Network Working Group                                 K. Majumdar
Internet Draft                                             Oracle
Intended status: Standard Track                        L. Dunbar
Expires: February 15, 2026                            Futurewei
                                                V.Kasiviswanathan
                                                           Arista
                                                    A. Ramchandra
                                                         Google
                                                   A. Choudhary
                                                      Aviatrix
                                                  August 18, 2025


                 Multi-segment SD-WAN via Cloud DCs
               draft-ietf-rtgwg-multisegment-sdwan-07

Abstract
   This document describes a method for seamlessly
   interconnecting geographically separated SD-WAN segments via
   a Cloud Backbone without requiring Cloud Gateways (GWs) to
   decrypt and re-encrypt traffic. By encapsulating IPsec-
   encrypted payloads within GENEVE headers (RFC 8926), the
   approach enables Cloud GWs to forward encrypted traffic
   directly between distant Customer Premises Equipment (CPEs).
   This reduces processing overhead, improves scalability, and
   preserves the confidentiality of enterprise data while
   ensuring secure and efficient multi-segment SD-WAN.
   connectivity.

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
   Engineering Task Force (IETF), its areas, and its working
   groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.









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   Internet-Drafts are draft documents valid for a maximum of
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   This Internet-Draft will expire on Dec 15, 2020.

Copyright Notice

   Copyright (c) 2025 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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   extracted from this document must include Simplified BSD
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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.................................................5
      3.1. Multi-segment SD-WAN via a Single Cloud GW...........5
      3.2. Multi-segment SD-WAN via Cloud Backbone..............7
      3.3. Traffic Steering Challenges in Multi-Segment SD-WAN..8
   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......................11
      4.3. SD-WAN Tunnel Originator Sub-TLV....................12


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      4.4. Egress GW Sub-TLV...................................13
      4.5. Restricted Regions Sub-TLV..........................14
      4.6. Exclude Transit Sub-TLV.............................15
   5. Packet Header Processing.................................17
   6. Error Handling...........................................18
   7. Control Plane considerations.............................19
      7.1. Control Plane for CPEs..............................19
      7.2. Control Plane between CPEs and Cloud GWs............19
   8. Observability Consideration..............................20
   9. Security Considerations..................................21
      9.1. Threat Analysis.....................................21
      9.2. HMAC-based Integrity and Authentication.............21
      9.3. AH based Integrity and Authentication...............23
   10. Manageability Considerations............................23
   11. IANA Considerations.....................................24
   12. References..............................................25
      12.1. Normative References...............................25
      12.2. Informative References.............................26
   13. Acknowledgments.........................................27
   Appendix A: Illustration of Packets through Cloud GWs.......27
   A.1 Single Hop Cloud GW.....................................27
   A.2 Multi-hop Transit GWs...................................29
   Appendix B: Illustration from Private VPN to IPsec Tunnel...30

1. Introduction

   Enterprises are increasingly turning to SD-WAN to connect on-
   premises CPEs with cloud services, as discussed in detail in
   [Net2Cloud]. Each SD-WAN segment typically connects a CPE to
   its nearest Cloud Gateway (GW). Some of this traffic
   terminates at the cloud services and must be decrypted by the
   Cloud GW. Other traffic is destined for remote CPEs located
   in different geographic regions and only require forwarding
   across a Cloud Backbone, without decryption.

   Multi-segment SD-WAN refers to the architecture in which two
   or more SD-WAN segments are interconnected via a Cloud
   Backbone. This model enables traffic that originates in one
   SD-WAN segment to reach a distant CPE through transit Cloud
   GWs without decryption. It supports hybrid traffic handling:
   local cloud-bound traffic is decrypted by the Cloud GW, while
   CPE-to-CPE traffic is forwarded securely across the backbone.




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   Interconnecting these SD-WAN segments via a Cloud Backbone
   provides several key benefits:

  a) Seamless connectivity - Enterprises can integrate
     geographically dispersed SD-WAN segments into a unified
     network without complex manual configurations.
  b) Scalability - The Cloud Backbone's elasticity accommodates
     increased traffic demands without requiring extensive on-
     premises infrastructure.
  c) Simplified operations - Centralized orchestration
     streamlines policy enforcement and network management
     across all segments.

  The challenges and motivations for this architecture are
  further detailed in [Net2Cloud], which outlines issues
  enterprises face when interconnecting branch sites with
  dynamic workloads in third-party Cloud DCs, particularly when
  leveraging existing VPN infrastructure.

  A key requirement in Cloud Backbone stitching SD-WAN segments
  is the ability to forward encrypted traffic across the Cloud
  Backbone without requiring decryption at Cloud GWs. Since
  IPsec Security Associations (SAs) are established end-to-end
  between CPEs, Cloud GWs cannot access the payload for routing.
  Introducing an additional IPsec tunnel layer between CPE and
  Cloud GW just for routing purposes is inefficient-it adds
  processing overhead, increases latency due to decryption and
  re-encryption, and imposes scalability limits due to cloud
  provider restrictions on IPsec capacity per GW instance.

