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Dynamic Networks to Hybrid Cloud DCs: Problem Statement and Mitigation Practices

Document Type Active Internet-Draft (rtgwg WG)
Authors Linda Dunbar , Andrew G. Malis , Christian Jacquenet , Mehmet Toy , Kausik Majumdar
Last updated 2023-09-22
Replaces draft-dm-net2cloud-problem-statement
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd Joel M. Halpern
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Network Working Group                                         L. Dunbar
Internet Draft                                                Futurewei
Intended status: Informational                                 A. Malis
Expires: March 22, 2024                                Malis Consulting
                                                           C. Jacquenet
                                                                 M. Toy
                                                            K. Majumdar
                                                     September 22, 2023

        Dynamic Networks to Hybrid Cloud DCs: Problem Statement and
                           Mitigation Practices


   This document describes the network-related problems enterprises
   face at the moment of writing this specification when
   interconnecting their branch offices with dynamic workloads in
   third-party data centers (DC) (a.k.a. Cloud DCs). The Net2Cloud
   problem statements are mainly for enterprises with traditional VPN
   services who want to leverage those networks (instead of altogether
   abandoning them). Other problems are out of the scope of this
   This document also describes the mitigation practices to alleviate
   the issues caused by the identified problems.

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Table of Contents

   1. Introduction...................................................3
   2. Definition of terms............................................3
   3. Issues and Mitigation Methods of Connecting to Cloud DCs.......4
      3.1. Increased BGP Peering Errors and Mitigation Methods.......4
      3.2. Site failures and Methods to Minimize Impacts.............5
      3.3. Limitation of DNS-based Cloud DC Location Selection.......6
      3.4. Network Issues for 5G Edge Clouds and Mitigation Methods..7
      3.5. DNS Practices for Hybrid Workloads........................8
      3.6. NAT Practice for Accessing Cloud Services.................9
      3.7. Cloud Discovery Practices.................................9
   4. Dynamic Connecting Enterprise Sites with Cloud DCs............10
      4.1. Sites to Cloud DC........................................10
      4.2. Inter-Cloud Connection...................................12
      4.3. Extending Private VPNs to Hybrid Cloud DCs...............13
   5. Methods to Scale IPsec tunnels to Cloud DCs...................14
      5.1. Improvement IPsec Tunnels Management.....................15
      5.2. Improving CPEs interconnection Over the Public Internet..15
   6. Requirements for Networks Connecting Cloud Data Centers.......16

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   7. Security Considerations.......................................16
   8. IANA Considerations...........................................18
   9. References....................................................18
      9.1. Normative References.....................................18
      9.2. Informative References...................................18
   10. Acknowledgments..............................................20

1. Introduction
   With the advent of widely available Cloud data centers (DC)
   providing services in diverse geographic locations and advanced
   tools for monitoring and predicting application behaviors, it is
   desirable for enterprises to instantiate applications and workloads
   in Cloud DCs. Some enterprises prefer that their specific
   applications be located close to their end users, as the proximity
   can improve end-to-end latency and overall user experience. In
   addition, applications and workloads in Cloud DCs can be shut down
   or moved along with end users in motion (thereby modifying the
   networking connection of subsequently relocated applications and
   Key characteristics of Cloud Services are on-demand, scalable,
   highly available, and usage-based billing. Most Cloud Operators
   provide Cloud network functions, such as, virtual Firewall services,
   virtual private network services, virtual PBX (Private Branch
   eXchange) services including voice and video conferencing systems,
   etc. Cloud DC is a shared infrastructure that hosts services to many
   This document describes the network-related problems enterprises
   face at the moment of writing this specification when
   interconnecting their branch offices with dynamic workloads in Cloud
   DCs and the mitigation practices.

2. Definition of terms

   Cloud DC:   Third party Data Centers that usually host applications
               and workload owned by different organizations or

   Heterogeneous Cloud: applications and workloads split among Cloud
               DCs owned or managed by different operators.

