Network Working Group A. Stone
Internet-Draft M. Aissaoui
Updates: 5440 (if approved) Nokia
Intended status: Standards Track S. Sidor
Expires: August 7, 2021 Cisco Systems, Inc.
S. Sivabalan
Ciena Coroporation
February 3, 2021
Local Protection Enforcement in PCEP
draft-ietf-pce-local-protection-enforcement-02
Abstract
This document updates [RFC5440] to clarify usage of the local
protection desired bit signalled in 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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 7, 2021.
Copyright Notice
Copyright (c) 2021 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
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified 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 . . . . . . . . . . . . . . . . . 6
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 7
6.1. Nokia Implementation . . . . . . . . . . . . . . . . . . 8
6.2. Cisco Implementation . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. LSPA Object . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] 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 [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 local protection is desired,
which indicates to transit 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
it's 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.
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PCEP Extensions for Segment Routing (draft-ietf-pce-segment-routing)
extends support in PCEP for Segment Routed LSPs (SR-LSPs) as defined
in the Segment Routing Architecture [RFC8402]. As per the Segment
Routing Architecture, Adjacency Segment Identifiers(Adj-SID) may be
eligible for protection (using IPFRR or MPLS-FRR). The protection
eligibility is advertised into IGP (draft-ietf-ospf-segment-routing-
extensions and draft-ietf-isis-segment-routing-extensions) as the
B-Flag part of the Adjacency SID sub-tlv and can be discovered by a
PCE via BGP-LS [RFC7752] using the BGP-LS Segment Routing Extensions
(draft-ietf-idr-bgp-ls-segment-routing-ext). An Adjacency SID may or
may not have protection eligibility and for a given adjacency between
two routers there may be multiple Adjacency SIDs, some of which are
protected and some which are not.
A Segment Routed path calculated by PCE may contain various types of
segments, as defined in [RFC8402] such as Adjacency, Node or Binding.
The protection eligibility for Adjacency SIDs can be discovered by
PCE, so therefore the PCE can take the protection eligibility into
consideration as a path constraint. If a path is calculated to
include other segment identifiers which are not applicable to having
their protection state advertised, as they may only be locally
significant for each router processing the SID such as Node SIDs, it
may not be possible for PCE to include the protection constraint as
part of the path calculation.
It is desirable for an operator to define the enforcement, or
strictness of the protection requirement when it can be applied.
This document updates [RFC5440] by further describing the behaviour
with Local Protection Desired Flag (L-Flag) and extends on it with
the introduction of Enforcement Flag (E-Flag).
2. Requirements Language
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14,
[RFC2119].
3. Terminology
This document uses the following terminology:
PROTECTION MANDATORY: path MUST have protection eligibility on all
links.
UNPROTECTED MANDATORY: path MUST NOT have protection eligibility on
all links.
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PROTECTION PREFERRED: path SHOULD have protection eligibility on all
links but MAY contain links which do not have protection eligibility.
UNPROTECTED PREFERRED: path SHOULD NOT have protection eligibility on
all links but MAY 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.
4. Motivation
4.1. Implementation differences
As defined in [RFC5440] the mechanism to signal protection
enforcement in PCEP is with 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 is
rooted in the RSVP use case. For RSVP, this 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 flag is unable to distinguish between the different
options of PROTECTION MANDATORY, UNPROTECTED MANDATORY, PROTECTION
PREFERRED and UNPROTECTED PREFERRED. The selection of the options
are typically dependent on the service level agreement the operator
wishes to impose on the LSP. When enforcement is used, the resulting
shortest path calculation is impacted.
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 anywhere along the
path that traffic will be fast re-routed at the point of failure.
For another example, UNPROTECTED MANDATORY is when an operator may
intentionally prefer an LSP to not be locally protected, and thus
would rather local failures to cause the LSP to go down and/or rely
on other protection mechanisms such as a secondary diverse path.
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There are also use cases where there is simply no requirement to
enforce protection or no protection along a path. This can be
considered as "do not care to enforce". This is a relaxation of the
protection constraint. The path calculation is permitted the use of
any SID which is available along the calculated path. The SID backup
availability does not impact the shortest path computation. Since
links may have both protected and unprotected SIDs available, the
option PROTECTION PREFERRED or UNPROTECTED PREFERRED is used to
instruction PCE a preference on which SID to select, as the behaviour
of the LSP would differ during a local failure depending on which SID
is selected.
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 new flag is
proposed in this document in the LSP Attributes Object which extends
the L-Flag to identify the protection enforcement.
