PCE Q. Xiong
Internet-Draft S. Peng
Intended status: Standards Track ZTE Corporation
Expires: January 8, 2022 F. Qin
China Mobile
July 7, 2021
PCEP Extension for SR-MPLS Entropy Label Position
draft-peng-pce-entropy-label-position-06
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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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 PATH-MINIMUM-ERLD TLV . . . . . . . . . . . . . . . . 6
4.4. The SR-ERO Object . . . . . . . . . . . . . . . . . . . . 6
5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8.1. New SR PCE Capability Flag Registry . . . . . . . . . . . 7
8.2. New LSP-EXTENDED-FLAG Flag Registry . . . . . . . . . . . 8
8.3. The PATH-MINIMUM-ERLD TLV . . . . . . . . . . . . . . . . 8
8.4. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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. But 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:
o a limited number of <ELI, EL> pairs SHOULD be inserted in the SR-
MPLS label stack;
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o the inserted positions SHOULD be whithin the ERLD of a maximize
number of transit LSRs;
o 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 MSD, ELC and
ERLD through IGP/BGP-LS protocol and can compute the minimum ERLD
along the end-to-end path. 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.
This document provides an option for the ingress nodes to get the
path minimum ERLD from PCE as defined in section 4.3 and the ingress
nodes can perform the insertion of ELI/ELs based on the minimum ERLD
value. For another option, the PCE can perform the computation of
the end-to-end path as well as the positions of entropy labels
defined in section 4.4. The ingress nodes can directly insert the
ELI/ELs based on the positions.
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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 as shown in Figure 2.
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=TBD11 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |E|N|X| MSD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: E-flag in 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]. The
format is shown as Figure 3:
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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=TBD | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |E|
// LSP Extended Flags //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: E-flag in LSP-EXTENDED-FLAG TLV
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 PATH-MINIMUM-ERLD TLV
The PATH-MINIMUM-ERLD TLV is an optional TLV for use in the LSP
Object for the path minimum ERLD configuration. The type of this TLV
is to be allocated by IANA. The format is as shown below.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Path Minimum ERLD|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The PATH-MINIMUM-ERLD TLV
Path Minimum ERLD: 8 bits, indicates the minimum ERLD of the nodes
along the path.
4.4. 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 as Figure 4 shown:
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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=36 | Length | NT | Flags |E|F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable, optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: E-flag in 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.
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
TBA
7. Acknowledgements
TBA
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:
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+--------+-----------------------------------------+----------------+
| Value | Name | Reference |
+--------+-----------------------------------------+----------------+
| TBD11 | Entropy Label Configuration is | [this |
| | supported (E) | 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:
+---------+-------------------------------------+------------------+
| Value | Name | Reference |
+---------+-------------------------------------+------------------+
| TBD | Request for ELP Configuration (E) | [this document] |
+---------+-------------------------------------+------------------+
Table 2
8.3. The PATH-MINIMUM-ERLD TLV
This document requests that a new sub-registry named "PATH-MINIMUM-
ERLD TLV" carried in LSP object.
+---------+------------------------+------------------+
| Value | Name | Reference |
+---------+------------------------+------------------+
| TBD | PATH-MINIMUM-ERLD TLV | [this document] |
+---------+------------------------+------------------+
Table 3
8.4. 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:
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+---------+-------------------------+------------------+
| Value | Name | Reference |
+---------+-------------------------+------------------+
| 36 | ELP Configuration (E) | [this document] |
+---------+-------------------------+------------------+
Table 4
9. Normative References
[I-D.ietf-pce-lsp-extended-flags]
Xiong, Q., "LSP Object Flag Extension of Stateful PCE",
draft-ietf-pce-lsp-extended-flags-00 (work in progress),
March 2021.
[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>.
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[RFC8623] Palle, U., Dhody, D., Tanaka, Y., and V. Beeram, "Stateful
Path Computation Element (PCE) Protocol Extensions for
Usage with Point-to-Multipoint TE Label Switched Paths
(LSPs)", RFC 8623, DOI 10.17487/RFC8623, June 2019,
<https://www.rfc-editor.org/info/rfc8623>.
[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>.
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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