PCEP Extension for SR-MPLS Entropy Label Position
draft-peng-pce-entropy-label-position-08
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Quan Xiong , Shaofu Peng , Fengwei Qin | ||
| Last updated | 2022-08-29 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-peng-pce-entropy-label-position-08
PCE Q. Xiong
Internet-Draft S. Peng
Intended status: Standards Track ZTE Corporation
Expires: 3 March 2023 F. Qin
China Mobile
August 2022
PCEP Extension for SR-MPLS Entropy Label Position
draft-peng-pce-entropy-label-position-08
Abstract
This document proposes a set of extensions for PCEP to configure the
entropy label position for SR-MPLS networks.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 2 February 2023.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Entropy Labels in SR-MPLS Scenario with PCE . . . . . . . . . 3
4. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 5
4.2. The LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . 5
4.3. The SR-ERO Object . . . . . . . . . . . . . . . . . . . . 5
5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8.1. New SR PCE Capability Flag Registry . . . . . . . . . . . 6
8.2. New LSP-EXTENDED-FLAG Flag Registry . . . . . . . . . . . 6
8.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[RFC5440] describes the Path Computation Element Protocol (PCEP)
which is used between a Path Computation Element (PCE) and a Path
Computation Client (PCC) (or other PCE) to enable computation of
Multi-protocol Label Switching (MPLS) for Traffic Engineering Label
Switched Path (TE LSP). PCEP Extensions for the Stateful PCE Model
[RFC8231] describes a set of extensions to PCEP to enable active
control of MPLS-TE and Generalized MPLS (GMPLS) tunnels. [RFC8281]
describes the setup and teardown of PCE-initiated LSPs under the
active stateful PCE model, without the need for local configuration
on the PCC, thus allowing for dynamic centralized control of a
network.
Segment Routing (SR) leverages the source routing paradigm. Segment
Routing can be instantiated on MPLS data plane which is referred to
as SR-MPLS [RFC8660]. SR-MPLS leverages the MPLS label stack to
construct the SR path. PCEP Extensions for Segment Routing [RFC8664]
specifies extensions to the PCEP that allow a stateful PCE to compute
and initiate TE paths, as well as a PCC to request a path subject to
certain constraint(s) and optimization criteria in SR networks.
Entropy label (EL) [RFC6790] is a technique used in the MPLS data
plane to improve load-balancing. Entropy Label Indicator (ELI) can
be immediately preceding an EL in the MPLS label stack. The idea
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behind the EL is that the ingress router computes a hash based on
several fields from a given packet and places the result in an
additional label, named "entropy label". Then, this entropy label
can be used as part of the hash keys used by an LSR. Using the
entropy label as part of the hash keys reduces the need for deep
packet inspection in the LSR while keeping a good level of entropy in
the load-balancing. When the entropy label is used, the keys used in
the hashing functions are still a local configuration matter and an
LSR may use solely the entropy label or a combination of multiple
fields from the incoming packet.
[RFC8662] proposes to use entropy labels for SR-MPLS networks and
mutiple <ELI, EL> pairs SHOULD be inserted in the SR-MPLS label
stack. The ingress node may decide the number and place of the ELI/
ELs which need to be inserted into the label stack. The extensions
for Border Gateway Protocol (BGP) to indicate the entropy label
position in the SR-MPLS label stack has been proposed in
[I-D.zhou-idr-bgp-srmpls-elp].
In some cases, the the controller(e.g. PCE) could be used to perform
the TE path computation as well as the Entropy Label Position (ELP)
which is useful for inter-domain scenarios. This document proposes a
set of extensions for PCEP to configure the ELP information for SR-
MPLS networks.
2. Conventions used in this document
2.1. Terminology
The terminology is defined as [RFC5440], [RFC6790], [RFC8664] and
[RFC8662].
