< draft-ietf-pce-association-diversity-07.txt   draft-ietf-pce-association-diversity-08.txt >
PCE Working Group S. Litkowski PCE Working Group S. Litkowski
Internet-Draft Orange Internet-Draft Orange
Intended status: Standards Track S. Sivabalan Intended status: Standards Track S. Sivabalan
Expires: December 6, 2019 Cisco Systems, Inc. Expires: January 5, 2020 Cisco Systems, Inc.
C. Barth C. Barth
Juniper Networks Juniper Networks
M. Negi M. Negi
Huawei Technologies Huawei Technologies
June 4, 2019 July 4, 2019
Path Computation Element communication Protocol (PCEP) extension for Path Computation Element Communication Protocol (PCEP) Extension for LSP
signaling LSP diversity constraint Diversity Constraint Signaling
draft-ietf-pce-association-diversity-07 draft-ietf-pce-association-diversity-08
Abstract Abstract
This document introduces a simple mechanism to associate a group of This document introduces a simple mechanism to associate a group of
Label Switched Paths (LSPs) via an extension to the Path Computation Label Switched Paths (LSPs) via an extension to the Path Computation
Element (PCE) Communication Protocol (PCEP) with the purpose of Element (PCE) communication Protocol (PCEP) with the purpose of
computing diverse paths for those LSPs. The proposed extension computing diverse paths for those LSPs. The proposed extension
allows a Path Computation Client (PCC) to advertise to a PCE that a allows a Path Computation Client (PCC) to advertise to a PCE that a
particular LSP belongs to a disjoint-group, thus the PCE knows that particular LSP belongs to a disjoint-group, thus the PCE knows that
LSPs in the same group needs to be disjoint from each other. the LSPs in the same group need to be disjoint from each other.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 6, 2019. This Internet-Draft will expire on January 5, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol extension . . . . . . . . . . . . . . . . . . . . . 7 4. Protocol Extension . . . . . . . . . . . . . . . . . . . . . 7
4.1. Association group . . . . . . . . . . . . . . . . . . . . 7 4.1. Association Group . . . . . . . . . . . . . . . . . . . . 7
4.2. Disjoint TLVs . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Disjoint TLVs . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Relationship to SVEC . . . . . . . . . . . . . . . . . . 10 4.3. Relationship to SVEC . . . . . . . . . . . . . . . . . . 10
4.4. Disjointness objective functions . . . . . . . . . . . . 10 4.4. Disjointness Objective functions . . . . . . . . . . . . 10
4.5. P-flag considerations . . . . . . . . . . . . . . . . . . 12 4.5. P Flag Considerations . . . . . . . . . . . . . . . . . . 12
4.6. Disjointness computation issues . . . . . . . . . . . . . 14 4.6. Disjointness Computation Issues . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6.1. Association Type . . . . . . . . . . . . . . . . . . . . 16 6.1. Association Type . . . . . . . . . . . . . . . . . . . . 16
6.2. PCEP TLVs . . . . . . . . . . . . . . . . . . . . . . . . 16 6.2. PCEP TLVs . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3. Objective Functions . . . . . . . . . . . . . . . . . . . 17 6.3. Objective Functions . . . . . . . . . . . . . . . . . . . 17
6.4. NO-PATH-VECTOR Bit Flags . . . . . . . . . . . . . . . . 17 6.4. NO-PATH-VECTOR Bit Flags . . . . . . . . . . . . . . . . 18
6.5. PCEP-ERROR codes . . . . . . . . . . . . . . . . . . . . 18 6.5. PCEP-ERROR Codes . . . . . . . . . . . . . . . . . . . . 18
7. Manageability Considerations . . . . . . . . . . . . . . . . 18 7. Manageability Considerations . . . . . . . . . . . . . . . . 18
7.1. Control of Function and Policy . . . . . . . . . . . . . 18 7.1. Control of Function and Policy . . . . . . . . . . . . . 18
7.2. Information and Data Models . . . . . . . . . . . . . . . 18 7.2. Information and Data Models . . . . . . . . . . . . . . . 19
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 18 7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 19
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 19 7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 19
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 19 7.5. Requirements On Other Protocols . . . . . . . . . . . . . 19
7.6. Impact On Network Operations . . . . . . . . . . . . . . 19 7.6. Impact On Network Operations . . . . . . . . . . . . . . 19
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . 19 9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 20 9.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 22 Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
[RFC5440] describes the Path Computation Element communication [RFC5440] describes the Path Computation Element communication
Protocol (PCEP) which enables the communication between a Path Protocol (PCEP) which enables the communication between a Path
Computation Client (PCC) and a Path Control Element (PCE), or between Computation Client (PCC) and a Path Control Element (PCE), or between
two PCEs based on the PCE architecture [RFC4655]. two PCEs based on the PCE architecture [RFC4655].
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OF: Objective Function. OF: Objective Function.
PCC: Path Computation Client. Any client application requesting a PCC: Path Computation Client. Any client application requesting a
path computation to be performed by a Path Computation Element. path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application, PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or or network node) that is capable of computing a network path or
route based on a network graph and applying computational route based on a network graph and applying computational
constraints. constraints.
PCEP: Path Computation Element Communication Protocol. PCEP: Path Computation Element communication Protocol.
SRLG: Shared Risk Link Group. SRLG: Shared Risk Link Group.
3. Motivation 3. Motivation
Path diversity is a very common use case in today's IP/MPLS networks Path diversity is a very common use case in today's IP/MPLS networks
especially for layer 2 transport over MPLS. A customer may request especially for layer 2 transport over MPLS. A customer may request
that the operator provide two end-to-end disjoint paths across the that the operator provide two end-to-end disjoint paths across the
IP/MPLS core. The customer may use those paths as primary/backup or IP/MPLS core. The customer may use those paths as primary/backup or
active/active. active/active.
