PCE Working Group Xian Zhang
Internet-Draft Young Lee
Intended status: Standards Track Fatai Zhang
Huawei
Ramon Casellas
CTTC
Oscar Gonzalez de Dios
Telefonica I+D
Zafar Ali
Cisco Systems
Expires: January 3, 2015 July 3, 2014
Path Computation Element (PCE) Protocol Extensions for Stateful PCE
Usage in GMPLS-controlled Networks
draft-ietf-pce-pcep-stateful-pce-gmpls-01.txt
Abstract
The Path Computation Element (PCE) facilitates Traffic Engineering
(TE) based path calculation in large, multi-domain, multi-region, or
multi-layer networks. [Stateful-PCE] provides the fundamental PCE
communication Protocol (PCEP) extensions needed to support stateful
PCE functions, without specifying the technology-specific extensions.
This memo provides extensions required for PCEP so as to enable the
usage of a stateful PCE capability in GMPLS-controlled networks.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
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as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 3, 2015.
Copyright Notice
Copyright (c) 2014 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must 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.
Conventions used in this document
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 RFC-2119 [RFC2119].
Table of Contents
Table of Contents .............................................. 2
1. Introduction ................................................ 3
2. PCEP Extensions ............................................. 4
2.1. Overview of Requirements................................ 4
2.2. Stateful PCE Capability Advertisement ................... 4
2.2.1. PCE Capability Advertisement in Multi-layer Networks 5
2.3. LSP Delegation in GMPLS-controlled Networks ............. 6
2.4. LSP Synchronization in GMPLS-controlled Networks......... 6
2.5. Modification of Existing PCEP Messages and Procedures .... 8
2.5.1. Use cases ......................................... 9
2.5.2. Modification for LSP Re-optimization ...............9
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2.5.3. Modification for Route Exclusion .................. 10
3. IANA Considerations ........................................ 11
3.1. New PCEP Error Codes................................... 11
3.2. New Subobject for the Exclude Route Object .............11
4. Manageability Considerations................................ 12
4.1. Requirements on Other Protocols and Functional Components12
5. Security Considerations..................................... 12
6. Acknowledgement ............................................ 12
7. References ................................................. 12
7.1. Normative References................................... 12
7.2. Informative References................................. 13
8. Contributors' Address....................................... 13
Authors' Addresses ............................................ 14
1. Introduction
[RFC 4655] presents the architecture of a Path Computation Element
(PCE)-based model for computing Multiprotocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) Traffic Engineering Label Switched
Paths (TE LSPs). To perform such a constrained computation, a PCE
stores the network topology (i.e., TE links and nodes) and resource
information (i.e., TE attributes) in its TE Database (TED). Such a
PCE is usually referred as a stateless PCE. To request path
computation services to a PCE, [RFC 5440] defines the PCE
communication Protocol (PCEP) for interaction between a Path
Computation Client (PCC) and a PCE, or between two PCEs. PCEP as
specified in [RFC 5440] mainly focuses on MPLS networks and the PCEP
extensions needed for GMPLS-controlled networks are provided in
[PCEP-GMPLS].
Stateful PCEs are shown to be helpful in many application scenarios,
in both MPLS and GMPLS networks, as illustrated in [Stateful-APP].
In order for these applications to able to exploit the capability of
stateful PCEs, extensions to PCEP are required.
[Stateful-PCE] provides the fundamental extensions needed for
stateful PCE to support general functionality, but leaves out the
specification for technology-specific objects/TLVs. Complementarily,
this document focuses on the extensions that are necessary in order
for the deployment of stateful PCEs in GMPLS-controlled networks.
