Network Working Group L. Dunbar
Internet Draft Futurewei
Intended status: Informational A. Sajassi
Expires: June 7, 2025 Cisco
J. Drake
Independent
B. Najem
Bell Canada
S. Hares
November 7, 2025
BGP Usage for SD-WAN Overlay Networks
draft-ietf-bess-bgp-sdwan-usage-27
Abstract
This document explores the complexities involved in managing large
scale Software Defined WAN (SD-WAN) overlay networks, along with
various SD-WAN scenarios. Its objective is to illustrate how a
BGP-based control plane can effectively manage these overlay
networks by distributing edge service reachability information,
WAN port attributes, and underlay path details, thereby minimizing
manual provisioning.
Status of this Memo
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progress."
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Copyright Notice
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Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................4
3. SD-WAN Scenarios and Their Requirements........................6
3.1. SD-WAN Functional Overview and Requirements...............6
3.1.1. Supporting SD-WAN Segmentation.......................6
3.1.2. Client Service Requirement...........................7
3.1.3. SD-WAN Traffic Segmentation..........................7
3.1.4. Zero Touch Provisioning..............................8
3.1.5. Constrained Propagation of SD-WAN Edge Properties....9
3.2. Scenario #1: Homogeneous Encrypted SD-WAN................10
3.3. Scenario #2: Differential Encrypted SD-WAN...............11
3.4. Scenario #3: Private VPN PE based SD-WAN.................13
4. Provisioning Model............................................14
4.1. Client Service Provisioning Model........................14
4.2. Policy Configuration.....................................15
4.3. IPsec Related Parameters Provisioning....................15
5. BGP Controlled SD-WAN.........................................16
5.1. Rational for Using BGP as Control Plane for SD-WAN.......16
5.2. BGP Scenario for Homogeneous Encrypted SD-WAN............17
5.3. BGP Scenario for Differential Encrypted SD-WAN...........18
5.4. BGP Scenario for Flow-Based Segmentation.................19
6. SD-WAN Forwarding Model.......................................20
6.1. Forwarding Model for Homogeneous Encrypted SD-WAN........20
6.1.1. Network and Service Startup Procedures..............20
6.1.2. Packet Walk-Through.................................21
6.2. Forwarding Model for Hybrid Underlay SD-WAN..............22
6.2.1. Network and Service Startup Procedures..............22
6.2.2. Packet Walk-Through.................................22
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6.3. Forwarding Model for PE based SD-WAN.....................24
6.3.1. Network and Service Startup Procedures..............24
6.3.2. Packet Walk-Through.................................24
7. Manageability Considerations..................................25
8. Security Considerations.......................................25
9. IANA Considerations...........................................26
10. References...................................................26
10.1. Normative References....................................26
10.2. Informative References..................................28
11. Acknowledgments..............................................29
1. Introduction
Software Defined Wide Area Network (SD-WAN), as described in
[MEF70.1] and [MEF70.2], provides overlay connectivity services
that optimize the transport of IP packets across one or more
underlay networks by identifying traffic types and applying
policies to determine forwarding behavior. Key characteristics of
SD-WAN networks include:
- Transport Augmentation: an SD-WAN path can utilize different
types of underlay networks, including private networks (with
or without encryption) and public networks (requiring
encryption).
- Direct Internet Breakout: Traffic from remote branch offices
can directly access the internet, avoiding backhauling to
corporate headquarters for centralized policy control.
- Policy-Based Traffic Steering: Traffic can be directed over
specific overlay paths based on predefined conditions, such as
matching one or multiple fields in the IP header, rather than
solely relying on destination IP addresses [RFC9522]. For IPv6
[RFC8200], attributes like the Flow Label, source address,
specific extension header fields, or a combination of these
can be used. Additional details are available in Tables 7 and
8 of [MEF70.1].
- Performance-Based Forwarding: Traffic can be steered based on
performance metrics (e.g., packet delay, loss, jitter),
selecting the underlay path that meets or exceeds policy
requirements.
This document outlines SD-WAN use cases and the complexities of
managing large-scale SD-WAN overlay networks, as described in
[Net2Cloud-Problem]. It demonstrates how a BGP-based control plane
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can efficiently manage these networks with minimal manual
intervention; additional operational drivers for standardized
protocol behavior are summarized in Section 6 of [MPLIFY-119].
It's important to distinguish the BGP instance as the control
plane for SD-WAN overlay from the BGP instances governing the
underlay networks. The document assumes a secure communication
channel between the SD-WAN controller and SD-WAN edges for
exchanging control plane information.
The need for an RFC documenting SD-WAN use cases lies in ensuring
standardization and interoperability. While BGP and IPsec are
well-established technologies, their application to SD-WAN
introduces challenges such as scalability, traffic segmentation,
and multi-homing. This document consolidates best practices and
defines guidelines to enable consistent implementations across
diverse networks, optimizing existing protocols for SD-WAN
scenarios rather than proposing new ones.
2. Conventions used in this document
Cloud DC: Third party data centers that host applications and
workloads owned by different organizations or tenants.
Controller: Used interchangeably with SD-WAN controller to manage
SD-WAN overlay networks in this document. In the
context of BGP-controlled SD-WAN, the SD-WAN
controller functions as or is integrated with the BGP
Route Reflector (RR).
Client service: A service (e.g., IP prefix or VLAN) attached to
the client-facing interface of an SD-WAN edge node.
Client route: A BGP-advertised route originated by an SDWAN-Edge
that represents the reachability of a client-facing
service (e.g., IP prefix or VLAN) and includes
associated path attributes used by the SDWAN-
Controller for policy enforcement and forwarding
decisions.
C-PE: SD-WAN Edge node, which can be Customer Premises
Equipment (CPE) for customer-managed SD-WAN, or
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Provider Edge (PE) for provider-managed SD-WAN
services.
