Internet DRAFT - draft-lm-spring-srv6-generalized-arguments
draft-lm-spring-srv6-generalized-arguments
Network Working Group Z. Li
Internet-Draft J. Mao
Intended status: Standards Track C. Li
Expires: 24 May 2024 Huawei Technologies
21 November 2023
Generalized Arguments of SRv6 Segment
draft-lm-spring-srv6-generalized-arguments-02
Abstract
This document analyzes the challenges of Arguments of SRv6 SID, and
the chance of using Arguments of SRv6 SID to reduce the length of the
IPv6 extension header. According to these analysis, this document
specifies a kind of generalized and structured Arguments for SRv6
SID, which can carry multiple Arguments parts for a SRv6 SID.
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 24 May 2024.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Problem Statement and Requirements . . . . . . . . . . . . . 2
5. Generalized Arguments . . . . . . . . . . . . . . . . . . . . 4
5.1. Method A . . . . . . . . . . . . . . . . . . . . . . . . 4
5.2. Method B . . . . . . . . . . . . . . . . . . . . . . . . 4
5.3. Consideration of SRv6 C-SID Compression . . . . . . . . . 5
6. Flavor for Generalized Arguments . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document analyzes the challenges of the Arguments of SRv6 SID,
and the chance of using Arguments of SRv6 SID to reduce the length of
the IPv6 extension header. According to these analysis, this
document specifies a kind of generalized and structured arguments for
SRv6 SID, which can carry multiple Arguments parts for a SRv6 SID.
2. 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 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
3. Terminologies
SRv6: Segment Routing over IPv6
4. Problem Statement and Requirements
With the development of SRv6, several kinds of SRv6 Arguments for the
SRv6 End SID and End.X SID
emerge[I-D.ietf-spring-srv6-srh-compression], including:
1. SRv6 C-SID compression (NEXT Flavor): using Arguments to carry
multiple C-SIDs.
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2. SRv6 C-SID compression (REPLACE Flavor): using Arguments to carry
the CL field.
3. SRv6 C-SID compression (NEXT & REPLACE Flavor): using Arguments
to carry multiple C-SIDs and the CL field.
In addition, some new features are created, including network
slicing[I-D.ietf-6man-enhanced-vpn-vtn-id], IOAM[RFC9197], Alternate
Marking[RFC9343][I-D.fz-spring-srv6-alt-mark],
APN6[I-D.li-apn-ipv6-encap][I-D.li-apn-header],
DetNet[I-D.pthubert-detnet-ipv6-hbh], etc.
The instructions of these new features can be processed at:
1. All nodes along a SR path: the instructions can be carried in the
IPv6 Hop-by-Hop Options header (HBH).
2. Endpoints of an SR path: the ones can be carried in the IPv6
Destination Options Header (DOH) or the SRH TLV.
In the second scenario, especially the second one, the usages of the
options or TLVs will cause the following two issues:
1. Lengthening the packet header, and reducing the transmission
efficiency.
2. Making the forwarding processing complex, affecting forwarding
performance.
Besides these issues, in the SRv6 C-SID compression (NEXT Flavor)
solution, if all the C-SIDs of the SID list which should have been
encapsulated in the SRH can be put in the IPv6 destination address of
the packet, because there is no SRH or DOH before SRH any more after
the compression there will be no space for the instructions which
should have been encapsulated in the IPv6 SRH or Destination Options
Header before SRH.
In order to address these challenges, a feasible solution is to use
the Arguments of the SRv6 SID to carry those instructions. Using
SRv6 Arguments to do that will bring following benefits:
1. Reducing the needed space of IPv6 extension header or SRH TLV, so
as to reduce the transmission overhead.
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2. SRv6 SID can reside in the IPv6 destination address field, so the
SRv6 Arguments can be read and processed as a part of IPv6 address,
from which the forwarding performance will benefit, because it avoids
to process the extension header or SRv6 TLV behind the IPv6 header.
3. Unify and simplify the processing: the instructions of both the
SRv6 and the new features are all put in the Arguments part of SRv6
SID or IPv6 address.
5. Generalized Arguments
In order to carry the instructions of multiple features in the SRv6
Arguments, this section defines two methods to make the SRv6
Arguments generalized and structured to allocate spaces for the
instructions.
5.1. Method A
Network devices are configured a template for the purpose of parsing
the SRv6 Arguments, and the devices read and process the content of
the Arguments according to the template.
The template defines what features are carried, and which bits they
are used.
For example, if the length of the Arguments is z bits and the number
x, y, and z have the relationship 0<x<y<z, then the template can
define that:
* The [0, x) bits carry the instructions of feature A;
* The [x, y) bits carry the instructions of feature B;
* The [y, z) bits carry the instructions of feature C.
5.2. Method B
Define a bitmap in the Arguments, and each bit in the bitmap
indicates whether the instructions of a specific feature exist. The
correspondence of the bit and the feature, the length of the space of
Arguments to carry the instructions for the feature, and the
instructions needed to be carried for a specific feature can be
defined further in a standardization way.
The bitmap can be encoded from the most significant bit (MSB) or the
least significant bit (LSB).
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MSB:
0
0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+------------------------------------
|A|B|C|D|E| the instructions of feature A~E
+-+-+-+-+-+------------------------------------
LSB:
------------------------------------+-+-+-+-+-+
the instructions of feature A~E |A|B|C|D|E|
------------------------------------+-+-+-+-+-+
When the bit is set (1), it indicates the instructions of the feature
exist. If the bit is reset (0), there can be two options:
Option 1: it indicates the instructions of the feature don't exist.
