IDR C. Lin
Internet Draft New H3C Technologies
Intended status: Standards Track J. Li
Expires: August 18, 2025 China Mobile
Ran.Chen
ZTE
February 18, 2025
BGP SR Policy Extensions for Administrative Flags
draft-lin-idr-sr-policy-admin-flags-01
Abstract
Segment Routing is a source routing paradigm that explicitly
indicates the forwarding path for packets at the ingress node. An SR
Policy is a set of candidate paths, each consisting of one or more
segment lists.
This document defines an extension to the BGP SR Policy that sets
the administrative state of the candidate path or segment list,
facilitating the operation and maintenance of the SR Policy.
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Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction...................................................2
1.1. Requirements Language.....................................3
2. Admin State in SR Policy.......................................3
2.1. Candidate Path Administrative Flags Sub-TLV...............5
2.2. Segment List Administrative Flags Sub-TLV.................6
3. Security Considerations........................................6
4. IANA Considerations............................................7
5. References.....................................................7
5.1. Normative References......................................7
5.2. Informative References....................................7
Authors' Addresses................................................8
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].
In order to distribute SR policies to the headend, [I-D.ietf-idr-sr-
policy-safi] specifies a mechanism by using BGP.
For management purposes, the controller may occasionally need to
temporarily divert traffic from a specific forwarding path and then
restore it later. In such cases, the controller can issue an
Administrative Down command to a specific path in the SR Policy on
the device without removing the path. When it is time to restore the
path, the controller can simply issue an Administrative Up command
to that same path.
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In another scenario, such as in 6PE or EPE situations where it is
necessary to conserve service route SIDs, the SR Policy Flag can be
extended to indicate settings. For example, configuring the
Candidate Path as "Ignore service routes Prefix SID" can help
optimize the segment list.
In some scenarios, the Candidate Path cannot be used as a backup
path. The operator needs to control the Candidate Path status to
identify whether this CP can serve as a backup path.
In [RFC9256], section 8.2 defines the Drop-Upon-Invalid behavior. An
SR Policy MAY be enabled for the Drop-Upon-Invalid behavior.
Currently, there is no behavior control for Drop-Upon-Invalid on the
path of an SR policy.
This document defines an extension to the BGP SR Policy that sets
the management state of the candidate path or the segment list,
facilitating the operation and maintenance of the SR Policy.
1.1. 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. Admin State in SR Policy
As defined in [I-D.ietf-idr-sr-policy-safi], the SR policy encoding
structure is as follows:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
SR policy with Administrative Flags are expressed as below:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Policy Candidate Path Administrative Flags
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment List Administrative Flags
Segment
Segment
...
...
The Candidate Path Administrative Flags can also be advertised using
the Candidate Path Administrative Flags sub-TLV, as defined in
Section 2.1.
The segment list Administrative Flags can be advertised using the
Segment List Administrative Flags sub-TLV, as defined in Section
2.2.
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2.1. Candidate Path Administrative Flags Sub-TLV
The Candidate Path Administrative Flags sub-TLV is used to indicate
the AdminState of the Candidate Path.
The Candidate Path Administrative Flags sub-TLV is optional and it
MUST NOT appear more than once inside the Segment List sub-TLV.
The Candidate Path Administrative Flags 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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD.
o Length: 2.
o Flags: 2 octet of flags.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|B|I|D| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Administrative Flags
where:
- S-Flag: Indicates the CP is in an administrative shut state
when set.
- B-Flag: Indicates the CP is configured as "backup
ineligible".
- I-Flag: Indicates the CP is configured as "Ignore service
route's Prefix SID". It allows traffic to a BGP service route
to be steered over an SR policy without imposing the service
route's prefix label or SRv6 Service SID.
- D-Flag: Indicates the CP has been marked as the "Drop Upon
Invalid" behavior as described in section 8.2 of [RFC9256].
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2.2. Segment List Administrative Flags Sub-TLV
The Segment List Administrative Flags sub-TLV is used to indicate
the AdminState of the Segment List of Candidate Path.
The Segment List Administrative Flags sub-TLV is optional and it
MUST NOT appear more than once inside the Segment List sub-TLV.
The Segment List Administrative Flags 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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD.
o Length: 2.
o Flags: 2 octet of flags.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Administrative Flags
where:
- S-Flag: Indicates the CP is in an administrative shut state
when set.
3. Security Considerations
The security requirements and mechanisms described in [I-D.ietf-idr-
sr-policy-safi] also apply to this document.
This document does not introduce any new security consideration.
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4. IANA Considerations
This document defines a new Sub-TLV in the registry "SR Policy
Segment List AdminState Sub-TLVs" [I-D.ietf-idr-sr-policy-safi]:
Value Description Reference
-------------------------------------------------------
TBD1 Candidate Path Administrative Flags sub-TLV This
document
TBD2 Segment List Administrative Flags sub-TLV This
document
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017
[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>.
[I-D.ietf-idr-sr-policy-safi] 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-sr-policy-safi-06, 30 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-safi-06>.
5.2. Informative References
[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>.
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Authors' Addresses
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Jinming Li
China Mobile
32 Xuanwumen West Street
Beijing
Xicheng District, 100053
China
Email: lijinming@chinamobile.com
Ran Chen
ZTE Corporation
Email: chen.ran@zte.com.cn
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