Internet DRAFT - draft-sidor-pce-circuit-style-pcep-extensions
draft-sidor-pce-circuit-style-pcep-extensions
PCE Working Group S. Sidor
Internet-Draft Z. Ali
Intended status: Standards Track Cisco Systems, Inc.
Expires: 13 July 2023 P. Maheshwari
Airtel India
R. Rokui
Ciena
A. Stone
Nokia
L. Jalil
Verizon
S. Peng
Huawei Technologies
T. Saad
Juniper Networks
D. Voyer
Bell Canada
9 January 2023
PCEP extensions for Circuit Style Policies
draft-sidor-pce-circuit-style-pcep-extensions-03
Abstract
This document proposes a set of extensions for Path Computation
Element Communication Protocol (PCEP) for Circuit Style Policies -
Segment-Routing Policy designed to satisfy requirements for
connection-oriented transport services. New TLV is introduced to
control path recomputation and new flag to add ability to request
path with strict hops only.
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Extensions to PCEP . . . . . . . . . . . . . . . 4
3.1. LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . . . 4
3.2. PATH-RECOMPUTATION TLV . . . . . . . . . . . . . . . . . 4
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Strict path enforcement . . . . . . . . . . . . . . . . . 5
4.2. Path recomputation . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6.1. LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . . . 6
6.2. PATH-RECOMPUTATION TLV . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
Usage of Segment-routing and PCEP in connection-oriented transport
services require path persistancy and hop-by-hop behavior for PCE
computed paths.
Circuit-Style Policy introduced in
[I-D.schmutzer-spring-cs-sr-policy] requires PCEP extensions, which
are covered in this document.
This document:
* Introduces possibility to request strict path from the PCE by
extending LSP-EXTENDED-FLAG TLV
* Adding new TLV to encode information about disabling path
recomputation for specific path to the PCE, to be carried inside
the LSPA object, which is defined in [RFC5440].
* Clarifies usage of existing O-flag from RP object in Segment-
routing
PCEP extensions described in this document are applicable to RSVP-TE
and SR-TE.
2. Terminology
The following terminologies are used in this document:
ERO: Explicit Route Object
IGP: Interior Gateway Protocol
LSP: Label Switched Path.
LSPA: Label Switched Path Attributes.
OTN: Optical Transport Network.
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: Path Computation Element Protocol.
SDH: Synchronous Digital Hierarchy
SID: Segment Identifier
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SONET: Synchronous Optical Network
SR: Segment Routing.
SR-TE: Segment Routing Traffic Engineering.
3. Overview of Extensions to PCEP
3.1. LSP-EXTENDED-FLAG TLV
O-flag is proposed in the LSP-EXTENDED-FLAG TLV, which was introduced
in 5.1.2 of [I-D.ietf-pce-lsp-extended-flags] and extended with
E-flag in [I-D.peng-pce-entropy-label-position]. TLV format will be
added after assigning O flag bit position by IANA.
Type (16 bits): the value is TBD1 by IANA.
Length (16 bits): multiple of 4 octets.
O (Strict-Path): If set to 1, this indicates to the PCE that a path
exclusively made of strict hops is required. Strict hop definition
is described in Section 4.1
3.2. PATH-RECOMPUTATION TLV
This document defines new TLV for the LSPA Object for encoding
information whether path recomputation is allowed for delegated LSP.
The TLV is optional. If the TLV is included in LSPA object, the PCE
MUST NOT recompute path in cases specified by flags in the TLV.
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 = TBD2 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |P|F|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (16 bits): the value is TBD2 by IANA.
Length (16 bits): 4 octets
Reserved: MUST be set to zero by the sender and MUST be ignored by
the receiver.
Flags: This document defines the following flag bits. The other
bits MUST be set to zero by the sender and MUST be ignored by the
receiver.
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* P (Permanent): If set to 1, the PCE MUST NOT recompute path
even if current path is not satisfying path computation
constraints. Otherwise, if this flag is cleared, then the PCE
MAY recompute path if original path is invalidated.
* F (Force): If set to 1, the PCE MUST NOT update path. If flag
is cleared, the PCE MAY update path based on explicit request
from operator.
4. Operation
4.1. Strict path enforcement
PCC MAY set the O flag in LSP-EXTENDED-FLAG TLV in PCRpt message to
the PCE to indicate that a path exclusively made of strict hops is
required.
O flag cleared or LSP-EXTENDED-FLAG TLV not included indicates that a
loose path is acceptable.
In PCUpdate or PCInitiate messages, PCE MAY set O bit if strict path
is provided.
The flag is applicable only for stateful messages. Existing O flag
in RP object MAY be used to indicate similar behavior in PCReq and
PCRep messages as described in as described in Section 7.4.1 of
[RFC5440].