Option 2: it indicates the instructions of the feature exist but is
invalid.
5.3. Consideration of SRv6 C-SID Compression
Since it is required to shift the C-SID in the SRv6 SID while
applying the NEXT or NEXT & REPLACE behavior for SRv6 C-SID
compression, when method A or B is adopted, when C-SIDs are encoded
in the generalized Arguments of the SRv6 SID which is used as the
IPv6 destination address, these C-SIDs MUST be placed from the most
significant bit (MSB), that is, these C-SIDs MUST immediately
following the LOC:FUNCT part of the SRv6 SID.
MSB:
0
0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+------------------------------------
|C-SID1 |C-SID2 |C-SIDn |A|B|C|D|E| the instructions of feature A~E
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+------------------------------------
LSB:
+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------------------+-+-+-+-+-+
|C-SID1 |C-SID2 |C-SIDn | the instructions of feature A~E |A|B|C|D|E|
+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------------------+-+-+-+-+-+
The remaining part of the generalized Arguments following the C-SIDs
SHOULD NOT be shifted when C-SIDs part is shifted. This means the
position of the remaining part after the C-SIDs in the generalized
arguments SHOULD be fixed.
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6. Flavor for Generalized Arguments
This section defines a new flavor to support processing the
Generalized Arguments, named as Structured Arguments flavor.
The pseudocode of the Structured Arguments flavor is as follows:
Method A:
S01. If (some NEXT-C-SIDs are encoded in the Generalized Arguments) {
S02. Left shift the C-SIDs by the length of one C-SID
S03. }
S04. Load the relative template
S05. Parse the Generalized Arguments as per section 4.1
S06. For each parsed feature {
S07. Perform actions according to the parsed instructions
as per the specifications of that feature
S08. }
Method B:
S01. If (some NEXT-C-SIDs are encoded in the Generalized Arguments) {
S02. Left shift the C-SIDs by the length of one C-SID
S03. }
S04. For each bit in the bitmap {
S05. If (the bit == 1) {
S06. Parse the instructions of the feature from the Generalized
Arguments as per section 4.2
S07. Perform actions according to the parsed instructions
as per the specifications of that feature
S08. }
S09. }
7. IANA Considerations
TBD
8. Security Considerations
TBD
9. References
9.1. Normative References
[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>.
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[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
9.2. Informative References
[I-D.fz-spring-srv6-alt-mark]
Fioccola, G., Zhou, T., Cociglio, M., Mishra, G. S., wang,
X., and G. Zhang, "Application of the Alternate Marking
Method to the Segment Routing Header", Work in Progress,
Internet-Draft, draft-fz-spring-srv6-alt-mark-07, 22
September 2023, <https://datatracker.ietf.org/doc/html/
draft-fz-spring-srv6-alt-mark-07>.
[I-D.ietf-6man-enhanced-vpn-vtn-id]
Dong, J., Li, Z., Xie, C., Ma, C., and G. S. Mishra,
"Carrying Virtual Transport Network (VTN) Information in
IPv6 Extension Header", Work in Progress, Internet-Draft,
draft-ietf-6man-enhanced-vpn-vtn-id-05, 6 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-
enhanced-vpn-vtn-id-05>.
[I-D.ietf-spring-srv6-srh-compression]
Cheng, W., Filsfils, C., Li, Z., Decraene, B., and F.
Clad, "Compressed SRv6 Segment List Encoding", Work in
Progress, Internet-Draft, draft-ietf-spring-srv6-srh-
compression-09, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-srh-compression-09>.
[I-D.li-apn-header]
Li, Z., Peng, S., and S. Zhang, "Application-aware
Networking (APN) Header", Work in Progress, Internet-
Draft, draft-li-apn-header-04, 12 April 2023,
<https://datatracker.ietf.org/doc/html/draft-li-apn-
header-04>.
[I-D.li-apn-ipv6-encap]
Li, Z., Peng, S., and C. Xie, "Application-aware IPv6
Networking (APN6) Encapsulation", Work in Progress,
Internet-Draft, draft-li-apn-ipv6-encap-07, 10 July 2023,
<https://datatracker.ietf.org/doc/html/draft-li-apn-ipv6-
encap-07>.
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[I-D.pthubert-detnet-ipv6-hbh]
Thubert, P. and F. Yang, "IPv6 Options for DetNet", Work
in Progress, Internet-Draft, draft-pthubert-detnet-ipv6-
hbh-07, 22 February 2022,
<https://datatracker.ietf.org/doc/html/draft-pthubert-
detnet-ipv6-hbh-07>.
[RFC3272] Awduche, D., Chiu, A., Elwalid, A., Widjaja, I., and X.
Xiao, "Overview and Principles of Internet Traffic
Engineering", RFC 3272, DOI 10.17487/RFC3272, May 2002,
<https://www.rfc-editor.org/info/rfc3272>.
[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>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/info/rfc9197>.
[RFC9343] Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
Pang, "IPv6 Application of the Alternate-Marking Method",
RFC 9343, DOI 10.17487/RFC9343, December 2022,
<https://www.rfc-editor.org/info/rfc9343>.
Authors' Addresses
Zhenbin Li
Huawei Technologies
Beijing
100095
China
Email: lizhenbin@huawei.com
Jianwei Mao
Huawei Technologies
Beijing
100095
China
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Email: MaoJianwei@huawei.com
Cheng Li
Huawei Technologies
Beijing
100095
China
Email: c.l@huawei.com
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