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2. PCEP Extensions
2.1. Overview of Requirements
This section notes the main functional requirements for PCEP
extensions to support stateful PCE for use in GMPLS-controlled
networks, based on the description in [Stateful-APP]. Many
requirements are common across a variety of network types (e.g.,
MPLS-TE networks and GMPLS networks) and the protocol extensions to
meet the requirements are already described in [Stateful-PCE]. This
document does not repeat the description of those protocol
extensions. Other requirements that are also common across a
variety of network types do not currently have protocol extensions
defined in [Stateful-PCE]. In these cases, this document presents
protocol extensions for discussion by the PCE working group and
potential inclusion in [Stateful-PCE]. In addition, this document
presents protocol extensions for a set of requirements which are
specific to the use of a stateful PCE in a GMPLS-controlled network.
The basic requirements are as follows:
o Advertisement of the stateful PCE capability. This generic
requirement is covered in Section 7.1.1. of [Stateful-PCE].
Section 2.2. of this document discusses other potential extensions
for this functionality.
o LSP delegation is already covered in Section 5.5. of [Stateful-
PCE]. Section 2.3. of this document provides extension for its
application in GMPLS-controlled networks. Moreover, further
discussion of some generic details that may need additional
consideration is provided.
o LSP state synchronization and LSP state report. This is a generic
requirement already covered in Section 5.4. of [Stateful-PCE].
However, there are further extensions required specifically for
GMPLS-controlled networks and discussed in Section 2.4. Reference
to LSPs by identifiers is discussed in Section 7.3. of [Stateful-
PCE]. This feature can be applied to reduce the data carried in
PCEP messages. Use cases and additional Error Codes are necessary,
as described in Section 2.5. of this draft.
2.2. Stateful PCE Capability Advertisement
Whether a PCE has stateful capability or not can be advertised
during the PCEP session establishment process. It can also be
advertised through routing protocols as described in [RFC5088]. In
either case, the following additional aspects should also be
considered.
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2.2.1. PCE Capability Advertisement in Multi-layer Networks
In multi-layer network scenarios, such as an IP-over-optical network,
if there are dedicated PCEs responsible for each layer, then the
PCCs should be informed of which PCEs they should synchronize their
LSP states with, as well as send path computation requests to. The
Layer-Cap TLV defined in [INTER-LAYER] can be used to indicate which
layer a PCE is in charge of. (Editor's note: this change is
currently not included in the current version of the [INTER-LAYER]
draft. It is expected that it will be included in its next version.)
This TLV is optional and MAY be carried in the OPEN object. It is
RECOMMMENDED that a PCC synchronizes its LSP states with the same
PCEs that it can use for path computation in a multi-layer network.
In a single layer, this TLV MAY not be used. However, if the PCE
capability discovery depends on IGP and if an IGP instance spans
across multiple layers, this TLV is still needed.
Alternatively, the extension to current OSPF PCED TLV and IS-IS PCED
sub-TLV are needed. A new domain-type denoting the layer
information can be defined:
domain-type: T.B.D. (suggested value: 3)
which denotes the network layer information, in which a stateful PCE
has the stateful capability.
When it is carried in PCE-DOMAIN sub-TLV, it denotes the layer for
which a PCE is responsible for path computation as well as LSP state
synchronization. When carried in the PCE-NEIG-DOMAIN sub-TLV, it
denotes its adjacent layers for which a PCE can compute paths and
synchronize the LSP states. The DOMAIN-ID information can be
represented using the following format, to denote the layer
information:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Enc. Type | Switching Type| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IS-IS PCE-DOMAIN sub-TLV is extended to have the following
format:
TYPE: 3
LENGTH: Variable
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VALUE: This is composed of one octet indicating the domain-type
(area ID, AS Number or Network Layer) and a variable length IS-IS
area ID, 32-bit AS number, or a 32-Bit Network-Layer, with encoding
specified above identifying a network layer where the PCE has
visibility and can compute paths.
A new domain-type value is defined:
Value Meaning
3 Network Layer
2.3. LSP Delegation in GMPLS-controlled Networks
To enable the PCE to control an LSP, the PCUpd message is defined in
[Stateful-PCE]. However, the specification of technology specific
extensions is not covered. The following defines the <path>
descriptor, present in the PCUpd message, that should be used in
GMPLS-controlled networks:
<path>::=<ERO><attribute-list>
Where:
<attribute-list> ::= [<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
<metric-list>::= <METRIC>[<metric-list>]
BANDWIDTH object used in the attribute-list is defined in [PCEP-
GMPLS]. Additional TLVs defined for <LSPA> object in [PCEP-GMPLS]
MAY also need to be included.
LSP parameter update controlled by a stateful PCE in a multi-domain
network is complex and requires well-defined operational procedures
as well as protocol design and is out of scope of this document and
left for further study.
2.4. LSP Synchronization in GMPLS-controlled Networks
For LSP state synchronization of stateful PCEs in GMPLS networks,
the LSP attributes, such as its bandwidth, associated route as well
as protection information etc, should be updated by PCCs to PCE LSP
database (LSP-DB). Note the LSP state synchronization described in
this document denotes both the bulk LSP report at the initialization
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phase as well as the LSP state report afterwards described in
[Stateful-PCE].
As per [Stateful-PCE], it does not cover technology-specific
specification for state synchronization. Therefore, extensions of
PCEP for stateful PCE usage in GMPLS networks are required. For LSP
state synchronization, the objects/TLVs that should be used for
stateful PCE in GMPLS networks are defined in [PCEP-GMPLS] and are
briefly summarized as below:
o BANDWIDTH (Generalized BANDWIDTH Object Type)
o END-POINTS (Generalized END-POINTS Object Type)
o PROTECTION ATTRIBUTE
o Use of IF_ID_ERROR_SPEC. [Stateful-PCE] section 7.3.4. only
considers RSVP ERROR_SPEC TLVs. GMPLS extends this to also support
IF_ID_ERROR_SPEC, for example, to report about failed unnumbered
interfaces.
o Extended objects to support the inclusion of the label and
unnumbered links.
Per [Stateful-PCE], the Path Computation Report (PCRpt) message is
defined for LSP state synchronization purposes. PCRpt is used by a
PCC to report one or more of its LSPs to a stateful PCE. However,
the <path> descriptor is technology-specific and left undefined.
For LSP state synchronization in GMPLS-controlled networks, the
encoding of the <path> descriptor is defined as follows:
<path>::=<ERO><attribute-list> [<RRO>]
Where:
<attribute-list> ::= [<END-POINTS>]
[<LSPA>]
[<BANDWIDTH>]
[<IRO>]
[<XRO>]
[<metric-list>]
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<metric-list>::= <METRIC>[<metric-list>]
The objects included in the <path> descriptor can be found in
[RFC5440], [PCEP-GMPLS] and [RFC5521].
For all the objects presented in this section, the P and I bit MUST
be set to 0 since they are only used by a PCC to report its LSP
information.
In GMPLS-controlled networks, the <ERO> object may include a list of
the label sub-object for SDH/SONET, OTN and DWDM networks. It may
also include a list of unnumbered interface IDs to denote the
allocated resource. The <RRO>, <IRO> and <XRO> objects MAY include
unnumbered interface IDs and labels for networks such as OTN and WDM
networks.
If the LSP being reported is a protecting LSP, the <PROTECTION-
ATTRIBUTE> TLV MUST be included in the <LSPA> object to denote its
attributes and restrictions. Moreover, if the status of the
protecting LSP changes from non-operational to operational, this
should be synchronized to the stateful PCE. For example, in 1:1
protection, the combination of S=0, P=1 and O=0 denotes the
protecting path is set up already but not used for carrying traffic.
Upon the working path failure, the operational status of the
aforementioned protecting LSP changes to in-use (i.e., O=1). This
information should be synchronized with a stateful PCE through a
PCRpt message.
The object type used here for <BANDWIDTH> and <END-POINTS> objects
MUST be the ones defined in [PCEP-GMPLS]. The <END-POINTS> are used
to report the end-points address associated with the LSP being
reported since the <ERO> may not carry such information.
2.5. Modification of Existing PCEP Messages and Procedures
One of the advantages mentioned in [Stateful-APP] is that the
stateful nature of a PCE simplifies the information conveyed in PCEP
messages, notably between PCC and PCE, since it is possible to refer
to PCE managed state for active LSPs. To be more specific, with a
stateful PCE, it is possible to refer to a LSP with a unique
identifier in the scope of the PCC-PCEP session and thus use such
identifier to refer to that LSP.
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2.5.1. Use cases
Use Case 1: Assuming a stateful PCE's LSP-DB is up-to-date, a PCC
(e.g. NMS) requesting for a re-optimization of one or several LSPs
can send the request with "R" bit set and only provides the relevant
LSP unique identifiers.
Upon receiving the PCReq message, PCE should be able to correlate
with one or multiple LSPs with their detailed state information and
carry out optimization accordingly.
The handling of RP object specified in [RFC5440] is stated as
following:
"The absence of an RRO in the PCReq message for a non-zero-bandwidth
TE LSP (when the R bit of the RP object is set) MUST trigger the
sending of a PCErr message with Error-Type="Required Object Missing"
and Error-value="RRO Object missing for re-optimization."
If a PCE has stateful capabilities, and such capabilities have been
negotiated and advertised, specific rules given in [RFC5440] may
need to be relaxed. In particular, the re-optimization case: if the
re-optimization request refers to a given LSP state, and the RRO
information is available, the PCE can proceed.
Use Case 2: in order to set up a LSP which has a constraint that its
route should not use resources used by one or more existing LSPs, a
PCC can send a PCReq with the identifiers of these LSPs. A stateful
PCE should be able to find the corresponding route and resource
information so as to meet the constraints set by the requesting PCC.
Hence, the LSP identifier TLV defined in [Stateful-PCE], encoded as
a subobject, can be used in XRO object for this purpose. Note that
if the PCC is a node in the network, the constraint LSP ID
information will be confined to the LSPs initiated by itself.
2.5.2. Modification for LSP Re-optimization
For re-optimization, upon receiving a path computation request and
the "R" bit is set, the stateful PCE SHOULD still perform the re-
optimization in the following two cases:
Case 1: the existing bandwidth and route information of the to-be-
optimized LSP is provided in the path computation request. This
information should be provided via <BANDWIDTH>, <ERO> objects.
Case 2: the existing bandwidth and route information can be found
locally in its LSP-DB. In this case, the PCRep and PCReq messages
need to be modified to carry LSP identifiers. This is specified in
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[Stateful-PCE]. The stateful PCE can find this information using the
per-node LSP ID (e.g., PLSP-ID defined in [Stateful-PCE]) together
with the PCC's address.
If no LSP state information is available to carry out re-
optimization, the stateful PCE should report the error "LSP state
information unavailable for the LSP re-optimization" (Error Type =
T.B.D., Error value= T.B.D.).
2.5.3. Modification for Route Exclusion
A LSP identifier sub-object is defined and its format as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|Type (TBD.) | Length | Attributes | Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PLSP-ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
X bit and Attribute fields are defined in [RFC5521].
X bit: indicates whether the exclusion is mandatory (X=1) and MUST
be accommodated, or desired (X=0) and SHOULD be accommodated.
Type: Subobject Type for a per-node LSP identifier.
Length: The Length contains the total length of the subobject in
bytes, including the Type and Length fields.
Attributes: indicates how the exclusion object is to be
interpreted. Currently, Interface (Attributes = 0), Node (Attributes
=1) and SRLG (Attributes =2) are defined in [RFC5521] and this
document does not define new values.
Flags: is used to further specify the exclusion constraint with
regard to the LSP. Currently, no values are defined.
PLSP-ID: This is the identifier given to a LSP and it is unique on a
node basis. It is defined in [Stateful-PCE].
Reserved: Reserved fields within subobjects MUST be transmitted as
zero and SHOULD be ignored on receipt.
One or multiple of these sub-objects can be present in the XRO
object. When a stateful PCE receives a path computation request
carrying this sub-object, it should find relevant information of
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these LSPs and preclude the resource during the path computation
process. If a stateful PCE cannot recognize one or more of the
received LSP identifiers, it should reply PCErr saying "the LSP
state information for route exclusion purpose cannot be found"
(Error-type = T.B.D., Error-value= T.B.D.). Optionally, it may
provide with the unrecognized identifier information to the
requesting PCC.
3. IANA Considerations
IANA is requested to allocate new Types for the TLV/Object defined
in this document.
3.1. New PCEP Error Codes
IANA is requested to make the following allocation in the "PCEP-
ERROR Object Error Types and Values" registry. The values here are
suggested for use by IANA.
Error Type Meaning Reference
21 LSP state information missing
Error-value 1: LSP state information unavailable [This document]
for the LSP re-optimization
Error-value 2: LSP state information for route
exclusion purpose cannot be found [This document]
3.2. New Subobject for the Exclude Route Object
The "PCEP Parameters" registry contains a subregistry "PCEP Objects"
with an entry for the XRO object (Exclude Route Object).
IANA is requested to add a further sub-object that can be carried in
the XRO as follows:
Value Description Reference
TBD (suggested value: 5) LSP identifier sub-object [this document]
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4. Manageability Considerations
The description and functionality specifications presented related
to stateful PCEs should also comply with the manageability
specifications covered in Section 8 of [RFC4655]. Furthermore, a
further list of manageability issues presented in [Stateful-PCE]
should also be considered.
Additional considerations are presented in the next sections.
4.1. Requirements on Other Protocols and Functional Components
When the detailed route information is included for LSP state
synchronization (either at the initial stage or during LSP state
report process), this require the ingress node of an LSP carry the
RRO object in order to enable the collection of such information.
5. Security Considerations
The security issues presented in [RFC5440] and [Stateful-PCE] apply
to this document.
6. Acknowledgement
We would like to thank Adrian Farrel and Cyril Margaria for the
useful comments and discussions.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J.-P., and Ash, J., "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
[RFC5440] Vasseur, J.-P., and Le Roux, JL., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5088] Le Roux, JL., Vasseur, J.-P., Ikejiri, Y., Zhang, R.,
"OSPF Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5088, January 2008.
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[RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"IS-IS Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5089, January 2008.
[INTER-LAYER] Oki, E., Takeda, Tomonori, Le Roux, JL., Farrel, A.,
Zhang, F., "Extensions to the Path Computation Element
communication Protocol (PCEP) for Inter-Layer MPLS and
GMPLS Traffic Engineering", draft-ietf-pce-inter-layer-ext,
work in progress.
[Stateful-PCE]Crabbe, E., Medved, J., Varga, R., Minei, I., "PCEP
Extensions for Stateful PCE", draft-ietf-pce-stateful-pce,
work in progress.
[PCEP-GMPLS] Margaria, C., Gonzalez de Dios, O., Zhang, F., "PCEP
extensions for GMPLS", draft-ietf-pce-gmpls-pcep-
extensions, work in progress.
7.2. Informative References
[Stateful-APP] Zhang, X., Minei, I., et al, "Applicability of
Stateful Path Computation Element (PCE) ", draft-ietf-pce-
stateful-pce-app, work in progress.
8. Contributors' Address
Dhruv Dhody
Huawei Technology
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruvd@huawei.com
Yi Lin
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972914
Email: yi.lin@huawei.com
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Authors' Addresses
Xian Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972645
Email: zhang.xian@huawei.com
Young Lee
Huawei
1700 Alma Drive, Suite 100
Plano, TX 75075
US
Phone: +1 972 509 5599 x2240
Fax: +1 469 229 5397
EMail: ylee@huawei.com
Fatai Zhang
Huawei
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
P.R. China
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
Ramon Casellas
CTTC
Av. Carl Friedrich Gauss n7
Castelldefels, Barcelona 08860
Spain
Phone:
Email: ramon.casellas@cttc.es
Oscar Gonzalez de Dios
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid, 28045
Spain
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Phone: +34 913374013
Email: ogondio@tid.es
Zafar Ali
Cisco Systems
Email: zali@cisco.com
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