Multi-segment SD-WAN via Cloud DCs
draft-ietf-rtgwg-multisegment-sdwan-15
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Authors | Kausik Majumdar , Linda Dunbar , Venkit Kasiviswanathan , Ashok Ramchandra , Aseem Choudhary | ||
| Last updated | 2026-08-18 (Latest revision 2026-08-04) | ||
| Replaces | draft-dmk-rtgwg-multisegment-sdwan | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
TSVART Telechat review
by Wesley Eddy
Almost ready
SECDIR Early review
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by Jon Geater
Has issues
SECDIR IETF Last Call Review due 2026-07-14
Incomplete
OPSDIR IETF Last Call Review due 2026-07-14
Incomplete
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Chongfeng Xie | ||
| Shepherd write-up | Show Last changed 2025-10-27 | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Jim Guichard | ||
| Send notices to | xiechf@chinatelecom.cn | ||
| IANA | IANA review state | IANA OK - Actions Needed |
draft-ietf-rtgwg-multisegment-sdwan-15
Network Working Group K. Majumdar
Internet Draft Upscale AI
Intended status: Standard Track L. Dunbar
Expires: February 4, 2027 Futurewei
V.Kasiviswanathan
NextHop AI
A. Ramchandra
Google
A. Choudhary
Cisco
August 4, 2026
Multi-segment SD-WAN via Cloud DCs
draft-ietf-rtgwg-multisegment-sdwan-15
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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Copyright Notice
Copyright (c) 2026 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
Provisions Relating to IETF Documents
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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 and Definitions...............................5
3. Use Cases.................................................6
3.1. Multi-segment SD-WAN via a Single Cloud GW...........6
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...................10
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.............................16
4.7. HMAC Authentication Value Sub-TLV...................17
5. Packet Header Processing.................................18
6. Error Handling...........................................20
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
9.1. Threat Analysis.....................................23
9.2. HMAC-based Integrity and Authentication.............23
9.3. AH based Integrity and Authentication...............25
10. Manageability Considerations............................26
11. IANA Considerations.....................................27
12. References..............................................27
12.1. Normative References...............................27
12.2. Informative References.............................28
13. Acknowledgments.........................................30
Appendix A: Illustration of Packets through Cloud GWs.......30
A.1 Single Hop Cloud GW.....................................30
A.2 Multi-hop Transit GWs...................................32
Appendix B: Illustration from Private VPN to IPsec Tunnel...33
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 Datacenters (DC),
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 and Definitions
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 BCP 14 [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown
here.
The IP addresses used in this document are for illustrative
purposes only. IPv4 examples use addresses from the
documentation blocks defined in [RFC5737] (192.0.2.0/24 and
198.51.100.0/24). All mechanisms described apply equally to
IPv6, where equivalent examples would use addresses from the
documentation prefix defined in [RFC3849] (2001:db8::/32).
The following acronyms and terms are used in this document:
Cloud Backbone: The global, private network infrastructure
operated by a cloud provider that interconnects
its regions, zones, and points of presence.
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.
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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. For
customers that have already chosen SD-WAN, stitching SD-WAN
segments through a Cloud Gateway provides a way to extend
policy enforcement and traffic control across branches using
their existing SD-WAN-to-cloud connectivity, while avoiding
the need to establish separate direct branch to branch SD-WAN
paths. This approach is beneficial for several reasons:
- The public Internet path from a branch to its nearby Cloud
GW is typically shorter and more controlled than a public
Internet path between branches, which can reduce exposure
to unpredictable performance, limited bandwidth, and
security risks.
- Centralized enforcement of enterprise security policies can
be enabled through cloud-hosted services. Traffic destined
to cloud-resident applications can be decrypted for full
inspection (e.g., firewall, threat detection), while CPE-
to-CPE traffic that remains IPsec-encrypted can still
benefit from header- or flow-based functions-such as DDoS
mitigation, rate limiting, anomaly detection, and SLA/usage
analytics-especially when the same CPE also sends traffic
terminating in the cloud.
