Extension for Stateful PCE to allow Optional Processing of PCEP Objects
draft-dhody-pce-stateful-pce-optional-08
PCE Working Group C. Li
Internet-Draft H. Zheng
Updates: 8231 (if approved) Huawei Technologies
Intended status: Standards Track S. Litkowski
Expires: November 6, 2021 Cisco
May 5, 2021
Extension for Stateful PCE to allow Optional Processing of PCEP Objects
draft-dhody-pce-stateful-pce-optional-08
Abstract
This document introduces a mechanism to mark some of the Path
Computation Element (PCE) Communication Protocol (PCEP) objects as
optional during PCEP messages exchange for the Stateful PCE model to
allow relaxing some constraints. This document introduces this
relaxation and updates RFC 8231.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Usage Example . . . . . . . . . . . . . . . . . . . . . . 4
3. PCEP Extension . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 4
3.2. Handling of P flag . . . . . . . . . . . . . . . . . . . 5
3.2.1. The PCRpt Message . . . . . . . . . . . . . . . . . . 5
3.2.2. The PCUpd Message and the PCInitiate Message . . . . 5
3.3. Handling of I flag . . . . . . . . . . . . . . . . . . . 5
3.3.1. The PCUpd Message . . . . . . . . . . . . . . . . . . 5
3.3.2. The PCRpt Message . . . . . . . . . . . . . . . . . . 6
3.3.3. The PCInitiate Message . . . . . . . . . . . . . . . 6
3.4. Delegation . . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Unknown Object Handling . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 7
6. Manageability Considerations . . . . . . . . . . . . . . . . 7
6.1. Control of Function and Policy . . . . . . . . . . . . . 7
6.2. Information and Data Models . . . . . . . . . . . . . . . 7
6.3. Liveness Detection and Monitoring . . . . . . . . . . . . 8
6.4. Verify Correct Operations . . . . . . . . . . . . . . . . 8
6.5. Requirements On Other Protocols . . . . . . . . . . . . . 8
6.6. Impact On Network Operations . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
[RFC5440] describes the Path Computation Element Communication
Protocol (PCEP) which enables the communication between a Path
Computation Client (PCC) and a Path Control Element (PCE), or between
two PCEs based on the PCE architecture [RFC4655].
PCEP Extensions for Stateful PCE Model [RFC8231] describes a set of
extensions to PCEP to enable active control of Multiprotocol Label
Switching Traffic Engineering (MPLS-TE) and Generalzied MPLS (GMPLS)
tunnels. [RFC8281] describes the setup and teardown of PCE-initiated
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LSPs under the active stateful PCE model, without the need for local
configuration on the PCC, thus allowing for dynamic control.
[RFC5440] defined the P flag (Processing-Rule) in the Common Object
Header to allow a PCC to specify in a Path Computation Request
(PCReq) message (sent to a PCE) whether the object must be taken into
account by the PCE during path computation or is optional. The I
flag (Ignore) is used by the PCE in a Path Computation Reply (PCRep)
message to indicate to a PCC whether or not an optional object was
considered by the PCE during path computation. Stateful PCE
[RFC8231] specified that the P and I flags of the PCEP objects
defined in [RFC8231] is to be set to zero on transmission and ignored
on receipt, since they are exclusively related to path computation
requests. The behavior for P and I flag in other messages defined in
[RFC5440] and other extension was not specified. This document
clarifies how the P and I flag could be used in the stateful PCE
model to identify optional objects in the Path Computation State
Report (PCRpt) [RFC8231], the Path Computation Update Request (PCUpd)
[RFC8231], and the LSP Initiate Request (PCInitiate) [RFC8281]
message.
This document updates [RFC8231] with respect to usage of the P and I
flag as well as the handling of unknown objects in the stateful PCEP
message exchange.
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. Overview
[RFC5440] describes the handling of unknown objects as per the
setting of the P flag for the PCReq message. Further, [RFC8231]
defined the usage of the LSP Error Code TLV in the PCRpt message in
response to failed LSP Update Request via the PCUpd message (for
example, due to an unsupported object/TLV).
This document clarifies the procedure of marking some objects as
'optional to be processed' by the PCEP peer in the stateful PCEP
messages. Furthermore, this document updates the procedure for
handling unknown objects in the stateful PCEP messages based on the P
flag.
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2.1. Usage Example
The PCRpt message is used to report the current state of an LSP. As
part of the message both the <intended-attribute-list> and <actual-
attribute-list> is encoded (see [RFC8231]). For example, the
<intended-attribute-list> could include the METRIC object to indicate
a limiting constraint (B flag set) for the Path Delay Variation
metric [RFC8233]. In some scenarios, it would be useful to state
that this limiting constraint can be relaxed by the PCE in case it
cannot find a path. Similarly in the case of an association group
[RFC8697] such as Disjoint Association [RFC8800], the PCE may need to
completely relax the disjointness constraint in order to provide a
path to all the LSPs that are part of the association. In these case
it would be useful to mark the objects as 'optional' and it could be
ignored by the PCEP peer. Also, it would be useful for the PCEP
speaker to learn if the PCEP peer has relaxed the constraint and
ignored the processing of the PCEP object.
