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Multi-segment SD-WAN via Cloud DCs
draft-ietf-rtgwg-multisegment-sdwan-00

Document Type Active Internet-Draft (rtgwg WG)
Authors Kausik Majumdar , Linda Dunbar , Venkit Kasiviswanathan , Ashok Ramchandra , Aseem Choudhary
Last updated 2024-05-15
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draft-ietf-rtgwg-multisegment-sdwan-00
Network Working Group                                 K. Majumdar
Internet Draft                                          Microsoft
Intended status: Standard Track                        L. Dunbar
Expires: November 14, 2024
Futurewei
                                                V.Kasiviswanathan
                                                           Arista
                                                    A. Ramchandra
                                                      Microsoft
                                                   A. Choudhary
                                                      Aviatrix
                                                     May 14, 2024

                 Multi-segment SD-WAN via Cloud DCs
               draft-ietf-rtgwg-multisegment-sdwan-00

Abstract
   This document describes a method for SD-WAN CPEs using GENEVE
   Encapsulation (RFC8926) to encapsulate the IPsec encrypted
   packets and send them to their closest Cloud GWs, who can
   steer the IPsec encrypted payload through the Cloud Backbone
   without decryption to the egress Cloud GWs which then forward
   the original IPsec encrypted payload to the destination CPEs.
   This method is for Cloud Backbone to connect multiple
   segments of SD-WAN without the Cloud GWs decrypting and re-
   encrypting the payloads.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet
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   other documents at any time.  It is inappropriate to use
   Internet-Drafts as reference material or to cite them other
   than as "work in progress."

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   Copyright (c) 2024 IETF Trust and the persons identified as
   the document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Provisions and are provided without warranty as described in
   the Simplified BSD License.

Table of Contents

   1. Introduction..............................................3
   2. Conventions used in this document.........................5
   3. Use Cases.................................................6
      3.1. Multi-segment SD-WAN via Single Cloud GW.............6
      3.2. Multi-segment SD-WAN via Cloud Backbone..............7
      3.3. Analysis of Policy-based Traffic Steering............8
      3.4. End to End Encryption................................9
   4. Data Plane encoding for SD-WAN Transit....................9
      4.1. Multi-Segment SD-WAN Option Class....................9
      4.2. SD-WAN Tunnel Endpoint Sub-TLV......................10
      4.3. SD-WAN Tunnel Originator Sub-TLV....................11
      4.4. Egress GW Sub-TLV...................................12
      4.5. Include Transit Sub-TLV.............................12
      4.6. Exclude-Transit Sub-TLV.............................13
   5. IPsec Flow through Cloud GWs Illustration................14
      5.1. Single Hop Cloud GW.................................14
      5.2. Multi-hop Transit GWs...............................16

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      5.3. Data Authentication and Integrity Check by Cloud GW.18
   6. Illustration of Traffic from Private VPN to IPsec Tunnel.19
   7. Control Plane considerations.............................21
      7.1. Control Plane for CPEs..............................21
      7.2. Control Plane between CPEs and Cloud GWs............21
   8. Observability Consideration..............................22
   9. Security Considerations..................................23
   10. Manageability Considerations............................26
   11. IANA Considerations.....................................27
   12. References..............................................28
      12.1. Normative References...............................28
      12.2. Informative References.............................29
   13. Acknowledgments.........................................29

1. Introduction

   SD-WAN is widely deployed to connect enterprises' on-premises
   CPEs with services in Cloud DCs. As described in Section 4.1
   of [Net2Cloud], there are multiple options for enterprises to
   connect to Cloud DCs:

     - Direct Interconnect model,
     - Direct Interconnect model with Enterprise's virtual
        appliances in the Cloud,
     - Indirect Interconnect model via SD-WAN paths and
     - Managed Hybrid WAN model using Enterprise's existing VPN
        connections.
        For the enterprise branches with private VPN circuits
        interconnecting with a Cloud GW via IXP (Internet
        eXchange Point), the Enterprise can extend into Cloud DC
        without setting up IPsec paths between their on-premises
        CPEs and the Cloud GWs.

   Enterprises connecting to Cloud DC may find significant
   benefits in leveraging the Cloud Backbone for transporting
   traffic between their CPEs, such as

  1. Enterprises can benefit from the robust and high-
     performance infrastructure cloud service providers provide
     by leveraging diverse paths and harnessing cloud backbones'
     scalability and global reach to reduce the risk of downtime
     or disruptions.

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  2. The scalability of the Cloud Backbone allows for efficient
     handling of increased data traffic, accommodating the
     growing demands of modern enterprises.
  3. Cloud Backbone's centralized management and orchestration
     capabilities contribute to simplified network
     administration, enabling organizations to streamline their
     operations and respond more effectively to changing
     business requirements.

   To ensure security, enterprise traffic between their CPEs is
   encrypted and remains inaccessible to any third parties,
   including the Cloud DC. For the encrypted packets to be
   steered through the Cloud Backbone, the packet header must
   contain information indicating the packet's intended route.
   Given that the IPsec SA between CPEs is exclusively
   maintained between the CPEs and is not accessible to Cloud
   GWs, the encrypted packet needs to be carried by a tunnel
   between the source CPE and the ingress Cloud GW. This tunnel
   can be another layer of IPsec, which adds processing overhead
   to the Cloud GW to decrypt the outer IPsec tunnel solely for
   steering the encrypted payload.

