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Network Working Group                                         L. Dunbar
Internet Draft                                              J. Guichard
Intended status: Informational                                Futurewei
Expires: January 13, 2021                                 Ali Sajassi
                                                                  Cisco
                                                               J. Drake
                                                                Juniper
                                                               B. Najem
                                                            Bell Canada
                                                         Ayan Barnerjee
                                                              D. Carrel
                                                                 Cisco

                                                          July 13, 2020



                   BGP Usage for SDWAN Overlay Networks
                   draft-dunbar-bess-bgp-sdwan-usage-08

Abstract

   The document describes three distinct SDWAN scenarios and discusses
   the applicability of BGP for each of those scenarios. The goal of
   the document is to demonstrate how BGP-based control plane is used
   for large scale SDWAN overlay networks with little manual
   intervention.

   SDWAN edge nodes are commonly interconnected by multiple underlay
   networks which can be owned and managed by different network
   providers.

Status of this Memo

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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79. This document may not be modified,
   and derivative works of it may not be created, except to publish it
   as an RFC and to translate it into languages other than English.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that



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   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
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   The list of current Internet-Drafts can be accessed at
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   This Internet-Draft will expire on January 13, 2009.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents


   1. Introduction...................................................3
   2. Conventions used in this document..............................4
   3. Use Case Scenario Description and Requirements.................6
      3.1. Requirements..............................................6
         3.1.1. Supporting Multiple SDWAN Segmentations..............6
         3.1.2. Client Service Requirement...........................6
         3.1.3. Application Flow Based Segmentation..................7
         3.1.4. Zero Touch Provisioning..............................8
         3.1.5. Constrained Propagation of SDWAN Edge Properties.....9


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      3.2. Scenarios #1: Homogeneous WAN............................10
      3.3. Scenario #2: CPE based SDWAN over Hybrid WAN Underlay....11
      3.4. Scenario #3: Private VPN PE based SDWAN..................14
   4. BGP Walk Through..............................................15
      4.1. BGP Walk Through for Homogeneous SDWAN...................15
      4.2. BGP Walk Through for Application Flow Based Segmentation.18
      4.3. Client Service Provisioning Model........................19
      4.4. WAN Ports Provisioning Model.............................20
      4.5. Why BGP as Control Plane for SDWAN?......................20
   5. SDWAN Traffic Forwarding Walk Through.........................21
      5.1. SDWAN Network Startup Procedures.........................21
      5.2. Packet Walk-Through for Scenario #1......................22
      5.3. Packet Walk-Through for Scenario #2......................22
      5.4. Packet Walk-Through for Scenario #3......................24
   6. Manageability Considerations..................................24
   7. Security Considerations.......................................24
   8. IANA Considerations...........................................25
   9. References....................................................25
      9.1. Normative References.....................................25
      9.2. Informative References...................................25
   10. Acknowledgments..............................................27

1. Introduction

   Here are some key characteristics of "SDWAN" networks:

     - Augment of transport, which refers to utilizing overlay paths
       over different underlay networks. Very often there are multiple
       parallel overlay paths between any two SDWAN edges, some of
       which are private networks over which traffic can traverse with
       or without encryption, others require encryption, e.g. over
       untrusted public networks.
     - Enable direct Internet access from remote sites, instead hauling
       all traffic to Corporate HQ for centralized policy control.
     - Some traffic are routed based on application IDs instead of
       based on destination IP addresses.
     - The Application Routing can also be based on specific
       performance criteria (e.g. packets delay, packet loos, jitter)
       to provide better application performance by choosing the right
       underlay that meets or exceeds the specified criteria.

   [Net2Cloud-Problem] describes the network related problems that
   enterprises face to connect enterprises' branch offices to dynamic
   workloads in different Cloud DCs, including using SDWAN to aggregate



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   multiple paths provided by different service providers to achieve
   better performance and to accomplish application ID based
   forwarding.

   Even though SDWAN has been positioned as a flexible way to reach
   dynamic workloads in third party Cloud data centers over different
   underlay networks, scaling becomes a major issue when there are
   hundreds or thousands of nodes to be interconnected by an SDWAN
   overlay networks.

   BGP is widely used by underlay networks. This document describes
   using BGP for edge nodes to exchange information across the SDWAN
   overlay networks.

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 SDWAN controller to manage
               SDWAN overlay path creation/deletion and monitor the
               path conditions between sites.

   CPE:        Customer Premise Equipment

   CPE-Based VPN: Virtual Private Secure network formed among CPEs.
               This is to differentiate from more commonly used PE-
               based VPNs [RFC 4364].

   Homogeneous SDWAN: A type of SDWAN network in which all traffic
               to/from the SDWAN edge nodes has to be encrypted
               regardless of underlay networks. For lack of better
               terminology, we call this Homogeneous SDWAN throughout
               this document.

   ISP:        Internet Service Provider

   NSP:        Network Service Provider. NSP usually provides more
               advanced network services, such as MPLS VPN, private
               leased lines, or managed Secure WAN connections, many


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               times within a private trusted domain, whereas an ISP
               usually provides plain internet services over public
               untrusted domains.

   PE:         Provider Edge

   SDWAN Edge Node:  an edge node, which can be physical or virtual,
               maps the attached clients' traffic to the wide area
               network (WAN) overlay tunnels.