- 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
PrivateLines / \
| +----------/-----+ 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
Note: For clarity, each line in this figure represents
connectivity that may consist of multiple parallel paths.
Multiple paths are not shown to avoid excessive complexity in
the illustration.
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 |
+-------+-----+ +----+ +-----+ |
| +-----| Edge+--+ GW1|============| GW2 | |
Direct| | | +-----+ +|--|+ +--|--+ |
Connect| | | | | | |
| | +------------|--|----------------|------+
| | IPsec +-----+
Private Lines / \ |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 [RFC8986] and MPLS Traffic Engineering (MPLS-TE)
[RFC2702], 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
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performance, enforce security, or ensure compliance can be
difficult to implement.
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.
Note: The mechanism described in this document does not alter
the forwarding behavior of the underlay network. Traffic from
the source CPE to the ingress Cloud GW and from the egress
Cloud GW to the destination CPE continues to follow normal
underlay forwarding. Since these are typically short hops,
the more useful traffic engineering (TE) occurs across the
longer-range Cloud Backbone. In this model, the overlay
steering defined here enables predictable selection of
ingress and egress Cloud GWs, while TE within the backbone is
offloaded to the Cloud Backbone provider
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[IEEE802.1Q], IP-in-IP[RFC2003], GRE[RFC2784], etc.,
can be used to steer traffic from a CPE to its nearest (or
chosen) 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.
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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.
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 Egress GW Sub-TLV).
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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
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 Endpoint 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).
- SD-WAN Dst Addr Family (16 bits): Identifies the address
family of the destination endpoint. Values follow the
Address Family Numbers registry. For example, a value of
1 indicates an IPv4 address and a value of 2 indicates
an IPv6 address.
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
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- SDWAN Origin (8 bits): Identifies the SDWAN Tunnel
Originator Sub-TLV with a Type value of 2.
- 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.
- SD-WAN Org Addr Family (16 bits): Identifies the family
address of the originator. A value of 1 indicates an
IPv4 address and a value of 2 indicates an IPv6 address.
This Sub-TLV allows Cloud GWs and transit nodes to identify
the packet's source, allowing them to apply source-specific
policies for forwarding. Such 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. Any such policy, however,
MUST be applied only after the ingress Cloud GW authenticates
the sender and validates the Originator value against
authorized policy state. A false, unauthorized, or
unverifiable Originator value MUST NOT be used to obtain
preferred treatment and such packets MUST be discarded.
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
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- SDWAN EgressGW (8 bits): Identifies 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.
- Egress GW Addr Family: Identifies the family address of
the Egress GW. A value of 1 indicates an IPv4 address
and a value of 2 indicates an IPv6 address.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|RestrictedReg | Length | Reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Region Len | UTF-8 encoding of Region Name or ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Region Len | UTF-8 encoding of Region Name or ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 Restricted Regions Sub-TLV
- RestrictedReg (8 bits): Identifies the Restricted
Regions Sub-TLV with a Type value of 4.
- 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:
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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:
- 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ExcludeTransit | 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
- ExcludeTransit (8 bits): identifies the Exclude Transit
Sub-TLV with a Type value of 5.
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- 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:
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.
4.7. HMAC Authentication Value Sub-TLV
To support integrity protection and authentication of the
Multi-Segment SD-WAN GENEVE metadata, this document defines
the HMAC (Hash-based Message Authentication Code)
Authentication Value (HMAC-Auth-Val) Sub-TLV. The Sub-TLV
carries the HMAC authentication value computed over the
GENEVE header, including the Multi-Segment SD-WAN Option
Class, allowing a receiving Cloud GW to verify that the
steering metadata has not been modified in transit.
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The selection of the HMAC algorithm, authentication value
length, key establishment, and verification procedures are
described in Section 9.2.
The HMAC Authentication Value Sub-TLV has the following
format:
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.
- HMAC Authentication Value (variable): Contains the HMAC
computed over the GENEVE header, including the Multi-
Segment SD-WAN Option Class and all included Sub-TLVs,
excluding the HMAC-Auth-Val Sub-TLV itself (i.e., its
Type, Length, Reserved, and Authentication Value
fields). The HMAC algorithm, keying method, and
authentication value length are specified in Section
9.2.
