Network Working Group                                         L. Dunbar
Internet Draft                                                Futurewei
Intended status: Informational                                 A. Malis
Expires: October 20, 2023                              Malis Consulting
                                                           C. Jacquenet
                                                                 M. Toy
                                                            K. Majumdar
                                                         April 24, 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 (a.k.a. Cloud DCs) and some mitigation
   practices. There can be many problems associated with connecting to
   or among Cloud DCs; the Net2Cloud problem statements are mainly for
   enterprises that already have traditional VPN services and are
   interested in leveraging those networks (instead of altogether
   abandoning them). Other problems are out of the scope of this
   This document also describes the mitigation practices for getting
   around the identified problems.

Status of this Memo

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   reference material or to cite them other than as "work in progress."

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   The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on October 24, 2023.

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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 errors and Mitigation Methods...............4
      3.2. Site failures and Methods to Minimize Impacts.............5
      3.3. Optimal Paths to Cloud DC locations.......................6
      3.4. Network Issues for 5G Edge Clouds and Mitigation Methods..6
      3.5. DNS Practices for Hybrid Workloads........................7
      3.6. NAT Practice for Accessing Cloud Services.................8
      3.7. Cloud Discovery Practices.................................8
   4. Dynamic Interconnecting Enterprise Sites with Cloud DCs........9
      4.1. Sites to Cloud DC.........................................9
      4.2. Inter-Cloud Connection...................................11
      4.3. Extending Private VPNs to Hybrid Cloud DCs...............13
   5. Methods to Scale IPsec tunnels to Cloud DCs...................14
      5.1. Scaling Issues with IPsec Tunnels........................14
      5.2. Poor performance when overlay public internet............15
   6. Requirements for Dynamic Cloud Data Center VPNs...............15

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   7. Security Considerations.......................................16
   8. IANA Considerations...........................................17
   9. References....................................................17
      9.1. Normative References.....................................17
      9.2. Informative References...................................18
   10. Acknowledgments..............................................19

1. Introduction
   With the advent of widely available third-party cloud DCs and
   services in diverse geographic locations and the advancement of
   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).
   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 party Cloud Operators. Examples of Cloud network functions
   are: 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.

2. Definition of terms

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

   Controller: Used interchangeably with SD-WAN controller to manage
               SD-WAN overlay path creation/deletion and monitoring the
               path conditions between two or more sites.

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

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   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, Salesforce, SAP, etc).

   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

   There are many problems associated with connecting to Cloud DCs,
   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. Increased BGP errors and Mitigation Methods

   Traditional network service providers usually have prior negotiated
   peering policies with their BGP peers over fixed interfaces. Cloud
   GWs need to peer with a larger variety of parties, via private
   circuits or IPsec over public internet. Many of those peering
   parties may not be traditional network service providers. Their BGP
   configurations practices might not be consistent, and some are done
   by less experienced personnel. 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 established properly.
   If a 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 RFC5492. When receiving a
   BGP UPDATE with a malformed attribute, the revised BGP error

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   handling procedure [RFC7606] should be followed instead of session

   Many Cloud DCs don't support multi hop eBGP peering with external
   devices. To get around this limitation, it is necessary for
   enterprises GWs to establish IPsec tunnels to the Cloud GWs to form
   IP adjacency.

   Some Cloud DC eBGP peering only supports limited number of routes
   from external entities. To get around this limitation, on-premises
   DCs need to set up default routes to be exchanged with the Cloud DC
   eBGP peers. When inbound routes exceed the maximum routes threshold
   for a peer, the current common practice is generating out of band
   alerts (e.g., Syslog) via management system to the peer, or
   terminating the BGP session (with cease notification messages [RFC
   4486] being sent).

3.2. Site failures and Methods to Minimize Impacts

   Failures within a site include (but not limited to) a site capacity
   degradation or entire site going down. The reasons for these
   capacity degradations or failures can include: a) 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, or
   other errors. Fiber-cut is not uncommon within a Cloud site or
   between sites.

   As described in RFC7938, Cloud DC BGP 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 capacity degrades or goes to zero, there are massive
   numbers of routes needing to be changed.

   The large number of routes switching over to another site can also
   cause overloading that triggers more failures.

   In addition, the routes (IP addresses) in a Cloud DC cannot be
   aggregated nicely, triggering very large number of BGP UPDATE
   messages when a failure occurs.

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   It might be more effective to do mass reroute, similar to EVPN
   [RFC7432] defined mass withdraw mechanism to signal a large number
   of routes being changed to remote PE nodes as quickly as possible.

3.3. Optimal Paths to Cloud DC locations

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

   To address the problems listed above, ANYCAST addresses can be
   utilized so that network proximity and conditions can be inherently
   considered in optimal path selection.

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

   The 5G edge clouds [3GPP-5G-Edge] may host edge computing servers
   (virtual or physical) for Ultra-low latency services that must be
   near the UEs (User equipment). Those edge computing applications
   have low latency connections to the UEs and regular connections to
   backend servers or databases in other locations.