   SDWAN:      Software Defined Wide Area Network. In this document,
               "SDWAN" refers to the solutions of pooling WAN bandwidth
               from multiple underlay networks to get better WAN
               bandwidth management, visibility & control. When the
               underlay networks are private, traffic can traverse
               without additional encryption; when the underlay
               networks are public, such as the Internet, some traffic
               may need to be encrypted when traversing through
               (depending on user provided policies).

   SDWAN IPsec SA: IPsec Security Association between two SDWAN ports
               or nodes.

   SDWAN over Hybrid Networks: SDWAN over Hybrid Networks typically
               have edge nodes utilizing bandwidth resources from
               multiple service providers. In Hybrid SDWAN network,
               packets over private networks can go natively without
               encryption and are encrypted over the untrusted network,
               such as the public Internet.

   WAN Port:   A Port or Interface facing an ISP or Network Service
               Provider (NSP), with address (usually public routable
               address) allocated by the ISP or the NSP.

   C-PE:       SDWAN Edge node, which can be CPE for customer managed
               SDWAN, or PE that is for provider managed SDWAN
               services).

   ZTP:        Zero Touch Provisioning





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3. Use Case Scenario Description and Requirements

   SDWAN networks can have different topologies and have different
   traffic patterns. To make it easier for the focused discussion in
   subsequent drafts on SDWAN control plane and data plane, this
   section describes several SDWAN scenarios that may have different
   impact on their corresponding control planes & data planes.

3.1. Requirements

3.1.1. Supporting Multiple SDWAN Segmentations

   The term "network segmentation", a.k.a. SDWAN instances, is
   referring to the process of dividing the network into logical sub-
   networks using isolation techniques on a forwarding device such as a
   switch, router, or firewall. For a homogeneous network, such as MPLS
   VPN or Layer 2 network, VRF or VLAN are used to achieve the network
   segmentation.

   As SDWAN is an overlay network arching over multiple types of
   networks, MPLS L2VPN/L3VPN or pure L2 underlay can continue using
   the VRF, VN-ID or VLAN to differentiate SDWAN network segmentations.
   For public internet, the IPsec inner encapsulation header can carry
   the SDWAN Instance Identifier to differentiate the packets belonging
   to different SDWAN instances.

   BGP already has the capability to differentiate control packets for
   different network instances. When using BGP for SDWAN, the SDWAN
   segmentations can be differentiated by the SDWAN Target ID in the
   BGP Extended Community in the same way as VPN instances being
   represented by the Route Target. Same as Route Target, need to use a
   different name to differentiate from VPN if a CPE supports
   traditional VPN with multiple VRFs and supports multiple SDWAN
   Segmentations (instances). The actual SDWAN Target ID encoding is
   proposed by [SDWAN-EDGE-Discovery].



3.1.2. Client Service Requirement

   Client interface of SDWAN nodes can be IP or Ethernet based.

   For Ethernet based client interfaces, SDWAN edge should support
   VLAN-based service interfaces (EVI100), VLAN bundle service
   interfaces (EVI200), or VLAN-Aware bundling service interfaces. EVPN
   service requirements are applicable to the Client traffic, as
   described in the Section 3.1 of RFC8388.



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   For IP based client interfaces, L3VPN service requirements are
   applicable.



3.1.3. Application Flow Based Segmentation

   Application Flow based Segmentation, also known as SDWAN Traffic
   Segmentation, enables the separation of the traffic based on the
   business and the security needs for different users' groups and/or
   application requirements. Each user group and/or applications may
   need different isolated topology and/or policies to fulfill the
   business requirements.

   The Application Flow based Segmentation concept is analogous to VLAN
   (in L2 network) and VRF (in L3 network).

   One can think about the Application Flow based Segmentation as a
   feature that can be provided or enabled on a single SDWAN service
   (or domain) to a single Subscriber. Each SDWAN Service can have one
   or more overlay Segments to support the business requirement; each
   Segment has its own policy, topology and application/user groups.
   Applications/users' group can belong to more than one Segment.

   For example, a retail business requires the point-of-sales (PoS)
   application in all stores to be isolated from other applications AND
   routed only to the payment processing entity at a hub site (i.e. hub
   and spoke); however, the same retail business requires the other
   applications to be routed to all sites (i.e. multipoint-to
   multipoint) AND isolated from the PoS application.

   In the figure below, the traffic from the PoS application follows a
   Tree topology, whereas other traffic can be multipoint-to-multipoint
   topology.
















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                              +--------+
              Payment traffic |Payment |
                +------+----+-+gateway +------+----+-----+
               /      /     | +----+---+      |     \     \
              /      /      |      |          |      \     \
           +-+--+  +-+--+  +-+--+  |   +-+--+  +-+--+  +-+--+
           |Site|  |Site|  |Site|  |   |Site|  |Site|  |Site|
           | 1  |  |  2 |  | 3  |  |   |4   |  |  5 |  | 6  |
           +--+-+  +--+-+  +--|-+  |   +--|-+  +--|-+  +--|-+
              |       |       |    |      |       |       |
            ==+=======+=======+====+======+=======+=======+===
                  Multi-point connection for Other traffic

   Another example is an enterprise who wants to isolate the traffic
   for each department and have different topology and policy for
   different department; the HR department may need to access certain
   applications that are NOT accessible by the engineering department.
   In addition, the contractors may have a limited access to the
   enterprise resources.

