PCEP Extensions of SR Policy for Headend Behavior
draft-lin-pce-sr-policy-headend-behavior-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Changwang Lin , Ran Chen | ||
| Last updated | 2024-11-14 | ||
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| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
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draft-lin-pce-sr-policy-headend-behavior-00
PCE Working Group C. Lin
Internet-Draft New H3C Technologies
Intended status: Standards Track R. Chen
Expires: May 15, 2025 ZTE Corporation
November 13, 2024
PCEP Extensions of SR Policy for Headend Behavior
draft-lin-pce-sr-policy-headend-behavior-00
Abstract
A Segment Routing (SR) Policy [RFC9256] is a non-empty set of SR
Candidate Paths, that share the same <headend, color, endpoint>
tuple. [I-D.draft-ietf-pce-segment-routing-policy-cp] extends
[RFC8664] to fully support the SR Policy construct. The header of a
packet steered in an SR Policy is augmented with an ordered list of
segments associated with that SR Policy. [RFC8986] defines H. Encaps
behavior, H. Encaps.Red behavior, H. Encaps.L2 behavior, and H.
Encaps.L2.Red behavior for SR policy. This document defines
extensions to PCEP to distribute SR policies carrying headend
behavior.
Status of this Memo
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This Internet-Draft will expire on May 15 2025.
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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. PCEP Extensions................................................3
2.1. SRPOLICY-CPATH-HEADEND-BEHAVIOR Sub-TLV...................4
2.2. SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR Sub-TLV................5
3. IANA Considerations............................................6
4. Security Considerations........................................6
5. References.....................................................7
5.1. Normative References......................................7
5.2. Informative References....................................8
Acknowledgments...................................................8
Authors' Addresses................................................8
1. Introduction
Segment Routing (SR) [RFC8402] allows a headend node to steer a
packet flow along any path. Intermediate per-path states are
eliminated thanks to source routing.
The headend node is said to steer a flow into an SR Policy
[RFC8402]. The packets steered into an SR Policy carry an ordered
list of segments associated with that SR Policy.
PCEP Extensions for Segment Routing [RFC8664] specifies extensions
that allow PCEP to work with basic SR-TE paths. PCEP extension to
support Segment Routing Policy Candidate Paths.[I-D.ietf-pce-
segment-routing-policy-cp] specifies extensions that allow PCEP to
signal additional attributes of an SR Policy, which are not covered
by [RFC8664]. SR Policy is modeled in PCEP as an Association and
the SR Candidate Paths are the members of that Association. Thus
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the PCE can take computation and control decisions about the
Candidate Paths, with the additional knowledge that these Candidate
Paths belong to the same SR Policy.
[RFC8986] defines End.B6.Encaps behavior and End.B6.Encaps.Red
behavior for SRv6 BSID. When receiving packets with an active SID
matching a local BSID of these kinds, the headend will perform
corresponding behaviors. Different BSID behaviors are suitable for
different scenarios. For example, comparing with End.B6.Encaps,
End.B6.Encaps.Red reduces the size of the SRH by excluding the first
SID, which can be useful for the devices with lower capacity of SID
depths, like the switches in data center network.
The SRv6 Binding SID sub-TLV is defined in [RFC9604] to signal the
SRv6 BSID information along with SR Policies. It enables the
specified SRv6 BSID behavior to be instantiated on the headend node.
However, if the packets are steering into an SR Policy in some other
way than using BSID, the headend behavior is not specified during
the distributing of SR Policy by PCEP. The network operator has to
use additional tools, like NETCONF, to signal the headend behavior.
[RFC8986] defines H. Encaps behavior, H. Encaps.Red behavior, H.
Encaps.L2 behavior, and H. Encaps.L2.Red behavior for SR policy.
This document defines extensions to PCEP to distribute SR policies
that carry headend behavior, so that the headend can be instructed
to perform specific behaviors when packets are steered into the SR
policy without a BSID.
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. PCEP Extensions
In accordance with [RFC8697], TE LSPs are associated by adding them
to a common association group by a PCEP peer. [I-D.ietf-pce-segment-
routing-policy-cp] defines the SR Policy Association (SRPA), where
the SR Candidate Paths are members of this association.
To specify the Headend behavior that the candidate path of an SR
policy is associated with, two new sub-TLVs, named "SRPOLICY-CPATH-
HEADEND-BEHAVIOR" and "SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR," are
defined within the SRPA object.
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2.1. SRPOLICY-CPATH-HEADEND-BEHAVIOR Sub-TLV
The SRPOLICY-CPATH-HEADEND-BEHAVIOR TLV encodes the default headend
behavior associated with the candidate path for L3 traffic. When the
headend steers L3 packets into that SR policy and the associated
candidate path is active, the specific headend behavior should be
performed by default. In the case of BSID steering, the behavior
defined by the BSID overrides the default headend behavior.
