Internet DRAFT - draft-sidor-pce-circuit-style-pcep-extensions
draft-sidor-pce-circuit-style-pcep-extensions
PCE Working Group S. Sidor
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track P. Maheshwari
Expires: 17 June 2024 Airtel India
A. Stone
Nokia
L. Jalil
Verizon
S. Peng
Huawei Technologies
15 December 2023
PCEP extensions for Circuit Style Policies
draft-sidor-pce-circuit-style-pcep-extensions-06
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.
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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This Internet-Draft will expire on 17 June 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Extensions to PCEP . . . . . . . . . . . . . . . 4
3.1. New flag in the 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. Manageability Considerations . . . . . . . . . . . . . . . . 6
5.1. Control of Function and Policy . . . . . . . . . . . . . 6
5.2. Information and Data Models . . . . . . . . . . . . . . . 6
5.3. Liveness Detection and Monitoring . . . . . . . . . . . . 6
5.4. Verify Correct Operations . . . . . . . . . . . . . . . . 7
5.5. Requirements On Other Protocols . . . . . . . . . . . . . 7
5.6. Impact On Network Operations . . . . . . . . . . . . . . 7
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 7
6.1. Cisco . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . . . 8
8.2. PATH-RECOMPUTATION TLV . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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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.ietf-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 can be used with any Path
Setup Type.
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. New flag in the LSP-EXTENDED-FLAG TLV
O-flag is proposed in the LSP-EXTENDED-FLAG TLV, which was introduced
in 3.1 of [RFC9357]. TLV format will be added after assigning O-flag
bit position by IANA.
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.
* P (Permanent): If set to 1, the PCE MUST NOT recompute path
even if current path is not satisfying path computation
constraints. If this flag is cleared, then the PCE SHOULD
recompute path if original path is invalidated.
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* 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).
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.
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.
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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. Manageability Considerations
All manageability requirements and considerations listed in
[RFC5440], [RFC8231] and [RFC8281] apply to PCEP protocol extensions
defined in this document. In addition, requirements and
considerations listed in this section apply.
5.1. Control of Function and Policy
A PCE or PCC implementation MAY allow the capability of supporting
PCEP extensions introduced in this document to be enabled/disabled as
part of the global configuration.
5.2. Information and Data Models
An implementation SHOULD allow the operator to view the capability
defined in this document. Section 4.1 and 4.1.1 of
[I-D.ietf-pce-pcep-yang] should be extended to include that
capability for PCEP peer.
Section 4.2 of [I-D.ietf-pce-pcep-yang] module should be extended to
add notification for blocked recomputation satisfying specified
constraints if recomputation is blocked using PATH-RECOMPUTATION TLV.
5.3. Liveness Detection and Monitoring
Circuit-Style Policy draft [I-D.ietf-spring-cs-sr-policy] is already
describing connectivity verification and path validity considerations
for Circuit Style Policies.
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5.4. Verify Correct Operations
A PCE implementation SHOULD notify operator in case blocked
recomputation for path, which is no longer satisfying specified
constraints and it SHOULD allow the operator to view LSPs on PCE,
which are not satisfying specified constraints.
5.5. Requirements On Other Protocols
The PCEP extensions defined in this document do not imply any new
requirements on other protocols. Overall concept of Circuit Style
policies requires interaction with other protocols, but those
requirements are already described in [I-D.ietf-spring-cs-sr-policy].
5.6. Impact On Network Operations
The mechanisms defined in [RFC5440], [RFC8231], and [RFC8281] also
apply to the PCEP extensions defined in this document.
6. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to RFC 7942.]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
6.1. Cisco
* Organization: Cisco Systems
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* Implementation: IOS-XR PCC and PCE.
* Description: PCEP extensions supported using VENDOR-INFORMATION
Object.
* Maturity Level: Production.
* Coverage: Partial.
* Contact: ssidor@cisco.com
7. Security Considerations
The security considerations described in [RFC5440], [RFC8231],
[RFC8253],[RFC8281] and [RFC8664] in itself.
Note that this specification introduces possibility to block path
recomputation after various topology events. This creates an
additional vulnerability if the security mechanisms of [RFC5440],
[RFC8231], and [RFC8281] are not used. If there is no integrity
protection on the session, then an attacker could block path updates
from PCE potentially resulting in traffic drop.
8. IANA Considerations
8.1. LSP-EXTENDED-FLAG TLV
[RFC9357] 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
8.2. 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
9. References
9.1. Normative References
[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>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[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>.
[RFC9357] Xiong, Q., "Label Switched Path (LSP) Object Flag
Extension for Stateful PCE", RFC 9357, February 2023,
<https://www.rfc-editor.org/info/rfc9357>.
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9.2. Informative References
[I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V. P., and J. Tantsura,
"A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-yang-22, 31 October
2019, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-22>.
[I-D.ietf-spring-cs-sr-policy]
Schmutzer, C., Ali, Z., Maheshwari, P., Rokui, R., and A.
Stone, "Circuit Style Segment Routing Policies", Work in
Progress, Internet-Draft, draft-ietf-spring-cs-sr-policy-
01, 16 June 2023, <https://www.ietf.org/archive/id/draft-
ietf-spring-cs-sr-policy-01.txt>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[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.
Contributors
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
Reza Rokui
Ciena
Email: rrokui@ciena.com
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Tarek Saad
Cisco Systems, Inc.
Email: tsaad.net@gmail.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Authors' Addresses
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Praveen Maheshwari
Airtel India
Email: Praveen.Maheshwari@airtel.com
Andrew Stone
Nokia
Email: andrew.stone@nokia.com
Luay Jalil
Verizon
Email: luay.jalil@verizon.com
Shuping Peng
Huawei Technologies
Email: pengshuping@huawei.com
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