  By steering the encrypted traffic through the Cloud Backbone
  without the need for decryption and re-encryption at Cloud
  GWs, processing demands at these GWs can be significantly
  reduced. This streamlined approach not only maintains the
  integrity of the encrypted traffic but also optimizes
  processing resources, enhancing overall efficiency within the
  cloud infrastructure.

   This document introduces a method for SD-WAN CPEs that
   utilizes GENEVE Encapsulation [RFC8926] to encapsulate IPsec
   encrypted packets, directing them to the nearest Cloud GWs.
   These gateways can determine whether the packet needs to
   traverse the backbone without decryption by inspecting Sub-
   TLVs within the GENEVE header, as specified in Section 4.
   Once determined that the packet is intended for backbone
   traversal, the IPsec encrypted payload is steered through the
   Cloud Backbone without decryption to optimal egress Cloud
   GWs. These gateways then forward the original IPsec encrypted

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   payload to the destination CPEs. This method facilitates the
   Cloud Backbone's connecting multiple SD-WAN segments without
   Cloud GWs decrypting and re-encrypting payloads.

   GENEVE is selected in this document as the encapsulation
   protocol due to its widespread usage in Cloud DC sites.

2. Conventions used in this document
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
   "MAY", and
   "OPTIONAL" in this document are to be interpreted as
   described in BCP14 [RFC2119] [RFC8174] when, and only when,
   they appear in all
   capitals, as shown here.

   The following acronyms and terms are used in this document:

   Cloud DC:   Off-Premises Data Center, managed by the third
               party, that hosts applications, services, and
               workload for different organizations or tenants.

   CPE:        Customer (Edge) Premises Equipment.

   OnPrem:     On Premises data centers and branch offices.

   RR          Route Reflector.

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

   VPN         Virtual Private Network.

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3. Use Cases

3.1. Multi-segment SD-WAN via Single Cloud GW

   For enterprise branches that have established SD-WAN paths to
   a Cloud GW for accessing Cloud services, the Cloud GW can be
   utilized to connect those branches, as shown in Figure 1.
   Here are some reasons for connecting those branches via a
   Cloud GW:
  - The public internet among those branches might have limited
     bandwidth, unpredictable connection performance, or be
     prone to cyber-attacks. In comparison, the network paths
     from CPEs to the Cloud GW have more reliable connections
     and are constantly monitored by sophisticated network
     functions.
  - It is easier to utilize Cloud based security functions,
     such as Firewall, DDoS, etc., to apply consistent policy
     enforcement for workloads/services to the Cloud and across
     the branches.
  - Proprietary cloud-based tools and SaaS (Software as a
     Service) may be available in specific deployments to
     collect and analyze the threat to the traffic.

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                          (^^^^^^^^^^^^)
                        (     Cloud     )
                        ( +----+  +----+  )
                 + -----(-|Edge|  + GW |  )
         Direct  |      ( +----+  +/--\+  )
        Connect  |        (^^^^^^^/^^^^\^)
               {-+---}           /      \  SD-WAN Path CPE<->GW
               { VPN }          /        \
               {-+---}         /          IPsec Tunnel
                 +-------+----/------+    \
                         |   /       |     \
                        ++--/+       |    +-\--+
                        |CPE1|       +----+CPE2|
                        +----+            +----+
       Client Route: 11.1.1.x             10.1.1.x
                     21.1.1.x             20.1.1.x
                                          30.1.1.x
   Figure 1 Multi-Segment SD-WAN stitching via a Cloud GW

3.2. Multi-segment SD-WAN via Cloud Backbone

   For geographic faraway enterprise branches that have
   established SD-WAN paths to their corresponding Cloud GWs to
   access Cloud services in different geographic locations, the
   Cloud backbone can connect those branches, as shown in Figure
   2. The reasons to utilize the Cloud Backbone to interconnect
   those branches are similar to interconnecting multiple
   branches via a single Cloud GW described in the previous
   section.

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                       (^^^^^^^^^^^^^^^)
                      (      Cloud      )
                      ( +----+  +----+  )               +-----+
                 + ---(-|Edge|==| GW1|=================== GW2 |
         Direct  |    ( +----+  +/--\+  )               +--|--+
        Connect  |      (^^^^^^^/^^^^\^)                   |
               {-+---}         /      \                    |
               { VPN }        /        \                 +-----+
               {-+---}       /          IPsec Tunnel     |CPE10|
                 +-------+--/--------+   \               +-----+
                         | /         |    \
   10.2.1.x
                        ++/--+       |    +\---+
   20.2.1.x
                        |CPE1|       +----+CPE2|
   30.2.1.x
                        +----+            +----+
       Client Route: 11.1.1.x             10.1.1.x
                     21.1.1.x             20.1.1.x
                                          30.1.1.x

     Figure 2 Multi-Segment SD-WAN Stitching via Cloud Backbone

3.3. Analysis of Policy-based Traffic Steering

     There are many well-developed methods, such as SRv6 or
     MPLS-TE, to steer traffic through specific nodes. Those
     traffic steering methods are effective when the entire
     network domain is under one administrative control.

     However, the traffic from on-premises CPEs to Cloud GWs via
     the public internet can only be forwarded based on the
     packets' destination addresses.