3.1.4. Zero Touch Provisioning

   Unlike traditional EVPN or L3VPN whose PEs are deployed for long
   term, SDWAN edge nodes (virtual or physical) deployment at a
   specific location can be ephemeral. Therefore, Zero Touch
   Provisioning (ZTP), or Plug and Play, is a common requirement for
   SDWAN. When an SDWAN edge is physically installed at a location or
   instantiated on a VM in a Cloud DC, ZTP automates follow-up steps,
   including updates to the OS, software version, and configuration
   prior to connection. From network control perspective, ZTP includes
   the following:

     -   Upon power up, an SDWAN node can establish transport layer
     secure connection (such as TLS, SSL, etc.) to its controller whose
     address can be burned or preconfigured on the device.

     -   The SDWAN Controller can designate a Local Network Controller
     in the proximity of the SDWAN node; the Local Network Controller
     manages and monitor the communication policies of the edge node.








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3.1.5. Constrained Propagation of SDWAN Edge Properties

   One SDWAN edge node may only be authorized to communicate with a
   small number of other SDWAN edge nodes. Under this circumstance, the
   property of the SDWAN edge node cannot be propagated to any other
   nodes who are not authorized to communicate. But a remote SDWAN edge
   node upon powering up might not have the proper policies to know who
   the authorized peers are. Therefore, it is very essential for SDWAN
   deployment have a central point to distribute the properties of each
   SDWAN edge node to its authorized peers.

   BGP is well suited for this purpose. RFC 4684 has specified the
   procedure to constrain the distribution of BGP UPDATE to only a
   subset of SDWAN edges. Basically, each edge node informs the Route
   Reflector (RR) [RFC4456] on its interested SDWAN instances. The RR
   only propagates the BGP UPDATE for the relevant SDWAN instances to
   the edge.

   Usually the connection between a SDWAN edge node and its RR is over
   insecure network. Therefore, upon power up, a SDWAN node needs to
   establish a secure transport layer connection (TLS, SSL, etc.) to
   its designated RR. The BGP UPDATE messages need to be sent over the
   secure channel (TLS, SSL, etc.) to the RR.



                              +---+
                 Peer Group 1 |RR |   Peer Group 2
                +======+====+=+   +======+====+=====+
               /      /     | +---+      |     \     \
              /      /      |            |      \     \
           +-+--+  +-+--+  +-+--+      +-+--+  +-+--+  +-+--+
           |C-PE|  |C-PE|  |C-PE|      |C-PE|  |C-PE|  |C-PE|
           | 1  |  |  2 |  | 3  |      |4   |  |  5 |  | 6  |
           +----+  +----+  +----+      +----+  +----+  +----+
                Tenant 1                   Tenant 2
          Figure 1: Peer Groups managed by RR


   Tenant separation is achieved by the SDWAN instance identification
   represented in control plane and data plane, respectively.





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3.2. Scenarios #1: Homogeneous WAN

   This is referring to a type of SDWAN network with edge nodes
   encrypting all traffic over WAN to other edge nodes, regardless of
   whether the underlay is private or public. For lack of better
   terminology, we call this Homogeneous SDWAN throughout this
   document.

   Some typical scenarios for the use of a Homogeneous SDWAN network
   are as follows:

   -  A small branch office connecting to its HQ offices via the
   Internet. All sensitive traffic to/from this small branch office has
   to be encrypted, which is usually achieved using IPsec SAs.

   -  A store in a shopping mall may need to securely connect to its
   applications in one or more Cloud DCs via the Internet. A common way
   of achieving this is to establish IPsec SAs to the Cloud DC gateway
   to carry the sensitive data to/from the store.

   As described in [SECURE-EVPN], the granularity of the IPsec SAs for
   Homogeneous SDWAN 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 subnets/tenants/site are
   encrypted.


                                       +---+
                        +--------------|RR |------------+
                       /  Untrusted    +-+-+             \
                      /                                   \
                     /                                     \
         +----+  +---------+                             +------+  +----+
         | CN3|--|         P1-----+ -------------+------ P1     |--| CN1|
         +----+  | C-PE1   P2-----+              |       | C-PE2|  +----+
         +----+  |         P3-----+     Wide     +------ P2     |  +----+
         | CN2|--|         |      |     area     +------ P3     |--| CN3|
         +----+  +---------+      |   network    |       +------+  +----+
                              |              |
         +----+  +---------+      | all packets  |       +------+  +----+
         | CN1|--|         P1-----+ encrypted    +------ P1     |--| CN1|
         +----+  | C-PE3   P2-----+     by       |       | C-PE4|  +----+
         +----+  |         P3-----+ IPsec SAs    +------ P2     |  +----+
         | CN2|--|         P4-----+--------------+       |      |--| CN2|
         +----+  +---------+                             +------+  +----+

          CN: Client Networks, which is same as Tenant Networks used by NVo3

                      Figure 2: Homogeneous SDWAN


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   One of the key properties of homogeneous SDWAN is that the SDWAN
   Local Network Controller (RR)is connected to C-PEs via untrusted
   public network, therefore, requiring secure connection between RR
   and C-PEs (TLS, DTLS, etc.).