  This document defines a GENEVE-based method that avoids these
  inefficiencies. SD-WAN CPEs encapsulate IPsec-encrypted
  packets with GENEVE headers [RFC8926] that include Sub-TLVs to
  signal when traffic should transit the Cloud Backbone without
  decryption. This enables Cloud GWs to forward encrypted
  traffic efficiently to remote CPEs, without accessing the
  payload. The result is secure, low-latency, and scalable
  interconnection of geographically distributed SD-WAN segments
  using the Cloud Backbone.





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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.

   SA          IPsec Security Association

   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.


3. Use Cases

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

   Enterprise branches with established SD-WAN paths to a Cloud
   GW for accessing cloud services can also use the Cloud GW to
   interconnect with one another, as shown in Figure 1.


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   Stitching SD-WAN segments through a Cloud Gateway provides a
   way to extend policy enforcement and traffic control across
   branches, particularly when direct branch-to-branch paths
   over the public internet are insufficient. This approach is
   beneficial for several reasons:

  - The public internet between branches may suffer from
     limited bandwidth, unpredictable performance, and security
     risks.
  - Centralized enforcement of enterprise security policies is
     possible through cloud-hosted security services (e.g.,
     firewalls, DDoS protection), ensuring consistent treatment
     of traffic across sites.
  - Cloud platforms often offer enhanced monitoring,
     proprietary threat detection tools, and analytics services
     that can inspect and respond to suspicious traffic crossing
     segments.






























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                          (^^^^^^^^^^^^)
                        (     Cloud     )
                        ( +----+  +----+  )
                 + -----(-|Edge|  + GW |  )
         Direct  |      ( +----+  +/--\+  )
        Connect  |        (^^^^^^^/^^^^\^)
               {-+---}           /      \  SD-WAN Path CPE<->GW
               { VPN }          /        \
               {-+---}         /          IPsec Tunnel
                 +-------+----/------+    \
                         |   /       |     \
                        ++--/+       |    +-\--+
                        |CPE1|       +----+CPE2|
                        +----+            +----+
       Client Route: 192.0.2.0/26       192.0.2.64/26
                     198.51.100.0/26    198.51.100.64/26

   Figure 1 Multi-Segment SD-WAN stitching via a Cloud GW


3.2. Multi-segment SD-WAN via Cloud Backbone

   For geographically distant enterprise branches that have
   established SD-WAN paths to their respective Cloud GWs for
   accessing cloud services, the Cloud Backbone provides an
   efficient way to interconnect these branches, as shown in
   Figure 2. As outlined in the Introduction section, this
   approach enhances network integration, supports dynamic
   scaling, and simplifies overall management, making it well-
   suited for multi-segment SD-WAN deployments across different
   regions.













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                    (^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^)
                    (             Cloud Backbone            )
                   (+-----+  +----+                  +-----+)
              + ---(|CEdge|==| GW1==================== GW2 |)
      Direct  |    (+-----+  +/--\+                  +--|--+)
     Connect  |    (^^^^^^^^/^^^^\^^^^^^^^^^^^^^^^^^^^^|^^^^)
            {-+---}        /      \                    |
            { VPN }       /        \                 +-----+
            {-+---}      /          IPsec Tunnel     |CPE10|
              +-------+-/--------+   \               +-----+
                      |/         |    \       192.0.2.128/25
                     ++---+      |  +--\-+ 198.51.100.128/25
                     |CPE1|      +--+CPE2|
                     +----+         +----+
       Client Route: 192.0.2.0/26      192.0.2.64/26
                     198.51.100.0/26   198.51.100.64/26


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



3.3. Traffic Steering Challenges in Multi-Segment SD-WAN

   Many well-established traffic engineering methods, such as
   SRv6 and MPLS-TE, effectively steer traffic through specific
   network nodes when the entire network operates under a single
   administrative domain.

   However, in typical SD-WAN deployments, CPE-to-CPE traffic is
   carried as best-effort over the public Internet or other
   shared transport. Forwarding in the underlay is destination-
   based, and the on-premises CPEs cannot directly control the
   specific path that packets take. This limits the ability to
   enforce precise traffic engineering (TE) to reach destination
   CPEs.

   This lack of predictable routing makes traffic steering
   between branch offices highly challenging. Unlike private
   MPLS networks or provider-controlled backbones, SD-WAN cannot
   inherently dictate the intermediate paths for branch-to-
   branch traffic. As a result, policies intended to optimize
   performance, enforce security, or ensure compliance can be
   difficult to implement.


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   To address this issue, this document describes a method where
   Cloud GWs explicitly interconnect SD-WAN segments, ensuring
   that branch-to-branch traffic is steered through the Cloud
   Backbone rather than taking unpredictable internet routes.
   This approach provides greater control over traffic flows,
   improving reliability, security, and policy enforcement.