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   Hybrid Clouds: A hybrid cloud is a mixed computing environment where
               applications are run using a combination of computing,
               storage, and services in different environments-public
               clouds and private clouds, including on-premises data
               centers or "edge" locations. [

   IXP:        Internet exchange points (IXes or IXPs) are common
               grounds of IP networking, allowing participant Internet
               service providers (ISPs) to exchange data destined for
               their respective networks.

   SD-WAN      An overlay connectivity service that optimizes transport
               of IP Packets over one or more Underlay Connectivity
               Services by recognizing applications (Application Flows)
               and determining forwarding behavior by applying Policies
               to them. [MEF-70.1]

   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. At the moment of of
               writing this specification, most Cloud operators' VPCs
               only support private addresses, some support IPv4 only,
               others support IPv4/IPv6 dual stack.

3. Issues and Mitigation Methods of Connecting to Cloud DCs

   This section identifies some of the high-level problems that IETF
   can address, especially by Routing area. Other Cloud DC problems are
   out of the scope of this document, e.g., managing cloud spending is
   not discussed here.

3.1. Increased BGP Peering Errors and Mitigation Methods

   Where traditional ISPs view peering as a means to improve network
   operations, Public Cloud DCs offer direct peering to get more
   customers to use their data centers and services. As such, there is
   pressure to peer more widely and to peer with customers, including

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   those who lack the expertise and experience in running complex BGP
   peering relationships. All those can contribute to increased BGP
   peering errors such as capability mismatch, unwanted route leaks,
   missing Keepalives, and errors causing BGP ceases. Capability
   mismatch can cause BGP sessions not to be adequately established.
   Those issues are more acute to Cloud DCs than they have
   traditionally been, even though they may apply to traditional ISPs,
   just to a lesser degree.
   Here are the recommended mitigation practices:

     - If a Cloud GW (BGP speaker) receives from its peer a capability
        that it does not itself support or recognize, it must ignore
        that capability, and the BGP session must not be terminated per
        Section 5 of [RFC5492]. When receiving a BGP UPDATE with a
        malformed attribute, the revised BGP error handling procedure
        [RFC7606] should be followed instead of session resetting.
     - When a Cloud DC doesn't support multi-hop eBGP peering with
        external devices (as many don't), enterprise GWs must establish
        tunnels (e.g., IPsec) to the Cloud GWs to form the IP
     - When a Cloud DC eBGP session supports a limited number of
        routes from external entities, the on-premises DCs need to set
        up default routes and filter as many routes as practical
        replacing them with that default in the eBGP advertisement to
        minimize the number of routes to be exchanged with the Cloud DC
        eBGP peers.
     - When a Cloud GW receives the inbound routes exceeding the
        maximum routes threshold for a peer, the currently common
        practice is generating out-of-band alerts (e.g., Syslog) via
        the management system or terminating the BGP session (with
        cease notification messages [RFC4486] being sent). More
        discussion is needed in the IETF IDR WG for potential in-band
        or autonomous notification directly to the peers when the
        inbound routes exceed the maximum routes threshold.

3.2. Site failures and Methods to Minimize Impacts

   Failures within a Cloud site, which can be a building, a floor, a
   POD, or a server rack, include capacity degradation or complete out-
   of-service. Here are some events that can trigger a site failure: a)

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   fiber cut for links connecting to the site or among pods within the
   site; b) cooling failures; c) insufficient backup power; d) cyber
   threat attacks; e) too many changes outside of the maintenance
   window; etc. Fiber-cut is not uncommon in a Cloud site or between

   As described in RFC7938, Cloud DC might not have an IGP to route
   around link/node failures within its domain. When a site failure
   happens, the Cloud DC GW visible to clients is running fine;
   therefore, the site failure is not detectable by the clients using
   Bidirectional Forwarding Detection (BFD).

