SPRING W. Cheng
Internet-Draft China Mobile
Intended status: Informational S. Steffann
Expires: May 3, 2021 SJM Steffann Consultancy
October 30, 2020
Compressed SRv6 SID List Requirements
draft-srcompdt-spring-compression-requirement-00
Abstract
This document specifies requirements for solutions to compress SRv6
SID lists.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. SRv6 SID List Compression Requirements . . . . . . . . . . . 4
3.1. Dataplane Efficiency and Performance Requirements . . . . 4
3.1.1. Encapsulation Header Size . . . . . . . . . . . . . . 4
3.1.2. Forwarding Efficiency . . . . . . . . . . . . . . . . 4
3.1.3. State Efficiency . . . . . . . . . . . . . . . . . . 5
4. SRv6 Specific Requirements . . . . . . . . . . . . . . . . . 5
4.1. Functional Requirements . . . . . . . . . . . . . . . . . 5
4.1.1. SRv6 Based . . . . . . . . . . . . . . . . . . . . . 5
4.1.2. SRv6 Functionality . . . . . . . . . . . . . . . . . 5
4.1.3. SID list length . . . . . . . . . . . . . . . . . . . 5
4.1.4. SID summarization . . . . . . . . . . . . . . . . . . 6
4.1.5. Heterogeneous SID lists . . . . . . . . . . . . . . . 6
4.2. Operational Requirements . . . . . . . . . . . . . . . . 6
4.2.1. Lossless Compression . . . . . . . . . . . . . . . . 6
4.3. Scalability Requirements . . . . . . . . . . . . . . . . 6
5. Protocol Design Requirements . . . . . . . . . . . . . . . . 6
5.1. Ships in the Night Deployment . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The SPRING working group defined SRv6, with [RFC8402] describing how
the Segment Routing (SR) architecture is instantiated on two data-
planes: SR over MPLS (SR-MPLS) and SR over IPv6 (SRv6). SRv6 uses a
routing header called the SR Header (SRH) [RFC8754], and defines SRv6
SID behaviors and a registry for identifying them in
[I-D.ietf-spring-srv6-network-programming]. SRv6 is a proposed
standard and is deployed today.
The SPRING working group has observed that some use cases, such as
strict path TE, may require long SRv6 SID lists. There are several
proposed methods to reduce the resulting SRv6 encapsulation size by
compressing the SID list.
The SPRING working group formed a design team to define requirements
for, and analyze, proposals to compress SRv6 SID lists.
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It is a goal of the design team to identify the solutions to SR over
IPv6 list compression.
In each category, the requirements are described under several sub-
categories including
o Efficiency and performance
o Functional requirements
o Operational requirements
o Scalability requirements
o Convergence requirements
o Security requirements
For each requirement, a description, rationale and metrics are
described.
The design team will produce a separate document to analyze the
proposals.
2. Conventions used in this document
2.1. 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.
2.2. Terminology
SR: Segment Routing
SRH: Segment Routing Header
MPLS: Multiprotocol Label Switching
SR-MPLS: Segment Routing over MPLS data plane
SID: Segment Identifier
SRv6: Segment Routing over IPv6
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SRv6 SID List: A list of SRv6 SIDs
Compression proposal: A proposal to compress SRv6 SID lists
SRv6 base: SRv6 as defined in [RFC8402], [RFC8754],
[I-D.ietf-spring-srv6-network-programming]
3. SRv6 SID List Compression Requirements
3.1. Dataplane Efficiency and Performance Requirements
3.1.1. Encapsulation Header Size
Description: The compression solution MUST reduce the size of the
SRv6 encapsulation header.
Rationale: A smaller SRv6 encapsulation results in better MTU
efficiency.
Metric: Compression is the ratio of the IPv6 encapsulation size of
SRv6 as defined in [RFC8402], [RFC8754],
[I-D.ietf-spring-srv6-network-programming] vs the IPv6 encapsulation
size of a given proposal. The encapsulation savings of a compression
proposal vs the SRv6 base is a useful measurement to compare
proposals.
The encapsulation metric (E) records the number of bytes required for
a proposal to encapsulate a packet given a specific segment list.
o E(proposal, segment list).
The encapsulation savings(ES)records the encapsulation savings for a
proposal to encapsulate a packet given a specific segment list.
o ES(proposal, segment list) = 1 - E(proposal, segment list)/E(SRv6
base, segment list).
3.1.2. Forwarding Efficiency
Description:The compression solution SHOULD minimize the number of
required hardware resources accessed to process a segment.
Rational:Efficiency in bits on the wire and processing efficiency are
both important. Optimizing one at the expense of the other may lead
to significant performance impact.
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Metric:The data plane efficiency metric (D) records the data plane
forwarding efficiency of the proposed solution. Two metrics are used
and recorded at the each segment endpoint:
o D.PRS(segment list): number of headers parsed during processing of
the segment list.
o D.LKU(segment list): number of FIB lookups during processing of
the segment list. The type of lookup is also recorded as longest
prefix match (LPM) or exact match (EM)
3.1.3. State Efficiency
Description:The compression solution SHOULD minimize the amount of
additional forwarding statestored at a node
Rational: Additional state increases the complexity of the control
plane and data plane. It can also result in an increase in memory
usage.
