Internet DRAFT - draft-ietf-pce-local-protection-enforcement
draft-ietf-pce-local-protection-enforcement
Network Working Group A. Stone
Internet-Draft M. Aissaoui
Updates: 5440 (if approved) Nokia
Intended status: Standards Track S. Sidor
Expires: 25 December 2023 Cisco Systems, Inc.
S. Sivabalan
Ciena Coroporation
23 June 2023
Local Protection Enforcement in PCEP
draft-ietf-pce-local-protection-enforcement-11
Abstract
This document updates RFC5440 to clarify usage of the local
protection desired bit signalled in the Path Computation Element
Protocol (PCEP). This document also introduces a new flag for
signalling protection strictness in PCEP.
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
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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."
This Internet-Draft will expire on 25 December 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Implementation differences . . . . . . . . . . . . . . . 4
4.2. SLA Enforcement . . . . . . . . . . . . . . . . . . . . . 4
5. Protection Enforcement Flag (E flag) . . . . . . . . . . . . 5
5.1. Backwards Compatibility . . . . . . . . . . . . . . . . . 7
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
6.1. Nokia Implementation . . . . . . . . . . . . . . . . . . 8
6.2. Cisco Implementation . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] enables the communication between a Path Computation Client
(PCC) and a PCE, or between two PCEs based on the PCE architecture
[RFC4655].
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PCEP [RFC5440] utilizes flags, values and concepts previously defined
in RSVP-TE Extensions [RFC3209] and Fast Reroute Extensions to RSVP-
TE [RFC4090]. One such concept in PCEP is the 'Local Protection
Desired' (L flag in the LSPA Object in [RFC5440]), which was
originally defined in the SESSION-ATTRIBUTE Object in RFC3209. In
RSVP, this flag signals to downstream routers that they may use a
local repair mechanism. The headend router calculating the path does
not know whether a downstream router will or will not protect a hop
during its calculation. Therefore, a local protection desired does
not require the transit router to satisfy protection in order to
establish the RSVP signalled path. This flag is signalled in PCEP as
an attribute of the LSP via the LSP Attributes object.
PCEP Extensions for Segment Routing ([RFC8664]) extends support in
PCEP for Segment Routed paths. The path list is encoded with Segment
Identifiers, each of which might offer local protection. The PCE may
discover the protection eligibility for a Segment Identifier (SID)
via BGP-LS [RFC9085] and take the protection into consideration as a
path constraint.
It is desirable for an operator to be able to define the enforcement,
or strictness of the protection requirement.
This document updates [RFC5440] by further describing the behaviour
with the Local Protection Desired Flag (L flag) and extends on it
with the introduction of the Enforcement Flag (E flag).
The document contains reference notes for Segment Routing, however
the content described is path setup type and data plane technology
agnostic.
2. 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.
3. Terminology
This document uses the following terminology:
PROTECTION MANDATORY: The Path MUST have protection eligibility on
all links.
UNPROTECTED MANDATORY: The Path MUST NOT have protection eligibility
on all links.
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PROTECTION PREFERRED: The Path should have protection eligibility on
all links but might contain links which do not have protection
eligibility.
UNPROTECTED PREFERRED: The Path should not have protection
eligibility on all links but might contain links which have
protection eligibility.
PCC: Path Computation Client. Any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application, or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints.
PCEP: Path Computation Element Protocol.
LSPA: LSP Attributes Object in PCEP, defined in RFC5440
4. Motivation
4.1. Implementation differences
As defined in [RFC5440] the mechanism to signal protection
enforcement in PCEP is the previously mentioned L flag defined in the
LSPA Object. The name of the flag uses the term "Desired", which by
definition means "strongly wished for or intended" and the use case
originated from the RSVP. For RSVP signalled paths, local protection
is not within control of the PCE. However, [RFC5440] does state
"When set, this means that the computed path must include links
protected with Fast Reroute as defined in [RFC4090]."
Implementations of [RFC5440] have either interpreted the L flag as
PROTECTION MANDATORY or PROTECTION PREFERRED, leading to operational
differences.
4.2. SLA Enforcement
The boolean bit L flag is unable to distinguish between the different
options of PROTECTION MANDATORY, UNPROTECTED MANDATORY, PROTECTION
PREFERRED and UNPROTECTED PREFERRED. Selecting one of the options is
typically dependent on the service level agreement the operator
wishes to impose on the LSP. A network may be providing transit to
multiple service agreement definitions against the same base topology
network, whose behavior could vary, such as wanting local protection
to be invoked on some LSPs and not wanting local protection on
others. When enforcement is used, the resulting shortest path
calculation is impacted.