4. Data Plane encoding for SD-WAN Transit

   To enable Cloud GWs to distinguish between packets requiring
   decryption for internal cloud services and transit packets
   that should be forwarded to destination CPEs, proper packet
   marking is essential. Many encapsulation methods, such as
   VLAN tags, IP-in-IP, GRE, etc., can be used to steer traffic
   from a CPE to its nearest Cloud GW. However, GENEVE
   encapsulation [RFC8926] offers significant advantages,
   including flexible option Sub-TLVs that can signal routing
   and policy preferences, such as Restricted Regions, Exclude
   Regions, preferred egress Cloud GWs, and other service
   specific requirements. In addition, GENEVE Encapsulation
   [RFC8926] is widely supported by major Cloud Service
   Providers, which allows Cloud GWs to efficiently steer IPsec-
   encrypted packets between CPEs via Cloud Backbone without
   decryption, reducing processing overhead and improving
   performance while maintaining end-to-end encryption.

4.1. Multi-Segment SD-WAN Option Class

   Geneve header format is specified in Section 3 of [RFC8926].
   This document uses the GENEVE Option Class value 0x0163,
   which has been assigned by IANA to identify Multi-Segment SD-
   WAN-specific Sub-TLVs encoded within the GENEVE header. This
   enables Cloud GWs to interpret and process SD-WAN transit
   packets efficiently without requiring decryption.











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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 3 Multi Segment SD-WAN Option Class

  - Multi-seg-SD-WAN Option Class: value 0x0163 (assigned by
     IANA).
  - C-bit: Must be set to ensure that a receiving node drops
     the packet if it does not recognize the option, as per
     [RFC8926].
  - Type (8 bits): Specifies the multi-segment SD-WAN
     forwarding model:
     Type = 1: Single-hop transit SD-WAN

     Type = 2: Multi-Hop transit SD-WAN with an explicitly
     specified egress Cloud GW (via Sub-TLV).

     Type = 3: Multi-hop transit SD-WAN without an explicitly
     specified egress Cloud GW.

  - Length (5 bits): Indicates the total length of the option
     fields in 4-byte units. If no options are present, this
     field is zero [RFC8926].
   Note: the payload following the multi-seg-SD-WAN Option Class
   can be IPv4 or IPv6. The Protocol Type of the GENEVE header



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   is set to 50, indicating the GENEVE payload carries IPsec ESP
   [RFC8926][IPsecOverGENEVE].

4.2. SD-WAN Tunnel Endpoint Sub-TLV

   The SD-WAN Endpoint sub-TLV indicates the destination CPE,
   which is the endpoint of the IPsec Tunnel between branch
   CPEs. This Sub-TLV is used by the Cloud Backbone to determine
   the optimal egress Cloud GW for forwarding the encrypted
   traffic.

   For example, in an SD-WAN deployment where CPE1 establishes
   an IPsec SA with CPE2 (as shown in Figure 1), this Sub-TLV
   within the GENEVE header contains CPE2's IP address, ensuring
   that encrypted traffic is correctly routed to the terminating
   CPE of the IPsec tunnel while enabling the Cloud Backbone to
   steer the packet to the most suitable egress Cloud GW.

    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 4 SD-WAN Endpoint Sub-TLV


     - SD-WAN Endpoint (8 bits): Identifies the SD-WAN Tunnel
        Endpoint Sub-TLV with a Type value of 1.

     - Length (8 bits): Specifies the total length of the value
        field in 4-byte units.













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     - TTL (Time to Live): This field is set by the originating
        CPE to indicate the maximum number of logical transit
        nodes or regions, those that are visible to the CPEs,
        that a packet is permitted to traverse across the Cloud
        Backbone. Only transit nodes or regions that are
        externally visible (i.e., known to or tracked by the
        CPEs) MUST decrement the TTL by one. Internal cloud
        forwarding elements that are opaque to the CPEs MUST NOT
        modify the TTL. If the TTL reaches zero, the packet MUST
        be dropped, and an alert MAY be generated. This
        mechanism allows enterprises to constrain the path scope
        of their packets, enforce traversal policies, and detect
        anomalies (e.g., excessive transit hops).


4.3. SD-WAN Tunnel Originator Sub-TLV

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

   For example, in an SD-WAN deployment where CPE1 establishes
   an IPsec SA with CPE2 (as shown in Figure 1), this Sub-TLV
   within the GENEVE header carries CPE1's address, allowing
   transit nodes and Cloud GWs to recognize the source of the
   encrypted traffic.

    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 5 SD-WAN Tunnel Originator Sub-TLV


     - SDWAN Origin (8 bits): Identifies the SDWAN Tunnel
        Originator Sub-TLV with a Type value of 2.





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     - Length (8 bits): Specifies the total length of the value
        field in 4-byte units, excluding the first 4 bytes,
        which include the SD-WAN Origin (1 byte), Length (1
        byte), and Reserved (2 bytes) fields.
     - Reserved (16 bits): Reserved for future. Must set to 0.
        Ignored by recipients.

   This Sub-TLV allows Cloud GWs and transit nodes to identify
   the packet's source, allowing them to apply source specific
   policies for forwarding. These policies may include traffic
   engineering rules specific to the originating CPE, security
   enforcement tailored to the source, or path selection
   constraints based on the origin.