2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Entropy Labels in SR-MPLS Scenario with PCE
[RFC8662] proposes to use entropy labels for SR-MPLS networks. The
Entropy Readable Label Depth (ERLD) is defined as the number of
labels which means that the router will perform load-balancing using
the ELI/EL. An appropriate algorithm should consider the following
criteria:
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* a limited number of <ELI, EL> pairs SHOULD be inserted in the SR-
MPLS label stack;
* the inserted positions SHOULD be whithin the ERLD of a maximize
number of transit LSRs;
* a minimum number of <ELI, EL> pairs SHOULD be inserted while
satisfying the above criteria.
As described in [RFC8662] section 7, the ERLD value is important for
inserting ELI/EL and the ingress node need to evaluate the minimum
ERLD value along the node segment path. But it will add complexity
in the ELI/EL insertion process. Moreover, the ingress node cannot
find the minimum ERLD along the path and does not support the
computation of the minimum ERLD especilly in inter-domain scenarios.
As the Figure 1 shown, in SR-MPLS inter-domain scenario, the ingress
node of the first domain could not get the ERLD information of other
nodes of other domains.
+-----+ +-----+ +-----+
|PCE-1| |PCE-2| |PCE-3|
+--+--+ +--+--+ +--+--+
| | |
.........+.......... .........+.......... .........+...........
. . . . . .
.+---+ +---+ . . +---+ +---+ . .+---+ +----+ .
.| A |-------| B |------ | C |------| X |-------| Y |------| Z | .
.+---+ +---+ . . +---+ +---+ . .+---+ +----+ .
. SR-AS 1 . . SR-AS 2 . . SR-AS 3 .
.................... .................... .....................
Figure 1: Entropy Labels in SR-MPLS Inter-Domain Scenario
The PCEs could get the information of all nodes such as Maximum SID
Depth (MSD) and ERLD through Interior Gateway Protocol (IGP) and can
compute the minimum ERLD along the end-to-end path. For example, the
ERLD value can be collected via IS-IS [I-D.ietf-isis-mpls-elc], and
OSPF [I-D.ietf-ospf-mpls-elc]. IS-IS [RFC8491] and OSPF [RFC8476]
provide examples of advertisement of the MSD. Moreover, the PCEs
also can compute the Entropy Label Position (ELP) including the
number and the places of the ELI/ELs. Then the ingress nodes MAY be
required to support the capabilities of inserting multiple ELI/ELs
and need to advertise the capabilities to the PCEs.
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This document proposes the extensions for PCE to perform the
computation of the end-to-end path as well as the positions of
entropy labels in SR-MPLS networks. The ingress nodes can directly
insert the ELI/ELs based on the positions.
4. PCEP Extensions
4.1. The OPEN Object
As defined in [RFC8664], PCEP speakers use SR PCE Capability sub-TLV
to exchange information about their SR capability when PST=1 in the
PST List of the PATH-SETUP-TYPE-CAPABILITY TLV carried in Open
object. This document defined a new flag (E-flag) for SR PCE
Capability sub-TLV.
E (Entropy Label Configuration is supported) : A PCE sets this flag
bit to 1 carried in Open message to indicate that it supports the
computation of SR path with ELP information. A PCC sets this flag to
1 to indicate that it supports the capability of inserting multiple
ELI/EL pairs and and supports the results of SR path with ELP from
PCE.
4.2. The LSP-EXTENDED-FLAG TLV
The LSP Object is defined in Section 7.3 of [RFC8231]. This document
defiend a new flag (E-flag) for the LSP-EXTENDED-FLAG TLV carried in
LSP Object as defined in [I-D.ietf-pce-lsp-extended-flags].
E (Request for ELP Configuration) : If the bit is set to 1, it
indicates that the PCC requests PCE to compute the SR path with ELP
information. A PCE would also set this bit to 1 to indicate that the
ELP information is included by PCE and encoded in the PCRep, PCUpd or
PCInitiate message.
4.3. The SR-ERO Object
SR-ERO subobject is used for SR-TE path which consists of one or more
SIDs as defined in [RFC8664]. This document defiend a new flag
(E-flag) for the SR-ERO subobject.
E (ELP Configuration) : If this flag is set, it means that the
position after this SR-ERO subobject is the position to insert <ELI,
EL>, otherwise it cannot insert <ELI, EL> after this segment.