   When a site failure occurs, many instances can be impacted. When the
   impacted instances' IP prefixes in a Cloud DC are not aggregated
   nicely, which is very common, one single site failure can trigger a
   huge number of BGP UPDATE messages. There are proposals, such as
   [METADATA-PATH], to enhance BGP advertisements to address this

   [RFC7432] specifies a mass withdrawal mechanism for EVPN to signal a
   large number of routes being changed to remote PE nodes as quickly
   as possible.

3.3. Limitation of DNS-based Cloud DC Location Selection

   Many applications have multiple instances instantiated in different
   Cloud DCs. A commonly deployed solution has DNS server(s) responding
   to an FQDN (Fully Qualified Domain Name) inquiry with an IP address
   of the closest or lowest cost DC that can reach the instance. Here
   are some problems associated with DNS-based solutions:
     - Dependent on client behavior
          - Misbehaving client can cache results indefinitely.
          - Client may not receive service even though there are
             servers available in other Cloud DCs because the failing
             IP address is still cached in the DNS resolver and has not
             expired yet.
     - No inherent leverage of proximity information present in the
        network (routing) layer, resulting in loss of performance.
     - Inflexible traffic control:

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        The Local DNS resolver becomes the unit of traffic management.
        This requires DNS to receive periodical update of the network
        condition, which is difficult.

   One method to mitigate the problems listed above is to use the
   ANYCAST [RFC4786] for the services so that network proximity and
   conditions can be inherently considered in optimal path selection.

   [SERVICE-METRICS] identifies the metrics that can utilized for the
   ingress routers to make path selections not only based on the
   routing cost but also the running environment of the edge services.

3.4. Network Issues for 5G Edge Clouds and Mitigation Methods

   The 5G Edge Clouds [3GPP-5G-Edge] may host edge computing
   applications for ultra-low latency services on virtual or physical
   servers. Those edge computing applications have low latency
   connections to the UEs (User Equipment) and might have other
   connections to backend servers or databases in other locations.

   The low latency traffic to/from the UEs is transported through the
   5G Core (gNB (Next Generation Node B))<-> UPFs (User Plane
   Function)) and the 5G Local Data Networks (LDN) to the edge Cloud
   DCs. The LDN's ingress routers connected to the UPFs might be co-
   located with 5G Core functions in the edge Clouds. The 5G Core
   functions include Radio Control Functions, Session Management
   Functions (SMF), Access Mobility Functions (AMF), User Plane
   Functions (UPF), and others.

   Here are some network problems with connecting the services in the
   5G Edge Clouds:

       1) The difference in routing distances to server instances in
          different edge Clouds is relatively small. Therefore, the
          instance in the Edge Cloud with the shortest routing distance
          from the 5G UPF might not be the best in providing the
          overall low latency service.
       2) Capacity status at the Edge Cloud might play a more
          significant role in end-to-end performance.
       3) Source (UEs) can ingress from different LDN Ingress routers
          due to mobility.

   [METADATA-PATH] describes a mechanism to get around those problem.
   [METADATA-PATH] extends the BGP UPDATE messages for a Cloud GW to

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   propagate the edge service-related metrics from Cloud GW to the
   ingress routers so that the ingress routers can incorporate the
   destination site's capabilities with the routing distance in
   computing the optimal paths.

   The CATS working group is examining general aspects of this space,
   and may come up with protocol recommendations for this information

3.5. DNS Practices for Hybrid Workloads

   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. When applications in one Cloud
   need to communicate with applications hosted in another Cloud, DNS
   queries from one Cloud DC could be forwarded to the enterprises' on-
   premises DNS, which in turn be forwarded to the DNS service in
   another Cloud. Configuration can be complex depending on the
   application communication patterns.

   However, collisions can still occur even with carefully managed
   policies and configurations. If an organization uses an internal
   name like .internal and wants its services to be available via or
   within some other Cloud provider that also uses .internal,
   collisions might occur. Therefore, using the global domain name is
   better 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 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 [Split-Horizon-DNS].

   Globally unique names do not equate to globally resolvable names or
   even global names that resolve the same way from every perspective.