4.4. Egress GW Sub-TLV

   In a multi-segment SD-WAN deployment over the Cloud Backbone,
   the originating CPE can use the Egress GW Sub-TLV to
   explicitly specify the egress Cloud GW responsible for
   forwarding traffic to the destination CPE. This ensures
   predictable routing behavior and enables policy-driven packet
   delivery across the Cloud Backbone.

    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 6 SD-WAN Egress GW Sub-TLV


     - SDWAN EgressGW (8 bits): Identifies the Egress GW Sub-
        TLV with a Type value of 3.
     - Length (8 bits): Specifies the total length of the value
        field in 4-byte units, excluding the first 4 bytes,
        which include the SD-WAN Origin Sub-TLV Type (1 byte),
        Length (1 byte), and Reserved (2 bytes) fields.
     - Reserved (16 bits): Reserved for future. Must set to 0.
        Ignored by recipients.



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   The Egress GW Sub-TLV allows the originating CPE to specify
   the Egress Cloud GW responsible for forwarding traffic to the
   destination CPE. This Egress GW address can be either
   preconfigured or dynamically discovered through a control
   plane protocol exchange with the destination CPE. By
   explicitly defining the egress GW, this Sub-TLV ensures
   predictable traffic steering, reducing reliance on
   destination-based routing and optimizing packet delivery
   across the Cloud Backbone. The details of the control plane
   protocol used for GW discovery are beyond the scope of this
   document.


 4.5. Restricted Regions Sub-TLV

   Some enterprises may require that traffic across the Cloud
   Backbone is strictly confined to a specific set of regions.
   This Sub-TLV allows the ingress SD-WAN CPE to express such
   restrictions as part of the encapsulation metadata.

   Traffic MUST be discarded if the Ingress Gateway, the Egress
   Gateway, or any transit node belongs to a region not listed
   in this Sub-TLV.

   This restriction is commonly used to enforce regulatory,
   security, or latency-based geographic constraints, where data
   must remain confined to specified regions.

   Format of the Restricted Regions Sub-TLV:

       0                   1                   2                   3
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Type (=4)   |    Length     |        Reserved (16 bits)     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Region Len   |  UTF-8 encoding of Region Name or ID          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Region Len   |  UTF-8 encoding of Region Name or ID          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             ...                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     - Type(8 bits): Assigned value identifying the Restricted
        Regions Sub-TLV. Suggested value: 4.




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     - Length (8 bits): Total length of the Value field
        (everything after the Type and Length fields), in
        octets.
     - Reserved (16 bits): Reserved for future use. MUST be set
        to zero and ignored on receipt.
     - Region Len (8 bits per region entry): Length of the UTF-
        8 encoding of the Region Name or identifier, in octets.
     - UTF-8 encoding of the Region Name (e.g., "us-west", "eu-
        central") or numeric identifier.

   Multiple regions MAY be present, each starting with its own Region
   Len field.

   Processing notes:
     - Receiving Cloud Gateway MUST check whether it and all
        intermediate transit regions are included in the listed
        regions.
     - If any component of the path falls outside the listed
        regions, the packet MUST be discarded.
     - Region interpretation is based on prior agreement
        between the enterprise and the Cloud Backbone provider
        (e.g., standard region names, operator-specific
        definitions, or standardized Region IDs).


   Note:
    It is beyond the scope of this document to specify how the
    Cloud Backbone enforces this restriction. Mechanisms for
    identifying region boundaries, enforcing region-based
    constraints, and generating alerts or alarm notifications
    when traffic violates region restrictions are subject to
    implementation decisions and based on prior agreement
    between the Cloud Backbone provider and the enterprise.


 4.6. Exclude Transit Sub-TLV

   Exclude Transit Sub-TLV is an optional field used to specify
   a list of Cloud Availability Regions, Zones, or Notes that
   must be avoided when forwarding packets across the Cloud
   Backbone. This can be used for:





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  - Regulatory compliance, ensuring traffic does not traverse
     restricted or non-compliant regions.
  - Risk mitigation, preventing traffic from passing through
     regions with known security, performance, or geopolitical
     concerns.
   Multiple region entries MAY be specified in a single Sub-TLV.
   Each region is identified by a variable length UTF-8 encoded
   name or numeric ID, preceded by a length field. This Sub-TLV
   expresses explicit exclusions and supports both soft and hard
   enforcement.
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type (=5)    | length        |E|      Reserved               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Region Len   |     UTF-8 encoding of Region Name or ID       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Region Len   |     UTF-8 encoding of Region Name  or ID      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             ...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Figure 8 Exclude Transit Sub-TLV

     - Type (8 bits): identifies the Exclude Transit Sub-TLV
        with a value of 5.
     - Length (8 bits): Total length of the Value field in
        octets (everything after the first 2 bytes).
     - E-bit (1 bit) - Exclusion severity indicator:
          o 0: Soft exclusion - the listed region is
             undesirable; avoid when feasible.
          o 1: Hard exclusion - the region MUST be avoided; if
             unavoidable, generate an alert or alarm.
     - Reserved (15 bits): MUST be set to zero on transmission
        and ignored on receipt.
     - Region Len (8 bits per region entry): Length of the UTF-
        8 encoding of the Region Name or identifier, in octets.
     - UTF-8 encoding of the Region Name (e.g., "us-west", "eu-
        central") or numeric identifier.
   Multiple region entries MAY be listed, each beginning with a
   Region Len byte.
   Processing Notes:


