Internet-Draft BGP-LS-SPF for Multi-segment SD-WAN October 2023
Sheng & Shi Expires 24 April 2024 [Page]
Intended Status:
Standards Track
C. Sheng
H. Shi, Ed.

Usage of BGP-LS-SPF in Multi-segment SD-WAN


This document introduces the usage of BGP-LS-SPF protocol in multi-segment SD-WAN scenarios. It allows SD-WAN tunnels to be published as logical links, which can cross the internet, MPLS networks, and various operator network. The BGP-LS-SPF protocol can construct an overlay network topology for logical links and physical links across these heterogeneous networks, and calculate the reachability routes of overlay network nodes based on this topology.

Status of This Memo

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

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This Internet-Draft will expire on 24 April 2024.

Table of Contents

1. Introduction

As pointed out in [I-D.draft-ietf-rtgwg-net2cloud-problem-statement], enterprises are migrating their workloads to cloud service. The enterprise branch interconnection and enterprise site to cloud DC connection may cross heterogeneous network such as operator networks, enterprise-owned backbone networks or direct connection lines.

For large enterprises to access the cloud service and interconnect their branches, a PoP GWs network can be built to provide multi-cloud, multi-tenant, and multi-branch interconnection. Depending on the geographical distribution of the enterprise branches, the PoP GWs network may be a cross-regional or even a global network. The PoP GW can be connected to the operator network or the enterprise-owned backbone network. The PoP GWs devices can also be directly connected through dedicated lines.

According to [I-D.draft-ietf-bess-bgp-sdwan-usage], SD-WAN tunnels can be established between two GWs devices connected to the operator network, MPLS VPN network, or internet network through the WAN ports of the two PoP GWs devices. All GWs are under the control of one BGP instance. [I-D.draft-ietf-idr-sdwan-edge-discovery] defines the mechanism for SD-WAN edges to discover each other's properties via BGP update through RR. This allows the interconnection between enterprise branches and multi-cloud to pass through multiple SD-WAN tunnels or direct connection lines, as shown in Figure 1.

This draft provides a way to use the BGP-LS-SPF protocol to collect the identification of PoP GW device node and the topology of SD-WAN tunnel and direct connection lines. In this way, each PoP GW device can learn the PoP GWs network topology, and calculate the route to any other PoP GW.

2. Terminology

This specification reuses terms defined in Section 5.2 of [I-D.draft-ietf-lsvr-bgp-spf] including BGP-LS-SPF Node NLRI, BGP-LS-SPF Link NLRI, Dijkstra Algorithm.

2.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Usage of BGP-LS-SPF in Multi-segment SD-WAN

   + - - - +- - - - - - - - - - - -|RR| - - - - - - - - - -+ - - - - +
   |       |                        |                      |         |
   |    +--|--+                  +--|--+                +--|--+      |
   |    | GW1 |------------------| GW2 | -Physical link-| GW3 |      |
   |    +--|--+                +--|--+      |
   |       |     SD-WAN Tunnel  /                 Physical | |
   |       |    ----------------                      Link |         |
   |       |   / over Internet                             | |
   |    +--|--+                                         +--|--+      |
   |+--+| GW5 |---------SD-WAN Tunnel over MPLS---------| GW4 |+-----+
        +--|--+                                         +--|--+
           |                                               |
+ - -+   + - -+                                         + - -+   + - -+
|User|---|CPE1|                                         |CPE2|---|APPs|
+ - -+   + - -+                                         + - -+   + - -+
Figure 1: PoP GWs network

As shown in Figure 1, GW1, GW2, GW5 are connected to the same internet/ISP network. The GW2 and GW3 are connected through direct dedicated links. GW5 and GW4 are connected by MPLS VPN. BGP-SD-WAN neighbors are established between GWs through RR. BGP-LS-SPF neighbors are established between each GW and RR. SD-WAN tunnel links are established between GWs through BGP-SD-WAN neighbors reflecting SD-WAN routes(see [I-D.draft-ietf-idr-sdwan-edge-discovery]), as shown in the SD-WAN Tunnel between GW1 and GW2 with WAN port IP addresses of and, respectively. GW nodes reflect the SD-WAN tunnel topology information to all GWs, including dedicated line-connected GWs, through BGP-LS-SPF neighbors with RR.

GW2-GW3-GW4 are connected through dedicated lines. BGP-LS-SPF neighbors are established between GWs through dedicated lines, and also between GWs and RR. The BGP-LS-SPF neighbors between dedicated lines are used to discover the topology information of the dedicated lines, such as the direct link with port IP addresses of and between GW3 and GW4 shown in the figure. The dedicated line topology information is reflected to all GWs, including SD-WAN tunnel-connected GWs, through BGP-LS-SPF neighbors with RR.

The BGP-LS-SPF LINK NLRI is used to carry the two endpoint IP address of the SD-WAN tunnel or dedicated lines. The BGP-LS-SPF NODE NLRI is used to carry PoP GW device node identification. They are advertised to other GWs through the RR. In this way, all GW learns the topology of whole PoP GWs network and can calculate the next hop to any other GW using Dijkstra Algorithm.

4. Extensions to BGP-LS

The link could be Overlay link (Such as Internet, MPLS, LTE etc.,) and Underlay/Physical link (Such as Dedicated line, Direct link etc.,). Different customer may require different types of link. For example, FinTech customer has very high security requirement and would like to exclude Internet and LTE, only use MPLS or Dedicated line; some customer only wants to use the Dedicated line/Direct link to get the highest quality path; some customer prefers to use LTE only as backup link to save the cost. The calculation of these customized SD-WAN path needs to include or exclude one or more specific link types, therefore, when SD-WAN link information is advertised through BGP-LS-SPF Link NLRI, the SD-WAN link type needs to be explicitly indicated.

In this document, a new BGP-LS-SPF Attribute TLV of the BGP-LS-SPF Link NLRI is added to identify a SD-WAN link type, called Link-Type TLV. The format of the Link-Type TLV is defined as follows:

where: Type: TBA

Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 1.


This BGP-LS-SPF Attribute TLV of the BGP-LS-SPF Link NLRI is defined to indicate the Link-Type of the SD-WAN link.

5. Security Considerations

This document does not introduce any new security considerations.

6. IANA Considerations


7. References

7.1. Normative References

Dunbar, L., Sajassi, A., Drake, J., and B. Najem, "BGP Usage for SD-WAN Overlay Networks", Work in Progress, Internet-Draft, draft-ietf-bess-bgp-sdwan-usage-17, , <>.
Dunbar, L., Majumdar, K., Hares, S., Raszuk, R., and V. Kasiviswanathan, "BGP UPDATE for SD-WAN Edge Discovery", Work in Progress, Internet-Draft, draft-ietf-idr-sdwan-edge-discovery-12, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

7.2. Informative References

Dunbar, L., Malis, A. G., Jacquenet, C., Toy, M., and K. Majumdar, "Dynamic Networks to Hybrid Cloud DCs: Problem Statement and Mitigation Practices", Work in Progress, Internet-Draft, draft-ietf-rtgwg-net2cloud-problem-statement-30, , <>.
Patel, K., Lindem, A., Zandi, S., and W. Henderickx, "BGP Link-State Shortest Path First (SPF) Routing", Work in Progress, Internet-Draft, draft-ietf-lsvr-bgp-spf-28, , <>.

Appendix A. Acknowledgements

The authors would like to thank Donglei Pang for his contribution to the document.

Appendix B. Contributors

Shunwan Zhuang Huawei Email:

Authors' Addresses

Cheng Sheng
Beiqing Road
Hang Shi (editor)
Beiqing Road