Homogeneous Encrypted SD-WAN: An SD-WAN network in which all
traffic to/from the SD-WAN edges are carried by IPsec
tunnels regardless of underlying networks. I.e., the
client traffic is carried by IPsec tunnel even over
MPLS private networks.
MP-NLRI: In this document, the term "MP-NLRI" serves as a
concise reference for "MP_REACH_NLRI".
NSP: Network Service Provider.
PE: Provider Edge
SD-WAN Edge Node: A device, either physical or virtual, that
participates in the SD-WAN overlay network. These
nodes advertise client routes to the SD-WAN Controller
(e.g., BGP RR).
SD-WAN: An overlay connectivity service that optimizes the
transport of IP packets over one or more Underlay
connectivity services by recognizing applications and
determining forwarding behavior by applying policies
to them. [MEF-70.1].
SD-WAN IPsec SA: IPsec Security Association between two WAN ports
of the SD-WAN edge nodes or between two SD-WAN edge
nodes.
SD-WAN over Hybrid Underlay Networks: SD-WAN over Hybrid Underlay
Networks typically have edge nodes utilizing bandwidth
resources from different types of underlay networks,
some being private networks and others being public
Internet.
WAN Port: A Port or Interface facing a Network Service Provider
(NSP), with an address allocated by the NSP.
Private VPN: refers to a VPN that is supported wholly by a single
network service provider without using any elements of
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the public Internet and without any traffic passing
out of the immediate control of that service provider.
ZTP: Zero Touch Provisioning
3. SD-WAN Scenarios and Their Requirements
This section outlines the core requirements for SD-WAN overlay
networks and introduces various SD-WAN scenarios. These scenarios
serve as examples that are further explored in subsequent sections
to illustrate how the BGP control plane is used to distribute
reachability and policy information within SD-WAN overlay
networks.
3.1. SD-WAN Functional Overview and Requirements
3.1.1. Supporting SD-WAN Segmentation
"SD-WAN Segmentation" refers to policy-driven network
partitioning, a common approach in SD-WAN deployment. An SD-WAN
segment is essentially a virtual private network (SD-WAN VPN)
consisting of a set of edge nodes interconnected by tunnels, such
as IPsec tunnels and/or MPLS VPN tunnels.
This document assumes that SD-WAN VPN configuration on PE devices
will, as with MPLS VPN [RFC4364] [RFC4659], make use of VRFs
[RFC4364] [RFC4659]. Notably, a single SD-WAN VPN can be mapped to
one or multiple virtual topologies governed by the SD-WAN
controller's policies.
When BGP is used for SD-WAN, the client route UPDATE is the same
as MPLS VPN. The Route Target in the BGP Extended Community
[RFC4360] can differentiate the routes belonging to different SD-
WAN VPNs.
As SD-WAN is an overlay network arching over multiple types of
networks, MPLS L2VPN[RFC4761] [RFC4762]/L3VPN[RFC4364] [RFC4659]
or pure L2 underlay can continue using the VPN ID (Virtual Private
Network Identifier), VN-ID (Virtual Network Identifier), or VLAN
(Virtual LAN) in the data plane to differentiate packets belonging
to different SD-WAN VPNs. For packets transported through an IPsec
tunnel, additional encapsulation, such as GRE [RFC2784] or VxLAN
[RFC7348], is needed to embed the SD-WAN VPN identifier inside the
IPsec ESP header.
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3.1.2. Client Service Requirement
The client service requirements describe the SD-WAN edge's ports,
also known as SD-WAN client interfaces, which connect the client
network to the SD-WAN service.
The SD-WAN client interface should support IPv4 & IPv6 addresses
as well as Ethernet in accordance with the [IEEE802.3] standard.
In [MEF 70.1], the "SD-WAN client interface" is called SD-WAN UNI
(User Network Interface). Section 11 of [MEF 70.1] defines a
comprehensive set of attributes for the SD-WAN UNI, detailing the
expected behavior and requirements to enable seamless connectivity
to the client network.
The client service at the SD-WAN edge must support the SD-WAN UNI
service attributes outlined in Section 11 of [MEF 70.1].
3.1.3. SD-WAN Traffic Segmentation
SD-WAN Traffic Segmentation allows traffic to be separated based
on business priorities, security requirements, and operational
needs. This ensures that different user groups or services can
operate within distinct topologies or follow tailored policies to
meet specific business and security objectives.
For example, in a retail environment, traffic from point-of-sales
(PoS) systems may require a different topology that is separate
from other traffic. The PoS traffic is routed exclusively to the
payment processing entity at a central hub site, while other types
of traffic can be routed among all branches or remote sites.
In the figure below, traffic from the PoS system follows a tree
topology (denoted as "----" in the figure below), whereas other
traffic can follow a multipoint-to-multipoint topology (denoted as
"===").
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+--------+
Payment traffic |Payment |
+------+----+-+gateway +------+----+-----+
/ / | +----+---+ | \ \
/ / | | | \ \
+-+--+ +-+--+ +-+--+ | +-+--+ +-+--+ +-+--+
|Site| |Site| |Site| | |Site| |Site| |Site|
| 1 | | 2 | | 3 | | |4 | | 5 | | 6 |
+--+-+ +--+-+ +--|-+ | +--|-+ +--|-+ +--|-+
| | | | | | |
==+=======+=======+====+======+=======+=======+===
Figure 1 multi-point connection for non-payment traffic
Another example is an enterprise that wants to isolate traffic by
departments, ensuring each department having its own unique
topology and policies. For instance, the HR department may need to
access specific systems or resources that are not accessible by
the engineering department. Similarly, contractors may have
limited access to the enterprise resources.
3.1.4. Zero Touch Provisioning
SD-WAN Zero-Touch Provisioning (ZTP) is a network automation
approach that enables the automatic provisioning and configuration
of SD-WAN devices, such as routers and switches, at remote
locations without requiring manual intervention. ZTP allows
devices to be shipped with factory default settings; upon
connection to the network, they automatically retrieve their
configurations. ZTP for a remote SD-WAN edge usually includes the
following steps:
- The SD-WAN edge's customer information and unique device
identifier (e.g., serial number, MAC address, or factory-
assigned ID) are registered with the SD-WAN Central Controller.