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     The E-bit determines how strictly the exclusions are
     enforced. A value of 1 (hard exclusion) mandates the Cloud
     Backbone to drop the packet or raise an alert if the
     excluded region is traversed. A value of 0 allows best-
     effort avoidance without enforcement or notification. The
     meaning and granularity of region identifiers MUST be
     agreed upon between the enterprise and the Cloud Backbone
     provider (e.g., standardized names, or operator-defined
     zones). It is beyond the scope of this document to define
     how enforcement or alerting is implemented. These are
     subject to operator policies and implementation specifics.

5. Packet Header Processing

   The procedures described in this section apply only to
   packets that carry the SD-WAN Option Class in the GENEVE
   header. Packets without this option are processed using
   default forwarding behavior.

   As illustrated in Figure 1, when Cloud GW receives a GENEVE-
   encapsulated packet with Protocol Type = 50 (ESP), it
   processes the packet as follows:

   Processing at the Ingress Cloud GW

      - Authenticate the packet using a preconfigured
         authentication method.
      - Check if the Egress GW Sub-TLV is present:
           o If the Egress GW Sub-TLV exists, the Cloud Backbone
             uses it to identify the egress Cloud GW.
           o If the Egress GW Sub-TLV is not present, the Cloud
             Backbone determines the optimal egress Cloud GW
             based on the destination CPE address.
      - Change the destination address in the outer IP header
         of the GENEVE packet to the address determined by the
         Cloud Backbone. This address is intended to reach the
         egress Cloud GW identified by the Egress GW Sub-TLV (if
         present), or the optimal egress GW selected based on
         the destination CPE address.
      - Forward the packet to the egress Cloud GW.



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     To prevent unauthorized access, Cloud GW SHOULD drop any
     packets containing unrecognized source addresses or invalid
     values in the GENEVE Sub-TLVs, ensuring that only
     registered entities can utilize Cloud services.

   Processing at the Egress Cloud GW:

      - Decapsulate the GENEVE header to extract the IPsec-
         encrypted payload.
      - Validate that the SD-WAN Tunnel Endpoint Sub-TLV
         corresponds to a registered destination CPE.
      - Ensure the source Cloud GW is an authorized forwarding
         node to prevent unauthorized traffic injection.
      - Forward the IPsec-encrypted payload to the destination
         CPE, preserving the end-to-end encryption.
      - Drop any packet that lacks a valid destination CPE or
         originates from an untrusted source.

   By enforcing these processing steps at both the ingress and
   egress Cloud GWs, the system ensures secure, efficient, and
   policy-compliant forwarding of SD-WAN traffic across the
   Cloud Backbone.



6. Error Handling

   To ensure secure and efficient traffic forwarding through the
   Cloud Backbone, Cloud GW SHOULD enforce the following error
   handling measures:

      - Drop packets with unregistered or invalid
         source/destination addresses to prevent unauthorized
         access.
      - Reject packets originating from unpaid or unregistered
         CPEs to enforce service subscription policies.
      - Validate the SD-WAN Endpoint Sub-TLV and drop packets
         if the destination CPE is unauthorized, unreachable, or
         mismatched.





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      - Discard malformed packets with incorrect GENEVE
         headers, invalid Sub-TLV formats, or authentication
         failures.
      - Drop packets with expired TTL values to prevent routing
         loops and log repeated occurrences.
      - Reject misrouted packets if the Cloud Backbone cannot
         determine an optimal egress Cloud GW or if the
         specified egress GW is unreachable.
      - Enforce rate limits on excessive traffic from a single
         source to prevent congestion and abuse.
      - Verify compliance with transit node policies (e.g.,
         ensuring mandatory transit nodes are included and
         excluded nodes are avoided).
      - Mitigate replay attacks by tracking sequence numbers
         and rejecting duplicate packets.

   By implementing these error handling mechanisms, Cloud GWs
   ensure network stability, security, and efficient resource
   utilization while preventing misconfigurations, abuse, and
   performance degradation.

7. Control Plane considerations

7.1. Control Plane for CPEs

   The control plane enables SD-WAN CPEs to discover their
   network attributes, establish connectivity, and exchange
   routing information. In an SD-WAN deployment, on-premises
   CPEs and virtual CPEs (vCPEs) in Cloud DCs may be managed
   under a common iBGP administrative domain, facilitating route
   propagation and policy enforcement.

   Mechanisms such as BGP-based SD-WAN Edge Discovery [SD-WAN-
   Edge-Discovery] allow CPEs to dynamically discover each
   other's properties, improving automation and reducing manual
   configurations. Additionally, IPsec SAs parameters between
   CPEs and Cloud GWs can be exchanged through the iBGP control
   plane using a RR to simplify security policy management.