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| | | | | | | |
| +------+ | | +------+ | | +------+ | | +------+ |
CE3 ****| PE 3 | ----- R3 ---- R4 ------- | PE 4 |**** CE4 CE3 ****| PE 3 | ----- R3 ---- R4 ------- | PE 4 |**** CE4
| +------+ ***********************> +------+ | | +------+ ***********************> +------+ |
| | | |
\ / \ /
\_________________________________________/ \_________________________________________/
Figure 1 - Disjoint paths with different head-ends and tail-ends Figure 1 - Disjoint paths with different head-ends and tail-ends
In the figure above, consider that the customer wants to have two In the figure above, let us consider that the customer wants to have
disjoint paths between CE1/CE2 and CE3/CE4. From an IP/MPLS network two disjoint paths between CE1/CE2 and CE3/CE4. From an IP/MPLS
point view, in this example, the CEs are connected to different PEs network point view, in this example, the CEs are connected to
to maximize their disjointness. When LSPs originate from different different PEs to maximize their disjointness. When LSPs originate
head-ends, distributed computation of diverse paths can be difficult. from different head-ends, distributed computation of diverse paths
Whereas, computation via a centralized PCE ensures path disjointness can be difficult, whereas, computation via a centralized PCE ensures
correctness and simplicity. path disjointness, correctness and simplicity.
Section 4.3 describes the relationship between the disjoint Section 4.3 describes the relationship between the disjoint
association group and Synchronization VECtor (SVEC) object. association group and Synchronization VECtor (SVEC) object.
The PCEP extension for stateful PCE [RFC8231] defined new PCEP The PCEP extension for stateful PCE [RFC8231] defined new PCEP
messages - Path Computation Report (PCRpt), Path Computation Update messages - Path Computation Report (PCRpt), Path Computation Update
(PCUpd) and Path Computation Initiate (PCInitiate) [RFC8281]. These (PCUpd) and Path Computation Initiate (PCInitiate) [RFC8281]. These
messages uses PLSP-ID in the LSP object for identification. Moreover messages use PLSP-ID in the LSP object for identification. Moreover
to allow diversity between LSPs originating from different PCCs, the to allow diversity between LSPs originating from different PCCs, the
generic mechanism to create a grouping of LSPs is described in generic mechanism to create a grouping of LSPs is described in
[I-D.ietf-pce-association-group] (that is equally applicable to the [I-D.ietf-pce-association-group] (that is equally applicable to the
active and passive modes of a stateful PCE). active and passive modes of a stateful PCE).
Using PCEP, the PCC could indicate that the disjoint path computation Using PCEP, the PCC could indicate that a disjoint path computation
is required, such indication should include disjointness parameters is required, such indication should include disjointness parameters
such as the type of disjointness, the disjoint group identifiers, and such as the type of disjointness, the disjoint group identifiers, and
any customization parameters according to the configured local any customization parameters according to the configured local
policy. As mentioned previously, the extension described in policy. As mentioned previously, the extension described in
[I-D.ietf-pce-association-group] is well suited to associate a set of [I-D.ietf-pce-association-group] is well suited to associate a set of
LSPs with a particular disjoint-group. LSPs with a particular disjoint-group.
The management of the disjoint group-ids will be a key point for the The management of the disjoint group IDs will be a key point for the
operator as the Association ID field is limited to 65535. The local operator as the Association ID field is limited to 65535. The local
configuration of IPv4/IPv6 association source, or Global Association configuration of IPv4/IPv6 association source, or Global Association
Source/Extended Association ID should allow to overcome this Source/Extended Association ID allows to overcome this limitation as
limitation as described in [I-D.ietf-pce-association-group]. When a described in [I-D.ietf-pce-association-group]. When a PCC or PCE
PCC or PCE initiates all the LSPs in a particular disjoint-group, it initiates all the LSPs in a particular disjoint-group, it can set the
can set the IPv4/IPv6 association source as one of its own IP IPv4/IPv6 association source as one of its own IP address. When
address. When disjoint LSPs are initiated from different head-ends, disjoint LSPs are initiated from different head-ends, the association
association source could be the PCE address or any other unique value source could be the PCE address or any other unique value to identify
to identify the disjoint association group. the disjoint association group.
Initiate Disjoint LSPs Initiate Disjoint LSPs
| |
| PCReq/PCRpt | PCReq/PCRpt
V {Disjoint-group Y} V {Disjoint-group Y}
+-----+ ----------------> +-----+ +-----+ ----------------> +-----+
_ _ _ _ _ _| PCE | | | PCE | _ _ _ _ _ _| PCE | | | PCE |
| +-----+ | ----------> +-----+ | +-----+ | ----------> +-----+
| PCInitiate | | PCReq/PCRpt | PCInitiate | | PCReq/PCRpt
|{Disjoint-group X} | | {Disjoint-group Y} |{Disjoint-group X} | | {Disjoint-group Y}
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session session
Using the disjoint-group within a PCEP messages may have two purpose: Using the disjoint-group within a PCEP messages may have two purpose:
o Configuration: Used to communicate the configured disjoint o Configuration: Used to communicate the configured disjoint
requirement to a PCEP peer. requirement to a PCEP peer.
o Status: Used to communicate the status of the computed o Status: Used to communicate the status of the computed
disjointness. disjointness.
