Internet DRAFT - draft-liu-idr-bgp-sr-policy-cp-threshold
draft-liu-idr-bgp-sr-policy-cp-threshold
IDR Working Group Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: April 14, 2024 New H3C Technologies
Y. Qiu
New H3C Technologies
October 11, 2023
BGP Extension for Distributing CP Threshold Constraints of SR Policy
draft-liu-idr-bgp-sr-policy-cp-threshold-00
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), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on April 14 2024.
Copyright Notice
Copyright (c) 2023 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
(http://trustee.ietf.org/license-info) in effect on the date of
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
XXX, et al. Expires April, 2024 [Page 1]
Internet-Draft BGP for CP Threshold Constraints October 2023
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.
Abstract
This document defines the extension of BGP to distribute threshold
and metric constraint parameters of candidate paths for SR Policy to
achieve flexible path selection.
Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Carrying Constraint Parameters of CP in BGP....................3
4. SR Bandwidth Constraint Sub-TLV................................4
5. SR Metric Constraint Sub-TLV...................................5
6. SR Segment List Bandwidth Constraint Sub-TLV...................6
7. Operations.....................................................7
8. IANA Considerations............................................7
9. Security Considerations........................................7
10. References....................................................8
10.1. Normative References.....................................8
10.2. Informative References...................................8
11. Acknowledgments...............................................9
Authors' Addresses...............................................10
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. The ingress node steers packets into a specific path according
to the Segment Routing Policy (SR Policy) as defined in [RFC9256].
An SR Policy may have multiple candidate paths that are provisioned
or signaled [I-D.ietf-idr-segment-routing-te-policy] [RFC8664] from
one of more sources.
[I-D.liu-spring-sr-policy-flexible-path-selection] proposes a
flexible SR policy candidate path selection method. Based on the
real-time resource usage and forwarding quality of candidate paths,
the head node can perform dynamic path switching among multiple
candidate paths in the SR policy.
Multiple threshold parameters for SR Policy candidate path selection
are listed in Section 4.1 of [I-D.liu-spring-sr-policy-flexible-
path-selection]. This document defines extensions to BGP to
XXX, et al. Expires April, 2024 [Page 2]
Internet-Draft BGP for CP Threshold Constraints October 2023
distribute threshold and metric constraint parameters of candidate
path (CP) for an SR Policy.
2. Terminology
The definitions of the basic terms are identical to those found in
Segment Routing Policy Architecture [RFC9256].
3. Carrying Constraint Parameters of CP in BGP
As defined in [I-D.ietf-idr-segment-routing-te-policy], a new SAFI
is defined (the SR Policy SAFI with codepoint 73) as well as a new
NLRI. The NLRI contains the SR Policy candidate path and, according
to [I-D.ietf-idr-segment-routing-te-policy], the content of the SR
Policy Candidate Path is encoded in the Tunnel Encapsulation
Attribute defined in [RFC9012] using a new Tunnel-Type called SR
Policy Type with codepoint 15.
This document defines the following three Sub-TLVs to carry
threshold and metric constraint parameters for candidate paths.
* SR Bandwidth Constraint Sub-TLV
* SR Metric Constraint Sub-TLV
* SR Segment List Bandwidth Constraint Sub-TLV
The new SR Policy encoding structure with Sub-TLVs of CP constraint
parameters is expressed as below:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
XXX, et al. Expires April, 2024 [Page 3]
Internet-Draft BGP for CP Threshold Constraints October 2023
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
SR Bandwidth Constraint Sub-TLV
SR Metric Constraint Sub-TLV
Segment List
Weight
Segment
Segment
SR Segment List Bandwidth Constraint Sub-TLV
...
...
4. SR Bandwidth Constraint Sub-TLV
The SR Bandwidth Constraint sub-TLV is used to carry the bandwidth
threshold constraint parameter of a candidate path.
The SR Bandwidth Constraint sub-TLV is optional and it MUST NOT
appear more than once in the SR Policy encoding.
The format of the SR Bandwidth Constraint Sub-TLV is defined as
follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: to be assigned by IANA
* Length: 4 octets
XXX, et al. Expires April, 2024 [Page 4]
Internet-Draft BGP for CP Threshold Constraints October 2023
* Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
* Bandwidth: 4 octets which specify the bandwidth threshold in unit
of bytes per second in IEEE floating point format.
* RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
5. SR Metric Constraint Sub-TLV
The SR Metric Constraint sub-TLV is used to carry the metric
Constraint of a candidate path.
The SR Metric Constraint sub-TLV is optional. Multiple instances of
this sub-TLV may be used to carry different metric type uses.
The format of the SR Metric Constraint Sub-TLV is defined as follows:
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 | Metric Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Margin |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: to be assigned by IANA
* Length: 8 octets
* Flags: 1-octet field that indicates the validity of the metric
fields and their semantics. The following bit positions are
defined and the other bits MUST be cleared by the originator and
MUST be ignored by a receiver.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|M|A|B| |
+-+-+-+-+-+-+-+-+
where:
- M-Flag: Indicates that the metric margin allowed is specified
XXX, et al. Expires April, 2024 [Page 5]
Internet-Draft BGP for CP Threshold Constraints October 2023
when set.