7.2. Control Plane between CPEs and Cloud GWs

   There are typically eBGP sessions between a CPE and a Cloud
   GW for exchanging routing information related to services
   that terminate within the cloud. This allows the CPE to learn


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   routes to cloud-hosted resources and enables the Cloud GW to
   learn routes to the CPE's on-premises networks. This control-
   plane relationship is separate from the CPE-to-CPE encrypted
   traffic that transits the Cloud Backbone, which remains end-
   to-end encrypted and is not decrypted at the Cloud GWs.

   When the connection between a CPE and a Cloud GW traverses a
   public or otherwise untrusted network, an IPsec tunnel may
   also be established to secure that traffic. In such cases,
   IKEv2 is used to exchange the necessary IPsec security
   parameters.

   Control plane mechanisms must ensure that Cloud GWs can
   identify and authenticate SD-WAN CPEs, validate SD-WAN
   metadata, and apply appropriate routing policies based on
   dynamic network conditions. This ensures that route exchanges
   are trustworthy, policy-compliant, and adaptive to changing
   operational requirements.

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.



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   - 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.

9. Security Considerations
9.1. Threat Analysis

   The GENEVE header used for steering is not encrypted, making
   it susceptible to man-in-the-middle (MitM) attacks between
   CPEs and Cloud GWs.

   Key risks include:

  a) Eavesdropping: Attackers can learn branch and Cloud GW
     locations, though payload remains protected by IPsec.
  b)         Header Manipulation: Altered Sub-TLVs may cause misrouting
     or packet drops.
  c) Bandwidth Theft: A malicious or misconfigured CPE could
     spoof SD-WAN metadata to use Cloud Backbone resources
     without authorization.
   Mitigation requires authenticating and validating SD-WAN
   metadata to ensure it originates from authorized 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 the GENEVE header between SD-WAN CPEs and
   Cloud GWs, protecting it from tampering. HMAC combines a
   shared secret key with a hash function to produce a fixed-
   size authentication value, which is appended to the packet.
   The receiver computes the HMAC over the received header and
   compares it with the transmitted value; a match confirms that
   the header has not been altered, provided the key remains
   secret.


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   This mechanism is scoped to communication between SD-WAN CPEs
   and Cloud GWs, with the shared key provisioned through a
   secure channel. Key management procedures and HMAC key
   generation for this purpose are discussed in more detail in
   [I-D.dunbar-ipsecme-lightweight-authenticate].

   To reduce packet overhead, truncated HMAC values of 4 or 8
   bytes are RECOMMENDED instead of full-length outputs (e.g.,
   32 bytes for HMAC-SHA-256). This is acceptable because the
   IPsec tunnel already protects the payload, and the HMAC only
   secures the steering metadata.

   The HMAC value is carried in the HMAC-Auth-Val Sub-TLV in the
   GENEVE header:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | HMAC-Auth-Val | length        |   reserved                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   |             HMAC Authentication Value                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 9 Multi Segment SD-WAN HMAC Sub-TLV

     - HMAC-Auth-Val (8 bits): HMAC Authentication Value Sub-
        TLV Type = 6 (Assigned by this document).
     - Length (8 bits): Total length of the value field, which
        is the length of the HMAC Authentication Value in bytes
        plus 2 reserved bytes. It is 6 bytes by default for a 4-
        byte HMAC. In deployments with higher security
        requirements, an 8-byte HMAC (total of 10 bytes) is
        RECOMMENDED.
     - The HMAC Authentication Value (4 bytes or 8 bytes):
        Computed over the entire GENEVE header (excluding this
        Sub-TLV) using a pre-configured algorithm such as HMAC-
        SHA-256 and the shared key.
   The advantages of using HMAC are:
     - Data Integrity: Protects steering metadata from
        modification.
     - Efficiency: Truncated values minimize overhead while
        retaining strong protection.
     - Resistance to Tampering: Even truncated, HMAC values
        resist message tampering and replay attacks.



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     - Flexibility: Compatible with various hash functions like
        SHA-256 or SHA-512.
     - Widely Supported: Mature and broadly implemented across
        platforms.
   While truncated HMACs reduce collision resistance compared to
   full-length values, this is an acceptable tradeoff because
   the payload is encrypted by IPsec SAs, the HMAC covers only
   steering metadata, and attackers must possess the shared key
   to generate valid values.

9.3. AH based Integrity and Authentication

   Some deployments may require stronger or more comprehensive
   integrity protection than a truncated HMAC, such as when
   mandated by security policy, regulatory compliance, or risk
   management practices. In these cases, an additional integrity
   layer can be applied using Authentication Header (AH)
   [RFC4301] or ESP-NULL [RFC2410] [RFC6071] on top of the
   existing IPsec encryption between CPEs.

   AH and ESP-NULL provide cryptographic integrity for the
   entire IP packet, not just the GENEVE metadata. All
   approaches (including the HMAC) require cryptographic keys.
   The operational difference is that AH/ESP-NULL require
   dedicated IPsec SAs and IKE state between each Cloud GW and
   CPE, increasing per-peer state and processing. By contrast,
   the HMAC Sub-TLV (Type = 6, defined in this document) can use
   controller-distributed symmetric keys (e.g., per-tenant or
   per-CPE) without establishing additional IPsec SAs between
   Cloud GWs and CPEs.