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 (i.e. Dst Port = 6081 (GENEVE); MultiSeg-
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SDWAN Option Class; inner IP header's 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.
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
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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.
- 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.
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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.
The iBGP control plane is used to exchange reachability and
policy information among CPEs through Route Reflectors; it
does not carry IPsec Security Association (SA) parameters,
which are established separately via IKEv2 or out-of-band
management systems.
The iBGP sessions among CPEs described in this section are a
logical control plane relationship among enterprise managed
nodes, using the enterprise's own management/control
connectivity. They are independent of the eBGP sessions
between a CPE and its attached Cloud GW described in Section
7.2.
7.2. Control Plane between CPEs and Cloud GWs
This section describes the control plane relationship between
a CPE and its attached Cloud GW, which is distinct from the
iBGP based control plane among CPEs described in Section 7.1.
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
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.
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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,
the IPsec Security Association (SA) parameters between the
CPE and its corresponding Cloud GW are established out-of-
band (e.g., via management or automation systems) or
negotiated dynamically using IKEv2.
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.
- Security Event Logging:
The security event logging is to capture and analyze
security-related events, including threat detection,
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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 above risks requires authenticating and validating
SD-WAN metadata to ensure it originates from authorized CPEs.
9.2. HMAC-based Integrity and Authentication
The HMAC-Auth-Val Sub-TLV defined in Section 4.7 provides
integrity protection and source authentication for the Multi-
Segment SD-WAN steering metadata carried in the GENEVE
header. It allows Cloud GW to verify that the steering
metadata originated from an authorized SD-WAN CPE has not
been modified while in transit.
HMAC is a widely deployed cryptographic mechanism that
provides message integrity and data origin authentication by
combining a shared secret key with a cryptographic hash
function. Upon receipt of a packet, the receiving Cloud GW
computes the HMAC over the received GENEVE header using the
shared key and compares the result with the authentication
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value carried in the HMAC-Auth-Val Sub-TLV. A successful
comparison confirms that the protected metadata has not been
altered and was generated by an entity possessing the shared
key.
This mechanism authenticates the GENEVE metadata exchanged
between SD-WAN CPEs and the Cloud GWs. For traffic that
transits the Cloud Backbone, the HMAC key can be derived from
the existing IPsec Security Associations (SAs) established
between each CPE and its attached Cloud GW using HKDF
[RFC5869] with a non-null salt. Unless otherwise specified,
the salt value is the ASCII string "Multisegment-SD-WAN".
This approach avoids establishing additional peer-to-peer
IKEv2 exchanges solely for protecting the GENEVE metadata.
Because the key derivation and distribution occur over
existing IPsec-protected CPE-to-GW channels, NAT traversal
does not introduce additional issues.
Unless otherwise configured, HMAC-SHA-256 [RFC4868] is the
default algorithm for computing the authentication value.
Other HMAC algorithms MAY be used when explicitly configured
and distributed by the SD-WAN controller together with the
corresponding keying parameters.
To reduce packet overhead, truncated HMAC authentication
values of 4 or 8 octets are RECOMMENDED instead of the full
HMAC output (for example, 32 octets for HMAC-SHA-256). Since
the IPsec tunnel already provides integrity and
confidentiality protection for the encapsulated payload, the
HMAC defined in this document protects only the GENEVE
steering metadata. Deployments with stronger security
requirements MAY configure longer authentication values.
The HMAC defined in this section provides the following
security properties:
- Data Integrity: Detects unauthorized modification of
the Multi-Segment SD-WAN GENEVE metadata.
- Source Authentication: Allows Cloud GWs to verify that
the steering metadata originated from an authorized
SD-WAN CPE possessing the shared authentication key.
- Low Overhead: Supports truncated authentication values
to minimize packet overhead while providing adequate
protection for steering metadata.
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- Algorithm Agility: Supports different HMAC algorithms
through controller configuration.
- Operational Simplicity: Reuses existing IPsec trust
relationships and key management, avoiding additional
Security Associations between Cloud GWs and CPEs.