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   Globally unique names can prevent any possibility of collisions at
   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

3.6. NAT Practice for Accessing Cloud Services

   Cloud resources, such as VMs (Virtual Machine) or application
   instances, are usually assigned private IP addresses. By
   configuration, some private subnets can have the NAT function to
   reach out to external networks, 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 [AWS-NAT]. AWS Direct Connect/VPN/VPC Peering does not
   currently support any NAT functionality.

   Google's Cloud NAT [Google-NAT] allows Google Cloud 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 the VPC network can only respond to established connections
   initiated by instances inside the Google Cloud; they cannot initiate
   new connections to Cloud instances via NAT.

   For enterprises with applications running in different Cloud DCs,
   proper configuration of NAT must be performed in Cloud DCs and their
   on-premises DC.

3.7. Cloud Discovery Practices

   One of the concerns of enterprises using Cloud services is the lack
   of awareness of the locations of their services hosted in the Cloud,
   as Cloud operators can move the service instances from one place to
   another. While the geographic locations are usually exposed to the
   enterprises, such as Availability Zones or Regions, the topological
   location is usually hidden. When applications in Cloud communicate
   with on-premises applications, it may not be clear where the Cloud
   applications are located or to which VPCs they belong.

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   Being able to detect Cloud services' location can help on-premises
   gateways (routers) to connect the services in a more optimal site
   when the enterprise's end users or policies change.

   For enterprises that instantiate virtual routers in Cloud DCs,
   metadata can be attached (e.g., GENEVE header or IPv6 optional
   header) to indicate additional properties, including useful
   information about the sites where they are instantiated.

4. Dynamic Connecting Enterprise Sites with Cloud DCs

   For many enterprises with established private VPNs (e.g., private
   circuits, MPLS-based L2VPN/L3VPN) interconnecting branch offices &
   on-premises data centers, connecting to Cloud services will be a mix
   of different types of networks. When an enterprise's existing VPN
   service providers do not have direct connections to the desired
   cloud DCs that the enterprise prefers to use, the enterprise faces
   additional infrastructure and operational costs to utilize the Cloud

   This section describes some mechanisms for enterprises with private
   VPNs to connect to Cloud services dynamically.

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. For example, AWS (Amazon Web Services) offers the following
   options to reach workloads in AWS Cloud DCs [AWS-Cloud-WAN]:

     - 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

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        Zones. AWS Transit Gateway acts as a hub that controls how
        traffic is forwarded among all the connected networks which act
        like spokes.

   Microsoft Azure's Virtual WAN [Azure-SD-WAN] 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
   the 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 1 below shows an example of a portion of workloads belonging
   to one tenant (e.g., TN-1) are accessible via a virtual router
   connected by AWS Internet Gateway; some of the same tenant (TN-1)
   are accessible via AWS vGW, and others are accessible via AWS Direct
   Connect. The workloads belonging to one tenant can communicate
   within a Cloud DC via virtual routers (e.g., vR1, vR2).

   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 customers
     |            +-------+ Gateway  +----------------------
     |                     \        / to reach via Internet
     |                      +-+----+
     |                        |
     |    ,---.         ,---. |
     |   (TN-1 )       ( TN-2)|
     |    `-+-'  +---+  `-+-' |
     |      +----|vR2|----+   |
     |           ++--+        |
     |            |         +-+----+
     |            |        / virtual\ For IPsec Tunnel
     |            +-------+ Gateway  +----------------------
     |            |        \        /  termination
     |            |         +-+----+
     |            |           |
     |            |    + - - - - - - - - - - - - - - - --+
     |            |    |    +-+----+          +----+
     |            |        /        \ Direct /      \   |
     |            +----|--+ Gateway  +------+ Fabric|--VPN-- CPE
     |                     \        / Connect\ edge /   |
     |                 |    +-+----+          +----+
     |                        |         IXP              |
     |                 + - - - - - - - - - - - - - - - --+
     TN: Tenant Network. One TN can be attached to both vR1 and vR2.
     Figure 1: Examples of Multiple Cloud DC connections.

