SPRING Working Group C. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track W. Cheng
Expires: May 7, 2020 China Mobile
M. Chen
D. Dhody
Z. Li
J. Dong
Huawei Technologies
R. Gandhi
Cisco Systems, Inc.
November 4, 2019

Path Segment for SRv6 (Segment Routing in IPv6)


Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of sub-paths, called "segments". Segment routing architecture can be implemented over an MPLS data plane as well as an IPv6 data plane.

Further, Path Segment has been defined in order to identify an SR path in SR-MPLS networks, and used for various use-cases such as end-to-end SR Path Protection and Performance Measurement (PM) of an SR path. Similar to SR-MPLS, this document defines the Path Segment in SRv6 networks in order to identify an SRv6 path.

Status of This Memo

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

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

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 reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on May 7, 2020.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction

Segment routing (SR) [RFC8402] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node by inserting an ordered list of instructions, called segments.

When segment routing is deployed on MPLS dataplane, called SR-MPLS [I-D.ietf-spring-segment-routing-mpls], a segment is an MPLS label. When segment routing is deployed on IPv6 dataplane, called SRv6 [I-D.ietf-6man-segment-routing-header], a segment is a 128 bit value, and it can be an IPv6 address of a local interface but it does not have to. For supporting SR, an extended header called Segment Routing Header (SRH), which contains a list of SIDs and several needed information such as Segments Left, has been defined in [I-D.ietf-6man-segment-routing-header].

In an SR-MPLS network, when a packet is transmitted along an SR path, the labels in the MPLS label stack will be swapped or popped, so no label or only the last label may be left in the MPLS label stack when the packet reaches the egress node. Thus, the egress node can not determine from which ingress node or SR path the packet came in. For identifying an SR-MPLS path, Path Segment is defined in [I-D.ietf-spring-mpls-path-segment].

Likewise, a path needs to be identified in an SRv6 network for several use cases such as binding bidirectional paths [I-D.li-pce-sr-bidir-path] and end-to-end performance measurement [I-D.gandhi-spring-udp-pm]. An SRv6 path can be identified by the content of segment list (i.e., the several SRv6 segments that are in the segment list).

However, the segment list may not be a good key to identify an SRv6 path, since the the length of segment list is flexible according to the number of SIDs. Also, the length of SID list will be too long to be a key when it contains many SIDs. For instance, if packet A uses the SRH with 3 SIDs while Packet B uses the SRH with 10 SIDs, the key to identify these two paths will be a 384-bits value and a 1280-bits value.

This document defines a new SRv6 segment called "SRv6 Path Segment", which is a 128-bits value, to identify an SRv6 path. Using the Path Segment as an SRv6 SID will improve performance and operations in both SR-MPLS and SRv6.

Also, In reduced mode [I-D.ietf-6man-segment-routing-header], an SRv6 path can not be indentified by the information carried by SRH. When the SRv6 Path Segment is used in reduced SRH [I-D.ietf-6man-segment-routing-header], the entire path information is indicated by the Path Segment, and the performance will be better than using SID list as the path identifier, while the overhead equals to the normal SRH.

The SRv6 Path Segment will be used for identifying an SRv6 path and path related services, and it will not be updated to the IPv6 destination address, so it is not routable.

1.1. 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.

1.2. Terminology

MPLS: Multiprotocol Label Switching.

PM: Performance Measurement.

SID: Segment ID.

SR: Segment Routing.

SR-MPLS: Segment Routing with MPLS data plane.

SRH: Segment Routing Header.

PSID: Path Segment Identifier.

PSP: Penultimate Segment Popping.

Further, this document makes use of the terms defined in [RFC8402] and [I-D.ietf-spring-srv6-network-programming].

2. Use Cases of SRv6 Path Segment

Similar to SR-MPLS Path Segment [I-D.ietf-spring-mpls-path-segment], SRv6 Path Segment also can be used for identifying an SRv6 Path in some use cases:

3. SRv6 Path Segment

As defined in [I-D.ietf-spring-srv6-network-programming], an SRv6 segment is a 128-bit value.

In order to identify an SRv6 path, this document defines a new segment called SRv6 Path Segment.

The SRv6 Path Segment MUST appear only once in a SID list. The detailed encoding of SRv6 Path Segment is out of scope of this document, and it is defined in [I-D.li-6man-srv6-path-segment-encap].

Depending on the use case, an SRv6 Path Segment identifies:

Note that, based on the use-case, the different SID-Lists of SR Policies may use the same SRv6 Path Segment.