   The low latency services traffic to/from the edge Clouds are
   transported through the 5G Local Data Networks (LDN) and 5G UPFs to
   the UEs. The LDN's ingress routers, directly connected to the User
   Plane Functions (UPF), might be co-located with 5G Core functions in
   the edge Cloud data centers. The 5G Core functions include Radio

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   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 Cloud DCs:

       1) The difference in routing distances to multiple server
          instances in different edge Clouds is relatively small.
          Therefore, the edge Cloud with the shortest routing distance
          might not be the best in providing the overall latency.
       2) Capacity status at the Edge Cloud DC might play a bigger role
          for E2E performance.
       3) Source (UEs) can ingress from different LDN Ingress routers
          due to mobility.

   To get around those problems, the ingress routers can incorporate
   the destination site's capabilities with the routing distance in
   computing the optimal paths.

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, even with carefully managed policies and configurations,
   collisions can still occur. If an organization uses an internal name
   like .internal and then want your services to be available via or
   within some other cloud provider which also uses .internal, then

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   collisions might occur. 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 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 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 VM 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 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 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 using Cloud services is not being aware of
   where the resource is located, especially that Cloud operators can

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   move application instances from one place to another. 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.

   Being able to detect Cloud services location can help on-premises
   gateways (routers) to switch the services to a more optimal site
   when the current cloud site encounters failures or degradation. 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.

   For enterprises that instantiate virtual routers in Cloud DCs,
   metadata can be attached (e.g., GENEVE header or IPv6 optional
   header) to indicate Geo-location of the Cloud DCs.

4. Dynamic Interconnecting Enterprise Sites with Cloud DCs

   For many enterprises with established provide 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 practices to connect to 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. 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

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        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.

   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 some of a tenant's workloads that
   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 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 own virtual routers in
   different Cloud DCs and administer IPsec tunnels among them, which
   by itself is not a trivial task. For example, open-source VPN
   software such as strongSwan can be leveraged to create an IPSec
   connection to the Azure gateway. 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.

   In summary, here are some approaches, available 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.
        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.

   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), NHRP [RFC2735] is used for spoke nodes to
   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.

   There are many differences between virtual routers in Public Cloud
   DCs and the nodes in an NBMA network. NHRP cannot be used for

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   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, existing NHRP based VPN
   technique cannot be used directly for connecting workloads in hybrid
   Cloud DCs.

4.3. Extending Private VPNs to Hybrid Cloud DCs

   Traditional private VPNs, including private circuits or MPLS based
   L2/L3 VPNs, have been widely deployed as an effective way to support
   businesses and organizations that require network performance and
   reliability. L2/L3 VPN shifts the burden of managing a VPN service
   from enterprises to service providers. The CPEs attached to a
   private VPN are simpler and less expensive because they do not need
   to manage routes to remote sites; they pass all outbound traffic to
   the private VPN PEs to which the CPEs are attached (albeit multi-
   homing scenarios require more processing logic on CPEs).  Private
   VPN has addressed the problems of scale, availability, and fast
   recovery from network faults, and incorporated traffic-engineering

   However, an enterprise's private VPN's PE (Provider Edge) nodes
   might not have the direct connections to the third-party cloud DCs
   needed by the enterprise to provide easy access to its end users.
   When the user base changes, the enterprise might want to migrate its
   workloads/applications to a new cloud DC location closest 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), which defeats one of the benefits
   of Clouds' geographically diverse locations allowing workloads to be
   as close to their end-users as possible.

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

   In order to support Explicit Congestion Notification (ECN) [RFC3168]
   usage by private VPN traffic, the PEs that establish the IPsec

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   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.

   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. Scaling Issues with IPsec Tunnels

   IPsec tunnels are a very convenient solution for an enterprise with
   limited 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*N number
   of IPsec tunnels among Cloud DC gateways and all those 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.

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

5.2. Poor performance when overlay public internet

   IPsec encap & decap are very processing intensive, which can degrade
   router performance. NAT also adds to the performance burden.

   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.

6. Requirements for Dynamic Cloud Data Center VPNs

   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:
     - 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 policy management: apply the appropriate polices to
        the newly instantiated application instances at any Cloud DC
     - The solution should allow enterprises to take advantage of the
        current state-of-the-art private VPN technologies, including

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        the traditional circuit-based, MPLS-based VPNs, or IPsec-based
        VPNs (or any combination thereof) that run over the public
     - 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
        party data centers, and easily allow these workloads to migrate
        both within a data center and between data centers.
     - Allow VPNs to provide bandwidth and other performance
     - Be a cost-effective solution for enterprises to incorporate
        dynamic cloud-based applications and workloads into their
        existing VPN environment.

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:

        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.

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     - 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.

   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 visibility to 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.

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.

   [RFC4271] Y. Rekhter, et al "BGP-4". Jan 2006

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

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

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

   [RFC7938]   P. Lapukkov, et al "Use of BGP for Routing in Large-
   Scale Data Centers", Aug. 2016

9.2. Informative References

   [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.

   [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.

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

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

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

   [Azure-NAT] What is Azure Virtual Network NAT? | Microsoft Learn

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

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

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

10. Acknowledgments

   Many thanks to 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 contributions.

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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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