay Problem Statement


   This document describes common approaches deployed by enterprises
   for interconnection of workloads & applications hosted in Cloud DCs
   with 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 hybrid data
   centers, especially for those enterprises with multiple sites that
   are already interconnected by VPNs (e.g. MPLS L2VPN/L3VPN) and
   leased lines.

   Current operational problems in the field are examined to determine
   whether there is a need for enhancements to existing protocols or
   whether a new protocol is necessary to solve them.

Status of this Memo

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   Internet-Drafts are working documents of the Internet Engineering
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Table of Contents

   1. Introduction...................................................3
   2. Definition of terms............................................4
   3. Current Practices in Interconnecting Enterprise Sites with Cloud
      3.1. Interconnect to Cloud DCs.................................5
      3.2. Interconnect to Hybrid Cloud DCs..........................6
      3.3. Connecting workloads among hybrid Cloud DCs...............7
   4. Desired Properties for Networking that interconnects Hybrid Cloud
   5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs....8
   6. Problem with using IPsec tunnels to Cloud DCs..................9

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      6.1. Complexity of multi-point any-to-any interconnection.....10
      6.2. Poor performance over long distance......................10
      6.3. Scaling Issues with IPsec Tunnels........................11
   7. Problems of Using SD-WAN to connect to Cloud DCs..............11
      7.1. SD-WAN among branch offices vs. interconnect to Cloud DCs12
   8. End-to-End Security Concerns for Data Flows...................14
   9. Requirements for Dynamic Cloud Data Center VPNs...............14
   10. Security Considerations......................................15
   11. IANA Considerations..........................................15
   12. References...................................................15
      12.1. Normative References....................................15
      12.2. Informative References..................................15
   13. Acknowledgments..............................................16

1. Introduction

   Cloud-based applications and services continue to change how
   businesses of all sizes work and share information. "Cloud-based
   applications & workloads" are those that are instantiated in third
   party DCs that also host services for other customers.

   With the advent of widely available third party cloud DCs in diverse
   geographic locations and the advancement of tools for monitoring and
   predicting application behaviors, it is technically feasible for
   enterprises to instantiate applications and workloads in locations
   that are geographically closest to their end users. This property
   aids in improving end-to-end latency and overall user experience.
   Conversely, an enterprise can easily shutdown applications and
   workloads when their end users' geographic base changes (therefore
   needing to change the networking connection to those relocated
   applications and workloads). In addition, an enterprise may wish to
   take advantage of more and more business applications offered by
   third party private cloud DCs, such as SAP HANA, Oracle Cloud,
   Salesforce Cloud, etc.

   However, typically, enterprise branch offices & on-premises data
   centers are connected via VPNs, such as MPLS based l2VPN/L3VPN, and
   therefore connecting to the cloud-based resources may not be
   straightforward if the provider of the VPN service does not have
   direct connections to the Cloud DCs. Under those circumstances, the
   enterprise can upgrade their existing CPEs to utilize SD-WAN to
   reach cloud resources, or wait for their VPN service provider to

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   make new agreements with data center providers to connect to the
   Cloud resources. Either way this is non-trivial and has additional
   infrastructure costs, and is slow to operationalize.

   In addition, it is an uptrend with more and more enterprises
   changing their Apps & workloads so that they can be split among
   hybrid DCs to maximize the benefits of geographical convenience &
   elasticity and special property of on-premises DCs.

2. Definition of terms

   Cloud DC:   Off-Premise 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.

   DMVPN:      Dynamic Multipoint Virtual Private Network. DMVPN 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 & workloads split among Cloud DCs
               owned & managed by different operators.

   Hybrid Cloud: applications & workloads split between on-premises
               Data centers and Cloud DCs. In this document Hybrid
               Cloud also include heterogeneous cloud as well.

   SD-WAN:     Software Defined Wide Area Network, which can mean many
               different things. In this document, "SD-WAN" refers to
               the solutions specified by ONUG (Open Network User
               network-sd-wan/, which is about pooling WAN bandwidth

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               from n service providers to get better WAN bandwidth
               management, visibility & control.

   VPC:        Virtual Private Cloud. A service offered by many Cloud
               DC operators to allocate a logically isolated cloud
               resources, including compute, networking and storage.