   Homogeneous SDWAN has some similarity to commonly deployed IPsec
   VPN, albeit the IPsec VPN is usually point-to-point among a small
   number of nodes and with heavy manual configuration for IPsec
   between nodes, whereas an SDWAN network can have a large number of
   edge nodes with an SDWAN controller to manage requiring zero touch
   provisioning upon powering up.

   Existing Private VPNs (e.g. MPLS based) can use homogeneous SDWAN to
   extend over public network to remote sites to which the VPN operator
   does not own or lease infrastructural connectivity, as described in
   [SECURE-EVPN] and [SECURE-L3VPN]

3.3. Scenario #2: CPE based SDWAN over Hybrid WAN Underlay

   In this scenario, SDWAN edge nodes (a.k.a. C-PEs) have some WAN
   ports connected to PEs of Private VPNs over which packets can be
   forwarded natively without encryption, and some WAN ports connected
   to the public Internet over which sensitive traffic have to be
   encrypted (usually by IPsec SA).

   In this scenario, the SDWAN edge nodes' egress WAN ports are all
   IP/Ethernet based, either egress to PEs of the VPNs or egress to the
   public Internet. Even if the VPN is a MPLS network, the VPN's PEs
   have IP/Ethernet links to the SDWAN edge (C-PEs). Throughout this
   document, this scenario is also called CPE based SDWAN over Hybrid
   Networks.

   Even though IPsec SA can secure the packets traversing the Internet,
   it does not offer the premium SLA commonly offered by Private VPNs,
   especially over long distance. Clients need to have policies to
   specify criteria for flows only traversing private VPNs or
   traversing either as long as encrypted when over the Internet. For
   example, client can have those polices for the flows:

      1. A policy or criteria for sending the flows over a private
         network without encryption (for better performance),
      2. A policy or criteria for sending the flows over any networks
         as long as the packets of the flows are encrypted when
         traversing untrusted networks, or
      3. A policy of not needing encryption at all.




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   If a flow traversing multiple segments, such as A<->B<->C<->D, has
   either Policy 2 or 3 above, the flow can traverse different
   underlays in different network segments, such as over Private
   network underlay between A<->B without encryption, or over the
   public internet between B<->C in an IPsec SA.

   As shown in the figure below, C-PE-1 has two different types of
   interfaces (A1 to Internet and A2 & A3 to VPN). The C-PEs' loopback
   addresses and addresses attached to C-PEs may or may not be visible
   to the ISPs/NSPs. The addresses for the WAN ports can have addresses
   allocated by service providers or dynamically assigned (e.g. by
   DHCP). One WAN port shown in the figure below (e.g. A1, A2, A3 etc.)
   is a logical representation of potential multiple physical ports on
   the C-PEs.




                                       +---+
                        +--------------|RR |----------+
                       /  Untrusted    +-+-+           \
                      /                                 \
                     /                                   \
     +----+  +---------+  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 3: Hybrid SDWAN





   Some key characteristics of a Hybrid SDWAN overlay network are as
   follows:



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  - one C-PE may be connected to different ISPs/NSPs, with some of its
     WAN ports addresses being assigned by different ISPs/NSPs.

  - The WAN ports connected to PEs of trusted private networks (e.g. MPLS
     VPN) hand off IP/Ethernet packets, just like today's CPE that do not
     handle MPLS packets and do not participate in the underlay VPN networks'
     control plane.  Traffic can flow natively without encryption when be
     forwarded out through those WAN ports for better performance.

  - The WAN ports connected to untrusted networks, e.g. the Internet,
     requires sensitive traffic to be encrypted, i.e. encrypted by IPsec SA.

  - An SDWAN local Network Controller (RR) is connected to C-PEs via
     the untrusted public network, therefore, requiring secure
     connection between RR and C-PEs via TLS, DTLS, etc.

   - The SDWAN nodes' [loopback] addresses might not be routable nor
     visible in the underlay ISP/NSP networks. Routes & services
     attached to SDWAN edges at the SDWAN overlay layer are in
     different address spaces than the underlay networks.

  - There could be multiple SDWAN devices sharing a common property,
     such as a geographic location. Some applications over SDWAN may
     need to traverse specific geographic locations for various
     reasons, such as to comply with regulatory rules, to utilize
     specific value added services, or others.

   - The underlay path selection between sites can be a local decision.
     Some policies allow one service from C-PE1 -> C-PE2 -> C-PE3 using
     one ISP/NSP underlay in the first segment (C-PE1 -> C-PE2) and
     using a different ISP/NSP in the second segment (C-PE2-> CPE3).

   - Services may not be congruent, i.e. the packets from A-> B may
     traverse one underlay network, and the packets from B -> A may
     traverse a different underlay.

   - Different services, routes, or VLANs attached to SDWAN nodes can
     be aggregated over one underlay path; same service/routes/VLAN can
     spread over multiple SDWAN underlays at different times depending
     on the policies specified for the service. For example, one
     tenant's packets to HQ need to be encrypted when sent over the
     Internet or have to be sent over private networks, while the same


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     tenant's packets to Facebook can be sent over the Internet without
     encryption.

3.4. Scenario #3: Private VPN PE based SDWAN

   This scenario refers to existing VPN (e.g. MPLS based VPN, such as
   EVPN or IPVPN) adding extra ports facing untrusted public networks
   allowing PEs to offload some low priority traffic to ports facing
   public networks when the VPN MPLS paths are congested. Throughout
   this document, this scenario is also called Internet Offload for
   Private VPN, or PE based SDWAN.