4. Protocol extension 4. Protocol Extension
4.1. Association group 4.1. Association Group
As per [I-D.ietf-pce-association-group], LSPs are associated with As per [I-D.ietf-pce-association-group], LSPs are associated with
other LSPs with which they interact by adding them to a common other LSPs with which they interact by adding them to a common
association group. The Association parameters, as described in association group. The Association parameters, as described in
[I-D.ietf-pce-association-group] as the combination of the mandatory [I-D.ietf-pce-association-group] as the combination of the mandatory
fields Association type, Association ID and Association Source in the fields Association type, Association ID and Association Source in the
ASSOCIATION object, that uniquely identify the association group ASSOCIATION object, that uniquely identify the association group
belonging to this association. If the optional TLVs - Global belonging to this association. If the optional TLVs - Global
Association Source or Extended Association ID are included, then they Association Source or Extended Association ID - are included, then
are included in combination with mandatory fields to uniquely they are included in combination with mandatory fields to uniquely
identifying the association group. This document defines a new identify the association group. This document defines a new
Association type, based on the generic Association object - Association type, based on the generic Association object:
o Association type = TBD1 ("Disjointness Association Type") for o Association type = TBD1 ("Disjointness Association Type") for
Disjoint Association Group (DAG). Disjoint Association Group (DAG).
[I-D.ietf-pce-association-group] specify the mechanism for the [I-D.ietf-pce-association-group] specifies the mechanism for the
capability advertisement of the association types supported by a PCEP capability advertisement of the association types supported by a PCEP
speaker by defining a ASSOC-Type-List TLV to be carried within an speaker by defining a ASSOC-Type-List TLV to be carried within an
OPEN object. This capability exchange for the association type OPEN object. This capability exchange for the association type
described in this document (i.e. Disjointness Association Type) MUST described in this document (i.e. Disjointness Association Type) MUST
be done before using the disjointness association. Thus the PCEP be done before using the disjointness association. Thus the PCEP
speaker MUST include the Disjointness Association Type (TBD1) in the speaker MUST include the Disjointness Association Type (TBD1) in the
ASSOC-Type-List TLV before using the disjoint association group (DAG) ASSOC-Type-List TLV before using the disjoint association group (DAG)
in the PCEP messages. in PCEP messages.
This association type is considered to be both dynamic and operator- This association type is considered to be both dynamic and operator-
configured in nature. The association group could be created by the configured in nature. The association group could be created by the
operator manually on the PCEP peers and the LSPs belonging to this operator manually on the PCEP peers and the LSPs belonging to this
associations is conveyed via PCEP messages to the PCEP peer; or the associations is conveyed via PCEP messages to the PCEP peer; or the
association group could be created dynamically by the PCEP speaker association group could be created dynamically by the PCEP speaker
and both the association group information and the LSPs belonging to and both the association group information and the LSPs belonging to
the association group is conveyed to the PCEP peer. The Operator- the association group is conveyed to the PCEP peer. The Operator-
configured Association Range MUST be set for this association-type to configured Association Range MUST be set for this association-type to
mark a range of association identifiers that are used for operator- mark a range of association identifiers that are used for operator-
configured associations to avoid any association identifier clash configured associations to avoid any association identifier clash
within the scope of the association source. (Refer within the scope of the association source. (Refer to
[I-D.ietf-pce-association-group].) [I-D.ietf-pce-association-group].)
A disjoint group can have two or more LSPs. But a PCE may be limited A disjoint group can have two or more LSPs, but a PCE may be limited
in how many LSPs it can take into account when computing in the number of LSPs it can take into account when computing
disjointness. If a PCE receives more LSPs in the group than it can disjointness. If a PCE receives more LSPs in the group than it can
handle in its computation algorithm, it SHOULD apply disjointness handle in its computation algorithm, it SHOULD apply disjointness
computation to only a subset of LSPs in the group. The subset of computation to only a subset of LSPs in the group. The subset of
disjoint LSPs will be decided by PCE as a local policy. Local disjoint LSPs will be decided by PCE as a local policy. Local
polices MAY define the computational behavior for the other LSPs in polices MAY define the computational behavior for the other LSPs in
the group. For example, the PCE may provide no path, a shortest the group. For example, the PCE may provide no path, a shortest
path, or a constrained path based on relaxing disjointness, etc. The path, or a constrained path based on relaxing disjointness, etc. The
disjoint status is informed to the PCC. disjoint status is informed to the PCC.
Associating a particular LSP to multiple disjoint groups is Associating a particular LSP to multiple disjoint groups is
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o DISJOINTNESS-CONFIGURATION-TLV: Used to communicate some o DISJOINTNESS-CONFIGURATION-TLV: Used to communicate some
disjointness configuration parameters. disjointness configuration parameters.
In addition, the disjoint group MAY carry the following TLV: In addition, the disjoint group MAY carry the following TLV:
o DISJOINTNESS-STATUS-TLV: Used to communicate the status of the o DISJOINTNESS-STATUS-TLV: Used to communicate the status of the
computed disjointness. This is applicable for messages from PCE computed disjointness. This is applicable for messages from PCE
to PCC (PCUpd, PCInitiate or PCRep message). to PCC (PCUpd, PCInitiate or PCRep message).
o VENDOR-INFORMATION-TLV: Used to communicate arbitrary vendor o VENDOR-INFORMATION-TLV: Used to communicate arbitrary vendor-
specific behavioral information, described in [RFC7470]. specific behavioral information, described in [RFC7470].
o OF-List TLV: Used to communicate the disjointness objective o OF-List TLV: Used to communicate the disjointness objective
function. See Section 4.4. function. See Section 4.4.