3. Current Practices in Interconnecting Enterprise Sites with Cloud DCs

3.1. Interconnect to Cloud DCs

   Most Cloud operators offer some type of network gateway through
   which an enterprise can reach their workloads hosted in the Cloud
   DC. For example, AWS (Amazon Web Services) offers the following
   options to reach workloads in AWS Cloud DCs:

     - Internet gateway for any external entities to reach the
        workloads hosted in AWS Cloud DC via the internet.
     - virtual gateway (vGW) to which IPsec tunnels [RFC6071] are
        established between an enterprise's own gateways and AWS vGW,
        so that the communications between those gateways can be
        secured from the underlay (which might be the public internet).
     - 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 co-located with the network operators.
     |    ,---.         ,---. |
     |   (TN-1 )       ( TN-2)|
     |    `-+-'  +--+   `-+-' |
     |      +----|vR|-----+   |
     |           ++-+         |
     |            |         +-+----+
     |            |        /Internet\ For External
     |            +-------+ Gateway  +----------------------
     |                     \        / to reach via Internet
     |                      +-+----+
     |                        |

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     |    ,---.         ,---. |
     |   (TN-1 )       ( TN-2)|
     |    `-+-'  +--+   `-+-' |
     |      +----|vR|-----+   |
     |           ++-+         |
     |            |         +-+----+
     |            |        / virtual\ For IPsec Tunnel
     |            +-------+ Gateway  +----------------------
     |                     \        /  termination
     |                      +-+----+
     |                        |

     |    ,---.         ,---. |
     |   (TN-1 )       ( TN-2)|
     |    `-+-'  +--+   `-+-' |
     |      +----|vR|-----+   |
     |           ++-+         |
     |            |         +-+----+              +------+
     |            |        /        \ For Direct /customer\
     |            +-------+ Gateway  +----------+ gateway  |
     |                     \        /  Connect   \        /
     |                      +-+----+              +------+
     |                        |

     Figure 1: Examples of connecting to a Cloud DC

3.2. Interconnect to Hybrid Cloud DCs

   According to Gartner, by 2020 "hybrid will be the most common usage
   of the cloud" as more enterprises see the benefits of integrating
   public and private cloud infrastructures. However, enabling the
   growth of hybrid cloud deployments in the enterprise requires fast
   and safe interconnection between public and private cloud services.
   The Hybrid Cloud scenario also includes heterogeneous Cloud DCs.

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   For enterprises to connect to workloads hosted in multiple Cloud
   DCs, enterprises can use IPsec tunnels or lease private lines to
   connect their own gateways to each of the Cloud DC's gateways or any
   other suitable design (including a combination thereof).

   Some users prefer to instantiate their own virtual CPEs inside the
   public Cloud DC to connect the workloads within the Cloud DC. Then
   an overlay path is established between customer gateways to the
   virtual CPEs for reaching the workloads inside the cloud DC.

3.3. Connecting workloads among hybrid Cloud DCs

   When workloads among different Cloud DCs need to communicate, one
   way is to hairpin all the traffic through the customer gateway,
   which creates additional transmission delay & incurs cost exiting
   Cloud DCs. Another way is to establish direct tunnels among
   different VPCs (Virtual Private Clouds), such as using DMVPN
   (Dynamic Multipoint Virtual Private Network) or DSVPN (Dynamic Smart
   VPN) to establish direct Multi-edge tunnels.

   DMVPN (and DSVPN) uses NHRP (Next Hop Resolution Protocol) [RFC2735]
   so that spoke nodes can register their IP addresses with the hub
   node. The IETF ION WG, Internetworking over NBMA (non-broadcast
   multiple access), standardized NHRP for connection-oriented NBMA
   network (such as ATM) network address resolution more than two
   decades ago.

   There are many differences between virtual routers in Public Cloud
   DCs and the nodes in an NBMA network. It would be useful for the
   IETF community to examine the effectiveness of NHRP as the
   registration protocol for registering virtual routers in Cloud DCs
   to gateways or entities that connect to enterprise private networks.
   As the result of this evaluation, enhancement or new registration
   protocols may result.

4. Desired Properties for Networking that interconnects Hybrid Cloud
   The networks that interconnect hybrid Cloud DCs have to enable users
   to take advantage of Cloud DCs:
     - High availability, any time usage for any length of time.

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        Many enterprises incorporate Cloud as their disaster recovery
        strategy, e.g. periodically backup data into the cloud, or
        running backup applications in the Cloud, etc. Therefore, the
        connection to the cloud DCs may not be permanent, but rather
        needs to be on-demand.