Bit 6 has been early allocated by IANA as the Protection Enforcement
flag.
Codespace of the Flag field (LSPA Object)
Bit Description Reference
7 Local Protection Desired RFC5440
6 Local Protection Enforcement This I-D
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 //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Flags (8 bits)
o L flag: As defined in [RFC5440] and further updated by this
document. When set, protection is desired. When not set,
protection is not desired. The enforcement of the protection is
identified via the E-Flag.
o E flag (Protection Enforcement): When set, the value of the L-Flag
MUST be treated as a MUST constraint where applicable, when
protection state of a SID is known. When E flag is not set, the
value of the L-Flag MUST be treated as a MAY constraint.
When L-flag is set and E-flag is set then PCE MUST consider the
protection eligibility as PROTECTION MANDATORY constraint.
When L-flag is set and E-flag is not set then PCE MUST consider the
protection eligibility as PROTECTION PREFERRED constraint.
When L-flag is not set and E-flag is not set then PCE SHOULD consider
the protection eligibility as UNPROTECTED PREFERRED but MAY consider
protection eligibility as UNPROTECTED MANDATORY constraint.
When L-flag is not set and E-flag is set then PCE MUST consider the
protection eligibility as UNPROTECTED MANDATORY constraint.
UNPROTECTED PREFERRED and PROTECTED PREFERRED may seem similar but
they indicate the preference of selection of a SID if PCE has an
option of either protected or unprotected available on a link. When
presented with either option, PCE SHOULD select the SID which has a
protection state matching the state of the L-Flag.
The protection enforcement constraint can only be applied to resource
selection in which the protection state is known to PCE. A PCE
calculating a path that includes resources which does not support the
protection state being known to PCE (such as Node SID), then the
protection state MAY ignore the protection enforcement constraint.
5.1. Backwards Compatibility
Considerations in the message passing between PCC and PCE for the
E-Flag bit which are not supported by the entity are outlined in this
section, with requirements for PCE and PCC implementing this document
described at the end.
For a PCC or PCE which does not yet support this document, the E-flag
bit 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's
important to note that [RFC8231] and [RFC8281] permit LSP Attribute
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Object to be included in PCUpd messages for PCC-initiated and PCE-
initiated LSPs. For PCC-initiated LSPs, PCUpd E-Flag (and L-Flag)
are an echo from the previous PCRpt however the bit value is ignored
on 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 unset for PCC-initated LSPs even if
set in the prior PCReq or PCRpt. A PCC which does not support this
document sends PCRpt messages with the E-Flag unset for PCE-initiated
LSPs even if set in the prior PCInitiate or PCUpd.
For a PCC which does support this document, it MAY set E-Flag bit
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 bit thus it will
not compute a path respecting the enforcement constraint.
For PCC-initiated LSPs, PCC SHOULD ignore the E-Flag value received
from PCE in a PCUpd message.
For PCE-initiated LSPs, PCC MAY process the E-Flag value received
from PCE in a PCUpd message. PCE SHOULD ignore the E-Flag value
received from PCC in a PCRpt message.
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".
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6.1. Nokia Implementation
o Organization: Nokia
o Implementation: NSP PCE and SROS PCC.
o Description: Implementation for calculation and conveying
intention described in this document
o Maturity Level: Demo
o Coverage: Full
o Contact: andrew.stone@nokia.com
6.2. Cisco Implementation
o Organization: Cisco Systems, Inc.
o Implementation: IOS-XR PCE and PCC.
o Description: Implementation for calculation and conveying
intention described in this document
o Maturity Level: Demo
o Coverage: Full
o 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
[RFC7525] is RECOMMENDED.
8. IANA Considerations
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8.1. LSPA Object
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 is requested to confirm the early-allocated
codepoint.
Bit Name Reference
6 Protection Enforcement This I-D
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>.
[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>.
[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>.
[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>.
[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>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[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>.
[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>.
[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>.
9.2. Informative References
[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>.
Acknowledgements
Thanks to Dhruv Dhody for comments and discussions on this document
and Mike Koldychev for reviews.
Authors' Addresses
Andrew Stone
Nokia
Email: andrew.stone@nokia.com
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Mustapha Aissaoui
Nokia
Email: mustapha.aissaoui@nokia.com
Samuel Sidor
Cisco Systems, Inc.
Email: ssidor@cisco.com
Siva Sivabalan
Ciena Coroporation
Email: ssivabal@ciena.com
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