If O flag is set to 1 for both stateful and stateless messages for SR
paths introduced in [RFC8664], PCE MUST use only SIDs, which will use
explicitly specified adjacencies for packet forwarding. For example
Adjacency SIDs MAY be used, but Prefix SIDs MUST NOT be used (even if
there is only one adjacency). the PCE MUST use Adjacency SIDs only.
4.2. Path recomputation
PCC MAY set flags in PATH-RECOMPUTATION TLV to control path
computation behavior on PCE side. If TLV is not included, then the
PCE MAY use local policy to trigger path-computation or LSP path
update.
The presence of the TLV is blocking path recomputation based on
various triggers like topology update, any periodic update or changed
state of other LSPs in the network. LSP path MAY be modified if
forwarded packets will still use same path - for example if same path
can be encoded using Adjacency and Prefix SIDs, then PCE MAY switch
between various representations of same path.
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If P flag is cleared, the PCE MAY recompute if current path is not
considered valid, for example after topology update resulting in path
not satisfying LSP's path constraints, but it MUST NOT recompute path
if current path is not optimal.
If P flag is set, the PCE MUST NOT recompute path during LSP lifetime
even if path is invalidated. Only exception is explicit request from
operator to recompute path
If F flag is cleared, path update triggered manually by operator or
any northbound interface of PCE MAY be done. If flag is set the PCE
CAN update path only to tear down LSP by sending PCUpdate message
with empty ERO.
TLV MAY be included in PCInitiate and PCUpdate messages to indicate,
which triggers will be disabled on the PCE. PCC should reflect flag
values in PCRpt messages to forward requirement to other PCEs in the
network.
5. Security Considerations
No additional security measure is required.
6. IANA Considerations
6.1. LSP-EXTENDED-FLAG TLV
[I-D.ietf-pce-lsp-extended-flags] defines the LSP-EXTENDED-FLAG TLV.
IANA is requested to make the following assignment from the "LSP-
EXTENDED-FLAG TLV Flag Field" registry:
+======+======================+===============+
| Bit | Description | Reference |
+======+======================+===============+
| TBD1 | Strict-Path Flag (O) | This document |
+------+----------------------+---------------+
Table 1
6.2. PATH-RECOMPUTATION TLV
IANA is requested to make the assignment of a new value for the
existing "PCEP TLV Type Indicators" registry as follows:
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+==========+========================+===============+
| TLV Type | TLV Name | Reference |
+==========+========================+===============+
| TBD2 | PATH-RECOMPUTATION TLV | This document |
+----------+------------------------+---------------+
Table 2
7. References
7.1. Normative References
[I-D.ietf-pce-lsp-extended-flags]
Xiong, Q., "LSP Object Flag Extension of Stateful PCE",
Work in Progress, Internet-Draft, draft-ietf-pce-lsp-
extended-flags-09, 23 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-pce-lsp-
extended-flags-09.txt>.
[I-D.peng-pce-entropy-label-position]
Xiong, Q., Peng, S., and F. Qin, "PCEP Extension for SR-
MPLS Entropy Label Position", Work in Progress, Internet-
Draft, draft-peng-pce-entropy-label-position-08, 29 August
2022, <https://www.ietf.org/archive/id/draft-peng-pce-
entropy-label-position-08.txt>.
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[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>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
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[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>.
7.2. Informative References
[I-D.schmutzer-spring-cs-sr-policy]
Schmutzer, C., Filsfils, C., Ali, Z., and F. Clad,
"Circuit Style Segment Routing Policies", Work in
Progress, Internet-Draft, draft-schmutzer-spring-cs-sr-
policy-00, 24 July 2022, <https://www.ietf.org/archive/id/
draft-schmutzer-spring-cs-sr-policy-00.txt>.
[SDH] International Telecommunication Union, "Network node
interface for the synchronous digital hierarchy (SDH)",
ITU-T Recommendation G.707, October 2020.
[SONET] American National Standards Institute, "Synchronous
Optical Network (SONET) Basic Description including
Multiplex Structure, Rates, and Formats", ANSI T1.105,
January 1995.
Authors' Addresses
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Praveen Maheshwari
Airtel India
Email: Praveen.Maheshwari@airtel.com
Reza Rokui
Ciena
Email: rrokui@ciena.com
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Andrew Stone
Nokia
Email: andrew.stone@nokia.com
Luay Jalil
Verizon
Email: luay.jalil@verizon.com
Shuping Peng
Huawei Technologies
Email: pengshuping@huawei.com
Tarek Saad
Juniper Networks
Email: tsaad@juniper.net
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
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