4. SRv6 Path Segment Allocation

A Path Segment is a local segment allocated by an egress node. A Path Segment can be allocated through several ways, such as CLI, BGP [I-D.ietf-idr-sr-policy-path-segment], PCEP [I-D.ietf-pce-sr-path-segment] or other ways. The mechanisms through which a Path Segment is allocated is out of scope of this document.

When the Path Segment is allocated by the egress, it MUST be distributed to the ingress node. In this case, only the egress will process the Path Segment, and other nodes specified by SIDs in the SID list do not know how to process the Path Segment.

Depending on the use case, a Path Segment may be distributed to the SRv6 nodes along the SRv6 path. In this case, the SRv6 nodes that learned Path Segment may process the Path Segment depending on the use case.

5. Operations

An egress node or other SRv6 nodes along the SRv6 path supporting the Path Segment processing will inspect the last entry of the segment list (giving the the node will inspect the last entry in the SID list and obtain the Path Segment. The processing of the Path Segment is described in [I-D.li-6man-srv6-path-segment-encap].

6. IANA Considerations

This document does not require any IANA actions.

7. Security Considerations

This document does not introduce additional security requirements and mechanisms other than the ones described in [RFC8402].

8. Acknowledgements

The authors would like to thank Stefano Previdi and Zafar Ali for their valuable comments and suggestions.

9. References

9.1. Normative References

[I-D.ietf-6man-segment-routing-header] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S. and D. Voyer, "IPv6 Segment Routing Header (SRH)", Internet-Draft draft-ietf-6man-segment-routing-header-26, October 2019.
[I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., Matsushima, S. and Z. Li, "SRv6 Network Programming", Internet-Draft draft-ietf-spring-srv6-network-programming-05, October 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8402] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018.

9.2. Informative References

[I-D.gandhi-spring-udp-pm] Gandhi, R., Filsfils, C., daniel.voyer@bell.ca, d., Salsano, S., Ventre, P. and M. Chen, "UDP Path for In-band Performance Measurement for Segment Routing Networks", Internet-Draft draft-gandhi-spring-udp-pm-02, September 2018.
[I-D.ietf-idr-sr-policy-path-segment] Li, C., Li, Z., Telecom, C., Cheng, W. and K. Talaulikar, "SR Policy Extensions for Path Segment and Bidirectional Path", Internet-Draft draft-ietf-idr-sr-policy-path-segment-00, October 2019.
[I-D.ietf-pce-sr-path-segment] Li, C., Chen, M., Cheng, W., Gandhi, R. and Q. Xiong, "Path Computation Element Communication Protocol (PCEP) Extension for Path Segment in Segment Routing (SR)", Internet-Draft draft-ietf-pce-sr-path-segment-00, October 2019.
[I-D.ietf-spring-mpls-path-segment] Cheng, W., Li, H., Chen, M., Gandhi, R. and R. Zigler, "Path Segment in MPLS Based Segment Routing Network", Internet-Draft draft-ietf-spring-mpls-path-segment-01, September 2019.
[I-D.ietf-spring-segment-routing-mpls] Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing with MPLS data plane", Internet-Draft draft-ietf-spring-segment-routing-mpls-22, May 2019.
[I-D.ietf-spring-segment-routing-policy] Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A. and P. Mattes, "Segment Routing Policy Architecture", Internet-Draft draft-ietf-spring-segment-routing-policy-03, May 2019.
[I-D.li-6man-srv6-path-segment-encap] Li, C., Cheng, W., Li, Z. and D. Dhody, "Encapsulation of Path Segment in SRv6", Internet-Draft draft-li-6man-srv6-path-segment-encap-00, July 2019.
[I-D.li-pce-sr-bidir-path] Li, C., Chen, M., Cheng, W., Li, Z., Dong, J., Gandhi, R. and Q. Xiong, "PCEP Extensions for Associated Bidirectional Segment Routing (SR) Paths", Internet-Draft draft-li-pce-sr-bidir-path-06, August 2019.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, May 2016.

Authors' Addresses

Cheng Li Huawei Technologies EMail: chengli13@huawei.com
Weiqiang Cheng China Mobile EMail: chengweiqiang@chinamobile.com
Mach(Guoyi) Chen Huawei Technologies EMail: mach.chen@huawei.com
Dhruv Dhody Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India EMail: dhruv.ietf@gmail.com
Zhenbin Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing, 100095 China EMail: lizhenbin@huawei.com
Jie Dong Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing, 100095 China EMail: jie.dong@huawei.com
Rakesh Gandhi Cisco Systems, Inc. Canada EMail: rgandhi@cisco.com