   In this scenario, the packets offloaded to untrusted public network
   must be encrypted.

   PE based SDWAN can be used by VPN service providers to temporarily
   increase bandwidth between sites when they are not sure if the
   demand will sustain for long period of time or as a temporary
   solution before the permanent infrastructure is built or leased.





                                   +---+
                           +-------|PE2|
                          /        +---+
                Internet /          ^
                offload /           || VPN
                       /     VPN    v
                      ++--+        ++-+       +---+
                      |PE1| <====> |RR| <===> |PE3|
                      +-+-+        +--+       +-+-+
                        |                       |
                        +--- Public Internet -- +

          Figure 4: Additional Internet paths added to the VPN


   Here are some key properties for PE based SDWAN:

       - For MPLS based VPN, PEs continue having MPLS encapsulation
          handoff to existing paths.




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       - The BGP RR is connected to PEs in the same way as VPN, i.e.
          via the trusted network.
       - For the added Internet ports, PEs have IP packets handoff,
          i.e. sending and receiving IP data frames. Internally, PEs
          can have the option to encapsulate the MPLS payload in IP, as
          specified by RFC4023.
       - The ports facing public internet might get IP addresses
          assigned by ISPs, which may not be in the same address domain
          as PEs'.
       - Ports facing public internet are not as secure as the ports
          facing private infrastructure. There could be spoofing, or
          DDOS attacks to the ports facing public internet. Extra
          consideration must be given when injecting the new routes
          learned from public network into VRFs.
       - Even though packets are encrypted over public internet, the
          performance SLA is not guaranteed over public internet.
          Therefore, clients may have policies only allowing some flows
          to be offloaded to internet path.



4. BGP Walk Through

4.1. BGP Walk Through for Homogeneous SDWAN

   In the figure below, packets destined towards multiple routes
   attached to the C-PE2 can be carried by one IPsec tunnel. Then one
   BGP UPDATE can be announced by C-PE2 to its RR.



















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                                  +---+
                        +---------|RR |----------+
                       / Untrusted+---+           \
                      /                            \
                C-PE1/                              \
             +---------+                       +------+
           --+---+--------------------------------->  |-10.1.x.x/16
             |  /      |                       |C-PE2 |- VLAN = 15
             | /       |                     +----->  |
           --|/        |                     | |      |-12.1.1.x/24
             +---------+                     | +------+
                                             |
               C-PE3                         |
             +---------+                     |
           --|---+---------------------------+
             |  /      |
             | /       |
           --|/        |
             +---------+
                      Figure 5: Homogeneous SDWAN


   The BGP UPDATE Message from C-PE2 to RR should have the client
   routes encoded in the MP-NLRI Path Attribute and the IPsec Tunnel
   associated information encoded in the Tunnel-Encap Path Attributes
   as described in the [SECURE-EVPN]:

     - MP-NLRI Path Attribute: to indicate multiple routes attached to
     the C-PE2:
         10.1.x.x/16
         VLAN #15
         12.1.1.x/24
     - Tunnel-Encap Path Attribute: to describe the IPsec attributes
     for routes encoded in the NLRI Path Attribute:
         IPsec attributes for remote nodes to establish the IPsec
         tunnel to C-PE2.

   If different client routes attached to C-PE2 needs to be reached by
   separate IPsec tunnels, then multiple BGP UPDATE messages need to be
   sent to the remote nodes via RR. If C-PE2 doesn't have the policy on
   authorized peers for the specific client routes, RR needs to check
   the client routes policies to propagate the BGP UPDATE messages to
   the remote authorized edge nodes.

   There could be policies governing the topologies of a client's
   different routes attached to an edge node. For example, VLAN #25 and


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   route 22.1.1.x/24 could be the Payment Applications described in the
   Section 3.1.2 that can only communicate with Payment Gateway
   attached to C-PE3. If C-PEs don't have the policy to govern the
   communication peers, RR can take over the responsibility of only
   send BGP UPDATE to the authorized peers.

                                    +---+
                        +-----------|RR |----------+
                       / Untrusted  +---+           \
                      /                              \
                     /                                \
             +---------+                         +------+
           --+ -------------------------------------->  |-10.1.x.x/16
             | C-PE1   |                         |C-PE2 |- VLAN = 15
             |         |                 +----------->  |- 12.1.1.x/24
           --|---------------------------+       |      |
             +---------+                      +------>  |- VLAN=25
                                             /   +------+  22.1.1.x/24
             +---------+                    /
           --| ----------------------------+
             | C-PE3   |                  /
             |         |                 /
           --| -------------------------+
             +---------+


               Figure 6: (see *.pdf for more accurate figure)


   UPDATE 1:
    -    MP-NLRI Path Attribute:
          10.1.x.x/16
          VLAN #15
          12.1.1.x/24

    -    Tunnel-Encap Path Attribute:
          IPsec SA attributes for IPsec tunnels to C-PE2 from any node
          for reaching 10.1.x.x/16, VLAN #15, and 12.1.1.x/24.