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For example, PROTECTION MANDATORY is for use cases where an operator
may need the LSP to follow a path which has local protection provided
along the full path, ensuring that if there is a failure anywhere
along the path that traffic will be fast re-routed at the point.
For example, UNPROTECTED MANDATORY is when an operator may
intentionally prefer an LSP to not be locally protected, and thus
would rather local failures cause the LSP to go down. An example
scenario is one where an LSP is protected with path protection via a
secondary diverse LSP. Each LSP is traffic engineered to follow
specific traffic engineered criteria computed by the PCE to satisfy
SLA. Upon a failure, if local protection is invoked on the active
LSP traffic, the traffic may temporarily traverse links which violate
the TE requirements and could negatively impact the resources being
traversed (e.g., insufficient bandwidth). In addition, depending on
the network topological scenario, it may be not feasible for the PCE
to reroute the LSP while respecting the TE requirements which include
path diversity, resulting in the LSP being torn down and switched to
the protected path anyways. In such scenarios its desirable for the
LSP to be simply torn down immediately and not re-routed through
local protection, so that traffic may be forwarded through an already
established traffic-engineered secondary path.
Both UNPROTECTED PREFERRED and PROTECTED PREFERRED options provide a
relaxation of the protection constraint. These options can be used
when an operator does not require protection enforcement. Regardless
of the option selected, the protection status of a resource does not
influence whether the link must be pruned during a path calculation.
Furthermore, the selection of either option indicates a priority
selection to PCE when there is an option to choose a protected or
unprotected instruction associated with a resource, ensuring
consistent PCE behavior across different implementations.
When used with Segment Routing, an adjacency may have both a
protected SID and an unprotected SID. If the UNPROTECTED PREFERRED
option is selected, PCE chooses the unprotected SID. Alternatively,
if the PROTECTED PREFERRED option is selected, PCE chooses the
protected SID
5. Protection Enforcement Flag (E flag)
Section 7.11 in Path Computation Element Protocol [RFC5440] describes
the encoding of the Local Protection Desired (L flag). A Protection
Enforcement flag "E" is specified below, extending the L flag.
[RFC Editor Note: The text below assumes the E bit remains the early
allocation value 6. Please adjust if this changes and remove this
note before publication.]
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Codespace of the Flag field (LSPA Object)
Bit Description Reference
7 Local Protection Desired RFC5440
6 Local Protection Enforcement This document
The format of the LSPA Object as defined in [RFC5440] is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exclude-any |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-any |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-all |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Setup Prio | Holding Prio | Flags |E|L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags (8 bits)
* L Flag: As defined in [RFC5440] and further updated by this
document. When set to 1, protection is desired. When set to 0,
protection is not desired. The enforcement of the protection is
identified via the E flag.
* E Flag (Protection Enforcement): This flag controls the strictness
in which the PCE must apply the L flag. When set to 1, the value
of the L flag needs to be respected during resource selection by
the PCE. When E flag is set to 0, an attempt to respect the value
of the L flag is made; however, the PCE could relax or ignore the
L flag when computing a path. The statements below indicate
preference when the E flag is set to 0 in combination with the L
flag value.
When both the L flag and E flag are set to 1, then the PCE MUST
consider the protection eligibility as a PROTECTION MANDATORY
constraint.
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When the L flag is set to 1 and the E flag is set to 0, then the PCE
MUST consider the protection eligibility as a PROTECTION PREFERRED
constraint.
When both L flag and E flag are set to 0, then the PCE SHOULD
consider the protection eligibility as an UNPROTECTED PREFERRED
constraint but MAY consider protection eligibility as an UNPROTECTED
MANDATORY constraint. An example of when the latter behavior might
be chosen is if the PCE has some means (outside the scope of this
document) to detect that it is interacting with a legacy PCC that
expects the legacy behavior.
When L flag is set to 0 and E flag is set to 1, then the PCE MUST
consider the protection eligibility as an UNPROTECTED MANDATORY
constraint.
If a PCE is unable to infer the protection status of a resource, the
PCE MAY use local policy to define protected status assumptions.