- Upon power-up, the SD-WAN edge can establish the transport
layer secure connection [BCP195] to its controller, whose URL
(or IP address) and credential for connection request can be
preconfigured on the edge device by the manufacture, external
USB drive or secure Email given to the installer. The external
USB method involves providing the installer with a pre-
configured USB flash drive containing the necessary
configuration files and settings for the SD-WAN device. The
secure Email approach entails sending a secure email containing
the configuration details for the SD-WAN device.
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- The SD-WAN Controller authenticates the ZTP request from the
remote SD-WAN edge with its configurations. Once the
authentication is successful, it can designate a local network
controller near the SD-WAN edge to pass down the initial
configurations via the secure channel. The local network
controller manages and monitors the communication policies for
traffic to/from the edge node.
3.1.5. Constrained Propagation of SD-WAN Edge Properties
For an SD-WAN Edge to establish an IPsec tunnel to another edge
and exchange the attached client routes, both edges need to know
each other's network properties, such as the IP addresses of the
WAN ports, the edges' loopback addresses, the attached client
routes, the supported encryption methods, etc.
In many cases, an SD-WAN edge node is authorized to communicate
with only a subset of other edge nodes. To maintain security and
privacy, the property of an SD-WAN edge node must not be
propagated to unauthorized peers. However, when a remote SD-WAN
edge node powers up, it may lack the policies to determine which
peers are authorized to communicate. Therefore, SD-WAN deployment
needs to have a central point to distribute the properties of an
SD-WAN edge node to its authorized peers.
BGP is well suited for this purpose. A Route-Reflector (RR)
[RFC4456], integrated into the SD-WAN controller, enforces
policies governing the communication among SD-WAN edges. The RR
ensures that BGP UPDATE messages from an SD-WAN edge are
propagated only to other edges within the same SD-WAN VPN.
An SD-WAN edge must use a secure channel, such as TLS (RFC5246)
[RFC8446] or IPsec, to its designated RR for exchanging BGP UPDATE
messages.
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+---+
Authorized Peers G1 |RR | Authorized Peer G2
+======+====+=+ +======+====+=====+
/ / | +---+ | \ \
/ / | | \ \
+-+--+ +-+--+ +-+--+ +-+--+ +-+--+ +-+--+
|C-PE| |C-PE| |C-PE| |C-PE| |C-PE| |C-PE|
| 1 | | 2 | | 3 | |4 | | 5 | | 6 |
+----+ +----+ +----+ +----+ +----+ +----+
Tenant 1 Tenant 2
Figure 2: Authorized Peer Groups managed by RR
Tenant separation is achieved by the SD-WAN VPN identifiers
represented in the control plane and data plane, respectively.
3.2. Scenario #1: Homogeneous Encrypted SD-WAN
Homogeneous Encrypted SD-WAN refers to an SD-WAN network where
edge nodes encrypt all client traffic destined to other edge
nodes, regardless of whether the underlay is private or public.
Typical use cases for Homogeneous Encryption:
- A small branch office connecting to its headquarters via the
Internet. All traffic to and from this small branch office must be
encrypted, usually achieved by IPsec Tunnels [RFC6071].
- A retail store in a shopping mall may need to securely connect
to its services hosted in one or more Cloud DCs via the Internet.
A common method involves establishing IPsec SAs with the Cloud DC
gateway to securely transport sensitive data to/from the store.
The granularity of the IPsec SAs for Homogeneous Encryption can be
per site, per subnet, per tenant, or per address. Once the IPsec
SA is established for a specific subnet/tenant/site, all traffic
to/from the subnet/tenant/site is encrypted.
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+---+
+--------------|RR |------------+
/ trusted +-+-+ \
/ \
/ \
+----+ +---------+ +------+ +----+
| CN3|--| P1-----+ -------------+------ P1 |--| CN3|
+----+ | C-PE1 P2-----+ | | C-PE2| +----+
+----+ | P3-----+ Wide +------ P2 | +----+
| CN2|--| | | area +------ P3 |--| CN1|
+-+--+ +---------+ | network | +------+ +-+--+
\ | | /
\ +---------+ | all packets | +------+ /
+--| P1-----+ encrypted +------ P1 |-+
| C-PE3 P2-----+ by | | C-PE4|
+----+ | P3-----+ IPsec SAs +------ P2 | +----+
| CN1|--| P4-----+--------------+ | |--| CN2|
+----+ +---------+ +------+ +----+
CN: Client Networks, which is same as Tenant Networks used by NVo3
Figure 3: Homogeneous Encrypted SD-WAN
A Homogeneous Encrypted SD-WAN shares certain similarities with
traditional IPsec VPN. However, unlike IPsec VPNs, which are
typically deployed in a point-to-point fashion among a limited
number of nodes, SD-WAN networks can comprise a large number of
edge nodes, all centrally managed by a controller responsible for
configurations and policies across the network.
Existing private VPNs (e.g., MPLS based) can use Homogeneous
Encrypted SD-WAN to extend over the public network to remote sites
to which the VPN operator does not own or lease infrastructural
connectivity.
3.3. Scenario #2: Differential Encrypted SD-WAN
Differential Encrypted SD-WAN refers to an SD-WAN network that
utilizes hybrid underlays, combining private VPNs and the public
Internet. In this model, traffic traversing the private VPN is
forwarded natively without encryption, while traffic over the
public Internet is encrypted for security. This approach balances
performance and security. Since IPsec encryption requires
significant processing power and traffic over the public Internet
typically lacks the premium SLA (Service Level Agreement) provided
by private VPNs-especially over long distances-current practice is
to forward traffic over private VPNs without encryption,
leveraging the inherent reliability and security of the private
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network. Meanwhile, encryption is applied only to traffic routed
over the public Internet to ensure data confidentiality.