     SD-WAN allows for the setup of multiple links (paths), some
     of which are the Public Internet, from the same SD-WAN
     branch CPE to a Cloud GW; each link (or path) represents a
     dual tunnel connection from a unique public IP of the SD-
     WAN CPE to two different instances of Cloud GW. Using Cloud
     GW to interconnect those on-premises CPEs eliminates the
     need to manage the multiple ISPs' links/paths between the
     CPEs.

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3.4. End to End Encryption

   To ensure the confidentiality, integrity, and availability of
   communication among CPEs, the traffic between the CPEs should
   be encrypted by the IPsec SAs if traversing the public
   Internet. When the traffic between the enterprise's CPEs
   doesn't terminate within the Cloud DCs, the processing burden
   on Cloud GWs can be significantly reduced if the Cloud GWs
   don't need to decrypt and re-encrypt transit IPsec encrypted
   traffic among CPEs. This document describes the mechanisms
   for the IPsec encrypted traffic between CPEs to traverse the
   Cloud GWs without being decrypted and re-encrypted by the
   Cloud GWs.

4. Data Plane encoding for SD-WAN Transit

   For Cloud GWs to differentiate the packets destined towards
   their internal hosts/services, which require decryption, and
   transit packets to be forwarded to the respective destination
   branch CPEs, proper marking is needed in the packets' header.
   As the GENEVE Encapsulation [RFC8926] is supported by most
   Cloud Service Providers, GENEVE is chosen as the
   encapsulation header for Cloud GWs to steer IPsec encrypted
   packets among CPEs without decryption.

4.1. Multi-Segment SD-WAN Option Class

   Geneve header is specified in Section 3 of [RFC8926].

   A new GENEVE Option Class (Type value=TBD) is added to
   indicate that the Multi-segment SD-WAN relevant Sub-TLVs are
   encoded in the GENEVE header.

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    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | multi-seg-SD-WAN Option Class |C|    Type     |R|R|R| Length  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                  SD-WAN Tunnel Endpoint Sub-TLV               ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~          Optional SD-WAN Tunnel Originator Sub-TLV            ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~          Optional Egress GW Sub-TLV                           ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                                                             //
   //         Optional Type Length Value objects (variable)       //
   //                                                             //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 4 Multi Segment SD-WAN Option Class

   C-bit needs to be set, so that receiving node can drop the
   packet if it does not recognize the option [RFC8926].

   Type indicates the various types of multi-segment SD-WAN.

     Type = Multi-seg-SDWAN_subType1 (To be assigned by IANA):
     Single Hop Transit SD-WAN

     Type = Multi-seg-SDWAN_subType3 (To be assigned by IANA):
     Multi-Hop Transit SD-WAN with explicitly specified egress
     Cloud GW.

     Type = Multi-seg-SDWAN_subType3 (To be assigned by IANA):
     Multi-Hop Transit SD-WAN without specified egress Cloud GW.

   Note: the payload after the multi-seg-SD-WAN Option Class can
   be IPv4 or IPv6. The IP header protocol type = 50 (ESP)
   [RFC4303] indicates the payload is IPsec ESP encrypted.

4.2. SD-WAN Tunnel Endpoint Sub-TLV

   The SD-WAN Endpoint sub-TLV indicates the destination CPE of
   the IPsec Tunnel.

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   For example, for the SD-WAN IPsec SA from CPE1 to CPE2 shown
   in Figure 1, the Tunnel Endpoint Sub-TLV of the Geneve Header
   has the CPE2's IP address.

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |SD-WAN Endpoint| length        |   Reserved    | TTL          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | SD-WAN Dst Addr Family        | Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable)                    +
   ~                                                               ~
   |    SD-WAN end point Address                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 5 SD-WAN Endpoint Sub-TLV

   TTL is set by the SD-WAN Tunnel Originator, e.g., CPE1. Each
   transit node or transit region/zone (visible to the CPEs) SHOULD
   decrement the TTL so that the destination CPE can know the number
   of logical transit nodes (cloud regions or zones) the packet has
   traversed. Enterprises can also use TTL to set the maximum transit
   nodes/regions the packets traverse.

4.3. SD-WAN Tunnel Originator Sub-TLV

   The SD-WAN Tunnel Originator Sub-TLV is an optional Sub-TLV
   inside the multi-seg-SD-WAN Option Class to indicate the
   originating CPE of the IPsec Tunnel.

   For example, for the SD-WAN IPsec SA from CPE1 to CPE2 shown
   in Figure 1, the Tunnel Originator Sub-TLV inside the Geneve
   Header of the packets indicates CPE1's address.

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |SDWAN Origin   | length        |   reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | SD-WAN Org Addr Family        | Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable)                    +
   ~                                                               ~
   |    SD-WAN Tunnel Originator Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 6 SD-WAN Tunnel Originator Sub-TLV

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   The Tunnel Originator Sub-TLV in the GENEVE header can assist
   Cloud transit nodes in applying appropriate policies when
   forwarding the packet.

4.4. Egress GW Sub-TLV

   For the multi-segment SD-WAN via Cloud Backbone scenario, the
   originator CPE can use the Egress GW Sub-TLV to specify the
   Egress Cloud GW for reaching the destination CPE.

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |SDWAN EgressGW | length        |   reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Egress GW Addr Family         | Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable)                    +
   ~                                                               ~
   |           Egress GW Address                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 7 SD-WAN Egress GW Sub-TLV

   The originator CPE can get the Egress GW address by
   configuration or by control plane protocol exchanged with
   destination CPEs. The detailed Control Plane protocol
   extension is out of the scope of this document.

