Internet DRAFT - draft-li-6man-srv6-path-segment-encap
draft-li-6man-srv6-path-segment-encap
6man Working Group C. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track W. Cheng
Expires: November 9, 2021 China Mobile
Y. Zhu
China Telecom
Z. Li
D. Dhody
Huawei Technologies
May 8, 2021
Encapsulation of Path Segment in SRv6
draft-li-6man-srv6-path-segment-encap-06
Abstract
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by encoding an ordered list of instructions, called "segments".
The SR architecture can be implemented over an IPv6 data plane,
called SRv6. In some use-cases such as end-to-end SR Path Protection
and Performance Measurement (PM), an SRv6 path needs to be
identified. An SRv6 Path Segment can be used for identifying an SRv6
path. This document defines a P-flag in the Segment Routing Header
to indicate the appearence of SRv6 Path Segment.
Status of This Memo
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Encoding of an SRv6 Path Segment . . . . . . . . . . . . . . 3
2.1. SRH.P-flag . . . . . . . . . . . . . . . . . . . . . . . 4
3. Processing of SRv6 Path Segment . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
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 an IPv6 data plane, it is called
SRv6, and it uses a new IPv6 [RFC8200] Routing Header (EH) called the
IPv6 Segment Routing Header (SRH) [RFC8754] to construct an SRv6
path. As per [RFC8986], an SRv6 segment identifier is a 128-bit
value.
In several use cases, such as binding bidirectional path
[I-D.ietf-pce-sr-bidir-path] and end-to-end performance measurement
[I-D.gandhi-spring-twamp-srpm], the ability to implement path
identification is a pre-requisite.
An SRv6 path MAY be identified by the content of a segment list in
the SRH. However, the segment list may not be a good key, since the
length of a segment list is flexible according to the number of
required SIDs. Also, the length of a segment list may be too long to
be a key when it contains many SIDs. For instance, if packet A uses
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an SRH with 3 SIDs while Packet B uses an SRH with 10 SIDs, the key
to identify these two paths will be a 384-bits value and a 1280-bits
value, respectively. Furthermore, an SRv6 path cannot be identified
by the information carried by the SRH in reduced mode [RFC8754] as
the first SID is not present. Also, different SRv6 policies may use
the same segment list for different candidate paths, so the traffic
of different SRv6 policies are merged, resulting in the inability to
measure the performance of the specific path. Therefore,
[I-D.ietf-spring-srv6-path-segment] defines an SRv6 Path Segment to
identify an SRv6 path.
This document defines a P-bit in SRH to indicate the appearence of
SRv6 Path Segment in SRH.
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
PM: Performance Measurement.
SID: Segment ID.
SL: Segment List.
SR: Segment Routing.
SRH: Segment Routing Header.
PSID: Path Segment Identifier.
PSP: Penultimate Segment Popping.
Further, this document makes use of the terms defined in [RFC8402]
and [RFC8986].
2. Encoding of an SRv6 Path Segment
This section describes the SRH encoding of an SRv6 Path Segment
[I-D.ietf-spring-srv6-path-segment].
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2.1. SRH.P-flag
As per [I-D.ietf-spring-srv6-path-segment], an SRv6 Path Segment is a
128-bits value, and it MUST appear only once in a SID list, and it
MUST appear as the last entry.
To indicate the existence of a Path Segment in the SRH, this document
defines a P-flag in the SRH flag field. The encapsulation of SRv6
Path Segment is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags |P| Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n-1] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 Path Segment (Segment List[n],128 bits IPv6 value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. SRv6 Path Segment in SID List
o P-bit: set when SRv6 Path Segment is inserted. It MUST be ignored
when a node does not support SRv6 Path Segment processing.
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SRH.P-bit processing can be enabled or disabled by configuration on
devices, it can be done by CLI, NETCONF YANG or other ways, and this
is out of the scope of this document.
The pseudo code of SRH.P-bit processing is described as below.
S01. if SRH.P-flag processing is enabled:
S02. if SRH.P-flag is set:
S03. SRv6 Path Segment processing ;;ref1
Ref1: The SRv6 Path Segment processing is accosiated with the
specific application, such as SRv6 Path Segment based Performance
measurement, and this is out of the scope of this document.
In some use cases, only the egress need to process the SRv6 Path
Segment, therefore, the P-bit processing can be done at the egress
node only while the intermediate nodes do not need to process it.
This feature can be enabled by configuration like CLI , NETCONF YANG
or other ways. In this case, the pseudo code is described as below.
S01. if SRH.P-flag processing is enabled:
S02. if intermediate node processing is disabled:
S03. if SRH.P-flag is set and SRH.SL == 0:
S03. SRv6 Path Segment processing
S04 else:
S05. if SRH.P-flag is set:
S06. SRv6 Path Segment processing
3. Processing of SRv6 Path Segment
The processing of SRv6 path segment is out of the scope of this
document and is defined in [I-D.ietf-spring-srv6-path-segment].
4. IANA Considerations
This document requests IANA to allocate bit position TBA within the
"Segment Routing Header Flags" registry defined in [RFC8402].
5. Security Considerations
TBA
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6. Acknowledgements
TBA
7. References
7.1. Normative References
[I-D.ietf-spring-srv6-path-segment]
Li, C., Cheng, W., Chen, M., Dhody, D., and R. Gandhi,
"Path Segment for SRv6 (Segment Routing in IPv6)", draft-
ietf-spring-srv6-path-segment-00 (work in progress),
November 2020.
[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[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>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
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7.2. Informative References
[I-D.gandhi-spring-twamp-srpm]
Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B.
Janssens, "Performance Measurement Using TWAMP Light for
Segment Routing Networks", draft-gandhi-spring-twamp-
srpm-11 (work in progress), October 2020.
[I-D.ietf-idr-sr-policy-path-segment]
Li, C., Li, Z., Chen, H., Cheng, W., and K. Talaulikar,
"SR Policy Extensions for Path Segment and Bidirectional
Path", draft-ietf-idr-sr-policy-path-segment-03 (work in
progress), March 2021.
[I-D.ietf-pce-sr-bidir-path]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
"Path Computation Element Communication Protocol (PCEP)
Extensions for Associated Bidirectional Segment Routing
(SR) Paths", draft-ietf-pce-sr-bidir-path-05 (work in
progress), January 2021.
[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)",
draft-ietf-pce-sr-path-segment-03 (work in progress),
February 2021.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-11 (work in progress),
April 2021.
Authors' Addresses
Cheng Li
Huawei Technologies
Email: c.l@huawei.com
Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
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Yongqing Zhu
China Telecom
Guangzhou
Email: zhuyq8@chinatelecom.cn
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore 560066
India
Email: dhruv.ietf@gmail.com
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