When computing a Segment Routed path, It is RECOMMENDED that a PCE
assume a Node SID is protected. It is also RECOMMENDED that a PCE
assume an Adjacency SID is protected if the backup flag advertised
with the Adjacency SID is set.
5.1. Backwards Compatibility
Considerations in the message passing between the PCC and the PCE for
the E flag bit which are not supported by the entity are outlined in
this section, with requirements for the PCE and the PCC implementing
this document described at the end.
For a PCC or PCE which does not yet support this document, the E flag
is ignored and set to zero in PCRpt and/or PCUpd as per [RFC5440] for
PCC-initiated or as per [RFC8281] for PCE-initiated LSPs. It is
important to note that [RFC8231] and [RFC8281] permit the LSP
Attribute Object to be included in PCUpd messages for PCC-initiated
and PCE-initiated LSPs.
For PCC-initiated LSPs, PCUpd E flag (and L flag) is an echo from the
previous PCRpt however the bit value is ignored on the PCE from the
previous PCRpt, therefore the E flag value set in the PCUpd is zero.
A PCE which does not support this document sends PCUpd messages with
the E flag set to 0 for PCC-initated LSPs even if set to 1 in the
prior PCReq or PCRpt.
A PCC which does not support this document sends PCRpt messages with
the E flag set to 0 for PCE-initiated LSPs even if set to 1 in the
prior PCInitiate or PCUpd.
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For a PCC which does support this document, it MAY set the E flag to
1 depending on local configuration. If communicating with a PCE
which does not yet support this document, the PCE follows the
behaviour specified in [RFC5440] and will ignore the E flag. Thus, a
computed path might not respect the enforcement constraint.
For PCC-initiated LSPs, the PCC SHOULD ignore the E flag value
received from the PCE in a PCUpd message as it may be communicating
with a PCE which does not support this document.
For PCE-initiated LSPs, the PCC MAY process the E flag value received
from the PCE in a PCUpd message. The PCE SHOULD ignore the E flag
value received from the PCC in a PCRpt message as it may be
communicating with a PCC which does not support 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 catalogue 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. Nokia Implementation
* Organization: Nokia
* Implementation: NSP PCE and SROS PCC.
* Description: Implementation for calculation and conveying
intention described in this document
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* Maturity Level: Demo
* Coverage: Full
* Contact: andrew.stone@nokia.com
6.2. Cisco Implementation
* Organization: Cisco Systems, Inc.
* Implementation: IOS-XR PCE and PCC.
* Description: Implementation for calculation and conveying
intention described in this document
* Maturity Level: Demo
* Coverage: Full
* Contact: ssidor@cisco.com
7. Security Considerations
This document clarifies the behaviour of an existing flag and
introduces a new flag to provide further control of that existing
behaviour. The introduction of this new flag and behaviour
clarification does not create any new sensitive information. No
additional security measure is required.
Securing the PCEP session using Transport Layer Security (TLS)
[RFC8253], as per the recommendations and best current practices in
[RFC9325] is RECOMMENDED.
8. IANA Considerations
[RFC Editor Note: The text below assumes the E bit remains the early
allocation value 6. Please adjust if this changes and remove this
note before publication.]
This document defines a new bit value in the sub-registry "LSPA
Object Flag Field" in the "Path Computation Element Protocol (PCEP)
Numbers" registry. IANA has made the following codepoint allocation.
Bit Name Reference
6 Protection Enforcement This document
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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>.
[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>.
[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>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.
[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>.
[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>.
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[RFC9325] Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/info/rfc9325>.
9.2. Informative References
[RFC4655] Farrel, A., Vasseur, J.-P., 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>.
[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>.
[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>.
[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
Acknowledgements
Thanks to Dhruv Dhody, Mike Koldychev, and John Scudder for reviewing
and providing very valuable feedback and discussions on this
document.
Thanks to Julien Meuric for shepherding this document.
Authors' Addresses
Andrew Stone
Nokia
600 March Road
Kanata Ontario K2K 2T6
Canada
Email: andrew.stone@nokia.com
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Mustapha Aissaoui
Nokia
600 March Road
Kanata Ontario K2K 2T6
Canada
Email: mustapha.aissaoui@nokia.com
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Siva Sivabalan
Ciena Coroporation
385 Terry Fox Drive
Kanata Ontario K2K 0L1
Canada
Email: ssivabal@ciena.com
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