- A-Flag: Indicates that the metric margin is specified as an
absolute value when set and is expressed as a percentage of
the minimum metric when clear.
- B-Flag: Indicates that the metric bound allowed for the path
is specified when set.
* Metric Type: 1-octet field which identifies the type of the metric
being used. The metric type code points are listed in Section 8.6
of [I-D.ietf-idr-bgp-ls-sr-policy].
* Metric Margin: 4-octet value which indicates the metric margin
when the M-flag is set. The metric margin is specified as either
an absolute value or as a percentage of the minimum computed path
metric based on the A-flag. The metric margin loosens the
criteria for minimum metric path calculation up to the specified
metric to accommodate for other factors such as bandwidth
availability, minimal SID stack depth, and maximizing of ECMP for
the SR path computed.
* Metric Bound: 4-octet value which indicates the maximum metric
that is allowed when the B-flag is set. If the computed path
metric crosses the specified bound value then the path is
considered invalid.
6. SR Segment List Bandwidth Constraint Sub-TLV
The SR Segment List Bandwidth Constraint sub-TLV is used to carry
the bandwidth allocated to the specific SID-List.
The SR Segment List Bandwidth Constraint sub-TLV is optional and it
MUST NOT appear more than once inside the Segment List sub-TLV.
The SR Segment List Bandwidth Constraint sub-TLV has the following
format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: to be assigned by IANA
* Length: 4 octets
XXX, et al. Expires April, 2024 [Page 6]
Internet-Draft BGP for CP Threshold Constraints October 2023
* Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
* Bandwidth: 4 octets which specify the bandwidth threshold in unit
of bytes per second in IEEE floating point format.
* RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
7. Operations
The document does not bring new operation beyond the description of
operations defined in Section 4 of [I-D.ietf-idr-segment-routing-te-
policy]. The existing operations defined in [I-D.ietf-idr-segment-
routing-te-policy] can apply to this document directly.
Typically, but not limit to, the SR policies carrying the constraint
parameters of CP are configured by a controller.
After configuration, the SR policies carrying the constraint
parameters of CP will be advertised by BGP update messages. The
operation of advertisement is the same as defined in [I-D.ietf-idr-
segment-routing-te-policy], as well as the reception.
8. IANA Considerations
This document defines a new sub-TLV in the registry "BGP Tunnel
Encapsulation Attribute sub-TLVs" to be assigned by IANA:
+=======+==================================+=================+
| Value | Description | Reference |
+=======+==================================+=================+
| TBA1 | SR Bandwidth Constraint sub-TLV | This document |
+-------+----------------------------------+-----------------+
| TBA2 | SR Metric Constraint sub-TLV | This document |
+-------+----------------------------------+-----------------+
| TBA3 | SR Segment List Bandwidth | This document |
| | Constraint sub-TLV | |
+-------+----------------------------------+-----------------+
9. Security Considerations
[I-D.ietf-idr-segment-routing-te-policy] has discussed the security
considerations for distributing SR Policy through BGP. This document
does not introduce any new security issues.
XXX, et al. Expires April, 2024 [Page 7]
Internet-Draft BGP for CP Threshold Constraints October 2023
10. References
10.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C.,
Talaulikar, K., Mattes, P., Jain, D., and S. Lin,
"Advertising Segment Routing Policies in BGP", draft-ietf-
idr-segment-routing-te-policy-25 (work in progress),
September 2023.
[I-D.liu-spring-sr-policy-flexible-path-selection] Liu, Y., Lin, C.,
Peng, S., and Qiu, Y., "Flexible Candidate Path Selection
of SR Policy", draft-liu-spring-sr-policy-flexible-path-
selection-02 (work in progress), September 2023.
[I-D.ietf-idr-bgp-ls-sr-policy] Previdi, S., Talaulikar, K., Dong,
J., Gredler, H., Tantsura, J., "Advertisement of Segment
Routing Policies using BGP Link-State", draft-ietf-idr-
bgp-ls-sr-policy-01 (work in progress), July 2023.
[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
Hardwick, J., "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC8664,
DOI 10.17487/RFC8664, December 2019, <https://www.rfc-
editor.org/info/rfc8664>.
[RFC9256] Filsfils, C., Talaulikar, K., 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>.
10.2. Informative References
TBD
XXX, et al. Expires April, 2024 [Page 8]
Internet-Draft BGP for CP Threshold Constraints October 2023
11. Acknowledgments
The authors would like to thank the following for their valuable
contributions of this document:
TBD
XXX, et al. Expires April, 2024 [Page 9]
Internet-Draft BGP for CP Threshold Constraints October 2023
Authors' Addresses
Yisong Liu
China Mobile
Beijing
China
Email: liuyisong@chinamobile.com
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
Yuanxiang Qiu
New H3C Technologies
Beijing
China
Email: qiuyuanxiang@h3c.com
XXX, et al. Expires April, 2024 [Page 10]