4.5. Include Transit Sub-TLV

   Include-Transit Sub-TLV is an optional Sub-TLV for explicitly
   including a list of Cloud Availability Regions or Zones for
   reasons like:

  - Those regions have certain OAM and security functions for
     the improved visibility.
  - To comply with regulations, etc.

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    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Include-Transit| length        |Transit_Type   |I|Reserved     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Transit node ID                    |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 8 Include-Transit Sub-TLV

   Multiple Include-Transit Sub-TLVs can be incorporated into a
   single GENEVE header to denote multiple nodes or regions
   intended for inclusion when steering the packet through the
   Cloud Backbone. It's important to note that the multiple
   Include-Transit Sub-TLVs constitute a set of the nodes to be
   included; they are not an ordered list.

   Transit_type:

    TBD1: when Transit node ID is represented as a numeric
    number, such as a Cloud Availability Region or Zone numeric
    identifier that the Cloud Operator provides.

    TBD2: when Transit node ID is represented as a character
    string, such as a Cloud Availability Region or Zone name
    that the Cloud Operator provides.

    TBD3: when Transit node ID is represented as an IP address.

   I-bit:

    When set to 0: it indicates it needs best effort to steer
    through the transit node ID.

    When set to 1, it indicates that the Transit Node ID must be
    included through the Cloud Backbone. If the Transit Node ID
    cannot be traversed, an alert or alarm must be generated to
    the enterprise via an out-of-band channel. It is out of the
    scope of this document to specify those alerts or alarms.

 4.6. Exclude Transit Sub-TLV

   Exclude-Transit Sub-TLV is an optional Sub-TLV for explicitly
   excluding a list of Cloud Availability Regions or Zones for
   reasons like

  - To comply with regulations,

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  - To avoid regions that impose certain risks.

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Exclude-Transit| length        |Transit_Type   |E| Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Transit node ID                    |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 9 Exclude-Transit Sub-TLV

   Multiple Exclude-Transit Sub-TLVs can be incorporated into a
   single GENEVE header to denote multiple nodes or regions to
   be exclouded when steering the packet through the Cloud
   Backbone. It's important to note that the multiple Enclude-
   Transit Sub-TLVs constitute a set of the nodes to be
   excluded; they are not an ordered list.

   Transit_type: same as Section 4.6

   E-bit:

    When set to 0: it indicates it needs best effort to avoid
    the transit node ID.

    When set to 1, it indicates that the Transit Node ID must be
    avoided through the Cloud Backbone. If the Transit Node ID
    cannot be avoided, an alert or alarm must be generated to
    the enterprise via an out-of-band channel. It is out of the
    scope of this document to specify those alerts or alarms.

5. IPsec Flow through Cloud GWs Illustration
   This section illustrates Cloud GWs connecting traffic flow
   carried by the IPsec tunnels.

5.1. Single Hop Cloud GW

     Assuming that all CPEs are under one administrative control
     (e.g., iBGP).

     Using Figure 1 as an example:

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       - There is a bidirectional IPsec tunnel between CPE1 and
          Cloud GW; with IPsec SA1 for the traffic from the CPE1
          to the Cloud-GW; and IPsec SA2 for the traffic from
          the Cloud-GW to the CPE1.
       - There is a bidirectional IPsec tunnel between CPE2 and
          Cloud GW; with IPsec SA3 for the traffic from the CPE2
          to the Cloud-GW; and IPsec SA4 for the traffic from
          the Cloud-GW to the CPE2.
       - All the CPEs are under one iBGP administrative domain,
          with a Route Reflector (RR) as their controller. The
          CPEs notify their peers of their corresponding Cloud
          GW addresses (which is out of the scope of this
          document).

     When 11.1.1.x and 10.1.1.x need to communicate with each
     other, CPE1 and CPE2 establish a bidirectional IPsec
     Tunnel, with SA5 for the traffic from CPE1 to CPE2 and SA6
     for the traffic from CPE2 to CPE1. Assume the IPsec ESP
     Tunnel Mode is used. A packet from 11.1.1.1 to 10.1.1.2 has
     the following outer header:

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     Outer IP header:
         +---------------------------+
         |    protocol = 17(UDP)     |
         |    src = CPE1             |
         |    dst = Cloud GW         |
         +---------------------------+
         |  Source Port =xxxx        |
         |  Dst Port = 6081 (GENEVE) |
         +===========================+
         | GENEVE Header             |
         | multi-seg-SD-WAN Option   |
         |GENEVE Proto = 50 (ESP)    |
         +- - --  -- - - --      - --+
         |SD-WAN EndPt SubTLV (CPE2) |
         +---------------------------+  < ----------+
         |SPI(Security Parameter Idx)|        Authenticated
         +---------------------------+              |
         |    sequence number        |              |
         +---------------------------+   <-+        |
         | payload IP header:        |     |        |
         |  src =  11.1.1.1          |     |        |
         |  dst =  10.1.1.2          |     |        |
         +---------------------------+  Encrypted   |
         |   TCP header +            |     |        |
         ~    payload (variable)     ~     |        |
         |                           |     |        |
         +===========================+   <-+ -------+
         |   Authentication Data     |
         +---------------------------+

     Figure 8 Packet header illustration of traffic to Cloud GWs

5.2. Multi-hop Transit GWs

     Traffic to/from geographic apart CPEs can cross multiple
     Cloud DCs via Cloud backbone.