One C-PE might have the Internet-facing WAN ports managed by
different NSPs with the WAN ports' addresses assigned by the
corresponding NSPs. Clients may define specific policies to govern
how traffic flows across the network, such as:
1) Certain flows can only be forwarded over private VPNs.
2) Certain flows can be forwarded over either private VPNs or the
public Internet. When forwarded over the public Internet, the
packets are encrypted.
3) Some flows, especially Internet-bound browsing ones, can be
handed off to the Internet without further encryption.
For example, consider a flow traversing multiple segments, A<->B,
B<->C, C<->D, has Policy 2) above. This flow can cross different
underlays in different segments, such as over Private underlay
between A<->B without encryption or over the public Internet
between B<->C protected by an IPsec SA.
In the figure below, C-PE1 has two different types of interfaces:
A1 to the Internet, and A2 & A3 to a private VPN. The WAN ports'
addresses can be allocated by the service providers or dynamically
assigned (e.g., by DHCP).
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+---+
+--------------|RR |----------+
/ +-+-+ \
/ \
/ \
+----+ +---------+ packets encrypted over +------+ +----+
| CN3|--| A1-----+ Untrusted +------ B1 |--| CN1|
+----+ | C-PE1 A2-\ | C-PE2| +----+
+----+ | A3--+--+ +---+---B2 | +----+
| CN2|--| | |PE+--------------+PE |---B3 |--| CN3|
+----+ +---------+ +--+ trusted +---+ +------+ +----+
| WAN |
+----+ +---------+ +--+ packets +---+ +------+ +----+
| CN1|--| C1--|PE| go natively |PE |-- D1 |--| CN1|
+----+ | C-PE3 C2--+--+ without encry+---+ | C-PE4| +----+
| | +--------------+ | |
| | | |
+----+ | | without encrypt over | | +----+
| CN2|--| C3--+---- Untrusted --+------D2 |--| CN2|
+----+ +---------+ +------+ +----+
CN: Client Network
Figure 4: SD-WAN with Hybrid Underlays
Services may not be congruent, i.e., the packets from A-> B may
traverse one underlay network, and the packets from B -> A may go
over a different underlay.
3.4. Scenario #3: Private VPN PE based SD-WAN
Private VPN PE-Based SD-WAN refers to extending an existing VPN
(e.g., EVPN [RFC7432] or IPVPN) by adding additional ports that
face the public Internet to address increased bandwidth
requirements between Provider Edge (PE) devices. This approach
allows VPN service providers to augment their networks without
immediately committing to building or leasing new infrastructure.
Key Characteristics of Private VPN PE-Based SD-WAN:
- For MPLS-based VPN, traffic between PEs uses MPLS
encapsulation within IPsec tunnels egressing the Internet
WAN ports, such as MPLS-in-IP or GRE-in-IPsec.
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- The BGP RR remains connected to the PEs via the same
trusted network as the original VPN, ensuring consistency
in routing policies and security.
The main use case for Private VPN PE-Based SD-WAN is Temporary
Bandwidth Expansion.
+======>|PE2|
// +---+
// ^
// || VPN
// VPN v
|PE1| <====> |RR| <=> |PE3|
+-+-+ +--+ +-+-+
| |
+--- Public Internet -- +
Offload
Figure 5: Additional Internet paths added to the VPN
For Ethernet-based client traffic, Private VPN PE based SD-WAN
should support VLAN-based service interfaces (EVPN Instances),
VLAN bundle service interfaces, or VLAN-Aware bundling service
interfaces. EVPN service requirement as described in Section 3.1
of [RFC8388] are applicable to the SD-WAN Ethernet-based Client
services. For IP-based client interfaces, L3VPN service
requirements are applicable.
4. Provisioning Model
This section defines the provisioning model, i.e., a conceptual
framework that scopes the roles (controller/RR and edges), the
artifacts (client-service constructs, policies, and IPsec
parameters), and their mapping to BGP attributes.
4.1. Client Service Provisioning Model
Provisioning of client-facing services in an SD-WAN network can
leverage approaches similar to those used for VRFs (Virtual
Routing and Forwarding) in MPLS based VPNs [RFC4364][RFC4659]. A
client VPN can define communication policies by specifying BGP
Route Targets for import and export. Alternatively, policy-based
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filtering using ACLs (Access Control List) can be employed to
control which routes are allowed or denied for a given client VPN.
In scenarios where an SD-WAN edge node is dedicated to a single
client with a single virtual network, all services attached to the
client facing interface(s) on the edge node can be grouped into a
single VRF. The RR can manage the policies for import/export
policies for that VRF.
4.2. Policy Configuration
Policy configuration is a key characteristic of an SD-WAN service,
enabling packets to be forwarded over multiple types of underlays
based on predefined rules. Policies determines which underlay
paths are allowed to carry specific flows, as outlined in Section
8 of [MEF70.1]. A flow is a collection of packets between the same
source and destination pair that are subject to the same
forwarding and policy decisions at the ingress SD-WAN edge node
and are identified by the settings of one or more fields in the
packet headers. For example, client-service-x can only be mapped
to a MPLS topology, ensuring traffic alignment with business or
security requirements.
4.3. IPsec Related Parameters Provisioning
IPsec-related parameter provision in an SD-WAN network involves
the negotiation and distribution of cryptographic parameters
required to establish IPsec tunnels among them. To streamline the
configuration process, SD-WAN edge nodes can retrieve those
parameters directly from the SD-WAN controller, reducing manual
intervention and ensuring consistency.
In a BGP-controlled SD-WAN, BGP UPDATE messages can be extended to
propagate IPsec-related attributes for each SD-WAN edge. This
approach allows peers to receive and apply compatible
cryptographic parameters distributed over a secure channel between
the SDWAN-Edge and its BGP RR, thereby simplifying IPsec tunnel
establishment and reducing reliance on traditional IKEv2
negotiation [RFC7296].