     - Global accessibility in different geographical zones, thereby
        facilitating the proximity of applications as a function of the
        end users' location, for improved latency.
     - Elasticity and mobility, to instantiate additional applications
        at Cloud DCs when end users' usages increase and shut down
        applications at locations with fewer end users.
        Some enterprises have front-end web portals running in Cloud
        DCs and Database servers in their on-premises DCs. Those Front-
        end web portals need to be reachable from the public Internet.
        The backend connection to the sensitive data in database
        servers hosted in the on-premises DCs might need secure

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 for MPLS VPN are also simpler and less expensive, since they do
   not need to manage how to send packets to remote sites; they simply
   pass all outbound traffic to the MPLS VPN PEs to which the CPE is
   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 not 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 connection to the third party cloud DCs that are

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        optimal for hosting workloads with the goal of easy access to
        enterprises' end users.

     - It takes a relatively long 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.

        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 moved to a new cloud DC
        location closest to the new user base.

     - Most of the cloud DCs do not expose their internal networks, so
        the provider MPLS based VPNs cannot reach the workloads

     - Many cloud DCs use an overlay to connect their gateways to the
        workloads inside the DC. There has not been any standard to
        address the interworking between the Cloud Overlay and the
        enterprise' existing underlay networks.

   Another roadblock is the lack of a standard way to express and
   enforce consistent security policies to workloads that not only use
   virtual addresses, do not have a port number, but also have a high
   chance of placement in different locations within the Cloud DC
   [RFC8192]. The traditional 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. If there is only

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   one enterprise location that needs to reach the Cloud DC, an IPsec
   tunnel is a very convenient solution.

   However, many medium-to-large enterprises usually have multiple
   sites and multiple data centers. For workloads and apps hosted in
   Cloud DCs, multiple sites need to communicate securely with those
   Cloud workloads and apps. This section documents some of the issues
   associated with using IPsec tunnels to connect enterprise' sites
   with Cloud operator's Gateways.

6.1. Complexity of multi-point any-to-any interconnection

   The dynamic workload instantiated in cloud DC needs to communicate
   with multiple branch offices and on-premises data centers. Most
   enterprises need multi-point interconnection among multiple
   locations, as done by MPLS L2/L3 VPNs.

   Using IPsec overlay paths to connect all branches & on-premises data
   centers to cloud DCs require CPEs to manage routing among Cloud DCs
   gateways and the CPEs located at other branch locations, which can
   dramatically increase the complexity of the design, possibly at the
   cost of jeopardizing the CPE performance.

   The complexity of requiring CPEs to maintain routing among other
   CPEs is one of the reasons why enterprises migrated from Frame Relay
   based services to MPLS-based VPN services.

   MPLS-based VPNs have their PEs directly connected to the CPEs.
   Therefore, CPEs only need to forward all traffic to the directly
   attached PEs, which are therefore responsible for enforcing the
   routing policy within the corresponding VPNs. Even for multi-homed
   CPEs, the CPEs only need to forward traffic among the directly
   connected PEs (note: the complexity may vary for IPv6 network).
   However, when using IPsec tunnels between CPEs and Cloud DCs, the
   CPEs need to manage the routing for traffic to Cloud DCs, to remote
   CPEs via VPN, or directly.

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

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   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 the database server in the on-premises DC. This kind of
   coordination requires predicable networking behavior/performance
   among those locations.

6.3. Scaling Issues with IPsec Tunnels

   IPsec can achieve secure overlay connections between two locations
   over any underlay networks, e.g., between CPEs and Cloud DC

   If there is only one enterprise location connected to the Cloud
   gateway, a small number of IPsec tunnels can be configured on-demand
   between the on-premises DC and the Cloud DC, which is an easy and
   flexible solution.

   However, for multiple enterprise locations to reach workloads hosted
   in cloud DCs, the Cloud DC gateway needs to maintain multiple IPsec
   tunnels to all those locations (e.g. hub & spoke topology). 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 not only very expensive (because Cloud
   Operators charge based on connections), but can be very processing
   intensive for the gateway. Many cloud operators only allow a limited
   number of IPsec tunnels 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 here is key distribution and
   maintenance of a key server etc.

7. Problems of Using SD-WAN to connect to Cloud DCs
   SD-WAN enables multiple parallel paths between two locations, for
   example, two CPEs interconnected by a traditional MPLS VPN
   ([RFC4364] or [RFC4664]) as well as overlay tunnels. The overlay,
   possibly secured by IPsec tunnels [RFC6071], can traverse over the
   public Internet using fiber, cable, DSL-based Internet access, Wi-
   Fi, or 4G/Long Term Evolution (LTE).