Metric:The state efficiency metric (S) records the amount of
additional forwarding state required by the proposed solution.
o S(node parameters): the number of additional forwarding states
that need to be stored at a node, given a set of node parameters
consisting of number of nodes in the network, number of local
interface, number of adjacencies. The forwarding state is counted
as entries required in a Forwarding Information Base (FIB) at a
node.
4. SRv6 Specific Requirements
4.1. Functional Requirements
4.1.1. SRv6 Based
TBD
4.1.2. SRv6 Functionality
TBD
4.1.3. SID list length
Description: The compression mechanism must be able to represent SR
paths that contain up to 16 segments.
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Rationale: Strict TE paths require SID list lengths proportional to
the diameter of the SR domain.
Metric: The compression mechanism must be able steer a packet through
an SR path that contains up to sixteen segments.
4.1.4. SID summarization
Description: The solution MUST be compatible with segment
summarization.
Rationale: Summarization of segments is a key benefit of SRv6 vs SR
MPLS. In interdomain deployments any node can reach any other node
via a single prefix segment. Without summarization, border router
SIDs must be leaked and an additional global prefix segment is
required for each domain border to be traversed.
Metric: A solution supports summarization when segments can be
summarized for advertisement into other IGP domains or levels.
4.1.5. Heterogeneous SID lists
TBD
4.2. Operational Requirements
4.2.1. Lossless Compression
Description: The segments of the compressed SID list MUST be
equivalent to the original SID List. For example, a strict path TE
SID List is not compressed to a loose path TE SID list.
Rational: In SRv6 we can represent a path to meet certain objectives.
A compressed solution needs to support the objectives in the same
way.
Metric: Information present in the pre-compression segment list MUST
also be present in the post-compression SID list.
4.3. Scalability Requirements
TBD
5. Protocol Design Requirements
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5.1. Ships in the Night Deployment
Description: The compression solution MUST support deployment in
existing SRv6 networks.
Rationale: SRv6 is deployed today. A compression solution that
interoperates well with SRv6, as deployed, will reduce the overhead
and simplify operations. For Network operators who would migrate to
compressed SRv6 SID lists, the move is expected to gradually occur
over a period time, as they upgrade networks, domains, device
families and software instances.
Metric: A compliant compression solution provides the following
o Supports simultaneous deployment at a node with current SRv6 SIDs.
o Supports simultaneous deployment at a node with current SRv6
control plane.
o Supports simultaneous operation of current SRv6 paths with
compressed paths.
o Supports the behaviors in
[I-D.ietf-spring-srv6-network-programming].
o Does not require removal of existing IPv6 planning.
6. IANA Considerations
This document has no requests to IANA.
7. Security Considerations
TBD
8. Contributors
The following individuals contributed to this draft
Chongfeng Xie, China Telecom, xiechf@chinatelecom.cn
Ron Bonica, Juniper Networks, rbonica@juniper.net
Darren Dukes, Cisco Systems, ddukes@cisco.com
Cheng Li, Huawei, c.l@huawei.com
Peng Shaofu, ZTE, peng.shaofu@zte.com.cn
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Wim Henderickx, Nokia, wim.henderickx@nokia.com
9. Acknowledgements
TBD
10. Normative References
[I-D.ietf-6man-spring-srv6-oam]
Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
Chen, "Operations, Administration, and Maintenance (OAM)
in Segment Routing Networks with IPv6 Data plane (SRv6)",
draft-ietf-6man-spring-srv6-oam-07 (work in progress),
July 2020.
[I-D.ietf-bess-srv6-services]
Dawra, G., Filsfils, C., Raszuk, R., Decraene, B., Zhuang,
S., and J. Rabadan, "SRv6 BGP based Overlay services",
draft-ietf-bess-srv6-services-04 (work in progress), July
2020.
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link
State Extensions for SRv6", draft-ietf-idr-bgpls-
srv6-ext-03 (work in progress), July 2020.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-13 (work in progress), October 2020.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11
(work in progress), October 2020.
[I-D.ietf-rtgwg-segment-routing-ti-lfa]
Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
Francois, P., Voyer, D., Clad, F., and P. Camarillo,
"Topology Independent Fast Reroute using Segment Routing",
draft-ietf-rtgwg-segment-routing-ti-lfa-04 (work in
progress), August 2020.
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[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-08 (work in progress),
July 2020.
[I-D.ietf-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
Henderickx, W., and S. Salsano, "Service Programming with
Segment Routing", draft-ietf-spring-sr-service-
programming-03 (work in progress), September 2020.
[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-24 (work in
progress), October 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>.
[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>.
Authors' Addresses
Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
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Sanders Steffann
SJM Steffann Consultancy
Email: sander@steffann.nl
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