This mechanism supports the ZTP requirement outlined in Section
3.1.4 by enabling IPsec tunnels to be provisioned without IKEv2
negotiation.
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5. BGP Controlled SD-WAN
5.1. Rational for Using BGP as Control Plane for SD-WAN
In small SD-WAN networks with a modest number of nodes,
traditional approaches such as the hub-and-spoke model, employing
Next Hop Resolution Protocol (NHRP)[RFC2332] or a centralized hub
managing edge nodes, including the mapping of local and public
addresses along with tunnel identifiers, has proven effective.
However, for larger SD-WAN networks, with more than 100 nodes and
encompassing diverse underlays, the conventional approach becomes
increasingly complex, error-prone, and difficult to manage.
BGP offers several key advantages when used as the control plane
for a large SD-WAN:
- Simplified peer authentication process:
With a secure management channel established between each edge
node and its RR, the RR can perform peer authentication on
behalf of the edge node. The RR has policies on peer
communication and the built-in capability to constrain the
propagation of the BGP UPDATE messages to the authorized edge
nodes only.
- Scalable IPsec tunnel management
In networks with multiple IPsec tunnels between SD-WAN edges,
BGP simplifies tunnel management by using the Tunnel
Encapsulation Attribute specified in [RFC9012] to carry
information that associates advertised client routes with
specific tunnels.
Unlike traditional IPsec VPN where IPsec tunnels between two
edge nodes are treated as independent parallel links requiring
duplicated control plane messages for load sharing.
- Simplified traffic selection configurations
BGP can simplify the configuration of IPsec tunnel associations
and related forwarding policies. By leveraging Route Targets to
identify SD-WAN VPN membership, administrators can apply
import/export policies that control the distribution of client
routes. These route attributes, in turn, inform the local
configuration of IPsec traffic selectors at each SDWAN-Edge.
- Centralized Management and Security
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When the BGP RR is integrated with the SD-WAN controller, it
supports a centralized model for managing route distribution
policies. The RR ensures that BGP UPDATE messages are
distributed only to authorized SD-WAN Edges based on
preconfigured policies, thereby reducing control-plane
complexity and limiting exposure compared to decentralized
architectures.
In summary, BGP combines scalability, robust policy enforcement,
interoperability, and centralized security, making it an ideal
choice for managing SD-WAN overlay networks, particularly as they
grow in size and complexity.
5.2. BGP Scenario for Homogeneous Encrypted SD-WAN
In a BGP-controlled Homogeneous Encrypted SD-WAN, an SD-WAN Edge
(i.e., C-PE) can advertise both its attached client routes and
associated IPsec tunnel parameters using BGP UPDATE messages,
potentially within in a single message that includes the Tunnel
Encapsulation Attribute.
For example, in the figure below, the BGP UPDATE message from C-
PE2 to RR can have the client routes encoded in the MP-NLRI Path
Attribute and the IPsec Tunnel associated parameters encoded in
the Tunnel Encapsulation Attribute [RFC9012].
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+---------|RR |----------+
/ trusted +---+ \
/ \
/ \
+---------+ +---------+
--+ WAN Port ------------WAN Port ClientPort-
| | | C-PE2 |192.0.2.4/30
| C-PE1 | WAN Port +-|192.0.2.2|
--|192.0.2.1| | | ClientPort-
+---------+ | +---------+192.0.2.8/30
|
|
|
+---------+ |
--| WAN Port -------------+
| |
| C-PE3 |
--|192.0.2.3|
+---------+
Figure 6: Homogeneous Encrypted SD-WAN
In scenarios where C-PE2 does not have a policy specifying the
authorized peers for specific client routes, the RR takes the
responsibility for ensuring that BGP UPDATE for these client
routes are propagated only to other authorized SD-WAN edges.
5.3. BGP Scenario for Differential Encrypted SD-WAN
In this scenario, client services may have distinct forwarding
requirements based on business or network policies. Some client
services can be routed through any WAN ports of the edge node,
while others must be routed through specific WAN ports (such as
only MPLS VPN). To address these requirements, the BGP speaker
employs two distinct BGP UPDATE messages:
- Update 1: Client Route Advertisement for advertising the
prefixes of client services attached to the client facing
interfaces. The Color (Section 8 of [RFC9012]) is used to
associate each client service with the corresponding WAN ports
for the desired underlay paths.
- Update 2: Underlay WAN Port Advertisement, which conveys
information about the underlay WAN facing interfaces of an SD-
WAN Edge, including attributes such as IPsec SA parameters, MPLS
label stacks, and other relevant attributes. These attributes
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are carried in the BGP Tunnel Encapsulation Attribute, along
with associated Color values that allow BGP receivers to
correlate the WAN facing interfaces with the client routes
advertised in Update 1.
This dual-update approach provides flexibility and efficiency in
managing IPsec tunnels terminated at the WAN ports of SD-WAN edge
nodes. By decoupling client route advertisements from IPsec tunnel
attributes, it accommodates the differing update frequencies
between these components-for example, client route changes may
occur independently of dynamic IPsec parameters such as key
values. Additionally, multiple client services can share a single
IPsec SA, optimizing resource usage and reducing control-plane
overhead.
BGP receivers associate the two UPDATE messages using the common
loopback address of the SDWAN-Edge (e.g., C-PE2). UPDATE 1
advertises client routes with the next-hop set to C-PE2's loopback
address. UPDATE 2 advertises underlay WAN port information using
an NLRI that contains the same loopback address, along with the
Tunnel Encapsulation Attribute conveying IPsec parameters and WAN
port properties. BGP receivers use the common loopback address to
match the next-hop in UPDATE 1 with the NLRI in UPDATE 2. This
enables recursive resolution, as specified in [RFC9012], allowing
client traffic to be forwarded based on the underlay
characteristics defined in UPDATE 2.