4.2. Inter-Cloud Connection

   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 virtual routers in different
   Cloud DCs and administer IPsec tunnels among them. In summary, here
   are some approaches, available to interconnect workloads among
   different Cloud DCs:

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     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.
        NHRP (Next Hop Resolution Protocol) [RFC2735] based multi-point
        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.
     d) Utilize a Cloud Aggregator or Cloud Services Broker (CSB) who
        acts as an intermediator among cloud service providers and
        network service providers to offer a combined total package for
        enterprises. The Cloud Aggregator can provide the network
        connections among one enterprise's services instantiated in
        multiple Clouds.

   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 Approach c), [SDWAN-EDGE-DISCOVERY] describes a mechanism for
   virtual routers to advertise their properties for establishing
   proper IPsec tunnels among them. There could be other approaches
   developed to address the problem.

   Approach d) is a method of third-party multi-cloud management
   business model.

4.3. Extending Private VPNs to Hybrid Cloud DCs

   Traditional private VPNs, including private circuits or MPLS-based
   L2/L3 VPNs, when purchased with premium paid services, have been
   widely deployed as an effective way to support businesses and
   organizations that require network performance and reliability.

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   Connecting an enterprise's on-prem CPEs to a Cloud DC via a private
   VPN requires the private VPN provider to have a direct path to the
   Cloud GW. When the user base changes, the enterprise might want to
   migrate its workloads/applications to a new cloud DC location closer
   to the new user base. The existing private VPN provider might not
   have circuits at the new location. Deploying PEs routers at new
   locations takes a long time (weeks, if not months).

   When the private VPN network can't reach the desired Cloud DCs,
   IPsec tunnels can dynamically connect the private VPN's PEs with the
   desired Cloud DCs GWs. As the private VPNs provide higher quality of
   services, choosing a PE closest to the Cloud GW for the IPsec tunnel
   is desirable to minimize the IPsec tunnel distance over the public

   In order to support Explicit Congestion Notification (ECN) [RFC3168]
   usage by private VPN traffic, the PEs that establish the IPsec
   tunnels with the Cloud GW need to comply with the ECN behavior
   specified by RFC6040 [RFC6040].

   An enterprise can connect to multiple Cloud DC locations and
   establish different BGP peers with Cloud GW routers at different
   locations. As multiple Cloud DCs are interconnected by the Cloud
   provider's own internal network, its topology and routing policies
   are not transparent or even visible to the enterprise customer's on-
   prem routers. One Cloud GW BGP session might advertise all of the
   prefixes of the enterprise's VPC, regardless of which Cloud DC a
   given prefix resides, which can cause improper optimal path
   selection for on-prem routers. To get around this problem, virtual
   routers in Cloud DCs can be used to attach metadata (e.g., in the
   GENEVE header or IPv6 optional header) to indicate the Geo-location
   of the Cloud DC, the delay measurement, or other relevant data.

5. Methods to Scale IPsec tunnels to Cloud DCs

   As described in Section 4.3, IPsec tunnels can be used to
   dynamically establish connection between private VPN PEs with Cloud
   GW. Enterprises can also instantiate virtual routers within Cloud
   DCs to connect to their on-premises devices via IPsec tunnels.

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   As described in [Int-tunnels], IPsec tunnels can introduce MTU
   problems. This document assumes that endpoints manage the
   appropriate MTU sizes, therefore, not requiring VPN PEs to perform
   the fragmentation when encapsulating user payloads in the IPsec

5.1. Improvement IPsec Tunnels Management

   IPsec tunnels are a very convenient solution for an enterprise with
   a small number of locations to reach a Cloud DC. However, for a
   medium-to-large enterprise with multiple sites and data centers to
   connect to multiple cloud DCs, there are N*C*2 bi-directional IPsec
   SAs (tunnels) between Cloud DC gateways and all those sites, with N
   being the number of enterprise sites and C being the number of Cloud
   sites. Each of those IPsec Tunnels requires pair-wise periodic key
   refreshment. For a company with hundreds or thousands of locations,
   managing hundreds (or even thousands) of IPsec tunnels can be very
   processing intensive. That is why many Cloud operators only allow a
   limited number of (IPsec) tunnels & bandwidth to each customer.