Although truncating the HMAC authentication value reduces the
security margin against forgery compared to the full HMAC
output, this tradeoff is acceptable because the HMAC protects
only the GENEVE steering metadata, while the payload remains
protected by IPsec. Furthermore, an attacker must possess the
shared secret key to generate a valid authentication value,
making successful forgery computationally infeasible when
appropriate key management practices are followed.
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.
When AH or ESP-NULL is used, the required IPsec SAs and
associated keying material SHOULD be established using IKEv2
[RFC7296]. Deployments MAY use manual or controller based key
provisioning when supported by the operational environment,
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but such provisioning MUST provide equivalent authentication,
authorization, replay protection, key freshness, and key
rollover properties.
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, consistent with the service
framework defined in MEF 70.1 [MEF70.1]. Key considerations
include:
- Cross-Domain Authentication and Authorization:
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.
- Coordination of Configuration Changes:
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.
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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.
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 4.7]
7-254 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.
[RFC4301] S. Kent and K. Seo, "Security Architecture for the
Internet Protocol", RFC4301, Dec. 2005.
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[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256,
HMAC-SHA-384, and HMAC-SHA-512 with IPsec", RFC
4868, May 2007.
[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.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and
T. Kivinen, "Internet Key Exchange Protocol Version
2 (IKEv2)", RFC 7296, October 2014.
[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.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC
2003, October 1996.
[RFC2410] R. Glenn and S. Kent, "The NULL encryption
Algorithm and Its Use with IPsec", RFC2310, Nov.
1998.
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[RFC2702] D. Awduche, L. Berger, D. Gan, T. Li, V.
Srinivasan, and G. Swallow, "Requirements for
Traffic Engineering Over MPLS", RFC2702, September
1999.
[RFC2784] D. Farinacci, T. Li, S. Hanks, D. Meyer, and P.
Traina, "Generic Routing Encapsulation (GRE)",
RFC2784, March 2000.
[RFC3849] S. Huston, M. Thomson, S. Kent, and J. Seo, "IPv6
Address Prefix Reserved for Documentation",
RFC3849, July 2004.
[RFC5737] J. Arkko, M. Cotton, and L. Vegoda, "IPv4 Address
Blocks Reserved for Documentation", RFC5737,
January 2010.
[RFC5869] H. Krawczyk and P. Eronen, "HMAC-based Extract-and-
Expand Key Derivation Function (HKDF)", RFC5869,
May 2010.
[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
[RFC8986] C. Filsfils, D. Dukes, S. Previdi, J. Leddy, S.
Matsushima, and D. Voyer, "Segment Routing over
IPv6 (SRv6) Network Programming", RFC8986, February
2021.
[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-43, 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-29, July. 2026.
[lightweight-authenticate] L. Dunbar, K. Majumdar, S.
Fluhrer, "Lightweight Authentication Methods for IP
Header", draft-dunbar-ipsecme-lightweight-
authenticate-01, July 2025.
[IEEE802.1Q] IEEE, "IEEE Standard for Local and Metropolitan
Area Networks--Bridges and Bridged Networks", IEEE
Std 802.1Q.
13. Acknowledgments
Acknowledgements to Adrian Farrel, Joel Halpern, Donald
Eastlake, Stephen Farrell, Ajeet Gill 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.
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- 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 CPE1 (192.0.2.0/26) and CPE2 (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) |
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| Protocol = TCP |
| TCP Header |
| Application Payload |
| 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 CPE1(192.0.2.0/26) and CPE10(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 |
+---------------------------------------------------+
Figure 11: Packet header to Cloud GWs
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
Upscale AI
Email: kmajumdar@upscaleai.com
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Venkit Kasiviswanathan
Nexthop AI
Email: venkit@nexthop.ai
Ashok Ramchandra
Google
Email: archiashok@gmail.com
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Aseem Choudhary
Cisco
Email: asechoud@cisco.com
Contributors' Addresses
Ajeet Pal Singh Gill
Microsoft Azure
Email: ajeetgill@microsoft.com
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