Internet DRAFT - draft-litkowski-pce-association-diversity
draft-litkowski-pce-association-diversity
PCE Working Group S. Litkowski
Internet-Draft Orange
Intended status: Standards Track S. Sivabalan
Expires: May 27, 2017 Cisco Systems, Inc.
C. Barth
Juniper Networks
November 23, 2016
Path Computation Element communication Protocol extension for signaling
LSP diversity constraint
draft-litkowski-pce-association-diversity-01
Abstract
This document introduces a simple mechanism to signal path diversity
for a group of Label Switched Paths (LSPs) via an extension to the
Path Computation Element Communication Protocol (PCEP).
Status of This Memo
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol extension . . . . . . . . . . . . . . . . . . . . . 6
4.1. Association group . . . . . . . . . . . . . . . . . . . . 6
4.2. Optional TLVs . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. Association object Type Indicators . . . . . . . . . . . 8
7. Manageability Considerations . . . . . . . . . . . . . . . . 9
7.1. Control of Function and Policy . . . . . . . . . . . . . 9
7.2. Information and Data Models . . . . . . . . . . . . . . . 9
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 9
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 9
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 9
7.6. Impact On Network Operations . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[I-D.ietf-pce-association-group] introduces a generic mechanism to
create a grouping of LSPs which can then be used to define
associations between a set of LSPs and a set of attributes (such as
configuration parameters or behaviours) and is equally applicable to
the active and passive modes of a stateful PCE
[I-D.ietf-pce-stateful-pce] or a stateless PCE [RFC5440].
This document specifies a PCEP extension to signal that a particular
group of LSPs should use diverse paths including the requested type
of diversity.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Terminology
The following terminology is used in this document.
LSR: Label Switch Router.
MPLS: Multiprotocol Label Switching.
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 Communication Protocol.
SRLG: Shared Risk Link Group.
3. Motivation
Path diversity is a very common use case today in IP/MPLS networks
especially for layer 2 transport over MPLS. A customer may request
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
active/active.
Different level of disjointness may be offered:
o Link disjointness: the paths of the associated LSPs should transit
different links (but may use common nodes or different links that
may have some shared fate).
o Node disjointness: the paths of the associated LSPs should transit
different nodes (but may use different links that may have some
shared fate).
o SRLG disjointness: the paths of the associated LSPs should transit
different links that do not share fate (but may use common transit
nodes).
o Node+SRLG disjointness: the paths of the associated LSPs should
transit different links that do not have any common shared fate
and should transit different nodes.
The associated LSPs may originate from the same or from different
head-end(s) and may terminate at the same or different tail-end(s).
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_________________________________________
/ \
/ +------+ \
| | PCE | |
| +------+ |
| |
| ***********************> |
| +------+ 10 +------+ |
CE1 ****| PE 1 | ----- R1 ---- R2 ------- | PE 2 |**** CE2
| +------+ | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
CE3 ****| PE 3 | ----- R3 ---- R4 ------- | PE 4 |**** CE4
| +------+ ***********************> +------+ |
| |
\ /
\_________________________________________/
Figure 1 - Disjoint paths with different head-ends
In the figure above, the customer wants to have two disjoint paths
between CE1/CE2 and CE3/CE4. From an IP/MPLS network point view, in
this example, the CEs are connected to different PEs to maximize
their disjointness. When LSPs originate from different head-ends,
distributed computation of diverse paths can be difficult. Whereas,
computation via a centralized PCE ensures path disjointness
correctness and simplicity.
Using PCEP, the PCC MUST indicate that disjoint path computation is
required, such indication SHOULD include disjointness parameters such
as the type of disjointness, the disjoint group-id, and any
customization parameters according to local policy.
The PCC can use the generic mechanism as per
[I-D.ietf-pce-association-group] to associate a set of LSPs with a
particular disjoint-group.