The SRPOLICY-CPATH-HEADEND-BEHAVIOR TLV is an optional TLV for the
SRPA object and MUST NOT appear more than once in the SR policy
encoding. If the SRPOLICY-CPATH-HEADEND-BEHAVIOR sub-TLV appears
more than once, only the first instance of the TLV SHOULD be
interpreted, and subsequent instances SHOULD be ignored.
The SRPOLICY-CPATH-HEADEND-BEHAVIOR 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Headend Behavior | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The SRPOLICY-CPATH-HEADEND-BEHAVIOR TLV
where:
o Type: to be assigned by IANA.
o Length: 4.
o RESERVED: 2 octets of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Headend Behavior: a 2-octet value. The following values are
defined.
* TBD: Headend Behavior = 0 Indicates it is of H. Encaps type. A
headend behavior defined in [RFC8986].
* TBD: Headend Behavior = 1 Indicates it is of H.Encaps.Red
type. A headend behavior defined in [RFC8986].
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* TBD: Headend Behavior = 2 Indicates it is of H.Insert type. A
headend behavior defined in [I-D.filsfils-spring-srv6-net-
pgm-insertion].
* TBD: Headend Behavior = 3 Indicates it is of H.Insert.Red
type. A headend behavior defined in [I-D.filsfils-spring-
srv6-net-pgm-insertion].
2.2. SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR Sub-TLV
The SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR TLV encodes the default
headend behavior associated with the candidate path for L2 traffic.
When the headend steers L2 packets into that SR Policy and the
associated candidate path is active, the specific headend behavior
should be performed by default. In the case of BSID steering, the
behavior defined by the BSID overrides the default headend behavior.
The SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR TLV is an optional TLV for
the SRPA object, and MUST NOT appear more than once in the SR Policy
encoding. If the SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR sub-TLV appears
more than once, only the first instance of the TLV SHOULD be
interpreted and subsequent instances SHOULD be ignored.
The SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 Headend Behavior | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR TLV
where:
o Type: to be assigned by IANA.
o Length: 4.
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o RESERVED: 2 octets of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o L2 Headend Behavior: a 2-octet value. The following values are
defined.
* TBD: L2 Headend Behavior = 0: H.Encaps.L2. A headend behavior
defined in [RFC8986].
* TBD: L2 Headend Behavior = 1: H.Encaps.L2.Red. A headend
behavior defined in [RFC8986].
3. IANA Considerations
This document defines the new TLV for carrying additional
information about SR Policy and SR Candidate Paths. IANA is
requested to make the assignment of a new value for the existing
"PCEP TLV Type Indicators" registry as follows:
+-------+-------------------------------------+---------------+
|Value | Description | Reference |
+=======+=====================================+===============+
| TBA | SRPOLICY-CPATH-HEADEND-BEHAVIOR | This document |
+-------+-------------------------------------+---------------+
| TBA | SRPOLICY-CPATH-L2-HEADEND-BEHAVIOR | This document |
+-------+-------------------------------------+---------------+
4. Security Considerations
[RFC8754] defines the notion of an SR domain and use of SRH within
the SR domain. Procedures for securing an SR domain are defined the
section 5.1 and section 7 of [RFC8754].
This document does not impose any additional security challenges to
be considered beyond security threats described in [RFC8754],
[RFC8679] and [RFC8986].
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in [I-D.ietf-pce-
segment-routing-policy-cp].
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5. References
5.1. Normative References
[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-11, 20 June
2023,<https://datatracker.ietf.org/doc/html/draft-ietf-
pce-segment-routing-policy-cp-11>.
[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>.
[RFC8679] Shen, Y., Jeganathan, M., Decraene, B., Gredler, H.,
Michel, C., and H. Chen, "MPLS Egress Protection
Framework", RFC 8679, DOI 10.17487/RFC8679, December 2019,
<https://www.rfc-editor.org/info/rfc8679>.
[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>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986, DOI
10.17487/RFC8986, February 2021, <https://www.rfc-
editor.org/info/rfc8986>.
[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>.
[RFC9604] Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
and C. Li, "Carrying Binding Label/Segment Identifier
(SID) in PCE-based Networks.", RFC 9604, DOI
10.17487/RFC9604 16 August 2024,
<https://datatracker.ietf.org/doc/rfc9604/>.
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5.2. Informative References
TBD
Acknowledgments
TBD
Authors' Addresses
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Ran Chen
ZTE Corporation
China
Email: chen.ran@zte.com.cn
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