5.4. BGP Scenario for Flow-Based Segmentation
In a flow-based segmentation scenario, as described in Section
3.1.3, a service flow is identified by specific fields in the
packet's IP header, such as source/destination IP addresses, port
numbers, or protocol types. Flow-based segmentation ensures that
traffic for a particular service flow is directed only to
authorized nodes or paths, meeting security and policy
requirements.
This can be achieved by constraining the propagation of BGP UPDATE
messages to nodes that meet the criteria of the service flow. For
instance, to enforce communication exclusively between the Payment
Application in branch locations and the Payment Gateway, as
depicted in Figure 6, the following BGP UPDATE messages can be
advertised:
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BGP UPDATE #1a: Propagated only to the Payment Gateway node for a
point-to-point (P2P) topology between the Payment Application and
the Payment Gateway.
BGP UPDATE #1b: Propagated to C-PE1 and C-PE3 for other prefixes
that can be reached by these edge nodes.
|Payment|
+------->| GW |<----+
/ +-------+ \
/ Blue Tunnel \
/for Payment App:192.0.2.9/30\
/ \
+------+--+ +----+----+
--| | | |-192.0.2.9/30
| | Red Tunnels | |
--| C-PE1 |------------------------| |-192.0.2.4/30
|192.0.2.1| | C-PE2 |
--| |------------------------|192.0.2.2|-192.0.2.8/30
| ------+ +| | VLAN=25;
/ | |-192.0.2.10/30
+---------+ / +---------+
--| |--------------------+
| C-PE3 | /
|192.0.2.3| /
--| |-----------------+
+---------+
Figure 7: Flow Based SD-WAN Segmentation
6. SD-WAN Forwarding Model
This section describes how client traffic is forwarded in a BGP
Controlled SD-WAN for the use cases described in Section 3.
The forwarding procedures described in Section 6 of [RFC8388] are
applicable for the SD-WAN client traffic. Similar to the BGP-based
VPN/EVPN client routes UPDATE message, Route Targets can be used
to distinguish routes from different clients.
6.1. Forwarding Model for Homogeneous Encrypted SD-WAN
6.1.1. Network and Service Startup Procedures
In the Homogeneous Encrypted SD-WAN scenario, two IPsec SAs are
required to secure bidirectional traffic between two C-PE nodes
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(or their client-facing interfaces), since each SA protects
traffic in only one direction.
For example, in the full mesh scenario in Figure 2 of Section 3.2,
where client CN2 is attached to C-PE1, C-PE3, and C-PE4, six uni-
directional IPsec SAs must be established: C-PE1 <-> C-PE3; C-PE1
<-> C-PE4; C-PE3 <-> C-PE4.
SD-WAN services to clients can be IP-based or Ethernet-based. For
IP-based services, an SD-WAN edge can learn client addresses from
the client-facing interfaces via OSPF, RIP, BGP, or static
configuration. For Layer-2 services, the EVPN parameters, such as
the ESI (Ethernet Segment Identifier), EVI (Ethernet Virtual
Instance), and CE-VID (Customer Edge Virtual Instance Identifier)
to EVI mapping, can be configured as described in [RFC8388].
Instead of running IGP within each IPsec tunnel, as is common in
traditional IPsec VPN, the BGP RR can propagate the client route
UPDATE messages to authorized SD-WAN Edges based on configured
policies. The SDWAN-Edges use BGP attributes-such as the Tunnel
Encapsulation Attribute and associated Color values-to associate
received client routes with the appropriate IPsec Security
Associations (SAs), thereby eliminating the need for manual
configuration of tunnel endpoints and service policies on each
edge node.
6.1.2. Packet Walk-Through
For unicast packets forwarding:
An IPsec SA terminated at a C-PE node can carry traffic for
multiple client services. Packets to and from these services are
encapsulated in an inner tunnel, such as GRE or VXLAN. Different
client traffic can be distinguished using a unique key or
identifier in the inner encapsulation header. This inner tunnel
is further encapsulated with an outer IP header, where the
source and destination addresses are the loopback addresses of
the C-PE nodes, and the protocol field is typically set to ESP
(50).
C-PE Node-based IPsec tunnel is inherently protected when the C-
PE has multiple WAN ports to different underlay paths. As shown
in Figure 2, when one of the underlay paths fails, the IPsec
tunnel can continue operating by rerouting traffic through an
alternate WAN port.
When a C-PE receives an IPsec encrypted packet from its WAN
ports, it decrypts the packet and forwards the inner packet to
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the client facing interface based on the inner packet's
destination address.
For multicast packets forwarding:
IPsec was created to be a security protocol between two and only
two devices, so multicast service using IPsec is problematic. An
IPsec peer encrypts a packet so that only one other IPsec peer
can successfully perform the de-encryption. A straightforward
way to forward a multicast packet for the Homogeneous Encrypted
SD-WAN is to encapsulate the multicast packet in separate
unicast IPsec SA tunnels. More optimized forwarding multicast
packets for the Homogeneous Encrypted SD-WAN is out of the scope
of this document.
6.2. Forwarding Model for Hybrid Underlay SD-WAN
In this scenario, as shown in Figure 3 of Section 3.3, traffic
forwarded over the trusted VPN paths can be native (i.e.,
unencrypted). The traffic forwarded over untrusted networks need
to be protected by IPsec SA.
6.2.1. Network and Service Startup Procedures
Infrastructure setup: The proper MPLS infrastructure must be
configured among the edge nodes, i.e., the C-PE1/C-PE2/C-PE3/C-PE4
of Figure 3. The IPsec SA between wAN ports or nodes must be set
up as well. IPsec SA related attributes on edge nodes can be
distributed by BGP UPDATE messages as described in Section 5.
There could be policies governing how flows can be forwarded, as
specified by [MEF70.1]. For example, "Private-only" indicates
that the flows can only traverse the MPLS VPN underlay paths.