   UPDATE 2 (only sent to C-PE3)
    -    MP-NLRI Path Attribute:
          VLAN #25
          22.1.1.x/24

    -    Tunnel-Encap:



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          IPsec SA attributes for IPsec tunnels to C-PE2 from C-PE3 for
          reaching VLAN #25 and subnet 22.1.1./24.




4.2. BGP Walk Through for Application Flow Based Segmentation

   If the applications are assigned with unique IP addresses, the
   Application Flow based Segmentation described in Section 3.1.2 can
   be achieved by advertising different BGP UPDATE messages to
   different nodes. In the Figure below, the following BGP Updates can
   be advertised to ensure that Payment Application only communicates
   with the Payment Gateway:

   BGP UPDATE #1 from C-PE2 to RR for the P2P topology that is only
   propagated to Payment GW node:

      - MP-NLRI Path Attribute:
            - 30.1.1.x/24
      - Tunnel Encap Path Attribute
            - IPsec Attributes for PaymentGW ->C-PE2

   BGP UPDATE #2 from C-PE2 to RR for the routes to be reached by C-PE1
   and C-PE2:

      - MP-NLRI Path Attribute:
            - 10.1.x.x
            - 12.4.x.x
      - Tunnel-Encap Path Attribute:
            - Any node to C-PE2
















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                                  +-------+
                                  |Payment|
                        +-------->|  GW   |<-------+
                       /Hub-spoke +-------+         \
                      /for Payment App               \
               C-PE1 /                                \ C-PE2
             +------/--+                          +----\-+
           --|-----/   |                          |     -|- 30.1.1.x/24
             + --------------------------------------->  |-10.1.x.x/16
             |         |                          |      |-
             |         |                 +------------>  |- 12.1.1.x/24
           --|---------------------------+        |      |
             +---------+                       +------>  |- VLAN=25;
                                              /   +------+  22.1.1.x/24
             +---------+                     /
           --| -----------------------------+
             | C-PE3   |                   /
             |         |                  /
           --| --------------------------+
             +---------+
               Figure 7: Application Based SDWAN Segmentation




4.3. Client Service Provisioning Model

   The provisioning tasks described in Section 4 of RFC8388 are the
   same for the SDWAN client traffic. When client traffic is multi-
   homed to two (or more) C-PEs, the Non-Service-Specific parameters
   need to be provisioned per the Section 4.1.1 of RFC8388.

   Since some SDWAN nodes are ephemeral and have small number of IP
   subnets or VLANs attached to their client ports, it is recommended
   to have default and simplified Service-specific parameters for each
   client port, remotely managed by the SDWAN Network Controller via
   the secure channel (TLS/DTLS) between the controller and the C-PEs.










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4.4. WAN Ports Provisioning Model

   Since the deployment of PEs to MPLS VPN are for relatively long
   term, the common provisioning procedure for PE's WAN ports is via
   CLI.

   A SDWAN node deployment can be ephemeral and its location can be in
   remote locations, manual provisioning for its WAN ports is not
   acceptable. In addition, a SDWAN WAN port's IP address can be
   dynamically assigned or using private addresses. Therefore, it is
   necessary to have a separate control protocol; something like NHRP
   did for ATM, for a SDWAN node to register its WAN property to its
   controller dynamically.

   Unlike a PE to MPLS based VPN where its WAN ports are homogeneously
   facing MPLS private network and all traffic are egressed in MPLS
   data frames through its WAN ports, the WAN ports of a SDWAN node can
   be connected to a PE of VPN with Ethernet/IP, MPLS private network
   directly via MPLS headers, or the public Internet.

   For Scenario #1 described in Section 3.2, the WAN ports can face
   public internet or VPN.

   For Scenario #2 described in Section 3.3, WAN ports are either
   configured as connecting to PEs of VPN where traffic can be sent as
   IP/Ethernet without encryption, or configured as connecting to
   public Internet that requires encryption for packets egress out.

   For Scenario #3 described in Section 3.4, the WAN ports are either
   configured as VPN egress ports (hand off MPLS data frames), or as
   connecting to the public internet that requires MPLS in IP in IPsec
   encapsulation.



4.5. Why BGP as Control Plane for SDWAN?

   For a small sized SDWAN network, traditional hub & spoke model using
   NHRP or DSVPN/DMVPN with a hub node (or controller) managing SDWAN
   node WAN ports mapping (e.g. local & public addresses and tunnel
   identifiers mapping) can work reasonably well. However, for a large
   SDWAN network, say more than 100 nodes with different types of
   topologies, the traditional approach becomes very messy, complex and
   error prone.

   Here are some of the compelling reasons of using BGP instead of
   extending NHRP/DSVPN/DMVPN. (Same as the reasons quoted by LSVR on
   why using BGP):


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   -  BGP has the built-in capability to constrain the propagation of
   SDWAN edge node properties to a small number of edge nodes
   [RFC4684].

   -  RR already has the capability to apply policies to communications
   among peers.

   -  BGP is widely deployed as sole protocol (see RFC 7938)

   -  Robust and simple implementation

   -  Wide acceptance - minimal learning

   -  Reliable transport

   -  Guaranteed in-order delivery

   -  Incremental updates

   -  Incremental updates upon session restart

   -  No flooding and selective filtering



5. SDWAN Traffic Forwarding Walk Through

   BGP based EVPN control plane are still applicable to routes attached
   to the client ports of SDWAN nodes. Section 5 of RFC8388 describes
   the BGP EVPN NLRI Usage for various routes of client traffic. The
   procedures described in the Section 6 of RFC8388 are same for the
   SDWAN client traffic.