   SD-WAN lets enterprises augment their current VPN network with cost-
   effective, readily available Broadband Internet connectivity,
   enabling some traffic offloaded to overlay paths based on traffic

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   forwarding policy (application-based or otherwise), or when the MPLS
   VPN connection between the two locations is congested, or otherwise
   undesirable or unavailable.

7.1. SD-WAN among branch offices vs. interconnect to Cloud DCs

   SD-WAN interconnection of branch offices is not as simple as it
   appears. For an enterprise with multiple sites, using SD-WAN overlay
   paths among sites requires each CPE to manage all the addresses that
   local hosts have the potential to reach, i.e. map internal VPN
   addresses to appropriate SD-WAN 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 though SD-WAN CPEs can get
   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.

   Even though originally envisioned for interconnecting branch
   offices, SD-WAN offers a very attractive way for enterprises to
   connect to Cloud DCs.

   The SD-WAN for interconnecting branch offices and the SD-WAN for
   interconnecting to Cloud DCs have some differences:

     - SD-WAN for interconnecting branch offices usually have two end-
        points (e.g. CPEs) controlled by one entity (e.g., a controller
        or management system operated by the enterprise).
     - SD-WAN for interconnecting to Cloud DCs may have CPEs owned or
        managed by the enterprise and remote end-points being managed
        or controlled by Cloud DCs (For the ease of description, let's
        call it asymmetrically managed CPEs).

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     - Cloud DCs may have different entering points (or devices) with
        one terminating private direct connect (such as MPLS, or direct
        line) and other points being the device terminating the IPsec
        tunnels, as shown in the following diagram.

     Therefore, the SD-WAN becomes asymmetric.
     |    ,---.         ,---. |
     |   (TN-1 )       ( TN-2)|
     |    `-+-'  +---+  `-+-' |
     |      +----|vR1|----+   |
     |           ++--+        |
     |            |         +-+----+
     |            |        /Internet\ One path via
     |            +-------+ Gateway  +---------------------+
     |                     \        /   Internet            \
     |                      +-+----+                         \
     +------------------------+                               \
     +------------------------+                                 \
     |    ,---.         ,---. |                                  |
     |   (TN-3 )       ( TN-4)|                                  |
     |    `-+-'  +--+   `-+-' |                                  |      +------+
     |      +----|vR|-----+   |                                  +------+ CPE  |
     |           ++-+         |                                  |      +------+
     |            |         +-+----+                             |
     |            |        / virtual\ One path via IPsec Tunnel  |
     |            +-------+ Gateway  +-------------------------- +
     |                     \        /                            |
     |                      +-+----+                             |
     +------------------------+                                  |
     +------------------------+                                  |
     |    ,---.         ,---. |                                  |
     |   (TN-5 )       ( TN-6)|                                  |
     |    `-+-'  +--+   `-+-' |                                  |
     |      +----|vR|-----+   |                                  |
     |           ++-+         |                                  |
     |            |         +-+----+              +------+       |
     |            |        /        \ Via Direct /customer\      |
     |            +-------+ Gateway  +----------+ gateway  |-----+
     |                     \        /  Connect   \        /
     |                      +-+----+              +------+

     Figure 2: Asymmetric Paths SD-WAN

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8. End-to-End Security Concerns for Data Flows

     When IPsec tunnels 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, it is necessary to have the IPsec tunnels go
     all the way to the workload (servers, or VMs) within the DC.

9. Requirements for Dynamic Cloud Data Center VPNs

   [Editor's note: this section is only a place holder. The requirement
   listed here are only to stimulate more discussions]

   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-top of the public Internet.
     - The solution should not require an enterprise to upgrade all
        their existing CPEs.
     - The solution should not require either CPEs or routers to
        support a large number of IPsec tunnels simultaneously.
     - The solution needs to support easy and fast VPN connections to
        dynamic workloads and applications in third 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

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     - Be a cost-effective solution for enterprises to incorporate
        dynamic cloud-based applications and workloads into their
        existing VPN environment.

10. Security Considerations

   For the most part, we introduce no new security concerns beyond
   those of existing MPLS based VPNs, which are widely deployed. The
   one addition to MPLS VPNs is selective use of SD-WAN, which uses
   IPsec tunnels for the privacy and separation of VPN traffic.

   Also see Section 8 for a discussion of end-to-end security for data

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

    [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.

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   [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.

13. Acknowledgments

   Many thanks to Ignas Bagdonas, Mehmet Toy, 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
   France Telecom
   Rennes, 35000
   France         E        m        i        a        :        l        C                 h        r        s        i        i        t        n        a        j        .        a        c        u        q        n        e        t        e        o        @        r        a        g        n        .        e        o        c        m

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