   NAT Considerations: AH is not compatible with NAT traversal
   because it authenticates the outer IP header, and any address
   change will cause verification to fail. ESP-NULL avoids this
   issue but still incurs additional per-packet processing.

10. Manageability Considerations

   In multi-segment SD-WAN deployments where the Cloud GW and
   CPEs belong to different administrative domains,
   manageability must address the challenges of secure,
   interoperable, and policy-compliant operation across
   organizational boundaries. Key considerations include:

   - Cross-Domain Authentication and Authorization:


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        Ensure that CPEs connecting to the Cloud GW are
        authenticated using mutually agreed methods, and that
        authorization policies are enforced to prevent
        unauthorized use of Cloud Backbone resources.

   - Metadata Validation and Policy Enforcement:
        Cloud GWs must validate SD-WAN metadata (e.g., GENEVE
        Sub-TLVs) against the registered information for each
        CPE. This prevents spoofing, misrouting, and cross-
        tenant traffic leakage.

   - Operational Coordination and Fault Handling:
        Define inter-organization procedures for troubleshooting
        and incident response. This should include point-of-
        contact directories, escalation processes, and shared
        logging formats for event correlation.

   - Change Management and Configuration Synchronization:
        Coordinate configuration changes-such as policy updates,
        region restrictions, or authentication parameters-so
        that both the Cloud GW and CPEs apply them consistently,
        avoiding mismatches that disrupt traffic.

   - Policy Automation Using I2NSF Principles ([RFC8192]):
        Where feasible, leverage I2NSF concepts to automate
        policy configuration, exchange, and enforcement between
        domains, reducing manual coordination and improving
        operational consistency.

11. IANA Considerations

   IANA has assigned a new GENEVE Option Class from the IETF
   Review range as shown below:

     Option
      Class     Description       Assignee/Contact  Reference
      ------  -------------------  ------------- -----------
    0x0163     Multi Segment SD-WAN    IETF   [this document]


   IANA has assigned GENEVE Option Class value 0x0163 for
   identifying Multi-Segment SD-WAN. No further Option Class
   assignments are requested in this document.


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   IANA is requested to create the following new registry under
   the "Multi Segment SD-WAN GENEVE Option Class (0x0163):

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

      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      Restricted Region         [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.

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







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   [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.

   [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

   [IPsecOverGENEVE] S. Boutros, et al, "IPsec over GENEVE
             Encapsulation", draft-boutros-nvo3-ipsec-over-
             geneve-01, work-in-progress, Jan, 2018.

   [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-42, Jan, 2025.





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   [SD-WAN-Edge-Discovery] L. Dunbar, et al, "BGP UPDATE for SD-
             WAN Edge Discovery", draft-ietf-idr-sdwan-edge-
             discovery-25, July. 2025.

   [I-D.dunbar-ipsecme-lightweight-authenticate] L. Dunbar, K.
             Majumdar, S. Fluhrer, "Lightweight Authentication
             Methods for IP Header", draft-dunbar-ipsecme-
             lightweight-authenticate-00, Feb 2025.

13. Acknowledgments

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

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


Appendix A: Illustration of Packets through Cloud GWs

   This section illustrates Cloud GWs connecting traffic flow
   carried by the IPsec tunnels.

A.1 Single Hop Cloud GW

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

     Using Figure 1 as an example:

       - 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




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          GW addresses (which is out of the scope of this
          document).

     When 192.0.2.0/26 and 192.0.2.64/26 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 192.0.2.1 to
     192.0.2.65 has the following outer header:

         +---------------------------------------------------+
         | Outer IP Header                                   |
         |   Protocol = 17 (UDP)                             |
         |   Src IP = CPE1 (underlay address)                |
         |   Dst IP = Cloud GW (underlay address)            |
         +---------------------------------------------------+
         | UDP Header                                        |
         |   Src Port = xxxx (ephemeral)                     |
         |   Dst Port = 6081 (GENEVE)                        |
         +===================================================+
         | GENEVE Header                                     |
         |   Protocol Type = 0x0800 (IPv4) or 0x86DD (IPv6)  |
         |     [Indicates the payload is an IP packet]       |
         +---------------------------------------------------+
         | MultiSeg-SDWAN Option Class                       |
         |   SD-WAN EndPt Sub-TLV (CPE2 address)             |
         |   [Optional other SD-WAN Sub-TLVs]                |
         |  HMAC-Auth-Val Sub-TLV (GENEVE Hdr Authentication)|
         |                          validated by GW          |
         +===================================================+
         | ESP Outer IP Header (Tunnel Mode)                 |
         |   Src IP = CPE1 (tunnel IP)                       |
         |   Dst IP = CPE2 (tunnel IP)                       |
         |   Protocol = 50 (ESP)                             |
         +---------------------------------------------------+
         | ESP Header                                        |
         |   SPI (Security Parameters Index)                 |
         |   Sequence Number                                 |
         +---------------------------------------------------+
         | Encrypted Payload                                 |
         |   Inner IP Header                                 |
         |     Src = 192.0.2.1 (host behind CPE1)            |
         |     Dst = 192.0.2.65 (host behind CPE2)           |
         |     Protocol = TCP                                |
         |   TCP Header                                      |
         |   Application Payload                             |