   To scale the IPsec key management, a solution like group encryption
   can be considered. But the drawback of the group encryption is
   higher security risk of the key distribution and maintenance of a
   key server.

   [SECURE-EVPN] leverages the BGP point-to-multipoint signaling to
   create private pair-wise IPsec Security Associations among peers
   without IKEv2 point-to-point signaling or any other direct peer-to-
   peer session establishment messages.

5.2. Improving CPEs interconnection Over the Public Internet

   When enterprise CPEs are far away from each other, e.g., across
   country/continent boundaries, the 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.

   [MULTI-SEG-SDWAN] describes some methods to utilize the Cloud
   backbone to interconnect enterprise CPEs in dispersed geographic
   locations without requiring the Cloud GW to decrypt and re-encrypt
   the traffic from the CPEs.

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6. Requirements for Networks Connecting Cloud Data Centers

   To address the issues identified in this document, network solutions
   for connecting enterprises with their dynamic workloads or
   applications in Cloud DCs should satisfy the following requirements:
     - Should support scalable policy management for the traffic to
        and from the newly instantiated application instances at any
        Cloud DC location.
     - Should allow enterprises to take advantage of the current
        state-of-the-art private VPN technologies, including the
        traditional circuit-based, MPLS-based VPNs, or IPsec-based VPNs
        (or any combination thereof) that run over the public Internet.
     - Should support scalable IPsec key management among all nodes
        involved in DC interconnect schemes.
     - Should support easy and fast, on-demand network connections to
        dynamic workloads and applications in Cloud DCs and easily
        reach these workloads when they migrate within or across data
     - Should support traffic engineering to distribute loads across
        regions/AZs based on performance/availability of workloads in
        addition to the network path conditions to the Cloud DCs.
     - Should support network traffic traceability, logging, and
     - Should support transit/spoke gateways interconnection
        scalability and consistent policy enforcement as workloads are
        increased/migrated. This requirement is mainly for the Cloud
        Aggregators or Cloud Service Brokers who provide managed
        services to enterprises over multiple Cloud service providers.

7. Security Considerations

   The security issues in terms of networking to clouds include:

     - Service instances in Cloud DCs are connected to users
        (enterprises) via Public IP ports which are exposed to the
        following security risks:

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        a) Potential DDoS attack to the ports facing the untrusted
        network (e.g., the public internet), which may propagate to the
        cloud edge resources. To mitigate such security risk, it is
        necessary for the ports facing internet to enable Anti-DDoS

        b) Potential risk of augmenting the attack surface with inter-
        Cloud DC connection by means of identity spoofing, man-in-the-
        middle, eavesdropping or DDoS attacks. One example of
        mitigating such attacks is using DTLS to authenticate and
        encrypt MPLS-in-UDP encapsulation (RFC 7510).

     - Potential attacks from service instances within the cloud. For
        example, data breaches, compromised credentials, and broken
        authentication, hacked interfaces and APIs, account hijacking.

     - When IPsec tunnels established from enterprise on-premises CPEs
        are terminated at the Cloud DC gateway where the workloads or
        applications are hosted, traffic to/from an enterprise's
        workload can be 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.

   The Cloud DC operator's security practices can affect the overall
   security posture and need to be evaluated by customers. Many Cloud
   operators offer monitoring services for data stored in Clouds, such
   as AWS CloudTrail, Azure Monitor, and many third-party monitoring
   tools to improve the visibility of data stored in Clouds.

   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.

   A full security evaluation will be needed before [SECURE-EVPN] can
   be recommended.

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8. IANA Considerations

   This document requires no IANA actions. RFC Editor: Please remove
   this section before publication.

