Internet DRAFT - draft-ietf-idr-bgp-ls-sr-policy-path-segment
draft-ietf-idr-bgp-ls-sr-policy-path-segment
Interdomain Routing Working Group C. Li
Internet-Draft Z. Li
Intended status: Standards Track Huawei Technologies
Expires: 22 August 2024 Y. Zhu
China Telecom
W. Cheng
China Mobile
K. Talaulikar
Cisco Systems
19 February 2024
SR Policies Extensions for Path Segment and Bidirectional Path in BGP-LS
draft-ietf-idr-bgp-ls-sr-policy-path-segment-06
Abstract
This document specifies the way of collecting configuration and
states of SR policies carrying Path Segment and bidirectional path
information by using BPG-LS. Such information can be used by
external conponents for many use cases such as performance
measurement, path re-optimization and end-to-end protection.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 22 August 2024.
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Copyright Notice
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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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Carrying SR Path Sub-TLVs in BGP-LS . . . . . . . . . . . . . 3
3.1. SR Path Segment Sub-TLV . . . . . . . . . . . . . . . . . 5
3.2. Reverse Segment List Sub-TLV . . . . . . . . . . . . . . 7
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. BGP-LS TLVs . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
allows the ingress node steers packets into a specific path according
to the Segment Routing Policy [RFC9256].
However, the SR Policies defined in [RFC9256] only supports
unidirectional SR paths and there is no path ID in a Segment List to
identify an SR path. For identifying an SR path and supporting
bidirectional path [I-D.ietf-spring-mpls-path-segment], new policies
carrying Path Segment and bidirectional path information are defined
in [I-D.ietf-idr-sr-policy-path-segment], as well as the extensions
to BGP to distribute new SR policies. The Path Segment can be a Path
Segment in SR-MPLS [I-D.ietf-spring-mpls-path-segment] and SRv6
[I-D.ietf-spring-srv6-path-segment], or other IDs that can identify a
path.
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In many network scenarios, the configuration and state of each TE
Policy is required by a controller which allows the network operator
to optimize several functions and operations through the use of a
controller aware of both topology and state information
[I-D.ietf-idr-te-lsp-distribution].
To collect the TE Policy information that is locally available in a
router, [I-D.ietf-idr-te-lsp-distribution] describes a new mechanism
by using BGP-LS update messages.
Based on the mechanism defined in [I-D.ietf-idr-te-lsp-distribution],
this document describes a mechanism to distribute configuration and
states of the new SR policies defined in
[I-D.ietf-idr-sr-policy-path-segment] to external components using
BGP-LS.
2. Terminology
This memo makes use of the terms defined in [RFC8402] and
[I-D.ietf-idr-te-lsp-distribution].
3. Carrying SR Path Sub-TLVs in BGP-LS
A mechanism to collect states of SR Policies via BGP-LS is proposed
by [I-D.ietf-idr-te-lsp-distribution]. The characteristics of an SR
policy can be described by a TE Policy State TLV, which is carried in
the optional non-transitive BGP Attribute "LINK_STATE Attribute"
defined in [RFC7752]. The TE Policy State TLV contains several sub-
TLVs such as SR TE Policy sub-TLVs.
[I-D.ietf-idr-sr-policy-path-segment] defines the BGP extensions for
Path Segment. The encoding is shown below.
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Path Segment
Segment
Segment
...
Segment List
Weight
Path Segment
Segment
Segment
...
...
Figure 1. Path Segment in SR policy
Also, [I-D.ietf-idr-sr-policy-path-segment] defines SR policy
extensions for bidirectional SR path, the encoding is shown below:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes: Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Path Segment
Segment
Segment
...
Reverse Segment List
Weight
Path Segment
Segment
Segment
...
Figure 2. SR policy for Bidirectional path
In order to collect configuration and states of unidirectional and
bidirectional SR policies defined in
[I-D.ietf-idr-sr-policy-path-segment], this document defines new sub-
TLVs in SR TE Policy sub-TLVs.