   The only additional consideration for SDWAN is to control how
   traffic egress the SDWAN edge node to various WAN ports.

5.1. SDWAN Network Startup Procedures

   A SDWAN network can add or delete SDWAN edge nodes on regular basis
   depending on user requests.

     - For Scenario #1: a SDWAN edge node in a shopping mall or Cloud DC can
        be added or removed on demand. The Zero Touch Provisioning described
        in 3.1.2 are required for the node startup.
     - For Scenario #2: this can be Data Centers or enterprises upgrading
        their CPEs to add extra bandwidth via public internet in addition to
        VPN services that they already purchased. Before the node powers up



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        or upgraded, there should be links connected to the PEs of a provider
        VPNs.
     - For Scenario #3, the Internet facing WAN ports are added to (or
        removed from) existing VPN PEs.


5.2. Packet Walk-Through for Scenario #1

   Upon power up, a SDWAN node can learn client routes from the Client
   facing ports, in the same way as EVPN described in RFC8388.
   Controller facilitates the IPsec SA establishment and rekey
   management as described in [SECURE-EVPN]. Controller manages how
   client's routes are associated with individual IPSec SA.

    [SECURE-EVPN] describes a solution for SDWAN Scenario #1. It
   utilizes the BGP RR to facilitate the key and policy exchange among
   PE devices to create private pair-wise IPsec Security Associations
   without IKEv2 point-to-point signaling or any other direct peer-to-
   peer session establishment messages.

   When C-PEs do not support MPLS, the approaches described by RFC8365
   can be used, with addition of IPsec encrypting the IP packets when
   sending packets over the Black Interfaces.



5.3. Packet Walk-Through for Scenario #2

   In this scenario, C-PEs have some WAN ports connected to the public
   internet and some WAN ports with direct connect to PEs of trusted
   VPN. The C-PEs in Scenario #2 have the plain IP/Ethernet data frames
   egress to the PEs of the VPN, encrypted data frames egress the WAN
   ports facing the public Internet.

   Users specify the policy or criteria on which flows can only egress
   WAN ports facing the trusted VPN without encryption, which can
   egress the WAN ports facing the public Internet with encryption, or
   which can egress WAN ports facing the public Internet without
   encryption.

   The internet facing WAN ports can face potential DDoS attacks,
   additional anti-DDoS mechanism has to be enabled on those WAN ports
   and the Control Plane should not learn routes from the Public
   Network facing WAN ports.

   For the Scenario #2, if a client route can be reached by MPLS VPN
   and IPsec Tunnel via public network, the BGP UPDATE for the client



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   route should indicate all available tunnels in the Tunnel Path
   Attribute of the BGP NLRI.

                                       +---+
                        +--------------|RR |----------+
                       /  Untrusted    +-+-+           \
                      /    Network                      \
                     /                                   \
     +----+  +---------+  packets encrypted over     +--------+  +----+
     | CN3|--|         A1-----+ Untrusted    +------ B1       |--| CN1|
     +----+  | C-PE-a  A2-----+              +-------B2 C-PE-b|  +----+
             |10.1.1.1 |                             |10.1.2.1|
     +----+  |         |   +--+              +---+   |        |  +----+
     | CN2|--|         A3  |PE+--------------+PE |---B3       |--| CN3|
     +----+  +---------+   +--+   trusted    +---+   +--------+  +----+
                              |     VPN      |
                              +--------------+
          Figure 8: SDWAN Scenario #2


   For example, if the CN1 route can be reached by both VPN and Public
   internet, the CN1's BGP route UPDATE should include the following:

   -  MP-NLRI Path Attribute:

      CN1

   -  Tunnel-Encap Path Attribute:

      Tunnel 1: MPLS-in-GRE encapsulation
         With the MPLS-in-GRE Sub-TLV specified by Tunnel-Encap;

      Tunnel 2: IPsec-GRE encapsulation
         With the IPsec Sub-TLVs specified by the [SECURE-EVPN] and
         [BGP-EDGE-DISCOVERY]

   There could be multiple IPsec SA tunnels terminated at the edge node
   loopback address or terminated at WAN ports. For the Scenario #2,
   there can be policies to determine which IPsec SA tunnels that the
   client route can be carried. When a client route can be carried by
   multiple IPsec SA tunnels terminated by two different WAN ports,
   multiple Tunnel Path Attributes with different Tunnel-end-point Sub-
   TLVs need to be included in the NLRI of the BGP UPDATE for the
   client route.





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5.4. Packet Walk-Through for Scenario #3

   The behavior described in [SECURE-L3VPN] applies to this scenario.

   [SECURE-L3VPN] describes how to extend the RFC4364 VPN to allow some
   PEs being connected to other PEs via public networks. In this
   scenario, the PEs is the SDWAN Edge nodes. [SECURE-L3VPN] introduces
   the concept of RED Interface & Black Interface on those PEs. RED
   interfaces face the VPN over which packets can be forwarded natively
   without encryption. Black Interfaces face public network over which
   only IPsec-protected packets are forwarded. [SECURE-L3VPN] assumes
   PEs terminate MPLS packets, and use MPLS over IPsec when sending
   over the Black Interfaces.

