Network Working Group K. Zhang
Internet-Draft Z. Hu
Intended status: Informational J. Dong
Expires: 27 August 2023 Huawei
23 February 2023
BGP SR Policy Extensions for template
draft-zhang-idr-sr-policy-template-02
Abstract
Segment Routing(SR) Policies can be advertised using BGP. An SR
Policy may has lots of constraints, and as the application and
features evolve, the SR Policy may need have more and more attribute
constraints. To avoid modifying BGP when constraints are added to an
SR Policy, we can define a template. The identifier and content of
the template are defined by the receiver of the SR Policy. The
advertiser of an SR policy only needs to know the ID of the template.
When advertising SR policy, the advertiser carries the template ID in
the tunnel encapsulation information of the SR policy. After
receiving the SR Policy information, the receiver obtains the
corresponding template and content according to the template ID,
thereby obtaining abundant constraint configuration information.
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 BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
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."
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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 (https://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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Template ID defination . . . . . . . . . . . . . . . . . . . 3
4. SR Policy and Tunnel Encapsulation Attribute Update . . . . . 3
4.1. Template ID sub-TLV . . . . . . . . . . . . . . . . . . . 4
5. SR Policy Operations . . . . . . . . . . . . . . . . . . . . 5
5.1. Advertisement of SR Policies . . . . . . . . . . . . . . 5
5.2. Reception of an SR Policy . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[I-D.ietf-idr-segment-routing-te-policy]defines some attributes
encoding of the SR Policy path. However, in actual applications,
there are many other constraints of SR Policy path. These
constraints are valid only on the device where the SR Policy path is
installed. Such constraints may include backup protection,
Bidirectional Forwarding Detection information, traffic statistics
collection, or in-situ Flow Information Telemetry detection
information, etc. If these constraints are directly delivered
through BGP, the BGP SR Policy protocol may change frequently. This
document defines a general method to carry the path constraints of SR
Policies.
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2. Terminology
SR Policy: An ordered list of segments.
Candidate Path: the unit for signaling of an SR Policy to a headend
via protocol extensions like Path Computation Element (PCE)
Communication Protocol (PCEP) [RFC8664]
[I-D.ietf-pce-segment-routing-policy-cp] or BGP SR Policy
[I-D.ietf-idr-segment-routing-te-policy].
SRPM: SR Policy Module.
Template: A collection of constraints sets.
Template ID: The identifier of a template.
3. Template ID defination
To support the constraints extension of SR Policies, this document
defines a constraint template identifier. The constraint template ID
is valid only for the recipient. The SR policy publisher only needs
to carry the template ID when publishing the SR policy. The receiver
of the SR Policy may create a template corresponding to the template
identifier in advance before receiving the SR Policy, or may define a
corresponding template after receiving the template definition of the
SR Policy. The template can contain any constraints on the SR Policy
path, including but not limited to backup protection, Bidirectional
Forwarding Detection information, traffic statistics collection, or
in-situ Flow Information Telemetry detection information, etc. After
receiving the SR Policy information, the receiver matches the
template information based on the template ID and adds constraints to
the SR Policy based on the constraints defined in the template.
4. SR Policy and Tunnel Encapsulation Attribute Update
As the template ID is defined, the tunnel attribute encapsulation of
the BGP SR Policy needs to be updated.
The SR Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
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Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Template ID
Segment List
Weight
Segment
Segment
....
....
Where Tempate ID indicates the template ID for the SR Policy
candidate path.
4.1. Template ID sub-TLV
A new sub-TLV called Template ID sub-TLV is defined. Template ID
sub-TLV specifies the template ID of an SR policy candidate path.
Each sub-TLV is encoded as shown in Figure 1.
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Template ID(4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: Figure 1: Template ID Sub-TLV
Type: Template ID, 1 octet, TBD.
Length: 6.
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.
RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
Template ID: a 4-octet value.
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5. SR Policy Operations
5.1. Advertisement of SR Policies
When BGP advertises an SR Policy, different candidate paths of the
same SR Policy may have different template IDs or the same template
ID, depending on the constraints required by the candidate paths of
the SR Policy.
5.2. Reception of an SR Policy
When a BGP speaker receives an SR Policy NLRI from a neighbor, BGP
Speaker determines determine if it's acceptable as described in
[I-D.ietf-idr-segment-routing-te-policy]. Once BGP on the receiving
node has determined that the SR Policy NLRI is usable, it passes the
SR Policy candidate path to the SRPM. The SRPM then determine how to
use the template ID in SR Policy.
The SRPM should find the template by template ID, and determines the
constraints to use when install the candidate path. If there is no
template find, the SRPM should ignore the template ID and use the
candidate path as there is no template ID.
6. Acknowledgements
TBD.
7. IANA Considerations
This document requests that IANA allocates a new sub-TLV type as
defined in Section 4.1 from the "Sub-TLVs for SR Policy" registry as
specified.
Value Description Reference
---------------------- ---------------------------- --------------
TBD SR Policy Template ID This document
Figure 2: Figure 2: Template ID sub-TLV
8. Security Considerations
These extensions to BGP SR Policy do not add any new security issues
to the existing protocol.
9. References
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[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", Work in Progress, Internet-Draft, draft-
ietf-idr-segment-routing-te-policy-20, 27 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-20>.
[I-D.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
Bidgoli, "PCEP extension to support Segment Routing Policy
Candidate Paths", Work in Progress, Internet-Draft, draft-
ietf-pce-segment-routing-policy-cp-08, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-policy-cp-08>.
[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
Authors' Addresses
Ka Zhang
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: zhangka@huawei.com
Zhibo Hu
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
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Email: huzhibo@huawei.com
Jie Dong
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: jie.dong@huawei.com
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