The DISJOINTNESS-CONFIGURATION-TLV is shown in the following figure: The DISJOINTNESS-CONFIGURATION-TLV is shown in the following figure:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* P (Shortest path) bit: when set, this indicates that the * P (Shortest path) bit: when set, this indicates that the
computed path of the LSP SHOULD satisfy all the constraints and computed path of the LSP SHOULD satisfy all the constraints and
objective functions first without considering the diversity objective functions first without considering the diversity
constraint. This means that an LSP with P flag set should be constraint. This means that an LSP with P flag set should be
placed as if the disjointness constraint has not been placed as if the disjointness constraint has not been
configured, while the other LSP in the association with P flag configured, while the other LSP in the association with P flag
unset should be placed by taking into account the disjointness unset should be placed by taking into account the disjointness
constraint. Setting P flag changes the relationship between constraint. Setting P flag changes the relationship between
LSPs to a one-sided relationship (LSP 1 with P=0 depends of LSP LSPs to a one-sided relationship (LSP 1 with P=0 depends of LSP
2 with P=1, but LSP 2 with P=1 does not depend of LSP 1 with 2 with P=1, but LSP 2 with P=1 does not depend of LSP 1 with
P=0). Multiple LSPs in the same disjoint group may have the P=0). Multiple LSPs in the same disjoint group may have the P
P-flag set. In such a case, those LSPs may not be disjoint flag set. In such a case, those LSPs may not be disjoint from
from each other but will be disjoint from others LSPs in the each other but will be disjoint from others LSPs in the group
group that have the P-flag unset. that have the P flag unset.
* T (Strict disjointness) bit: when set, if disjoint paths cannot * T (Strict disjointness) bit: when set, if disjoint paths cannot
be found, PCE SHOULD return no path for LSPs that could not be be found, PCE SHOULD return no path for LSPs that could not be
be disjoint. When unset, PCE is allowed to relax disjointness be disjoint. When unset, the PCE is allowed to relax
by using either applying a requested objective function or any disjointness by either applying a requested objective function
other behavior if no objective function is requested (e.g.: (cf. Section 4.4 below) or using any other behavior if no
using a lower disjoint type (link instead of node) or relaxing objective function is requested (e.g. using a lower disjoint
disjointness constraint fully). type (link instead of node) or fully relaxing disjointness
constraint).
* Unassigned bits are considered reserved. They MUST be set to 0 * Unassigned bits are considered reserved. They MUST be set to 0
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
If a PCEP speaker receives a disjoint-group without DISJOINTNESS- If a PCEP speaker receives a disjoint-group without DISJOINTNESS-
CONFIGURATION-TLV, it SHOULD reply with a PCErr Error-type=6 CONFIGURATION-TLV, it SHOULD reply with a PCErr Error-type=6
(Mandatory Object missing) and Error-value=TBD8 (DISJOINTNESS- (Mandatory Object missing) and Error-value=TBD8 (DISJOINTNESS-
CONFIGURATION-TLV missing). CONFIGURATION-TLV missing).
The DISJOINTNESS-STATUS-TLV uses the same format as the DISJOINTNESS- The DISJOINTNESS-STATUS-TLV uses the same format as the DISJOINTNESS-
CONFIGURATION-TLV with a different type TBD3 (in the TLV). The flags CONFIGURATION-TLV with a different type TBD3 (in the TLV). The L, N,
L, N, and S are set based if the computed path meet the disjointness and S flags are set based if the computed path meet the disjointness
criteria. The flag P is set to indicate that the computed path is criteria. The P flag is set to indicate that the computed path is
the shortest and the flag T has no meaning in the DISJOINTNESS- the shortest and the T flag has no meaning in the DISJOINTNESS-
STATUS-TLV and MUST NOT be set while sending and ignored on receipt. STATUS-TLV and MUST NOT be set while sending and ignored on receipt.
Any new flag defined for the DISJOINTNESS-CONFIGURATION-TLV is be Any new flag defined for the DISJOINTNESS-CONFIGURATION-TLV is be
automatically applicable to the DISJOINTNESS-STATUS-TLV. automatically applicable to the DISJOINTNESS-STATUS-TLV.
4.3. Relationship to SVEC 4.3. Relationship to SVEC
[RFC5440] defines a mechanism for the synchronization of a set of [RFC5440] defines a mechanism for the synchronization of a set of
path computation requests by using the SVEC object, that specifies path computation requests by using the SVEC object, that specifies
the list of synchronized requests that can either be dependent or the list of synchronized requests that can either be dependent or
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set of path computation requests, identified by 'Request-ID-number' set of path computation requests, identified by 'Request-ID-number'
in RP (Request Parameters) object. [RFC6007] further clarified the in RP (Request Parameters) object. [RFC6007] further clarified the
use of the SVEC list for synchronized path computations when use of the SVEC list for synchronized path computations when
computing dependent requests as well as described a number of usage computing dependent requests as well as described a number of usage
scenarios for SVEC lists within single-domain and multi-domain scenarios for SVEC lists within single-domain and multi-domain
environments. environments.
The SVEC object includes a Flags field that indicates the potential The SVEC object includes a Flags field that indicates the potential
dependency between the set of path computation request in a similar dependency between the set of path computation request in a similar
way as the Flags field in the TLVs defined in this document. The way as the Flags field in the TLVs defined in this document. The
path computation request in the PCReq message MAY use both SVEC and path computation request in the PCReq message MAY use both the SVEC
ASSOCIATION object to identify the related path computation request and ASSOCIATION objects to identify the related path computation
as well as the diversity association group. The PCE MUST try to find request as well as the diversity association group. The PCE MUST try
a path that meets both the constraints. It is possible that the to find a path that meets both the constraints. It is possible that
diversity requirement in the association group is different from the the diversity requirement in the association group is different from
one in SVEC object. The PCE would consider both the objects as per the one in the SVEC object. The PCE would consider both the objects
the processing rules and aim to find a path that meets both these as per the processing rules and aim to find a path that meets both of
constraints. In case no such path is possible (or the constraints these constraints. In case no such path is possible (or the
are incompatible), the PCE MUST send a path computation reply (PCRep) constraints are incompatible), the PCE MUST send a path computation
with NO-PATH object indcating path computation failure as per reply (PCRep) with a NO-PATH object indicating path computation
[RFC5440]. failure as per [RFC5440].