     The on-premises CPEs are under one administrative control
     (e.g., iBGP).

     Using Figure 2 as an example:

       - There is a bidirectional IPsec tunnel between CPE1 and
          the Cloud GW1; with IPsec SA1 for the traffic from the
          CPE1 to the Cloud-GW1; and IPsec SA2 for the traffic
          from the Cloud-GW1 to the CPE1.

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       - There is a bidirectional IPsec tunnel between CPE10
          and the Cloud GW2; with IPsec SA3 for the traffic from
          the CPE10 to the Cloud-GW2; and IPsec SA4 for the
          traffic from the Cloud-GW2 to the CPE10.
       - All the CPEs are under one iBGP administrative domain,
          with a Route Reflector (RR) as their controller. CPEs
          notify their peers of their corresponding Cloud GW
          addresses.

     When 11.1.1.x and 10.2.1.x need to communicate with each
     other, CPE1 and CPE10 establish a bidirectional IPsec
     Tunnel, with SA5 for the traffic from CPE1 to CPE10 and SA6
     for the traffic from CPE10 to CPE1. Assume the IPsec ESP
     Tunnel Mode is used, a packet from 11.1.1.1 to 10.2.1.2 has
     the following outer header:

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     Outer IP header:
         +---------------------------+
         |    proto = 17 (UDP)       |
         |    src = CPE1             |
         |    dst = Cloud GW1        |
         +===========================+
         | GENEVE Header             |
         | multi-seg-SD-WAN Option   |
         |GENEVE Proto = 50 (ESP)    |
         +- - --  -- - - --      - --+
         |SD-WAN EndPt SubTLV (CPE10)|
         +---------------------------+
         |   EgressGW-SubTLV         |
         +---------------------------+  < ----------+
         |SPI(Security Parameter Idx)|        Authenticated
         +---------------------------+              |
         |    sequence number        |              |
         +---------------------------+   <-+        |
         | payload IP header:        |     |        |
         |  src =  11.1.1.1          |     |        |
         |  dst =  10.2.1.2          |     |        |
         +---------------------------+  Encrypted   |
         |   TCP header +            |     |        |
         ~    payload (variable)     ~     |        |
         |                           |     |        |
         +===========================+   <-+ -------+
         |   Authentication Data     |
         +---------------------------+
      Figure 9 GENEVE header encapsulated IPsec packet

5.3. Data Authentication and Integrity Check by Cloud GW

     The IPsec SA already encrypts the client payload between
     the CPEs, the Cloud GW doesn't need to decrypt and re-
     encrypt the payload when relaying it to the destination
     CPE. However, data authentication and integrity check are
     needed as the traffic traverse an untrusted network.

     [RFC2403] and [RFC2404] define the authentication
     algorithms used in AH and ESP. SHA2 224/256/384/512 are
     some of the cryptographic hashing algorithms. They are part
     of a Hashed Message Authentication Code.

5.4. Packet Header Processing

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     In Figure 1, upon receiving a GENEVE encapsulated packet
     with the GENEVE Protocol Type = 50 (ESP), the Cloud GW does
     the following:

      - Authenticate the packet using a preconfigured
         authentication method.
      - Extract the destination CPE address from the SD-WAN
         Endpoint Sub-TLV inside the GENEVE header. Replace the
         outer IP destination address with the destination CPE
         address.
      - Optionally replace the outer IP source address with the
         Cloud GW address.
      - GENEVE header is unchanged.
      - Forward the packet to the destination CPE.

     The cloud GW SHOULD drop all packets with the source
     addresses or the values in the Sub-TLVs of the GENEVE
     header that are not recognized or registered to prevent
     unauthorized users from using the Cloud services.

5.5. Error Handling

   As traffic through Cloud Backbone takes precious resources,
   the Cloud GW SHOULD drop the packets with unregistered source
   or destination addresses.

   Cloud GW SHOULD drop the packets originated from unpaid (or
   unregistered) address (CPE).

   Cloud GW SHOULD validate the value of the SD-WAN Endpoint
   Sub-TLV and drop the packet if the value of the SD-WAN
   Endpoint Sub-TLV is an unpaid (or unregistered) address.

6. Illustration of Traffic from Private VPN to IPsec Tunnel

   This section illustrates a Cloud GW connecting client traffic
   from a branch CPE via a Private VPN to another CPE via an
   IPsec tunnel.

   Using Figure 1 as an example:

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       - CPE1 send traffic via a Private VPN (Direct Connect to
          the Cloud Edge) to the Cloud GW. The traffic is not
          encrypted.
       - There is a bidirectional IPsec tunnel between CPE2 and
          the Cloud GW; with IPsec SA1 for the traffic from the
          CPE2 to the Cloud-GW; and IPsec SA2 for the traffic
          from the Cloud-GW to the CPE2.
       - All the CPEs are under one iBGP administrative domain,
          with a Route Reflector (RR) as their controller. CPEs
          notify their peers of their corresponding Cloud GW
          addresses.