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
configuration of IPv4/IPv6 association source, or Global Association
Source/Extended Association ID should allow to overcome this
limitation. For example, when a PCC or PCE initiates all the LSPs in
a particular disjoint-group, it can set the IPv4/IPv6 association
source can be set to one of its IP address. When disjoint LSPs are
initiated from different head-ends, a unique association identifier
SHOULD be used for those LSPs: this can be achieved by setting the
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IPv4/IPv6 source address to a common value (zero value can be used)
as well as the Association ID.
Initiate & Monitor LSP
|
| PCReq
V {Disjoint-group Y}
+-----+ ----------------> +-----+
_ _ _ _ _ _| PCE | | | PCE |
| +-----+ | ----------> +-----+
| PCEInitiate | | PCReq
|{Disjoint-group X} | | {Disjoint-group Y}
| | |
| .-----. | | .-----.
| ( ) | +----+ ( )
| .--( )--. | |PE 1|--.--( )--.
V ( ) | +----+ ( )
+---+ ( ) | ( )
|PCC|----( (G)MPLS network ) +----+ ( (G)MPLS network )
+---+ ( ) |PE 3|------( )
Disjoint-group X ) +----+ ( )
{Monitor LSP} '--( )--' '--( )--'
( ) ( )
'-----' '-----'
Case 1: Disjointness initiated by Case 2: Disjointness initiated by
PCE and enforced by PCC PCC and enforced by PCE
Figure 2 - Sample use-cases for carrying disjoint-group over PCEP
session
Using the disjoint-group within a PCUpdate or PCInit may have two
purposes:
o Information: in case the PCE is performing the path computation,
it may communicate to the PCC the locally used configured
parameters in the attribute-list of the LSP.
o Configuration: in case the PCC is performing the path computation
but the PCE (without computation engine) is managing the LSP
parameters, the PCE should add the disjoint-group within the
PCUpdate message to communicate to the PCC the disjointness
constraint.
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4. Protocol extension
4.1. Association group
As per [I-D.ietf-pce-association-group], LSPs are associated with
other LSPs with which they interact by adding them to a common
association group. The Association ID will be used to identify the
disjoint group a set of LSPs belongs to. This document defines four
new Association types, based on the generic Association object -
o Association type = TBD1 ("Disjointness Association Type") for link
disjoint group.
o Association type = TBD2 ("Disjointness Association Type") for node
disjoint group.
o Association type = TBD3 ("Disjointness Association Type") for srlg
disjoint group.
o Association type = TBD4 ("Disjointness Association Type") for
node+srlg disjoint group.
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
disjointness: usually PCEs are able to compute a pair of disjoint
paths. If a PCE receives more LSPs in the group than it can handle
in its computation algorithm, it SHOULD apply disjointness
computation to only a subset of LSPs in the group. The subset of
disjoint LSPs will be decided by the implementation.
Local polices on the PCC or PCE MAY define the computational behavior
for the other LSPs in the group. For example, the PCE may provide no
path, a shortest path, or a constrained path based on relaxing
disjointness, etc.
Associating a particular LSP to multiple disjoint groups is
authorized from a protocol perspective, however there is no insurance
that the PCE will be able to compute properly the multi-disjointness
constraint.
4.2. Optional TLVs
The disjoint group MAY carry some optional TLVs including but not
limited to:
o VENDOR-INFORMATION-TLV: Used to communicate arbitrary vendor
specific behavioral information, described in [RFC7150].
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o DISJOINTNESS-INFORMATION-TLV: Used to communicate some
disjointness specific parameters.
The DISJOINTNESS-INFORMATION-TLV is shown in the following figure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = [TBD5] | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags:
* P: shortest path, this particular LSP in the group SHOULD use
the shortest constrained path and others MAY use a non shortest
constrained path. The shortest constrained path is the
shortest path (from the requested metric point of view) that
fills all the LSP constraints without taking into account the
disjointness constraint. This means that an LSP with P flag
set should be placed as if the disjointness constraint has not
been configured, while the other LSP in the association with P
flag unset should be placed by taking into account the
disjointness constraint. Setting P flag changes the
relationship between LSPs to a unidirectional 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 P=0).
