Network Working Group W. J
Internet-Draft Y. Liu
Intended status: Standards Track China Mobile
Expires: January 14, 2021 Y. Gu
July 13, 2020

Traffic Steering using BGP Flowspec with SRv6 Policy


BGP Flow Specification (FlowSpec) [I-D.ietf-idr-rfc5575bis] has been proposed to distribute BGP FlowSpec NLRI to FlowSpec clients to mitigate (distributed) denial-of-service attacks, and to provide traffic filtering in the context of a BGP/MPLS VPN service. Recently, traffic steering applications in the context of SRv6 using FlowSpec aslo attract attention. This document introduces the usage of BGP FlowSpec to steer packets into an SRv6 Policy.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Status of This Memo

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This Internet-Draft will expire on January 14, 2021.

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Table of Contents

1. Introduction

Segment Routing IPv6 (SRv6) is a protocol designed to forward IPv6 data packets on a network using the source routing model. SRv6 enables the ingress to add a segment routing header (SRH) [RFC8754] to an IPv6 packet and push an explicit IPv6 address stack into the SRH. After receiving the packet, each transit node updates the IPv6 destination IP address in the packet and segment list to implement hop-by-hop forwarding.

SRv6 Policy [I-D.ietf-spring-segment-routing-policy] is a tunneling technology developed based on SRv6. An SRv6 Policy is a set of candidate paths consisting of one or more segment lists, that is, segment ID (SID) lists. Each SID list identifies an end-to-end path from the source to the destination, instructing a device to forward traffic through the path rather than the shortest path computed using an IGP. The header of a packet steered into an SRv6 Policy is augmented with an ordered list of segments associated with that SRv6 Policy, so that other devices on the network can execute the instructions encapsulated into the list.

The headend of an SRv6 Policy may learn multiple candidate paths for an SRv6 Policy. Candidate paths may be learned via a number of different mechanisms, e.g., CLI, NetConf, PCEP, or BGP.

[I-D.ietf-idr-rfc5575bis] defines the flow specification (FlowSpec) that allows to convey flow specifications and traffic Action/Rules associated (rate- limiting, redirect, remark ...). BGP Flow specifications are encoded within the MP_REACH_NLRI and MP_UNREACH_NLRI attributes. Rules (Actions associated) are encoded in Extended Community attribute. The BGP Flow Specification function allows BGP Flow Specification routes that carry traffic policies to be transmitted to BGP Flow Specification peers to steer traffic.

This document proposes BGP flow specification usage that are used to steer data flow into an SRv6 Policy as well as to indicate Tailend function.

2. Definitions and Acronyms

3. Operations

An SRv6 Policy [I-D.ietf-spring-segment-routing-policy] is identified through the tuple <headend, color, endpoint>. In the context of a specific headend, one may identify an SRv6 policy by the <color, endpoint> tuple. The headend is the node where the SRv6 policy is instantiated/implemented. The headend is specified as an IPv4 or IPv6 address and is expected to be unique in the domain. The endpoint indicates the destination of the SRv6 policy. The endpoint is specified as an IPv6 address and is expected to be unique in the domain. The color is a 32-bit numerical value that associates the SRv6 Policy, and it defines an application-level network Service Level Agreement (SLA) policy.

Assume one or multiple SRv6 Policies are already setup in the SRv6 HeadEnd device. In order to steer traffic into a specific SRv6 policy at the Headend, one can use the SRv6 color extended community and endpoint to map to a satisfying SRv6 policy, and steer traffic into this specific policy.

[I-D.ietf-idr-flowspec-redirect-ip] defines the redirect to IPv4 and IPv6 Next-hop action. The IPv6 next-hop address in the FlowSpec NLRI can be used to specify the endpoint of the SRv6 Policy. When the packets reach to the TailEnd device, some specific function imformation identifiers can be used decide how to further process the flows. Several endpoint functions are already defined, e.g., End.DT6: Endpoint with decapsulation and IPv6 table lookup, and End.DX6: Endpoint with decapsulation and IPv6 cross-connect. The BGP Prefix-SID defined in [RFC8669] is utilized to enable SRv6 VPN services [I-D.ietf-bess-srv6-services]. SRv6 Services TLVs within the BGP Prefix-SID Attribute can be used to indicate the endpoint functions.

