Internet DRAFT - draft-ietf-pce-entropy-label-position
draft-ietf-pce-entropy-label-position
PCE Q. Xiong
Internet-Draft S. Peng
Intended status: Standards Track ZTE Corporation
Expires: 28 August 2024 F. Qin
China Mobile
J. Zhao
CAICT
25 February 2024
Path Computation Element Communication Protocol (PCEP) Extension for SR-
MPLS Entropy Label Positions
draft-ietf-pce-entropy-label-position-01
Abstract
Entropy label (EL) can be used in the SR-MPLS data plane to improve
load-balancing and multiple Entropy Label Indicator (ELI)/EL pairs
may be inserted in the SR-MPLS label stack as per RFC8662.
This document proposes a set of extensions for Path Computation
Element Communication Protocol (PCEP) to configure the Entropy Label
Positions (ELP) for SR-MPLS networks.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 28 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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
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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 . . . . . . . . . . . . . . . . . . 4
3. Entropy Labels in SR-MPLS Scenario with PCE . . . . . . . . . 4
4. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 5
4.2. The LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . 5
4.3. The SR-ERO Object . . . . . . . . . . . . . . . . . . . . 6
5. Operational Example . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7.1. New SR PCE Capability Flag Registry . . . . . . . . . . . 6
7.2. New LSP-EXTENDED-FLAG Flag Registry . . . . . . . . . . . 7
7.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 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 Computation 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.
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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
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 Label Switch Router
(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
multiple <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 Entropy
Label Position (ELP) is used to indicate the positions of the ELI/ELs
which need to be inserted into the label stack as per
[I-D.ietf-idr-bgp-srmpls-elp].
In some cases, the controller(e.g. PCE) could be used to perform the
TE path computation as well as ELP information 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].
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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 in [RFC8662] section 4.
As described in [RFC8662] section 7.2.1, the ELRD value is an
important consideration when inserting ELI/EL and the minimum ELRD
must be evaluated for each node along a computed path. This
necessary step adds additional complexity in the ELI/EL insertion
process and it may not be feasible for an ingress router to compute
the appropriate ERLD for each node in the path, since a SR-MPLS path
may contain segments the ingress router can resolve such as 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 .
.................... .................... .....................
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Figure 1: Entropy Labels in SR-MPLS Inter-Domain Scenario
When computing the ELI/EL positions, the PCE MUST take into
consideration Maximum SID Depth (MSD) imposition. The PCEs could get
the information of all nodes such as MSD (e.g. Base MPLS Imposition
MSD (BMI-MSD) or ERLD-MSD) through Interior Gateway Protocol (IGP)
and can compute the minimum ERLD along the end-to-end path. IS-IS
[RFC8491] and OSPF [RFC8476] provide examples of advertisement of the
MSD. The ERLD value can be collected via IS-IS [RFC9088], and OSPF
[RFC9089]. Moreover, the PCEs also can compute the ELP information
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.
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 defines a new flag (E-flag) for SR PCE
Capability sub-TLV.
E (ELP 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
defines a new flag (E-flag) for the LSP-EXTENDED-FLAG TLV carried in
LSP Object as defined in [RFC9357].
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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. The PCE SHOULD set this bit to 1 to indicate that the
ELP information is included by PCE and encoded in the Path
Computation Reply (PCRep) message as per [RFC5440]. And in a
stateful PCE model, it also CAN be carried in Path Computation Update
Request (PCUpd) message as per [RFC8231] or LSP Initiate Request
(PCInitiate) message as per [RFC8281].
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 defined a new flag
(E-flag) for the SR-ERO subobject.
E (ELP Configuration) : If this flag is set, the PCC SHOULD insert
<ELI, EL> into the position after this SR-ERO subobject, otherwise it
SHOULD not insert <ELI, EL> after this segment.
5. Operational Example
A PCC can request the computation of SR path and a PCE may respond
with PCRep message. And the SR path can also be initiated by PCE
with PCInitiate or PCUpd message in stateful PCE mode. When the E
bit in LSP object is set to 1 within the message, it indicates to
request the ELP configuration with the SR path. The SR path being
received by PCC encoded in SR-ERO, for example, <S1, S2, S3, S4, S5,
S6>, especially S3 and S6 with E-flag set. It indicates that two
<ELI, EL> pairs SHOULD be inserted into the label stack of the SR
forwarding entry, respectively 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
This document defines a new E bit for entropy label, which do not
introduce any new security considerations beyond those already listed
in [RFC9357], [RFC8662] and [RFC8664].
7. IANA Considerations
7.1. 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:
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+=======+====================================+=================+
| Value | Name | Reference |
+=======+====================================+=================+
| TBD1 | ELP Configuration is supported (E) | [this document] |
+-------+------------------------------------+-----------------+
Table 1
7.2. New LSP-EXTENDED-FLAG Flag Registry
[RFC9357] defines the LSP-EXTENDED-FLAG TLV. IANA is requested to
make allocations from the Flag field registry, as follows:
+=======+===================================+=================+
| Value | Name | Reference |
+=======+===================================+=================+
| TBD2 | Request for ELP Configuration (E) | [this document] |
+-------+-----------------------------------+-----------------+
Table 2
7.3. 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 |
+=======+=======================+=================+
| TBD3 | ELP Configuration (E) | [this document] |
+-------+-----------------------+-----------------+
Table 3
8. Acknowledgements
The authors would like to thank Stephane Litkowski, Dhruv Dhody,
Tarek Saad, Zhenbin Li, Jeff Tantsura, Andrew Stone, Xuesong Geng,
Ran Chen, Gyan Mishra, Weiqiang Cheng and Samuel Sidor for their
review, suggestions and comments to this document.
9. References
9.1. Normative References
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[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>.
[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>.
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[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>.
[RFC9088] 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", RFC 9088,
DOI 10.17487/RFC9088, August 2021,
<https://www.rfc-editor.org/info/rfc9088>.
[RFC9089] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using OSPF", RFC 9089,
DOI 10.17487/RFC9089, August 2021,
<https://www.rfc-editor.org/info/rfc9089>.
[RFC9357] Xiong, Q., "Label Switched Path (LSP) Object Flag
Extension for Stateful PCE", RFC 9357,
DOI 10.17487/RFC9357, February 2023,
<https://www.rfc-editor.org/info/rfc9357>.
9.2. Informative References
[I-D.ietf-idr-bgp-srmpls-elp]
Liu, Y. and S. Peng, "BGP Extension for SR-MPLS Entropy
Label Position", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-srmpls-elp-01, 5 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
srmpls-elp-01>.
Authors' Addresses
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan
Hubei, 430223
China
Email: xiong.quan@zte.com.cn
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Shaofu Peng
ZTE Corporation
No.50 Software Avenue
Nanjing
Jiangsu, 210012
China
Email: peng.shaofu@zte.com.cn
Fengwei Qin
China Mobile
Beijing
China
Email: qinfengwei@chinamobile.com
Junfeng Zhao
CAICT
Beijing
China
Email: zhaojunfeng@caict.ac.cn
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