     Assume the IPsec ESP Tunnel Mode is used for the IPsec SA
     between Cloud GW and CPE2. For a packet from 11.1.1.1 to
     10.2.1.2, the following header is added by CPE1 sending
     over the Private VPN:

     Outer IP header:
         +---------------------------+
         |    proto = 17 (UDP)       |
         |    src = CPE1             |
         |    dst = Cloud GW        |
         +===========================+
         | GENEVE Header             |
         | multi-seg-SD-WAN Option   |
         |GENEVE Proto =TCP/UDP/etc. |
         +- - --  -- - - --      - --+
         |SD-WAN EndPt SubTLV (CPE2) |
         +---------------------------+  < -+
         | payload IP header:        |     |
         |  src =  11.1.1.1          |     |
         |  dst =  10.2.1.2          |     |
         +---------------------------+  Not Encrypted
         |   TCP header +            |     |
         ~    payload (variable)     ~     |
         |                           |     |
         +===========================+   <-+
    Figure 10 Illustration of packet through VPN

   Upon receiving the GENEVE encapsulated packet with the
   "Multi-Segment-SD-WAN" option, the Cloud GW extracts the
   destination CPE from the GENEVE header and encrypts the
   packet with the IPsec SA2 to forward to the destination
   (i.e., CPE2). The GENEVE Header is carried to the CPE2.

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      Outer IP header:
         +---------------------------+
         |    proto = 17 (UDP)       |
         |    src = Cloud GW         |
         |    dst = CPE2             |
         +===========================+
         | GENEVE Header             |
         | multi-seg-SD-WAN Option   |
         |GENEVE Proto =50 (ESP)     |
         +- - --  -- - - --      - --+
         |SD-WAN EndPt SubTLV (CPE2) |
         +---------------------------+  < ----------+
         |SPI(Security Parameter Idx)|        Authenticated
         +---------------------------+              |
         |    sequence number        |              |
         +---------------------------+   <-+        |
         | payload IP header:        |     |        |
         |  src =  11.1.1.1          |     |        |
         |  dst =  10.2.1.2          |     |        |
         +---------------------------+  Encrypted   |
         |   TCP header +            |     |        |
         ~    payload (variable)     ~     |        |
         |                           |     |        |
         +===========================+   <-+ -------+
         |   Authentication Data     |
         +---------------------------+
 Figure 11 Illustration of packet from the Egress Cloud GW

7. Control Plane considerations

7.1. Control Plane for CPEs

   The control plane enables SD-WAN edges to discover their
   properties and attached routes. The on-premises CPEs and
   their vCPEs (or Virtual Appliances in Cloud DC) can be
   controlled by one iBGP instance. [SD-WAN-Edge-Discovery]
   describes the mechanism for SD-WAN edges to discover each
   other's properties. The IPsec Key Exchange between on-
   premises CPEs and the vCPE is via the iBGP Update through RR.
   [SD-WAN-Edge-Discovery].

7.2. Control Plane between CPEs and Cloud GWs

   It is common to have eBGP sessions between enterprises CPEs
   and the Cloud GWs. An enterprise-owned vCPE can establish an
   eBGP session with the Cloud VPN GW for accessing the

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   workloads hosted in the Cloud DCs. If an IPsec tunnel is
   required between the Cloud DC GW and the vCPE, the full suite
   of IPSec IKEv2 must be exchanged between the vCPE and the
   Cloud GW.

8. Observability Consideration
   Observability considerations encompass monitoring, analysis,
   and reporting mechanisms to gain insights into the behavior
   and performance of the multi-segment SD-WAN infrastructure.
   Key observability aspects include:

   - Performance Metrics:
     Monitor and collect performance metrics related to link
     utilization, latency, and packet loss across the SD-WAN
     segments and Cloud DC backbone. This data provides insights
     into the overall health and efficiency of the network. IP
     Flow Information Export (IPFIX) [RFC7011] is one of the
     standardized methods to expose traffic flow over the
     network.

   - Global Network Topology Visualization:
     Utilize visualization tools to depict the global network
     topology, showcasing the interconnections and traffic flows
     between different SD-WAN segments and Cloud DCs.

   - Control Plane Monitoring:
     Monitor the control plane for both CPEs and the
     communication between CPEs and Cloud GWs. This includes
     tracking route discovery, path selection, and any changes
     in network state to ensure proper functioning of the SD-WAN
     control plane.

   - Security Event Logging:
     The security event logging is to capture and analyze
     security-related events, including threat detection,
     authentication failures, and any unauthorized access
     attempts. Syslog [RFC5424] is a valuable tool for security
     monitoring and auditing.

   These considerations contribute to the overall success of the
   multi-segment SD-WAN deployment connecting edge devices via a
   Cloud DC backbone.

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9. Security Considerations
9.1. Threat Analysis
   As shown in Figure 3, the information carried by the GENEVE
   Header is not encrypted, which is susceptible to Man-in-the-
   Middle (MitM) attacks. An attacker can intercept and
   potentially alter the information in the GENEVE header
   between the branch CPEs and the Cloud GWs without the
   enterprise and the Cloud provider's knowledge or consent.
   Here is the threat analysis of the MitM attacks between CPEs
   and Cloud GWs:

  a) Eavesdropping: Attackers can get knowledge of the
     enterprise's branch locations and their respective
     contracted Cloud GWs. As the payload between the CPEs is
     encrypted, attackers can't get any data exchanged between
     CPEs. This threat is no different from direct IPsec SAs
     between two CPEs.
  b) Data Manipulation: Attackers alter the content (Sub-TLVs)
     in the GENEVE header. As packets with unrecognized source
     addresses or invalid values in the Sub-TLVs of the GENEVE
     header are dropped by Cloud GWs, there might be a higher
     packet drop rate between the CPEs.
     Packet drop is not a new problem. The transport layer, such
     as TCP or QUIC, can handle packet drop well.