This document proposes to carry the Color Extended Community and BGP Prefix-SID Attribute in the context of a Flowspec NLRI [I-D.ietf-idr-rfc5575bis] to an SRv6 Headend to steer traffic into one or multiple SRv6 policies, as well as to indicate specific Tailend functions.

4. Application Example

In following scenario, BGP FlowSpec Controller signals the function imformation (SRv6 SID: Service_id_x) to the HeadEnd device.

   |  BGP FS    |
   | Controller |
      | Flowspec route to HeadEnd:
      |   NLRI: Filter Rules
      |   Redirect to IPv6 Nexthop: TailEnd's Address
      |   Policy Color: C1
      |   PrefixSID: Service_id_x
      |          .-----.
      |         (       )
      V     .--(         )--.
+-------+  (                 )  +-------+
|       |_( SRv6 Core Network )_|       |
|HeadEnd| ( ================> ) |TailEnd|
+-------+  (SR List<S1,S2,S3>)  +-------+
            '--(         )--'   Service SID: Service_id_x
                (       )       (e.g.: End.DT4 or End.DT6 or others)

      Figure 1: Steering the Flow into SRv6 Policy 

When the headend device (as a Flowspec client) receives such instructions, it will steer the flows matching the criteria in the Flowspec route into the SRv6 Policy matching the tuple (Endpoint: TailEnd's Address, Color: C1). And the packets of such flows will be encapsulated with SRH using the SR List<S1, S2, S3, Service_id_x>. When the packets reach to the TailEnd device, they will be further processed per the function denoted by the Service_id_x.

5. IANA Considerations


6. Security Considerations

This document does not change the security properties of SRv6 and BGP.

7. Contributors

The following people made significant contributions to this document:

Shunwan Zhaung

Haibo Wang

Jie Dong

8. Acknowledgements


9. References

9.1. Normative References

[I-D.ietf-bess-srv6-services] Dawra, G., Filsfils, C., Raszuk, R., Decraene, B., Zhuang, S. and J. Rabadan, "SRv6 BGP based Overlay services", Internet-Draft draft-ietf-bess-srv6-services-03, July 2020.
[I-D.ietf-idr-flowspec-redirect-ip] Uttaro, J., Haas, J., Texier, M., Andy, A., Ray, S., Simpson, A. and W. Henderickx, "BGP Flow-Spec Redirect to IP Action", Internet-Draft draft-ietf-idr-flowspec-redirect-ip-02, February 2015.
[I-D.ietf-idr-rfc5575bis] Loibl, C., Hares, S., Raszuk, R., McPherson, D. and M. Bacher, "Dissemination of Flow Specification Rules", Internet-Draft draft-ietf-idr-rfc5575bis-25, May 2020.
[I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Rosen, E., Jain, D. and S. Lin, "Advertising Segment Routing Policies in BGP", Internet-Draft draft-ietf-idr-segment-routing-te-policy-09, May 2020.
[I-D.ietf-idr-tunnel-encaps] Patel, K., Velde, G. and S. Ramachandra, "The BGP Tunnel Encapsulation Attribute", Internet-Draft draft-ietf-idr-tunnel-encaps-15, December 2019.
[I-D.ietf-spring-segment-routing-policy] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A. and P. Mattes, "Segment Routing Policy Architecture", Internet-Draft draft-ietf-spring-segment-routing-policy-08, July 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Sreekantiah, A. and H. Gredler, "Segment Routing Prefix Segment Identifier Extensions for BGP", RFC 8669, DOI 10.17487/RFC8669, December 2019.

9.2. Informative References

[RFC4456] Bates, T., Chen, E. and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006.
[RFC8754] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S. and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020.

Authors' Addresses

Wenying Jiang China Mobile Beijing, China EMail:
Yisong Liu China Mobile Beijing, China EMail:
Yunan Gu Huawei Beijing, China EMail: