Network 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
Expires: August 21, 2013 February 22, 2013
Path Computation Element (PCE) Protocol Extension for Stateful PCE
Usage in GMPLS Networks
draft-zhang-pce-pcep-stateful-pce-gmpls-02.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 21, 2013.
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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 PCEP
extensions needed to support stateful PCE functions, without
specifying the technology-specific extensions. This memo provides
extensions required for PCE communication protocol (PCEP) so as to
enable the usage of a stateful PCE capability in GMPLS networks.
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 ............................................. 3
2.1. Overview of Requirements................................ 3
2.2. Stateful PCE Capability Advertisement and Negotiation....4
2.2.1. PCE Capability Negotiation/Advertisement in Multi-layer
Networks ................................................. 4
2.3. LSP Delegation in GMPLS Networks ........................5
2.4. LSP Synchronization in GMPLS networks ...................6
2.5. Modification of Existing PCEP Messages and Procedures....8
2.5.1. Use cases ......................................... 8
2.5.2. Modification for LSP Re-optimization ...............9
2.5.3. Modification for Route Exclusion ...................9
2.6. Additional Error Type and Error Values Defined..........10
3. IANA Considerations ........................................ 10
4. Manageability Considerations................................ 10
4.1. Requirements on Other Protocols and Functional Components11
5. Security Considerations..................................... 11
6. Acknowledgement ............................................ 11
7. References ................................................. 11
7.1. Normative References................................... 11
7.2. Informative References................................. 12
8. Contributors' Address....................................... 12
Authors' Addresses ............................................ 13
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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). To
request path computation services to a PCE, [RFC 5440] defines the
PCE Communication Protocol (PCEP) for communications between a Path
Computation Client (PCC) and a PCE, or between two PCEs. PCEP
protocol 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 the PCE communication protocol (i.e.,
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 its deployment in GMPLS-controlled networks.
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 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:
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o Advertisement and negotiation 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 synchronization (see [Stateful-APP] Section 2.2). This is a
generic requirement already covered in Section 5.4 of [Stateful-
PCE]. However, there are further extensions required specifically
for GMPLS networks and discussed in Section 2.4.o Reference to
LSPs by identifiers is discussed in Section 7.2 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 and 2.6.
2.2. Stateful PCE Capability Advertisement and Negotiation
Whether a PCE has stateful capability or not can be negotiated
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.
2.2.1. PCE Capability Negotiation/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. 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 is needed. A
new domain-type denoting the layer information can be defined:
domain-type: T.B.D.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.3. LSP Delegation in GMPLS Networks
To enable the PCE to control an LSP, the PCUpd message is defined in
[Stateful-PCE]. However, technology-specific specification is not
covered. The following defines the <path> descriptor that should be
used in GMPLS networks:
<path>::=<ERO><attribute-list>
Where:
<attribute-list> ::= [<LSPA>]
[<BANDWIDTH>]
[<GENERALIZED-BANDWIDTH>...]
[<metric-list>]
<metric-list>::= <METRIC>[<metric-list>]
The O bit in the <GENERALIZED-BANDWIDTH> object has no meaning for
LSP state synchronization and MUST be set to 0. Furthermore, this
object MAY appear twice, one with R set to 1 and the other with R
set to 0. This is to denote the asymmetric bandwidth property of the
updated bi-directional LSP.
As explained in [stateful-APP], LSP state synchronization and/or LSP
parameter change controlled by a stateful PCE in a multi-domain
network is complex and requires well-defined operational procedures
as well as protocol design.
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[TBD: protocol extensions]
2.4. LSP Synchronization in GMPLS 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
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 protocol 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 GENERALIZED BANDWIDTH
o GENERALIZED ENDPOINTS
o PROTECTION ATTRIBUTE
o Use of IF_ID_ERROR_SPEC. [Stateful-PCE] section 7.2.2 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 PCRpt message is defined for LSP state
synchronization purpose. 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 networks, the encoding of the
<path> descriptor is defined as follows:
<path>::=<ERO><attribute-list>
Where:
<attribute-list> ::= [<LSPA>]
[<BANDWIDTH>]
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[<GENERALIZED-BANDWIDTH>...]
[<RRO>]
[<IRO>]
[<XRO>]
[<metric-list>]
<metric-list>::= <METRIC>[<metric-list>]
The objects included in the <path> descriptor can be found in
[RFC5440], [PCE-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 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 stateul PCE through a
PCRpt message.
The O bit in the <GENERALIZED-BANDWIDTH> object has no meaning for
LSP state synchronization and MUST be set to 0. Furthermore, this
object MAY appear twice, one with R set to 1 and the other with R
set to 0. This is to denote the asymmetric bandwidth property of the
updated bi-directional LSP.
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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 an unique
identifier in the scope of the PCC-PCEP session and thus use such
identifier to refer to that LSP.
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] 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.
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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>, <GENERARLIZED-
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. The stateful PCE can
find this information using the per-node LSP ID 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type (T.B.D.) | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP ID | Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L bit:
The L bit SHOULD NOT be set, so that the subobject represents
a strict hop in the explicit route.
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.
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LSP ID:
This is the identifier given to a LSP and it is unique on a
node basis. It is defined in [Stateful-PCE].
Flags:
This field is defined in [Stateful-PCE]. It is not used in
this sub-object and should be ignored upon receipt.
Optional TLVs:
Additional TLVs can be defined in the future to provide
further information to identify a LSP. In this document, no TLVs are
defined.
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
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.
2.6. Additional Error Type and Error Values Defined
Error Type Meaning
21(TBD) LSP state information missing
Error-value 1: LSP state information unavailable for the
LSP re-optimization
3. Error-value 2: the LSP state information for route exclusion purpose
cannot be found IANA Considerations
IANA is requested to allocate new Types for the TLV/Object defined
in this document.
T.B.D.
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.
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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.
[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-08.txt, XX 2013.
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7.2. Informative References
[Stateful-APP] Zhang, F., Zhang, X., Lee, Y., Casellas, R., Gonzalez
de Dios, O., "Applicability of Stateful Path Computation
Element (PCE) ", draft-zhang-pce-stateful-pce-app-03, 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.
[PCE-IA-WSON] Lee, Y., Bernstein G., Takeda, T., Tsuritani, T.,
''PCEP Extensions for WSON Impairments'', draft-lee-pce-
wson-impairments, 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.
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: +86-755-28972913
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
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