  c) Potential steeling of Cloud Backbone bandwidth:
     A threat actor might want to leverage Cloud Backbones to
     transport its own traffic between two locations without
     paying for the services. For example, a legitimate Cloud
     subscriber pays for the Cloud Backbone transport services
     for traffic between CPE-A and CPE-B. The attacker, who has
     two locations far apart (say Node-A and Node-B), can use
     CPE-A's address as the source address and CPE-B as the
     value in the SD-WAN Endpoint Sub-TLV for a packet from
     Node-A to Node-B before reaching the ingress Cloud GW. When
     the packet is sent from the egress Cloud GW via the
     Internet towards CPE-B, the actor can change the source
     address back to Node-A and the destination address to Node-
     B. By doing so, Node-A and Node-B can maintain the IPsec

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     tunnel via the Cloud Backbone without paying for the
     service.
     Therefore, it is necessary to have some level data
     integrity and authentication for traffic between CPEs and
     Cloud GWs even though it is not necessary for Cloud GWs to
     decrypt and re-encrypt the payload between CPEs.

9.2. HMAC-based Integrity and Authentication
   HMAC (Hash-based Message Authentication Code), a widely used
   cryptographic technique for ensuring both data integrity and
   authentication, can be used to ensure the integrity and
   authenticity of data between CPEs and Cloud GWs to verify
   that GENEVE header has not been tampered with.

   The basic idea behind HMAC is to combine a secret key and a
   hash function to produce a fixed-size authentication code for
   the GENEVE header between CPEs and the Cloud GW. This
   authentication code is then sent along with the data itself.
   When the Cloud GW and the destination CPEs receive the data
   and the authentication code, they can independently compute
   the HMAC using the same key and hash function. If the
   computed HMAC matches the received authentication code, it
   indicates that the data has not been altered, as long as the
   secret key remains confidential.

   The HMAC authentication code can be carried by an HMAC Sub-
   TLV in the GENEVE Header, as specified below:

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |MultiSDWAN-HMAC| length        |   reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   |    HMAC Authentication Code for entire GENEVE Header          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 12 Multi Segment SD-WAN HMAC Sub-TLV

   The HMAC Authentication Code, a.k.a. the HMAC hash value, is
   computed including all the bytes in the GENEVE header and with the
   MultiSDWAN-HMAC value field setting to 0.

   The advantages of using HMAC are:
     - Data Integrity: HMAC provides a strong mechanism for
        verifying the integrity of data. By hashing the message

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        and using a secret key, it generates a fixed-size hash
        value that ensures the data has not been tampered with
        during transmission.
     - Authentication: HMAC also verifies the authenticity of
        the sender. Since HMAC requires a shared secret key
        between the sender and receiver, it confirms that the
        sender is who they claim to be.
     - Efficiency: HMAC is computationally efficient, making it
        suitable for real-time and resource-constrained devices.
        It uses simple bitwise operations and hash functions.
     - Resistance to Tampering: HMAC is designed to resist
        various forms of tampering, including replay attacks,
        message insertion, and message deletion. Any change in
        the message will result in a different HMAC value.
     - Flexibility: HMAC can be used with various hash
        functions, such as SHA-256 or SHA-512, depending on the
        desired level of security requirements.
     - Widely Supported: HMAC is a well-established and widely
        supported authentication mechanism, making it easy to
        integrate into different systems.

   Here are some common problems associated with using the HMAC
   and why their risks are acceptable in the scenario described
   in this draft.
   - Key Management: The security of HMAC depends heavily on the
     confidentiality and management of the shared secret key. If
     the key is compromised, the data packets from CPEs to Cloud
     GW can be dropped but not compromised because the user
     payloads are protected by IPsec SA encryption.
   - Lack of Non-Repudiation: HMAC provides data integrity and
     sender authentication but does not provide non-repudiation.
     Non-repudiation is the ability to prove that a message was
     sent by a specific sender, which HMAC alone cannot
     guarantee. This risk is same as two IPsec protected traffic
     between CPEs.
   - Limited to Symmetric Cryptography: HMAC relies on symmetric
     key cryptography, which means that both parties must share
     the same secret key. As the Cloud backbone interconnecting
     CPEs are paid services, there are established channels to
     distribute the symmetric key.

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   - No Protection Against Eavesdropping: While HMAC ensures
     data integrity and sender authentication, it does not
     provide encryption. Eavesdropping does pose additional
     risks to payloads encrypted by IPsec SA.

   In summary, HMAC-based integrity and authentication offer
   strong security benefits in terms of data integrity and
   sender authentication. Even though it does not provide non-
   repudiation or protection against eavesdropping, the IPsec
   encrypted payload between CPEs won't be impacted.

9.3. AH based Integrity and Authentication
   For enterprises or Cloud providers worrying about secret HMAC
   keys being compromised, they can add another layer of AH
   encryption [RFC4301] or ESP-NULL [RFC2410] [RFC6071] on top
   of the IPsec encryption between the two CPEs. Both AH and
   ESP-NULL IPsec encryption require pairwise IPsec key
   management between Cloud GWs and the CPEs, therefore
   requiring more processing on Cloud GWs and CPEs. In addition,
   the AH encrypted packets can't traverse NAT because of outer
   IP address changes.