Thus, this document simply clarifies, how the already existing P and
I flag in the PCEP common object header could be used during the
stateful PCEP message exchange.
3. PCEP Extension
3.1. STATEFUL-PCE-CAPABILITY TLV
A PCEP speaker indicates its ability to support the handling of the P
and I flag in the stateful PCEP message exchange during the PCEP
initialization phase, as follows. When the PCEP session is
established, a PCC sends an Open message with an OPEN object that
contains the STATEFUL-PCE-CAPABILITY TLV, as defined in [RFC8231]. A
new flag, the R (RELAX) flag, is added in this TLV to indicate the
support for relaxing the processing of some objects via the use of
the P and I flag in the PCEP common object header.
R (RELAX bit - TBD1): If set to 1 by a PCEP Speaker, the R flag
indicates that the PCEP Speaker is willing to send and receive PCEP
objects with the P and I flags in the PCEP common object header for
the stateful PCE messages. In case the bit is unset, it indicates
that the PCEP Speaker would not handle the P and I flags in the PCEP
common object header for stateful PCE messages.
The R flag MUST be set by both a PCC and a PCE to indicate support
for the handling of the P and I flag in the PCEP common object header
to allow relaxing some constraints by marking objects as optional to
process. If the PCEP speaker did not set the R flag but receives
PCEP objects with P or I bit set, it MUST behave as per the
processing rule in [RFC8231] i.e., the bits are simply ignored.
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3.2. Handling of P flag
3.2.1. The PCRpt Message
The P flag in the PCRpt message [RFC8231] allows a PCC to specify to
a PCE whether the object must be taken into account by the PCE
(during path computation, re-optimization, or state maintenance) or
is optional o process. When the P flag is set in the PCRpt message
received on a PCEP session on which R bit was set by both peers, the
object MUST be taken into account by the PCE. Conversely, when the P
flag is cleared, the object is optional and the PCE is free to ignore
it. The P flag for the mandatory objects such as the LSP and the ERO
object (intended path) MUST be set in the PCRpt message. If a
mandatory object is received with the P flag set incorrectly
according to the rules stated above, the receiving peer MUST send a
PCErr message with Error-Type=10 (Reception of an invalid object) and
Error-value=1 (reception of an object with P flag not set). On a
PCEP session on which R bit was set by both peers, the PCC SHOULD set
the P flag by default, unless a local configuration or local policy
indicates that some constraints (corresponding PCEP objects) can be
marked as optional and could be ignored by the PCE.
3.2.2. The PCUpd Message and the PCInitiate Message
The P flag in the PCUpd message [RFC8231] and the PCInitiate message
[RFC8281] allows a PCE to specify to a PCC whether the object must be
taken into account by the PCC (during path setup) or is optional to
process. When the P flag is set in the PCUpd/PCInitiate message
received on a PCEP session on which R bit was set by both peers, the
object MUST be taken into account by the PCC. Conversely, when the P
flag is cleared, the object is optional and the PCC is free to ignore
it. The P flag for the mandatory objects such as the SRP, the LSP
and the ERO MUST be set in the PCUpd/PCInitiate message. If a
mandatory object is received with the P flag set incorrectly
according to the rules stated above, the receiving peer MUST send a
PCErr message with Error-Type=10 (Reception of an invalid object) and
Error-value=1 (reception of an object with P flag not set). By
default, the PCE SHOULD set the P flag, unless a local configuration
or local policy indicates that some constraints (corresponding PCEP
objects) can be marked as optional and could be ignored by the PCC.
3.3. Handling of I flag
3.3.1. The PCUpd Message
The I flag in the PCUpd message [RFC8231] allows a PCE to indicate to
a PCC whether or not an optional object was processed. The PCE MAY
include the ignored optional object in its update request and set the
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I flag to indicate that the optional object was ignored. When the I
flag is cleared, the PCE indicates that the optional object was
processed.
3.3.2. The PCRpt Message
The I flag in the PCRpt message [RFC8231] allows a PCC to indicate to
a PCE whether or not an optional object was processed in response to
an LSP Update Request (PCUpd) or LSP Initiate Request (PCInitiate).
The PCC MAY include the ignored optional object in its report and set
the I flag to indicate that the optional object was ignored at PCC.
When the I flag is cleared, the PCC indicates that the optional
object was processed. The I flag has no meaning if the PCRpt message
is not in response to a PCUpd or PCInitiate message (i.e. without the
SRP object in the PCRpt message).