6.2.2. Packet Walk-Through
Unicast packets forwarding:
When C-PE-a in Figure 7 receives a packet from a client facing
interface, the forwarding decision depends on the flow's routing
policy. If a packet belonging to a flow that must be forwarded
over the MPLS VPN, the forwarding processing is the same as the
MPLS VPN. Otherwise, C-PE-a can select the least cost path,
including the previously established MPLS paths and IPsec
Tunnels, to forward the packet. Packets forwarded over the
trusted MPLS VPN do not require additional encryption, while
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those sent over untrusted networks must be encrypted by IPsec
SA.
For a c-PE with multiple WAN ports provided by different NSPs,
separate IPsec SAs can be established for the WAN ports. In this
case, the C-PE have multiple IPsec tunnels in addition to the
MPLS path to choose from to forward the packets from the client
facing interfaces.
If the IPsec SA is chosen, the packet is encapsulated by the
IPsec header and encrypted by the IPsec SA before forwarding it
to the WAN.
Packets received over MPLS paths are processed as in standard
MPLS VPNs. For packets encrypted with IPsec received from WAN
ports, the C-PE decrypts and decapsulates the inner payload
before forwarding it according to the local forwarding table. To
protect against potential attacks, traffic received through
Internet-facing WAN ports must undergo anti-DDoS mechanisms,
which are beyond the scope of this document. Additionally, the
control plane must avoid learning routes from Internet-facing
WAN ports to ensure network integrity.
+--------------|RR |----------+
/ +-+-+ \
/ \
/ \
+----+ +---------+ packets encrypted over +---------+ +----+
| CN3|--| A1-----+ Untrusted +----- B1 |--| CN1|
+----+ | C-PE-a A2-----+ +------B2 C-PE-b | +----+
|192.0.2.1| |192.0.2.2|
+----+ | A3 |PE+--------------+PE |--B3 |--| CN3|
+----+ +---------+ +--+ trusted +---+ +---------+ +----+
| VPN |
+-----------+
Figure 7: Over hybrid SD-WAN
Multicast packets forwarding:
For multicast traffic, MPLS multicast [RFC6513, RFC6514, or
RFC7988] can be utilized to forward multicast traffic across the
network.
If IPsec tunnels are used for multicast traffic, the packet must
be encapsulated and encrypted separately for each destination,
creating multiple unicast IPsec tunnels to deliver the multicast
packet to all intended recipients.
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6.3. Forwarding Model for PE based SD-WAN
6.3.1. Network and Service Startup Procedures
In this scenario, all PEs have secure interfaces facing the
clients and facing the MPLS backbone. Some PEs have additional
interfaces to the untrusted public Internet which are for
offloading low priority traffic when the MPLS paths get congested.
The PEs are already connected to their RRs, and the configurations
for the clients and policies are already established.
6.3.2. Packet Walk-Through
When offloading MPLS packets to the Internet path, each MPLS
packet is encapsulated by an outer IP header as MPLS-in-IP or
MPLS-in-GRE [RFC4023]. The outer IP address can be an interface
address or the PE's loopback address.
When IPsec Tunnel mode is used to protect an MPLS-in-IP packet,
the entire MPLS-in-IP packet is placed after the IPsec tunnel
header. In IPsec transport mode, the MPLS-in-IP packet's IP header
becomes the outer IP header of the IPsec packet, followed by an
IPsec header, and then followed by the MPLS label stack. The IPsec
header must set the payload type to MPLS by using the IP protocol
number specified in section 3 of [RFC4023]. For the MPLS-in-GRE
packets protected by IPsec Transport Mode, the GRE header follows
the IPsec header.
The IPsec SA's endpoints should not be the client-facing interface
addresses unless the traffic to/from those clients always goes
through the IPsec SA even when the MPLS backbone has enough
capacity to transport the traffic.
When the PEs' Internet-facing ports are behind the NAT [RFC3715],
additional measures are necessary to support NAT traversal. In
this Case, an outer UDP field is added to the encrypted payload
[RFC3948]. Three specific ports and protocols must remain open on
the PEs: UDP port 4500 (used for NAT traversal), UDP port 500
(used for IKE), and IP protocol 50 (ESP). The IPsec IKE (Internet
Key Exchange) sessions between PEs navigate NAT environment using
the mechanisms outlined in [RFC3947].
When a packet is received from a client facing interface, it is
initially processed according to the MPLS VPN forwarding rules. If
the MPLS backbone path to the destination is congested, the packet
is encapsulated as an MPLS-in-IP packet and encrypted using the
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IPsec tunnel to the target PE. Conversely, when a packet is
received from an Internet-facing WAN port, it is decrypted, and
the inner MPLS payload is extracted and forwarded to the MPLS VPN
engine for further processing.
Same as Scenario #2, the additional anti-DDoS mechanism must be
enabled to prevent potential attacks from the Internet-facing
port. Control Plane should not learn routes from the Internet-
facing WAN ports.
7. Manageability Considerations
A BGP-controlled SD-WAN uses RR to propagate client routes and
underlay tunnel properties among authorized SD-WAN edges. Since
the RR is configured with policies that identify authorized peers,
the peer-wise IPsec IKE (Internet Key Exchange) authentication
process is significantly simplified.
8. Security Considerations
In a BGP-controlled SD-WAN network, secure operation replies in
part on the correct configuration and behavior of the RR, which
acts as the central distribution point for BGP routing
information. RR applies preconfigured routing policies to control
the propagation of BGP UPDATE messages to authorized SD-WAN Edges,
help minimizing the risk of unintended route exposure or
unauthorized communication.
The security model for the SD-WAN described in this document is
based on the following principles:
1) Centralized Control: The RR governs all routing and policy
decisions. This centralized architecture simplifies security
management compared to distributed models, as it limits the
potential attack surface to a smaller, more controlled set of
components.