10. Manageability Considerations

   The following manageability considerations are crucial for
   the successful deployment and ongoing operation of the
   proposed strategies outlined in this document:

   - Centralized Orchestration:
        A centralized orchestration system is needed to manage
        and authenticate multiple SD-WAN segments through the
        Cloud GWs.

   - Policy-based Configuration:
        Utilize policy-driven configurations to streamline the
        deployment of SD-WAN segments and their connectivity
        options. This approach allows for efficient management
        of network policies, ensuring consistent and coherent
        behavior across diverse deployment scenarios. [RFC8192]
        can be used to automate the security policy
        configurations.

   - Real-time Monitoring and Analytics:

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        Integrate robust monitoring and analytics tools to
        provide real-time visibility into the performance and
        health of SD-WAN segments. This includes monitoring
        bandwidth utilization, latency, packet loss, and other
        key performance indicators to promptly identify and
        address any issues.

   - Automated Alerting and Reporting:
        Implement automated alerting mechanisms to promptly
        notify network administrators of potential issues or
        anomalies within the SD-WAN infrastructure.
        Additionally, generate regular reports to facilitate
        performance analysis, capacity planning, and compliance
        monitoring.

11. IANA Considerations

   IANA is requested to assign a new GENEVE Option Class from
   the IETF Review range as shown below:

     Option
      Class     Description       Assignee/Contact  Reference
      ------  -------------------  ------------- -----------
      TBD     Multi Segment SD-WAN    IETF      [this document]

   IANA is requested to assign the following types inside the
   Multi Segment SD-WAN Option Class:

    Multi-seg-
   SDWAN_Types   Description    Assignee/Contact  Reference
      ------    --------------  ------------- -----------
     Val-1     Single Hop Transit    IETF      [Section 4.1]
     Val-2     MultiHopTransit       IETF      [Section 4.1]
     Val-3     MultiHop wo egress    IETF      [Section 4.1]

   IANA is requested to create a registry as below with the
   initial values shown in the Multi Segment SD-WAN Geneve
   Option Class registry group:

      Registry:  Multi Segment SD-WAN Sub-TLVs
      Assignment Policy:  IETF Review
      Reference:  [this document]

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      Sub-TLV Type       Description             Reference
      ------------  ----------------------    ---------------
             0      Reserved
             1      SD-WAN Endpoint           [Section 4.2]
             2      SD-WAN Originator         [Section 4.3]
             3      SD-WAN Egress GW          [Section 4.4]
             4      Include Transit           [Section 4.5]
             5      Exclude Transit           [Section 4.6]
             6      Multi SD-WAN-HMAC         [Section 9.2]
         5-254      Unassigned
           255      Reserved

12. References

12.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2403] C. Madson, R. Glenn, "The Use of HMAC-MD5-96 within
             ESP and AH", RFC2403, Nov. 1998.

   [RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96
             within ESP and AH", RFC2404, Nov. 1998.

   [RFC4301] S. Kent and K. Seo, "Security Architecture for the
             Internet Protocol", RFC4301, Dec. 2005.

   [RFC4303] S. Kent, "IP Encapsulating Security Payload (ESP)".
             RFC4303, Dec. 2005.

   [RFC5424] R. Gerhards, "The Syslog Protocol", RFC5424, March
             2009.

   [RFC7011] B. Claise, B. Trammell, and P. Aitken,
             "Specification of the IP Flow Information Export
             (IPFIX) Protocol for the Exchange of Flow
             Information", RFC7011, Sept 2013.

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   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
             RFC   2119 Key Words", BCP 14, RFC 8174, DOI
             10.17487/RFC8174, May 2017, <https://www.rfc-
             editor.org/info/rfc8174>.

   [RFC8926] J. Gross, et al, "Geneve: Generic Network
             Virtualization Encapsulation", RFC8926, Nov 2020.

12.2. Informative References

   [RFC2410] R. Glenn and S. Kent, "The NULL encryption
             Algorithm and Its Use with IPsec", RFC2310, Nov.
             1998.

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

   [RFC8192] S. Hares, et al, "Interface to Network Security
             Functions (I2NSF) Problem Statement and Use Cases",
             July 2017

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

   [Net2Cloud] L. Dunbar and A. Malis, "Dynamic Networks to
             Hybrid Cloud DCs Problem Statement", draft-ietf-
             rtgwg-net2cloud-problem-statement-39, April, 2024.

   [SD-WAN-Edge-Discovery] L. Dunbar, et al, "BGP UPDATE for SD-
             WAN Edge Discovery", draft-ietf-idr-sdwan-edge-
             discovery-12, Oct. 2023.

13. Acknowledgments

   Acknowledgements to Adrian Farrel, Donald Eastlake, Stephen
   Farrell for their extensive review and suggestions.

   This document was prepared using 2-Word-v2.0.template.dot.

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Authors' Addresses

   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com

   Kausik Majumdar
   Microsoft
   Email: kmajumdar@microsoft.com

   Venkit Kasiviswanathan
   Arista
   Email: venkit@arista.com

   Ashok Ramchandra
   Microsoft
   Email: aramchandra@microsoft.com

   Aseem Choudhary
   Aviatrix
   Email: achoudhary@aviatrix.com

Contributors' Addresses

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