3.3.3. The PCInitiate Message
The I flag has no meaning in the PCinitiate message [RFC8281] and is
ignored.
3.4. Delegation
Delegation is an operation to grant a PCE temporary rights to modify
a subset of parameters on one or more LSPs by a PCC as described in
[RFC8051]. Note that for the delegated LSPs, the PCE can update and
mark some objects as ignored even when the PCC had set the P flag
during delegation. Similarly, the PCE can update and mark some
object as a must to process even when the PCC had not set the P flag
during delegation.
The PCC MUST acknowledge this by sending the PCRpt message with the P
flag set as per the PCE expectation for the corresponding object. In
case PCC cannot accept this, it would react as per the processing
rules of unacceptable update in [RFC8231].
3.5. Unknown Object Handling
This document updates the handling of unknown objects in the stateful
PCEP messages as per the setting of the P flag in the common object
header in a similar way as [RFC5440], i.e. if a PCEP speaker does not
understand an object with the P flag set or understands the object
but decides to ignore the object, the entire stateful PCEP message
MUST be rejected and the PCE MUST send a PCErr message with Error-
Type="Unknown Object" or "Not supported Object" [RFC5440]. In case
the P flag is not set, the PCEP speaker is free to ignore the object
and continue with message processing as defined.
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[RFC8231] defined LSP Error Code TLV to be carried in PCRpt message
in the LSP object to convey error information. This document does
not change that procedure.
4. Security Considerations
This document clarifies how the already existing P and I flag in PCEP
common object header could be used during stateful PCEP exchanges.
It updates the unknown object error handling in stateful PCEP message
exchange. These changes on their own do not add any new security
concerns. The security considerations identified in [RFC5440],
[RFC8231], and [RFC8281] continue to apply.
As per [RFC8231], it is RECOMMENDED that these PCEP extensions only
be activated on authenticated and encrypted sessions across PCEs and
PCCs belonging to the same administrative authority, using Transport
Layer Security (TLS) [RFC8253] as per the recommendations and best
current practices in [RFC7525] (unless explicitly set aside in
[RFC8253]).
5. IANA Considerations
5.1. STATEFUL-PCE-CAPABILITY TLV
[RFC8231] defines the STATEFUL-PCE-CAPABILITY TLV; per that RFC, IANA
created a "STATEFUL-PCE-CAPABILITY TLV Flag Field" subregistry to
manage the value of the STATEFUL-PCE-CAPABILITY TLV's Flag field.
IANA is requested to allocate a new bit in the subregistry, as
follows:
Bit Description Reference
-------------------------------------------------
TBD1 RELAX bit [This-I.D.]
6. Manageability Considerations
6.1. Control of Function and Policy
An operator MUST be allowed to configure the capability to support
relaxation of constraints in the stateful PCEP message exchange.
They SHOULD also allow configuration of related LSP constraints (or
parameters) that are optional to process.
6.2. Information and Data Models
An implementation SHOULD allow the operator to view the capability
defined in this document. To serve this purpose, the PCEP YANG
module [I-D.ietf-pce-pcep-yang] could be extended in the future.
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6.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
6.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].
6.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
6.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [RFC5440].
7. Acknowledgments
Thanks to Jonathan Hardwick for discussion and suggestions around
this draft.
8. References
8.1. 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>.
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[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>.
8.2. 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)", draft-ietf-pce-pcep-
yang-16 (work in progress), February 2021.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8233] Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
"Extensions to the Path Computation Element Communication
Protocol (PCEP) to Compute Service-Aware Label Switched
Paths (LSPs)", RFC 8233, DOI 10.17487/RFC8233, September
2017, <https://www.rfc-editor.org/info/rfc8233>.
[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>.
[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>.
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[RFC8697] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Dhody, D., and Y. Tanaka, "Path Computation Element
Communication Protocol (PCEP) Extensions for Establishing
Relationships between Sets of Label Switched Paths
(LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
<https://www.rfc-editor.org/info/rfc8697>.
[RFC8800] Litkowski, S., Sivabalan, S., Barth, C., and M. Negi,
"Path Computation Element Communication Protocol (PCEP)
Extension for Label Switched Path (LSP) Diversity
Constraint Signaling", RFC 8800, DOI 10.17487/RFC8800,
July 2020, <https://www.rfc-editor.org/info/rfc8800>.
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Appendix A. Contributors
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Authors' Addresses
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
EMail: c.l@huawei.com
Haomian Zheng
Huawei Technologies
H1, Huawei Xiliu Beipo Village, Songshan Lake
Dongguan, Guangdong 523808
China
EMail: zhenghaomian@huawei.com
Stephane Litkowski
Cisco
EMail: slitkows.ietf@gmail.com
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