4.4. Disjointness objective functions 4.4. Disjointness Objective functions
An objective function (OF) MAY be applied to the disjointness An objective function (OF) MAY be applied to the disjointness
computation to drive the PCE computation behavior. In this case, the computation to drive the PCE computation behavior. In this case, the
OF-List TLV (defined in ([RFC5541]) is used as an optional TLV in the OF-List TLV (defined in ([RFC5541]) is used as an optional TLV in the
Association Group Object. The PCEP OF-List TLV allow multiple OF- Association Group Object. Whereas the PCEP OF-List TLV allows
Codes inside the TLV, a sender SHOULD include a single OF-Code in the multiple OF-codes inside the TLV, a sender SHOULD include a single
OF-List TLV when included in the Association Group, and the receiver OF-code in the OF-List TLV when included in the Association Group,
MUST consider the first OF-code only and ignore others if included. and the receiver MUST consider the first OF-code only and ignore
others if included.
To minimize the common shared resources (Node, Link or SRLG) between To minimize the common shared resources (Node, Link or SRLG) between
a set of paths during path computation three new OF codes are a set of paths during path computation three new OF-codes are
proposed: proposed:
MSL MSL
* Name: Minimize the number of shared (common) Links. * Name: Minimize the number of shared (common) Links.
* Objective Function Code: TBD4 * Objective Function Code: TBD4
* Description: Find a set of paths such that it passes through the * Description: Find a set of paths such that it passes through the
least number of shared (common) links. least number of shared (common) links.
skipping to change at page 11, line 32 skipping to change at page 11, line 36
MSN MSN
* Name: Minimize the number of shared (common) Nodes. * Name: Minimize the number of shared (common) Nodes.
* Objective Function Code: TBD6 * Objective Function Code: TBD6
* Description: Find a set of paths such that it passes through the * Description: Find a set of paths such that it passes through the
least number of shared (common) nodes. least number of shared (common) nodes.
If the OF-list TLV is included in the Association Object, the OF Code If the OF-list TLV is included in the Association Object, the OF-code
inside the OF Object MUST include one of the disjoint OFs defined in inside the OF Object MUST include one of the disjoint OFs defined in
this document. If this condition is not met, the PCEP speaker MUST this document. If this condition is not met, the PCEP speaker MUST
respond with a PCErr message with Error-Type=10 (Reception of an respond with a PCErr message with Error-Type=10 (Reception of an
invalid object) and Error-Value=TBD9 (Incompatible OF codes). invalid object) and Error-Value=TBD9 (Incompatible OF code).
[RFC5440] uses SVEC diversity flag for node, link or SRLG to describe [RFC5440] uses SVEC diversity flag for node, link or SRLG to describe
the potential disjointness between the set of path computation the potential disjointness between the set of path computation
requests used in PCEP protocol. requests used in PCEP protocol.
This document defines three new OF codes to maximize diversity as This document defines three new OF-codes to maximize diversity as
much as possible, in other words, minimize the common shared much as possible, in other words, minimize the common shared
resources (Node,Link or SRLG) between a set of paths. resources (Node, Link or SRLG) between a set of paths.
It may be interesting to note that the diversity flags in the SVEC It may be interesting to note that the diversity flags in the SVEC
object and OF for diversity can be used together. Some example of object and OF for diversity can be used together. Some examples of
usage are listed below - usage are listed below:
o SVEC object with node-diverse bit=1 - ensure full node-diversity. o SVEC object with node-diverse bit=1 - ensure full node-diversity.
o SVEC object with node-diverse bit=1 and OF=MSS - full node diverse o SVEC object with node-diverse bit=1 and OF=MSS - full node diverse
with as much as SRLG-diversity as possible. with as much as SRLG-diversity as possible.
o SVEC object with domain-diverse bit=1;link diverse bit=1 and o SVEC object with domain-diverse bit=1;link diverse bit=1 and
OF=MSS - full domain and node diverse path with as much as SRLG- OF=MSS - full domain and node diverse path with as much as SRLG-
diversity as possible. diversity as possible.
o SVEC object with node-diverse bit=1 and OF=MSN - ensure full node- o SVEC object with node-diverse bit=1 and OF=MSN - ensure full node-
diversity. diversity.
4.5. P-flag considerations In the last example above, it is interesting to note that "OF"
becomes redundant as "SVEC object" ensures full node-diversity,
however this specification does not prohibit redundant constraints
while using "SVEC object" and "OF" together for diversity.
As mentioned in Section 4.2, the P-flag (when set) indicates that the 4.5. P Flag Considerations
As mentioned in Section 4.2, the P flag (when set) indicates that the
computed path of the LSP SHOULD satisfies all constraints and computed path of the LSP SHOULD satisfies all constraints and
objective functions first without considering the diversity objective functions first without considering the diversity
constraint. This could be required in some primary/backup scenarios constraint. This could be required in some primary/backup scenarios
where the primary path should use the more optimal path available where the primary path should use the more optimal path available
(taking into account the other constraints). When disjointness is (taking into account the other constraints). When disjointness is
computed, it is important for the algorithm to know that it should computed, it is important for the algorithm to know that it should
try to optimize the path of one or more LSPs in the disjoint group try to optimize the path of one or more LSPs in the disjoint group
(for instance the primary path) while other paths are allowed to be (for instance the primary path) while other paths are allowed to be
costlier (compared to a similar path without the disjointness costlier (compared to a similar path without the disjointness
constraint). Without such a hint, the disjointness algorithm may set constraint). Without such a hint, the disjointness algorithm may set
a path for all LSPs that may not completely fulfill the customer a path for all LSPs that may not completely fulfill the customer's
requirement. requirement.
_________________________________________ _________________________________________
/ \ / \
/ +------+ \ / +------+ \
| | PCE | | | | PCE | |
| +------+ | | +------+ |
| | | |
| | | |
| +------+ 10 +------+ | | +------+ 10 +------+ |
skipping to change at page 13, line 6 skipping to change at page 13, line 29
| +------+ \ | / +------+ | | +------+ \ | / +------+ |
| \ | 10 / | | \ | 10 / |
\ +-- R5 --------- R6 / \ +-- R5 --------- R6 /
\_________________________________________/ \_________________________________________/
Cost of all the links is 1, unless explicitly marked otherwise. Cost of all the links is 1, unless explicitly marked otherwise.