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         |   Padding                                         |
         |   Pad Length                                      |
         |   Next Header                                     |
         +---------------------------------------------------+
         | Integrity Check Value (ICV)                       |
         |   (Generated by CPE1, validated by CPE2)          |
         +---------------------------------------------------+
    Figure 10 Packet header illustration to Cloud GWs

A.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.
       - 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 192.0.2.0/26 and 192.0.2.128/25 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 192.0.2.1 to
     192.0.2.129 has the following outer header:









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+---------------------------------------------------+
| Outer IP Header                                   |
|   Protocol = 17 (UDP)                             |
|   Src IP = CPE1 (underlay address)                |
|   Dst IP = Cloud GW1 (underlay address)           |
+---------------------------------------------------+
| UDP Header                                        |
|   Src Port = xxxx (ephemeral)                     |
|   Dst Port = 6081 (GENEVE)                        |
+===================================================+
| GENEVE Header                                     |
|   Protocol Type = 0x0800 (IPv4) or 0x86DD (IPv6)  |
|     [Indicates payload is an IP packet]           |
+---------------------------------------------------+
| MultiSeg-SDWAN Option Class                       |
|   SD-WAN EndPt Sub-TLV (CPE10 address)            |
|   EgressGW Sub-TLV (explicit egress Cloud GW2)    |
| HMAC-Auth-Val Sub-TLV (GENEVE Hdr Authentication) |
|                       ( validated by GW           |
+===================================================+
| ESP Outer IP Header (Tunnel Mode)                 |
|   Src IP = CPE1 (tunnel IP)                       |
|   Dst IP = CPE10 (tunnel IP)                      |
|   Protocol = 50 (ESP)                             |
+---------------------------------------------------+
| ESP Header                                        |
|   SPI (Security Parameters Index)                 |
|   Sequence Number                                 |
+---------------------------------------------------+
| Encrypted Payload                                 |
|   Inner IP Header                                 |
|     Src = 192.0.2.1  (host behind CPE1)           |
|     Dst = 192.0.2.129 (host behind CPE10)         |
|     Protocol = TCP                                |
|   TCP Header                                      |
|   Application Payload                             |
|   Padding                                         |
|   Pad Length                                      |
|   Next Header                                     |
+---------------------------------------------------+
| Integrity Check Value (ICV)                       |
|   <- validated by CPE10                           |
+---------------------------------------------------+

Appendix B: Illustration from Private VPN to IPsec Tunnel




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   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:

       - CPE1 sends 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 192.0.2.1 to
     192.0.2.129, the following header is added by CPE1 sending
     over the Private VPN:

























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     Outer IP header:
         +---------------------------+
         |    proto = 17 (UDP)       |
         |    src = CPE1             |
         |    dst = Cloud GW         |
         +===========================+
         | GENEVE Header             |
         | Protocol=50(ESP payload)  |
         +- - --  -- - - --      - --+
         |MultiSeg-SDWAN Option Class|
         +- - --  -- - - --      - --+
         |SD-WAN EndPt SubTLV (CPE2) |
         +---------------------------+
         |GENEVE Hdr Authentication  |<-validated by GW
         +---------------------------+  < -+
         | payload IP header:        |     |
         |  src =  192.0.2.1         |     |
         |  dst =  192.0.2.129       |     |
         +---------------------------+  Not Encrypted
         |   TCP header +            |     |
         ~    payload (variable)     ~     |
         |                           |     |
         +===========================+   <-+
    Figure 12 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             |
         | Proto=50(ESP payload)     |
         +- - --  -- - - --      - --+
         |MultiSeg-SDWAN Option Class|
         +- - --  -- - - --      - --+
         |SD-WAN EndPt SubTLV (CPE2) |
         +---------------------------+
         |GENEVE Hdr Authentication  |<-validated by GW
         +---------------------------+  < ----------+
         |SPI(Security Parameter Idx)|              |
         +---------------------------+              |
         |    sequence number        |              |
         +---------------------------+   <-+        |
         | payload IP header:        |     |        |
         |  src =  192.0.2.1         |     |        |
         |  dst =  192.0.2.129       |     |        |
         +---------------------------+  Encrypted   |
         |   TCP header +            |     |        |
         ~    payload (variable)     ~     |        |
         |                           |     |        |
         +===========================+   <-+ -------+
         |Integrity Check Value (ICV)|<-validated by CPE2
         +---------------------------+
 Figure 13 Illustration of packet from the Egress Cloud GW


















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Authors' Addresses

   Kausik Majumdar
   Oracle
   Email: kausik.majumdar@oracle.com

   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com



   Venkit Kasiviswanathan
   Arista
   Email: venkit@arista.com

   Ashok Ramchandra
   Google
   Email: archiashok@gmail.com
























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   Aseem Choudhary
   Aviatrix
   Email: achoudhary@aviatrix.com

Contributors' Addresses










































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