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5. Operations
The SR path is initiated by PCE or PCC with PCReq, PCInitiated or
PCUpd messages and the E bit is set to 1 in LSP object to request the
ELP configuration. The SR-TE path being recieved by PCC with SR-ERO
segment list, for example, <S1, S2, S3, S4, S5, S6>, especially S3
and S6 with E-flag set. It indicates that two <ELI, EL> pairs MUST
be inserted into the label stack of the SR-TE forwarding entry,
repectively after the label for S3 and label for S6. With EL
information, the label stack for SR-MPLS would be <label1, label2,
label3, ELI, EL, label4, label5, label6, ELI, EL>.
6. Security Considerations
Procedures and protocol extensions defined in this document do not
introduce any new security considerations beyond those already listed
in [RFC8662] and [RFC8664].
7. Acknowledgements
The authors would like to thank Stephane Litkowski, Dhruv Dhody,
Tarek Saad, Zhenbin Li and Jeff Tantsura for their review,
suggestions and comments to this document.
8. IANA Considerations
8.1. New SR PCE Capability Flag Registry
SR PCE Capability TLV is defined in [RFC8664], and the registry to
manage the Flag field of the SR PCE Capability TLV is requested in
[RFC8664]. IANA is requested to make allocations from the registry,
as follows:
+=======+==============================================+===========+
| Value | Name | Reference |
+=======+==============================================+===========+
| TBD11 | Entropy Label Configuration is supported (E) | [this |
| | | document] |
+-------+----------------------------------------------+-----------+
Table 1
8.2. New LSP-EXTENDED-FLAG Flag Registry
[I-D.ietf-pce-lsp-extended-flags] defines the LSP-EXTENDED-FLAG TLV.
IANA is requested to make allocations from the Flag field registry,
as follows:
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+=======+===================================+=================+
| Value | Name | Reference |
+=======+===================================+=================+
| TBD | Request for ELP Configuration (E) | [this document] |
+-------+-----------------------------------+-----------------+
Table 2
8.3. New SR-ERO Flag Registry
SR-ERO subobject is defined in [RFC8664], and the registry to manage
the Flag field of SR-ERO is requested in [RFC8664]. IANA is
requested to make allocations from the registry, as follows:
+=======+=======================+=================+
| Value | Name | Reference |
+=======+=======================+=================+
| 36 | ELP Configuration (E) | [this document] |
+-------+-----------------------+-----------------+
Table 3
9. References
9.1. Normative References
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", Work in
Progress, Internet-Draft, draft-ietf-isis-mpls-elc-13, 28
May 2020,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-isis-mpls-elc/>.
[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using OSPF", Work in
Progress, Internet-Draft, draft-ietf-ospf-mpls-elc-15, 1
June 2020,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-ospf-mpls-elc/>.
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[I-D.ietf-pce-lsp-extended-flags]
Xiong, Q., "Label Switched Path (LSP) Object Flag
Extension of Stateful PCE", Work in Progress, Internet-
Draft, draft-ietf-pce-lsp-extended-flags-03, 7 June 2022,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-pce-lsp-extended-flags/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
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[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy Label for Source
Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
DOI 10.17487/RFC8662, December 2019,
<https://www.rfc-editor.org/info/rfc8662>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
9.2. Informative References
[I-D.zhou-idr-bgp-srmpls-elp]
Liu, Y. and S. Peng, "BGP Extension for SR-MPLS Entropy
Label Position", Work in Progress, Internet-Draft, draft-
zhou-idr-bgp-srmpls-elp-05, 7 June 2022,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
zhou-idr-bgp-srmpls-elp/>.
Authors' Addresses
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan
Hubei, 430223
China
Email: xiong.quan@zte.com.cn
Shaofu Peng
ZTE Corporation
No.50 Software Avenue
Nanjing
Jiangsu, 210012
China
Email: peng.shaofu@zte.com.cn
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Fengwei Qin
China Mobile
Beijing
China
Email: qinfengwei@chinamobile.com
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