Figure 3 Figure 3
In the figure above, a customer has two dual homed sites (CE1/CE3 and In the figure above, a customer has two dual homed sites (CE1/CE3 and
CE2/CE4). Consider, this customer wants two disjoint paths between CE2/CE4). Let us consider that this customer wants two disjoint
the two sites. Due to physical meshing, the customer wants to use paths between the two sites. Due to physical meshing, the customer
CE1 and CE2 as primary ( and CE3 and CE4 are hosted in a remote site wants to use CE1 and CE2 as primary (and CE3 and CE4 are hosted in a
for redundancy purpose). remote site for redundancy purpose).
Without any hint (constraint) provided, the PCE may compute the two Without any hint (constraint) provided, the PCE may compute the two
disjoint LSPs together, leading to PE1->PE2 using a path disjoint LSPs together, leading to PE1->PE2 using a path
PE1->R1->R2->PE2 and PE3->PE4 using PE3->R3->R4->PE4. In this case, PE1->R1->R2->PE2 and PE3->PE4 using PE3->R3->R4->PE4. In this case,
even if the disjointness constraint is fulfilled, the path from PE1 even if the disjointness constraint is fulfilled, the path from PE1
to PE2 does not use the best optimal path available in the network to PE2 does not use the best optimal path available in the network
(path delay may be higher): the customer requirement is thus not (path delay may be higher): the customer requirement is thus not
completely fulfilled. completely fulfilled.
The usage of the P-Flag allows the PCE to know that a particular LSP The usage of the P flag allows the PCE to know that a particular LSP
should be tied to the best path as if the disjointness constraint was should be tied to the best path as if the disjointness constraint was
not requested. not requested.
In our example, if the P-Flag is set to the LSP PE1->PE2, the PCE In our example, if the P flag is set to the LSP PE1->PE2, the PCE
should use the path PE1->R1->R3->R4->R2->PE2 for this LSP, while the should use the path PE1->R1->R3->R4->R2->PE2 for this LSP, while the
other LSP should be disjoint from this path. The second LSP will be other LSP should be disjoint from this path. The second LSP will be
placed on PE3->R5->R6->PE4 as it is allowed to be costlier. placed on PE3->R5->R6->PE4 as it is allowed to be costlier.
Driving the PCE disjointness computation may be done in other ways, Driving the PCE disjointness computation may be done in other ways,
for instance setting a metric boundary reflecting an path delay for instance setting a metric boundary reflecting an path delay
boundary. Other constraints may also be used. boundary. Other constraints may also be used.
The P-Flag allows a simple expression that the disjointness The P flag allows to simply express that the disjointness constraint
constraint should not make the LSP worst. should not make the LSP worst.
Any constraint added to a path disjointness computation may reduce Any constraint added to a path disjointness computation may reduce
the chance to find suitable paths. The usage of the P-flag, as any the chance to find suitable paths. The usage of the P flag, as any
other constraint, may prevent to find a disjoint path. In the other constraint, may prevent to find a disjoint path. In the
example above, if we consider that the router R5 is down, if PE1->PE2 example above, if we consider that the router R5 is down, if PE1->PE2
has the P-flag set, there is no room available to place PE3->PE4 (the has the P flag set, there is no room available to place PE3->PE4 (the
disjointness constraint cannot be fulfilled). If PE->PE2 has the disjointness constraint cannot be fulfilled). If PE1->PE2 has the P
P-flag unset, the algorithm may be able to place PE1->PE2 on R1->R2 flag unset, the algorithm may be able to place PE1->PE2 on R1->R2
link leaving a room for PE3->PE4 using the R3->R4 link. When using link leaving a room for PE3->PE4 using the R3->R4 link. When using P
P-flag or any additional constraint on top of the disjointness flag or any additional constraint on top of the disjointness
constraint, the user should be aware that there is less chance to constraint, the user should be aware that there is less chance to
fulfill the disjointness constraint. fulfill the disjointness constraint.
_________________________________________ _________________________________________
/ \ / \
/ +------+ \ / +------+ \
| | PCE | | | | PCE | |
| +------+ | | +------+ |
| | | |
| | | |
skipping to change at page 14, line 29 skipping to change at page 14, line 48
| +------+ +------+ | | +------+ +------+ |
| | | |
\ / \ /
\_________________________________________/ \_________________________________________/
Cost of all the links is 1, unless explicitly marked otherwise. Cost of all the links is 1, unless explicitly marked otherwise.
Figure 4 Figure 4
In the figure above, we still consider the same previous In the figure above, we still consider the same previous
requirements, so PE1->PE2 LSP should be optimized (P-flag set) while requirements, so PE1->PE2 LSP should be optimized (P flag set) while
PE3->PE4 should be disjoint and may use a costlier path. PE3->PE4 should be disjoint and may use a costlier path.
Regarding PE1->PE2, there are two paths that are satisfying the Regarding PE1->PE2, there are two paths that are satisfying the
constraints (ECMP): PE1->R1->R4->R2->PE2 (path 1) and constraints (ECMP): PE1->R1->R4->R2->PE2 (path 1) and
PE1->R1->R3->R4->R2->PE2 (path 2). An implementation may choose one PE1->R1->R3->R4->R2->PE2 (path 2). An implementation may choose one
of the paths. of the paths.