   The C-PEs not only have RED interfaces facing clients but also have
   RED interface facing MPLS backbone, with additional BLACK interfaces
   facing the untrusted public networks for the WAN side. The C-PEs
   cannot mix the routes learned from the Black Interfaces with the
   Routes from RED Interfaces. The routes learned from core-facing RED
   interfaces are for underlay and cannot be mixed with the routes
   learned over access-facing RED interfaces that are for overlay.
   Furthermore, the routes learned over core-facing interfaces (both
   RED and BLACK) can be shared in the same GLOBAL route table.

   There may be some added risks of the packets from the ports facing
   the Internet. Therefore, special consideration has to be given to
   the routes from WAN ports facing the Internet. RFC4364 describes
   using an RD to create different routes for reaching same system. A
   similar approach can be considered to force packets received from
   the Internet facing ports to go through special security functions
   before being sent over to the VPN backbone WAN ports.



6. Manageability Considerations

     SDWAN overlay networks utilize the SDWAN controller to facilitate
     route distribution, central configurations, and others. SDWAN Edge
     nodes need to advertise the attached routes to their controller
     (i.e. RR in BGP case).

7. Security Considerations


   Having WAN ports facing the public Internet introduces the following
   security risks:


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   1) Potential DDoS attack to the C-PEs with ports facing internet.

   2) Potential risk of provider VPN network being injected with
   illegal traffic coming from the public Internet WAN ports on the C-
   PEs.

8. IANA Considerations

       None

9. References


9.1. Normative References

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

   [RFC4364] E. rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
             networks (VPNs)", Feb 2006.

   [RFC7296] C. Kaufman, et al, "Internet Key Exchange Protocol Version
             2 (IKEv2)", Oct 2014.

   [RFC7432] A. Sajassi, et al, "BGP MPLS-Based Ethernet VPN", Feb
             2015.

   [RFC8365] A. Sajassi, et al, "A network Virtualization Overlay
             Solution Using Ethernet VPN (EVPN)", March 2018.


9.2. Informative References

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

   [RFC5521] P. Mohapatra, E. Rosen, "The BGP Encapsulation Subsequent
             Address Family Identifier (SAFI) and the BGP Tunnel
             Encapsulation Attribute", April 2009.

   [BGP-SDWAN-Port] L. Dunbar, H. Wang, W. Hao, "BGP Extension for
             SDWAN Overlay Networks", draft-dunbar-idr-bgp-sdwan-
             overlay-ext-03, work-in-progress, Nov 2018.


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   [Net2Cloud-Gap] L. Dunbar, A. Malis, C. Jacquenet, "Gap Analysis of
             Interconnecting Underlay with Cloud Overlay", draft-dm-
             net2cloud-gap-analysis-02, work in progress, Oct. 2018.

   [SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K. Majumdar,
             "BGP UPDATE for SDWAN Edge Discovery", draft-dunbar-idr-
             sdwan-edge-discovery-00, work-in-progress, July 2020.

   [VPN-over-Internet] E. Rosen, "Provide Secure Layer L3VPNs over
             Public Infrastructure", draft-rosen-bess-secure-l3vpn-00,
             work-in-progress, July 2018

   [DMVPN] Dynamic Multi-point VPN:
             https://www.cisco.com/c/en/us/products/security/dynamic-
             multipoint-vpn-dmvpn/index.html

   [DSVPN] Dynamic Smart VPN:
             http://forum.huawei.com/enterprise/en/thread-390771-1-
             1.html

   [SECURE-EVPN] A. Sajassi, et al, "Secure EVPN", draft-sajassi-bess-
             secure-evpn-01, Work-in-progress, March 2019.

   [SECURE-L3VPN] E. Rosen, R. Bonica, "Secure Layer L3VPN over Public
             Infrastructure", draft-rosen-bess-secure-l3vpn-00, Work-
             in-progress, June 2018.

   [ITU-T-X1036] ITU-T Recommendation X.1036, "Framework for creation,
             storage, distribution and enforcement of policies for
             network security", Nov 2007.

   [Net2Cloud-Problem] L. Dunbar and A. Malis, "Seamless Interconnect
             Underlay to Cloud Overlay Problem Statement", draft-dm-
             net2cloud-problem-statement-02, June 2018

   [Net2Cloud-gap] L. Dunbar, A. Malis, and C. Jacquenet, "Gap Analysis
             of Interconnecting Underlay with Cloud Overlay", draft-dm-
             net2cloud-gap-analysis-02, work-in-progress, Aug 2018.

   [Tunnel-Encap] E. Rosen, et al "The BGP Tunnel Encapsulation
             Attribute", draft-ietf-idr-tunnel-encaps-10, Aug 2018.



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10. Acknowledgments

   Acknowledgements to Jim Guichard, John Scudder, Darren Dukes, Andy
   Malis and Donald Eastlake 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

   James Guichard
   Futurewei
   Email: james.n.guichard@futurewei.com

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   John Drake
   Juniper
   Email: jdrake@juniper.net

   Basil Najem
   Bell Canada
   Email: basil.najem@bell.ca

   David Carrel
   Cisco
   Email: carrel@cisco.com

   Ayan Banerjee
   Cisco
   Email: ayabaner@cisco.com
















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