3.1. SR Path Segment Sub-TLV
This section defines the SR Path Segment sub-TLV to describe a Path
Segment, and it can be included in the Segment List sub-TLV as
defined in [I-D.ietf-idr-te-lsp-distribution] . An SR Path Segment
sub-TLV can be associated with an SR path specified by a Segment List
sub-TLV. Multiple Path Segment MAY be included in a Segment List for
different use cases. When all the SID Lists within a candidate path
share the same Path Segment ID, the Path Segment can be used to
collect the aggregated information of the candidate path. The format
of Path Segment TLV is shown below.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flag | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Segment ID (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. Path Segment sub-TLV
Where,
* Type: to be assigned by IANA.
* Length: the total length of the value field not including Type and
Length fields.
* Flags: 2 octet field that indicates attribute and status of the
Path Segment. The following bit positions are defined. Other
bits SHOULD be cleared by originator and MUST be ignored by
receiver.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|B| |L| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
* - D-Flag : Indicates the dataplane for the BSIDs, it is set when
Path Segment ID is a 16-octet SRv6 SID unset when the Path
Segment ID is a 4-octet SR/MPLS label value.
- B-Flag: This flag, when set, indicates the presence of the SRv6
Endpoint Behavior and SID Structure encoding specified in
[I-D.ietf-idr-bgpls-srv6-ext]. It MUST be ignored when D-flag
is unset. They indicate the SRv6 Endpoint behavior and SID
structure for the Path Segment ID value in the TLV.
- L-Flag: Local flag. Set when the Path Segment has local
significance on an SR node.
* RESERVED: 2 octets. SHOULD be set to 0 by originator and MUST be
ignored by receiver.
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* Path Segment ID: It indicates the Path Segment ID value based on
the status flags.
The SRv6 Endpoint Behavior TLV (1250) and the SRv6 SID Structure TLV
(1252) defined in [I-D.ietf-idr-bgpls-srv6-ext] are used as sub-TLVs
of the SR Path Segment Sub-TLV to optionally indicate the SRv6
Endpoint behavior and SID structure for the Binding SID value in the
TLV when the Path Segment is an SRv6 Path Segment.
3.2. Reverse Segment List Sub-TLV
In some scenarios like mobile backhaul transport network, there are
requirements to support bidirectional path. In SR, a bidirectional
path can be represented as a binding of two unidirectional SR paths
[I-D.ietf-spring-mpls-path-segment]. An SR policy carrying SR
bidirectional path information is expressed in Figure 2.
[I-D.ietf-idr-sr-policy-path-segment] defines a new sub-TLV to
describe a reversed SR path of an SID list.
This section defines a Reverse Segment List sub-TLV to specify a
reverse SR path associated with the path specified by the Segment
List, and it reuses the format of SR Segment List TLV defined in
[I-D.ietf-idr-te-lsp-distribution]:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTID | Algorithm | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5. Reverse Segment List Sub-TLV
All fields, except the type are defined in
[I-D.ietf-idr-te-lsp-distribution], and this TLV reuses it directly.
The Type of this TLV is TBA.
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The SR Segment sub-TLV [I-D.ietf-idr-te-lsp-distribution] MUST be
included as an ordered set of sub-TLVs within the SR Segment List TLV
when the SID-List is not empty. A SID-List may be empty in certain
cases (e.g. for a dynamic path) where the headend has not yet
performed the computation and hence not derived the segments required
for the path; in such cases, the SR Segment List TLV SHOULD NOT
include any SR Segment sub-TLVs [I-D.ietf-idr-te-lsp-distribution].
Note: currently, only one reverse SID list is supported, so the
weight field CAN be ignored when processing. However, multiple
reverse SID list MAY be supported in the future, and the use case of
supporting this still need to be discussed.
4. Operations
The operations procedures of [RFC7752] can apply to this document.
Typically but not limited to, the uni/bidirectional SR policies
carrying path identification information can be distributed by the
ingress node.
