SPRING Working Group C. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track W. Cheng
Expires: December 28, 2019 China Mobile
M. Chen
D. Dhody
Z. Li
J. Dong
Huawei Technologies
R. Gandhi
Cisco Systems, Inc.
June 26, 2019
Path Segment for SRv6 (Segment Routing in IPv6)
draft-li-spring-srv6-path-segment-01
Abstract
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by encoding paths as sequences of topological 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 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 Path Segment in SRv6
networks 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.
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This Internet-Draft will expire on December 28, 2019.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. SRv6 Path Segment . . . . . . . . . . . . . . . . . . . . . . 4
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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
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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 comes. 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 path
[I-D.li-pce-sr-bidir-path] and end-to-end performance measurement
[I-D.gandhi-spring-udp-pm]. A SRv6 path can be identified by the
full segment list that made up of several SRv6 segments. However,
the segment list may not be a good key to identify an SRv6 path,
since the the length of segment list is too long and flexible
according to the number of SIDs.
This document defines a new SRv6 segment called "SRv6 Path Segment"
to identify an SRv6 path. Using of Path Segment as an SRv6 SID
(instead of path ID carried by an SRH TLV) will see benefit in
performance and also ease of using the same concept in SR,
irrespective of SR-MPLS and SRv6 data planes. The Path Segment is
inserted as the last segment in the segment list and will not affect
the order of the original SID list.
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
DM: Delay Measurement.
LM: Loss Measurement.
MPLS: Multiprotocol Label Switching.
PM: Performance Measurement.
PSID: Path Segment ID.
SID: Segment ID.
SL: Segment List.
SR: Segment Routing.
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SR-MPLS: Segment Routing with MPLS data plane.
SRH: Segment Routing Header.
PSID: Path Segment ID.
PSP: Penultimate Segment Popping.
Further, this document makes use of the terms defined in [RFC8402]
and [I-D.ietf-spring-srv6-network-programming].
2. SRv6 Path Segment
As defined in [I-D.ietf-spring-srv6-network-programming], a SRv6
segment is a 128 bit value, which can be present as LOC:FUNCT.
For identifying an SRv6 path, this document defines a new segment
called SRv6 Path Segment.
A Path Segment (consisted of LOC and FUNCT part) can identify an SRv6
path within an SRv6 domain. Also, the SRv6 Path Segment may be used
to identify an SRv6 Policy, its Candidate-path or a SID-List
[I-D.ietf-spring-segment-routing-policy] terminating on an egress
node depending on the use-case.
Note that, based on the use-case, the different SID-Lists of SR
Policy may use the same SRv6 Path Segment.
3. Operation
A Path Segment is a local segment of egress node, it is allocated by
the egress node. A Path Segment can be allocated by several ways,
such as CLI, BGP [I-D.li-idr-sr-policy-path-segment-distribution],
PCEP [I-D.li-pce-sr-path-segment] or other ways. The procedure of
Path Segment allocation is out of scope of this document.
When the Path Segment is allocated by the egress, it MUST be
distributed to the ingress node at minimum. In this case, the
transit nodes do not know how to process the Path Segment.
A Path Segment is used for path identification and it MUST NOT be
copied to the IPv6 destination address.
The SRv6 Path Segment MUST be inserted as the last entry in the SID
list without affecting the segment left field in the SRH. The last
entry field in SRH should be set as the index of the Path Segment,
which is the last entry in the SID list. In this case, Path Segment
presenting to a transit node is an error condition.
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Also, PSP of the SRH MUST be disabled.
The Path Segment SHOULD appear only once in a SID list, and the one
that appears at the last entry in the SID list will be processed
while the rests will be ignored.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| ... |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n-1] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Path Segment(Segment List[n], 128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. SRv6 Path Segment in SID List
If an egress node supports Path Segment processing and related OAM
mechanisms are enabled, the node will inspect the last entry in the
SID list to obtain the Path Segment. The behavior of Path Segment
related function will be defined in the future version of this draft
or related use-case drafts.
4. IANA Considerations
This document does not require any IANA actions.
5. Security Considerations
This document does not introduce additional security requirements and
mechanisms other than the ones described in [RFC8402].
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6. Acknowledgements
The authors would like to thank Zafar Ali for his valuable comments
and suggestions.
7. References
7.1. Normative References
[]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-
header-21 (work in progress), June 2019.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-ietf-spring-srv6-network-
programming-00 (work in progress), April 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
7.2. 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", draft-gandhi-spring-udp-pm-02 (work in
progress), September 2018.
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[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",
draft-ietf-spring-mpls-path-segment-00 (work in progress),
March 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", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-03 (work in progress), May 2019.
[I-D.li-idr-sr-policy-path-segment-distribution]
Li, C., Chen, M., Dong, J., and Z. Li, "Segment Routing
Policies for Path Segment and Bidirectional Path", draft-
li-idr-sr-policy-path-segment-distribution-01 (work in
progress), October 2018.
[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", draft-li-pce-
sr-bidir-path-05 (work in progress), March 2019.
[I-D.li-pce-sr-path-segment]
Li, C., Chen, M., Cheng, W., Dong, J., Li, Z., Gandhi, R.,
and Q. Xiong, "Path Computation Element Communication
Protocol (PCEP) Extension for Path Segment in Segment
Routing (SR)", draft-li-pce-sr-path-segment-05 (work in
progress), March 2019.
Authors' Addresses
Cheng Li
Huawei Technologies
Email: chengli13@huawei.com
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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
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