2) Secure Communication Channels: All communication between SD-WAN
edge nodes and the RR must occur over a secure channel, such as
TLS or IPsec, to ensure the confidentiality and integrity of BGP
UPDATE messages.
3) Policy Enforcement: The RR is responsible for enforcing policies
that restrict the propagation of edge node properties and
routing updates to only authorized peers. This prevents
sensitive information from being exposed to unauthorized nodes.
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4) Mitigation of Internet-Facing Risks: In scenarios where SD-WAN
edge nodes include Internet-facing WAN ports, additional
measures must be taken to mitigate security risks:
- Anti-DDoS mechanisms must be enabled to protect against
potential attacks on Internet-facing ports.
- The control plane must avoid learning routes from Internet-
facing WAN ports to prevent unauthorized traffic from being
injected into the SD-WAN.
By concentrating the security within the RR and using secure
communication channels, the SD-WAN network achieves consistent
enforcement of security policies and reduces the likelihood of
misconfigurations at individual edge nodes. However, the
robustness of this security model depends critically on the proper
configuration and ongoing maintenance of the RR. Operators must
ensure that the RR itself is adequately protected against
compromise or misconfiguration, as its failure or exploitation
could impact the entire network.
This model emphasizes simplicity and efficiency, leveraging
centralized governance to mitigate risks while ensuring
scalability and interoperability of the SD-WAN.
9. IANA Considerations
No Action is needed.
10. References
10.1. Normative References
[BCP195] Consists of RFC8996 and RFC9325.
[RFC2332] J. Luciani, et al, "NBMA Next Hop Resolution Protocol
(NHRP)", RFC2332, April 1998.
[RFC2784] D. Farinacci, et al, "Generic Routing Encapsulation
(GRE)" RFC2784, March 2000.
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[RFC3715] B. Aboba, W. Dixon, "IPsec-Network Address Translation
(NAT) Compatibility Requirements", March 2004.
[RFC3947] T. Kivinen, et al, "Negotiation of NAT Traversal in the
IKE", Jan. 2005.
[RFC3948] A. Huttunen, et al, "UDP Encapsulation of IPsec ESP
Packets", Jan 2005.
[RFC4023] T. Worster, Y. Rekhter, E. Rosen, "Encapsulating MPLS in
IP or Generic Routing Encapsulation (GRE)", March 2005.
[RFC4360] S. Sangli, et al, "BGP Extended Communities Attribute",
RFC4360, Feb. 2006.
[RFC4364] E. Rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
networks (VPNs)", Feb 2006.
[RFC4456] T. Bates, E. Chen, R. Chandra, "BGP Route Reflection: An
Alternative to Full Mesh Internal BGP (IBGP)", April
2006.
[RFC4659] J. De clercq, et al, "BGP-MPLS IP Virtual Private
Network (VPN) Extension for IPv6 VPN", RFC4659, Sept
2006.
[RFC4761] K. Kompella and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling",
RFC4761, Jan. 2007.
[RFC4762] M. Lasserre and V. Kompella, "Virtual Private LAN
Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC4762, Jan. 2007.
[RFC6071] S. Frankel, S. Krishan, "IP Security (IPsec) and
Internet Key Exchange (IKE) Document Roadmap", Feb 2011.
[RFC7296] C. Kaufman, et al, "Internet Key Exchange Protocol
Version 2 (IKEv2)", Oct 2014.
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[RFC7348] M. Mahalingam, et al, "Virtual eXtensible Local Area
Network (VXLAN): A Framework for Overlaying Virtualized
Layer 2 Networks over Layer 3 Networks", RFC7348, Aug
2014.
[RFC7432] A. Sajassi, et al, "BGP MPLS-Based Ethernet VPN",
RFC7432, Feb 2015.
[RFC8200] S. Deering and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification". July 2017.
[RFC8365] A. Sajassi, et al, "A Network Virtualization Overlay
Solution Using Ethernet VPN (EVPN)", March 2018.
[RFC8388] J. Rabadan, et al, "Usage and Applicability of BGP MPLS-
Based Ethernet VPN", RFC8388, May 2018.
[RFC9012] K.Patel, et al "The BGP Tunnel Encapsulation Attribute",
RFC9012, April 2021.
[RFC9522] A. Farrel, "Overview and Principles of Internet Traffic
Engineering", RFC9522, Jan. 2024.
10.2. Informative References
[Net2Cloud-Problem] L. Dunbar and A. Malis, "Dynamic Networks to
Hybrid Cloud DCs: Problems and Mitigation Practices",
draft-ietf-rtgwg-net2cloud-problem-statement-41, April.
2024.
[IEEE802.3] "IEEE Standard for Ethernet" by The Institute of
Electrical and Electronics Engineers (IEEE) 802.3.
[MEF70.1] SD-WAN Service Attributes and Service Framework,
https://www.mef.net/resources/mef-70-1-sd-wan-service-
attributes-and-service-framework/. Nov 2021.
[MEF70.2] "SD-WAN Service Attributes and Service Framework" by
MEF, https://www.mef.net/resources/mef-70-2-sd-wan-
service-attributes-and-service-framework/. Oct 2023.
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11. Acknowledgments
Acknowledgements to Gunter van de Velde, Andrew Alston, Adrian
Farrel, Jim Guichard, Joel Halpern, John Scudder, Darren Dukes,
Andy Malis, Donald Eastlake, Stephen Farrell, and Victo Sheng for
their review and contributions.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Ali Sajassi
Cisco
Email: sajassi@cisco.com
John Drake
Independent
Email: je_drake@yahoo.com
Basil Najem
Bell Canada
Email: basil.najem@bell.ca
Sue Hares
Email: shares@ndzh.com
Contributor's Addresses
David Carrel
Graphiant
Email: carrel@graphiant.com
Ayan Banerjee
Cisco
Email: ayabaner@cisco.com
Dunbar, et al. [Page 30]