Generally, BGP-LS is used for collecting link states and
synchronizing with the external component. The consumer of the uni/
bidirectional SR policies carrying path identification information is
not BGP LS process by itself, and it can be any applications such as
performance measurement [I-D.gandhi-spring-udp-pm] and path re-
coputation or re-optimization, etc. The operation of sending
information to other precesses is out of scope of this document.
5. IANA Considerations
5.1. BGP-LS TLVs
IANA maintains a registry called "Border Gateway Protocol - Link
State (BGP-LS) Parameters" with a sub-registry called "Node Anchor,
Link Descriptor and Link Attribute TLVs". The following TLV
codepoints are suggested (for early allocation by IANA):
Codepoint Description Reference
-------------------------------------------------------------
TBA Path Segment sub-TLV This document
TBA Reverse Segment List sub-TLV This document
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6. Security Considerations
TBA
7. Contributors
Mach(Guoyi) Chen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: Mach.chen@huawei.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
James N Guichard
Futurewei Technologies
2330 Central Express Way
Santa Clara
USA
Email: james.n.guichard@futurewei.com
8. Acknowledgements
Many thanks to Shraddha Hedge for her detailed review and
professional comments.
9. References
9.1. Normative References
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[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
Bernier, D., and B. Decraene, "BGP Link State Extensions
for SRv6", Work in Progress, Internet-Draft, draft-ietf-
idr-bgpls-srv6-ext-14, 17 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
bgpls-srv6-ext-14>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-segment-
routing-te-policy-26, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-26>.
[I-D.ietf-idr-te-lsp-distribution]
Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler,
H., and J. Tantsura, "Distribution of Traffic Engineering
(TE) Policies and State using BGP-LS", Work in Progress,
Internet-Draft, draft-ietf-idr-te-lsp-distribution-19, 24
January 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-te-lsp-distribution-19>.
[I-D.ietf-spring-mpls-path-segment]
Cheng, W., Li, H., Li, C., Gandhi, R., and R. Zigler,
"Path Segment Identifier in MPLS Based Segment Routing
Network", Work in Progress, Internet-Draft, draft-ietf-
spring-mpls-path-segment-22, 30 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
mpls-path-segment-22>.
[I-D.ietf-spring-srv6-path-segment]
Li, C., Cheng, W., Chen, M., Dhody, D., and Y. Zhu, "Path
Segment for SRv6 (Segment Routing in IPv6)", Work in
Progress, Internet-Draft, draft-ietf-spring-srv6-path-
segment-07, 19 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-path-segment-07>.
[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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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[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>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
9.2. Informative References
[I-D.gandhi-spring-udp-pm]
Gandhi, R., Filsfils, C., Voyer, D., Salsano, S., Ventre,
P. L., and M. Chen, "UDP Path for In-band Performance
Measurement for Segment Routing Networks", Work in
Progress, Internet-Draft, draft-gandhi-spring-udp-pm-02,
14 September 2018, <https://datatracker.ietf.org/doc/html/
draft-gandhi-spring-udp-pm-02>.
[I-D.ietf-idr-sr-policy-path-segment]
Li, C., Li, Z., Yin, Y., Cheng, W., and K. Talaulikar, "SR
Policy Extensions for Path Segment and Bidirectional
Path", Work in Progress, Internet-Draft, draft-ietf-idr-
sr-policy-path-segment-08, 16 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-path-segment-08>.
[I-D.ietf-mpls-bfd-directed]
Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
"Bidirectional Forwarding Detection (BFD) Directed Return
Path for MPLS Label Switched Paths (LSPs)", Work in
Progress, Internet-Draft, draft-ietf-mpls-bfd-directed-25,
31 December 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-mpls-bfd-directed-25>.
Authors' Addresses
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Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: c.l@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: lizhenbin@huawei.com
Yongqing Zhu
China Telecom
109 West Zhongshan Ave
Guangzhou
China
Email: zhuyq8@chinatelecom.cn
Weiqiang Cheng
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
Ketan Talaulikar
Cisco Systems
Email: ketant.ietf@gmail.com
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