9. References

9.1. Normative References

   [RFC2735] B. Fox, et al "NHRP Support for Virtual Private networks".
   Dec. 1999.

   [RFC3168] K. Ramakrishnan, et al, "The Addition of Explicit
   Congestion Notification (ECN) to IP", RFC3168, Sept. 2001.

   [RFC4486] E. Chen and V. Gillet, "Subcodes for BGP Cease
   Notification Message", RFC4486, April 2006.

   [RFC4786] J. Abley and K. Lindqvist, "Operation of Anycast
   Services", RFC4786, Dec. 2006.

   [RFC5492] J. Scudder and R. Chandra, "Capabilities Advertisement
   with BGP-4", RFC5492, Feb. 2009.

   [RFC6040] B. Briscoe, "Tunnelling of Explicit Congestion
   Notification", RFC6040, Nov 2010.

   [RFC7606] E. Chen, et al "Revised Error Handling for BGP UPDATE
   Messages". Aug 2015.

   [RFC7432] A. Sajassi, et al "BGP MPLS-Based Ethernet VPN", RFC7432,
   Feb. 2015.

9.2. Informative References

   [RFC6071] S. Frankel and S. Krishnan, "IP Security (IPsec) and
             Internet Key Exchange (IKE) Document Roadmap", Feb 2011.

   [3GPP-5G-Edge] 3GPP TS 23.548 v18.1.1, "5G System Enhancements for
             Edge Computing", April 2023.

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   [SDWAN-EDGE-DISCOVERY] L. Dunbar, S. Hares, R. Raszuk, K. Majumdar,
             G. Mishra, V. Kasiviswanathan, "BGP UPDATE for SD-WAN Edge
             Discovery", draft-ietf-idr-sdwan-edge-discovery-10, June

   [AWS-NAT] NAT gateways - Amazon Virtual Private Cloud.

   [AWS-Cloud-WAN] Introducing AWS Cloud WAN (Preview) | Networking &
             Content Delivery (

   [Azure-SD-WAN] Architecture: Virtual WAN and SD-WAN connectivity -
             Azure Virtual WAN | Microsoft Learn.

   [Google-NAT] Cloud NAT overview  |  Google Cloud.

   [Int-tunnels] J. Touch and W Townsley, "IP Tunnels in the Internet
             Architecture", draft-ietf-intarea-tunnels-13.txt, March,

   [MEF-70.1] MEF 70.1 SD-WAN Service Attributes and Service Framework.
             Nov. 2021.

   [METADATA-PATH] L. Dunbar, et al, "BGP Extension for 5G Edge Service
             Metadata" draft-ietf-idr-5g-edge-service-metadata-09,
             Sept. 2023.

   [MULTI-SEG-SDWAN] K. Majumdar, et al, "Multi-segment SD-WAN via
             Cloud DCs", draft-dmk-rtgwg-multisegment-sdwan-02, Sept

   [SECURE-EVPN] A. Sajassi, et al, "Secure EVPN", draft-ietf-bess-
             secure-evpn-00, June 2023.

   [SERVICE-METRICS] L. Dunbar, et al, "5G Edge Services Use Cases and
             Metrics", draft-dunbar-cats-edge-service-metrics-01, July

   [Split-Horizon-DNS] K. Tirumaleswar, et al, "Establishing Local DNS
             Authority in Validated Split-Horizon Environments", draft-
             ietf-add-split-horizon-authority-04, Mar. 2023.

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10. Acknowledgments

   Many thanks to Joel Halpern, Aseem Choudhary, Adrian Farrel, Alia
   Atlas, Chris Bowers, Paul Vixie, Paul Ebersman, Timothy Morizot,
   Ignas Bagdonas, Donald Eastlake, 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
   Malis Consulting

   Christian Jacquenet
   Rennes, 35000

   Mehmet Toy
   One Verizon Way
   Basking Ridge, NJ 07920

   Kausik Majumdar
   Microsoft Azure

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