* S: strict disjointness, when set if disjoint paths cannot be
found, PCE should return no path for LSPs that could not be be
disjoint. When unset, PCE is allowed to relax disjointness by
using either using a lower disjoint type (link instead of node)
or relaxing disjointness constraint at all.
If a PCEP speaker receives a disjoint-group without DISJOINTNESS-
INFORMATION-TLV, it SHOULD use its locally configured parameters or
use the following default parameters:
o Strict disjointness is assumed.
o LSP can use a non shortest-path.
If a PCEP speaker receives two LSPs with the same disjoint-group but
with a different S flag value, it SHOULD apply a strict disjointness
path computation for this disjoint-group (it considers S flag set for
all LSPs).
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5. Security Considerations
This document defines one new type for association, which do not add
any new security concerns beyond those discussed in [RFC5440],
[I-D.ietf-pce-stateful-pce] and [I-D.ietf-pce-association-group] in
itself.
6. IANA Considerations
6.1. Association object Type Indicators
This document defines the following new association type originally
defined in [I-D.ietf-pce-association-group].
Value Name Reference
TBD1 Link Disjoint-group
Association Type [This I.D.]
TBD2 Node Disjoint-group
Association Type [This I.D.]
TBD3 SRLG Disjoint-group
Association Type [This I.D.]
TBD4 Node+SRLG Disjoint-group
Association Type [This I.D.]
This document defines the following new PCEP TLV:
Value Name Reference
TBD5 DISJOINTNESS-INFORMATION-TLV [This I.D.]
IANA is requested to manage the space of flags carried in the
DISJOINTNESS-INFORMATION TLV defined in this document, numbering them
from 0 as the least significant bit.
New bit numbers may be allocated in future.
IANA is requested to allocate the following bit numbers in the
DISJOINTNESS-INFORMATION-TLV flag space:
Bit Number Name Reference
0 Strict disjointness [This I.D.]
1 Shortest-path [This I.D.]
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7. Manageability Considerations
7.1. Control of Function and Policy
An operator MUST be allowed to configure the disjointness
associations and parameters at PCEP peers and associate it with the
LSPs.
7.2. Information and Data Models
[RFC7420] describes the PCEP MIB, there are no new MIB Objects for
this document.
7.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
7.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].
7.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
7.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [RFC5440].
8. Acknowledgments
A special thanks to author of [I-D.ietf-pce-association-group], this
document borrow some of the text from it.
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,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<http://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,
<http://www.rfc-editor.org/info/rfc5440>.
[I-D.ietf-pce-association-group]
Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Zhang, X., and Y. Tanaka, "PCEP Extensions for
Establishing Relationships Between Sets of LSPs", draft-
ietf-pce-association-group-01 (work in progress), July
2016.
[I-D.ietf-pce-stateful-pce]
Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
Extensions for Stateful PCE", draft-ietf-pce-stateful-
pce-17 (work in progress), November 2016.
9.2. Informative References
[RFC7150] Zhang, F. and A. Farrel, "Conveying Vendor-Specific
Constraints in the Path Computation Element Communication
Protocol", RFC 7150, DOI 10.17487/RFC7150, March 2014,
<http://www.rfc-editor.org/info/rfc7150>.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module",
RFC 7420, DOI 10.17487/RFC7420, December 2014,
<http://www.rfc-editor.org/info/rfc7420>.
[I-D.ietf-pce-pce-initiated-lsp]
Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", draft-ietf-pce-pce-initiated-lsp-07 (work in
progress), July 2016.
Authors' Addresses
Stephane Litkowski
Orange
EMail: stephane.litkowski@orange.com
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Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
EMail: msiva@cisco.com
Colby Barth
Juniper Networks
EMail: cbarth@juniper.net
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