6man Working Group C. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track W. Cheng
Expires: September 5, 2020 China Mobile
Z. Li
D. Dhody
Huawei Technologies
March 4, 2020
Encapsulation of Path Segment in SRv6
draft-li-6man-srv6-path-segment-encap-02
Abstract
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 IPv6 data plane,
called SRv6. In some use-cases such as end-to-end SR Path Protection
and Performance Measurement (PM), SRv6 path need to be identified.
This document defines the encoding and processing of Path Segment in
SRv6 networks.
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 September 5, 2020.
Copyright Notice
Copyright (c) 2020 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
Li, et al. Expires September 5, 2020 [Page 1]
Internet-Draft SRv6 PSID Encap March 2020
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Encoding of SRv6 Path Segment . . . . . . . . . . . . . . . . 3
2.1. Encapsulation of SRv6 Path Segment . . . . . . . . . . . 4
2.2. Format of SRv6 Path Segment . . . . . . . . . . . . . . . 5
2.2.1. SRv6 Path Segment: Locator and Local ID . . . . . . . 5
2.2.2. SRv6 Path Segment: Global ID . . . . . . . . . . . . 5
3. Processing of SRv6 Path Segment . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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 IPv6 dataplane, it is called SRv6
[I-D.ietf-6man-segment-routing-header], and it uses the a new IPv6
[RFC8200] Extension Header (EH) called the IPv6 Segment Routing
Header (SRH) [I-D.ietf-6man-segment-routing-header] to construct SRv6
path. As per [I-D.ietf-spring-srv6-network-programming], an SRv6
segment is a 128-bit value, which can be represented as LOC:FUNCT,
where LOC is the L most significant bits and FUNCT is the 128-L least
significant bits. Most often the LOC part of the SID is routable and
leads to the node which instantiates that SID. The FUNCT part of the
SID is an opaque identification of a local function bound to the SID.
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. In SRv6, an SRv6 path can be
identified by the content of the segment list. However, the segment
Li, et al. Expires September 5, 2020 [Page 2]
Internet-Draft SRv6 PSID Encap March 2020
list may not be a good key to identify an SRv6 path, since the length
of segment list is too long and flexible according to the number of
SIDs. Therefore, [I-D.li-spring-srv6-path-segment] defines SRv6 Path
Segment in order to identify an SRv6 path.
This document defines the encoding and processing of SRv6 Path
Segment in SRv6 networks.
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 [I-D.ietf-spring-srv6-network-programming].
2. Encoding of SRv6 Path Segment
This section will describe the encoding of SRv6 Path Segment
[I-D.li-spring-srv6-path-segment] in SRH. As per
[I-D.li-spring-srv6-path-segment], an SRv6 Path Segment is a 128-bits
value, which identifies an SRv6 path. Depending on the use case, an
SRv6 Path Segment can identify:
o an SRv6 path within an SRv6 domain
o an SRv6 Policy
Li, et al. Expires September 5, 2020 [Page 3]
Internet-Draft SRv6 PSID Encap March 2020
o a Candidate-paths or a SID-List in a SRv6 Policy
[I-D.ietf-spring-segment-routing-policy].
2.1. Encapsulation of SRv6 Path Segment
The SRv6 Path Segment MUST appear only once in a SID list, and it
MUST appear at the last entry, so the SRv6 Path Segment MUST NOT be
copied to the IPv6 destination address. The format of the SRv6 Path
Segment follows the format described in section 2.2.
In order to indicate the existence of Path Segment in the SRH, this
document defines a P-bit in 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
Li, et al. Expires September 5, 2020 [Page 4]
Internet-Draft SRv6 PSID Encap March 2020
o P-bit: set when SRv6 Path Segment is inserted. It SHOULD be
ignored when a node does not support SRv6 Path Segment processing.
2.2. Format of SRv6 Path Segment
This document proposes two types of SRv6 Path Segment format.
Editor's Note: Authors would like to request comments of these
encoding mechanisms of SRv6 Path Segment. The appropriate encoding
will be maintained while the rest will be deleted in the future
version of this document.
2.2.1. SRv6 Path Segment: Locator and Local ID
As per [I-D.ietf-spring-srv6-network-programming], an SRv6 segment is
a 128-bit value, which can be represented as LOC:FUNCT, where LOC is
the L most significant bits and FUNCT is the 128-L least significant
bits. L is called the locator length and is flexible. Each operator
is free to use the locator length it chooses. Most often the LOC
part of the SID is routable and leads to the node which instantiates
that SID. The FUNCT part of the SID is an opaque identification of a
local function bound to the SID. The FUNCT value zero is invalid.
SRv6 Path Segment can follow the format, where the LOC part
identifies the egress node that allocates the Path Segment, and the
FUNCT part is an unique local ID to identify an SRv6 Path towards to
the egress on the egress.