If the implementation elects only one path, there is a chance that If the implementation elects only one path, there is a chance that
picking up one path may prevent disjointness. In our example, if picking up one path may prevent disjointness. In our example, if
path 2 is used for PE1->PE2, there is no room left for PE3->PE4 while path 2 is used for PE1->PE2, there is no room left for PE3->PE4 while
if path 1 is used, PE3->PE4 can be placed on R3->R4 link. if path 1 is used, PE3->PE4 can be placed on R3->R4 link.
When P-flag is set for an LSP and when ECMPs are available, an When P flag is set for an LSP and when ECMPs are available, an
implementation should aim to select a path that allows disjointness. implementation should aim to select a path that allows disjointness.
4.6. Disjointness computation issues 4.6. Disjointness Computation Issues
There may be some cases where the PCE is not able to provide a set of There may be some cases where the PCE is not able to provide a set of
disjoint paths for one or more LSPs in the association. disjoint paths for one or more LSPs in the association.
When the T-bit is set (Strict disjointness requested), if When the T flag is set (Strict disjointness requested), if
disjointness cannot be ensured for one or more LSPs, the PCE SHOULD disjointness cannot be ensured for one or more LSPs, the PCE MUST
reply with a PCUpd message containing an empty ERO. In addition to reply to a Path Computation Request (PCReq) with a Path Computation
the empty ERO Object, the PCE MAY add the NO-PATH-VECTOR TLV Reply (PCRep) message containing a NO-PATH object. In case of
([RFC5440]) in the LSP Object. network event leading to an impossible strict disjointness, the PCE
MUST send a PCUpd message containing an empty ERO to the
corresponding PCCs. In addition to the empty ERO Object, the PCE MAY
add the NO-PATH-VECTOR TLV ([RFC5440]) in the LSP Object.
This document adds new bits in the NO-PATH-VECTOR TLV: This document adds new bits in the NO-PATH-VECTOR TLV:
bit "TBD7": when set, the PCE indicates that it could not find a bit "TBD7": when set, the PCE indicates that it could not find a
disjoint path for this LSP. disjoint path for this LSP.
bit "TBD8": when set, the PCE indicates that it does not support bit "TBD8": when set, the PCE indicates that it does not support
the requested disjointness computation. the requested disjointness computation.
When the T-bit is unset, the PCE is allowed to reduce the required When the T flag is unset, the PCE is allowed to reduce the required
level of disjointness. The actual level of disjointness computed by level of disjointness. The actual level of disjointness computed by
the PCE can be reported through the DISJOINTNESS-STATUS-TLV by the PCE can be reported through the DISJOINTNESS-STATUS-TLV by
setting the appropriate flags in the TLV. While the DISJOINTNESS- setting the appropriate flags in the TLV. While the DISJOINTNESS-
CONFIGURATION-TLV defines the expected level of disjointness required CONFIGURATION-TLV defines the expected level of disjointness required
by configuration, the DISJOINTNESS-STATUS-TLV defines the actual by configuration, the DISJOINTNESS-STATUS-TLV defines the actual
level of disjointness computed. level of disjointness computed.
There are some cases where the PCE may need to completely relax the There are some cases where the PCE may need to completely relax the
disjointness constraint in order to provide a path to all the LSPs disjointness constraint in order to provide a path to all the LSPs
that are part of the association. A mechanism that allows the PCE to that are part of the association. A mechanism that allows the PCE to
fully relax a constraint is considered by the authors as more global fully relax a constraint is considered by the authors as more global
to PCEP rather than linked to the disjointness use case. As a to PCEP rather than linked to the disjointness use case. As a
consequence, it is considered as out of scope of the document. consequence, it is considered as out of scope of the document.
All LSPs in a particular disjoint group MUST use the same combination All LSPs in a particular disjoint group MUST use the same combination
of T,S,N,L flags in the DISJOINTNESS-CONFIGURATION-TLV. If a PCEP of T, S, N, L flags in the DISJOINTNESS-CONFIGURATION-TLV. If a PCEP
peer receives a PCEP messages for LSPs belonging to the same disjoint peer receives a PCEP messages for LSPs belonging to the same disjoint
group but having an inconsistent combination of T,S,N,L flags, the group but having an inconsistent combination of T, S, N, L flags, the
PCEP peer SHOULD NOT try to add the LSPs in disjoint group and SHOULD PCEP peer SHOULD NOT try to add the LSPs in disjoint group and SHOULD
reply with a PCErr with Error-type 26 (Association Error) and Error- reply with a PCErr with Error-type 26 (Association Error) and Error-
Value 6 (Association information mismatch). Value 6 (Association information mismatch).
5. Security Considerations 5. Security Considerations
This document defines one new type for association, which do not add This document defines one new type for association, which does not
any new security concerns beyond those discussed in [RFC5440], add any new security concerns beyond those discussed in [RFC5440],
[RFC8231] and [I-D.ietf-pce-association-group] in itself. [RFC8231] and [I-D.ietf-pce-association-group] in itself.
As stated in [I-D.ietf-pce-association-group], much of the As stated in [I-D.ietf-pce-association-group], much of the
information carried in the Disjointness Association object, as per information carried in the Disjointness Association object, as per
this document is not extra sensitive. It often reflects information this document is not extra sensitive. It often reflects information
that can also be derived from the LSP Database, but association that can also be derived from the LSP Database, but association
provides a much easier grouping of related LSPs and messages. The provides a much easier grouping of related LSPs and messages. The
disjointness association could provides an adversary with the disjointness association could provide an adversary with the
opportunity to eavesdrop on the relationship between the LSPs. Thus opportunity to eavesdrop on the relationship between the LSPs. Thus
securing the PCEP session using Transport Layer Security (TLS) securing the PCEP session using Transport Layer Security (TLS)
[RFC8253], as per the recommendations and best current practices in [RFC8253], as per the recommendations and best current practices in
[RFC7525], is RECOMMENDED. [RFC7525], is RECOMMENDED.