The Function Type of SRv6 Path Segment is END.PSID (End Function with
Path Segment Identifier, to be allocated by IANA).
The proposed P bit can be used to identify that the last SID is an
SRv6 Path Segment.
+--------------------------------------------------------------+
| Locator | Function ID |
+--------------------------------------------------------------+
|<-------------------------128 bits--------------------------->|
Figure 2. PSID in Format LOC:FUNCT
2.2.2. SRv6 Path Segment: Global ID
An SRv6 Path Segment ID can be a Global ID, and its format depends on
the use case.
Li, et al. Expires September 5, 2020 [Page 5]
Internet-Draft SRv6 PSID Encap March 2020
The SRv6 Path Segment will not be copied to the IPv6 Destination
Address, so the SRv6 Path Segment ID can be allocated from an
independent 128-bits ID Space. In this case, a new table should be
maintained at the node for SRv6 Path Segment. The proposed P bit can
be used to identify that the last SID is an SRv6 Path Segment and
need to be looked up in the SRv6 Path Segment table.
+--------------------------------------------------------------+
| Global ID/PSID |
+--------------------------------------------------------------+
|<-------------------------128 bits--------------------------->|
Figure 3. A Global ID as an PSID
3. Processing of SRv6 Path Segment
As per [I-D.li-spring-srv6-path-segment], an SRv6 Path Segment is a
local segment allocated by an egress node. An SRv6 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 means. The mechanisms
through which an SRv6 Path Segment is allocated is out of scope of
this document.
When the SRv6 Path Segment is allocated by the egress, it MUST be
distributed to the ingress node. In this case, only the egress will
process the SRv6 Path Segment, and other nodes specified by SIDs in
the SID list do not know how to process the SRv6 Path Segment.
An SRv6 Path Segment may be distributed to the SRv6 nodes along the
SRv6 path. In this case, the SRv6 nodes that learn SRv6 Path Segment
may process the SRv6 Path Segment depending on the use case.
When the SRv6 Path Segment is used, the following rules apply:
o The SRv6 Path Segment MUST appear only once in a SID list, and it
MUST appear at the last entry. Only the one that appears at the
last entry in the SID list will be processed. SRv6 Path Segment
appears at other location in the SID list will be treated as an
error.
o When an SRv6 Path Segment is inserted, the SL MUST be initiated to
be less than the value of Last Entry, and will not point to SRv6
Path Segment. For instance, when the Last entry is 4, the SID
List[4] is the SRv6 Path Segment, so the SL MUST be set to 3 or
other numbers less than Last entry.
Li, et al. Expires September 5, 2020 [Page 6]
Internet-Draft SRv6 PSID Encap March 2020
o The SRv6 Path Segment MUST NOT be copied to the IPv6 destination
address.
o Penultimate Segment Popping (PSP, as defined in
[I-D.ietf-spring-srv6-network-programming]) MUST be disabled.
o The ingress needs to set the P-bit when an SRv6 Path Segment is
inserted in the SID List. Nodes that supporting SRv6 Path Segment
processing will inspect the last entry to process SRv6 Path
Segment when the P-bit is set. When the P-bit is unset, the nodes
will not inspect the last entry.
o The specific SRv6 Path Segment processing depends on use cases,
and it is out of scope of this document.
4. IANA Considerations
TBA
5. Security Considerations
TBA
6. Acknowledgements
TBA
7. References
7.1. Normative References
[]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), 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",
draft-ietf-spring-srv6-network-programming-11 (work in
progress), March 2020.
[I-D.li-spring-srv6-path-segment]
Li, C., Cheng, W., Chen, M., Dhody, D., Li, Z., Dong, J.,
and R. Gandhi, "Path Segment for SRv6 (Segment Routing in
IPv6)", draft-li-spring-srv6-path-segment-04 (work in
progress), November 2019.
Li, et al. Expires September 5, 2020 [Page 7]
Internet-Draft SRv6 PSID Encap March 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>.
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 and
STAMP for Segment Routing Networks", draft-gandhi-spring-
twamp-srpm-06 (work in progress), March 2020.
[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", draft-ietf-idr-sr-policy-path-segment-00 (work in
progress), October 2019.
[I-D.ietf-pce-sr-bidir-path]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
"PCEP Extensions for Associated Bidirectional Segment
Routing (SR) Paths", draft-ietf-pce-sr-bidir-path-01 (work
in progress), February 2020.
[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-00 (work in progress),
October 2019.
Li, et al. Expires September 5, 2020 [Page 8]
Internet-Draft SRv6 PSID Encap March 2020
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-06 (work in progress),
December 2019.
Authors' Addresses
Cheng Li
Huawei Technologies
Email: chengli13@huawei.com
Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
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
Li, et al. Expires September 5, 2020 [Page 9]