6. IANA Considerations 6. IANA Considerations
6.1. Association Type 6.1. Association Type
This document defines a new Association type, originally described in This document defines a new Association type, originally described in
[I-D.ietf-pce-association-group]. IANA is requested to make the [I-D.ietf-pce-association-group]. IANA is requested to make the
assignment of a new value for the sub-registry "ASSOCIATION Type assignment of a new value for the sub-registry "ASSOCIATION Type
skipping to change at page 16, line 26 skipping to change at page 16, line 48
as follows: as follows:
+------------------+-----------------------------+-------------+ +------------------+-----------------------------+-------------+
| Association type | Association Name | Reference | | Association type | Association Name | Reference |
+------------------+-----------------------------+-------------+ +------------------+-----------------------------+-------------+
| TBD1 | Disjoint-group Association | [This.I-D] | | TBD1 | Disjoint-group Association | [This.I-D] |
+------------------+-----------------------------+-------------+ +------------------+-----------------------------+-------------+
6.2. PCEP TLVs 6.2. PCEP TLVs
This document defines following new PCEP TLVs and the IANA is This document defines the following new PCEP TLVs and the IANA is
requested to make the assignment of new values for the existing "PCEP requested to make the assignment of new values for the existing "PCEP
TLV Type Indicators" registry as follows: TLV Type Indicators" registry as follows:
+----------+---------------------------------+-------------+ +----------+---------------------------------+-------------+
| TLV Type | TLV Name | Reference | | TLV Type | TLV Name | Reference |
+----------+---------------------------------+-------------+ +----------+---------------------------------+-------------+
| TBD2 | Disjointness Configuration TLV | [This.I-D] | | TBD2 | Disjointness Configuration TLV | [This.I-D] |
| TBD3 | Disjointness Status TLV | [This.I-D] | | TBD3 | Disjointness Status TLV | [This.I-D] |
+----------+---------------------------------+-------------+ +----------+---------------------------------+-------------+
skipping to change at page 18, line 5 skipping to change at page 18, line 22
+------------+-----------------------------------------+------------+ +------------+-----------------------------------------+------------+
| Bit Number | Name | Reference | | Bit Number | Name | Reference |
+------------+-----------------------------------------+------------+ +------------+-----------------------------------------+------------+
| TBD7 | Disjoint path not found | [This.I-D] | | TBD7 | Disjoint path not found | [This.I-D] |
| TBD8 | Requested disjoint computation not | [This.I-D] | | TBD8 | Requested disjoint computation not | [This.I-D] |
| | supported | | | | supported | |
+------------+-----------------------------------------+------------+ +------------+-----------------------------------------+------------+
Table 2: NO-PATH-VECTOR TLV Table 2: NO-PATH-VECTOR TLV
6.5. PCEP-ERROR codes 6.5. PCEP-ERROR Codes
This document defines new Error-Type and Error-Value related to path This document defines new Error-Value within existing Error-Type
protection association. IANA is requested to allocate new error related to path protection association. IANA is requested to
values within the "PCEP-ERROR Object Error Types and Values" sub- allocate new error values within the "PCEP-ERROR Object Error Types
registry of the PCEP Numbers registry, as follows: and Values" sub-registry of the PCEP Numbers registry, as follows:
+----------+-------------------------+------------------------------+ +----------+-------------------------+------------------------------+
| Error- | Meaning | Reference | | Error- | Meaning | Reference |
| Type | | | | Type | | |
+----------+-------------------------+------------------------------+ +----------+-------------------------+------------------------------+
| 6 | Mandatory Object | [I-D.ietf-pce-association-gr | | 6 | Mandatory Object | [I-D.ietf-pce-association-gr |
| | missing | oup] | | | missing | oup] |
| | Error-value=TBD8: | [This.I-D] | | | Error-value=TBD8: | [This.I-D] |
| | DISJOINTNESS- | | | | DISJOINTNESS- | |
| | CONFIGURATION TLV | | | | CONFIGURATION TLV | |
| | missing | | | | missing | |
| 10 | Reception of an invalid | [RFC5440] | | 10 | Reception of an invalid | [RFC5440] |
| | object | | | | object | |
| | Error-value=TBD9: | [This.I-D] | | | Error-value=TBD9: | [This.I-D] |
| | Incompatible OF codes | | | | Incompatible OF code | |
+----------+-------------------------+------------------------------+ +----------+-------------------------+------------------------------+
7. Manageability Considerations 7. Manageability Considerations
7.1. Control of Function and Policy 7.1. Control of Function and Policy
An operator SHOULD be allowed to configure the disjointness An operator SHOULD be allowed to configure the disjointness
association groups and disjoint parameters at the PCEP peers and association groups and disjoint parameters at the PCEP peers and
associate it with the LSPs. The Operator-configured Association associate it with the LSPs. The Operator-configured Association
Range MUST be allowed to be set by the operator. Operator SHOULD be Range MUST be allowed to be set by the operator. Operator SHOULD be
skipping to change at page 19, line 25 skipping to change at page 19, line 42
7.6. Impact On Network Operations 7.6. Impact On Network Operations
Mechanisms defined in [RFC5440], Section 8.6 also apply to PCEP Mechanisms defined in [RFC5440], Section 8.6 also apply to PCEP
extensions defined in this document. Additionally, a PCEP extensions defined in this document. Additionally, a PCEP
implementation SHOULD allow a limit to be placed on the number of implementation SHOULD allow a limit to be placed on the number of
LSPs that can belong to a disjoint association group. LSPs that can belong to a disjoint association group.
8. Acknowledgments 8. Acknowledgments
A special thanks to author of [I-D.ietf-pce-association-group], this A special thanks to authors of [I-D.ietf-pce-association-group], this
document borrow some of the text from it. Authors would also like to document borrow some of the text from it. Authors would also like to
thank Adrian Farrel for his useful comments. thank Adrian Farrel and Julien Meuric for the valuable comments.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
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