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Routing PCE PCEP RFC 8231 describes a set of extensions to Path Computation Element Communication Protocol (PCEP) to enable stateful control of MPLS-TE and GMPLS Label Switched Paths (LSPs) via PCEP. One of the extensions is the LSP object which includes a Flag field of the length of 12 bits. However, all bits of the Flag field have already been assigned in RFC 8231, RFC 8281, RFC 8623 and I-D.ietf-pce-binding-label-sid. [Note to RFC Editor - Replace I-D.ietf-pce-binding-label-sid to RFC XXXX, once the RFC number is assigned.] This document proposes to define a new LSP-EXTENDED-FLAG TLV for the LSP object for an extended flag field.

Introduction describes the Path Computation Element (PCE) Communication Protocol (PCEP) which is used between a 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 describes a set of extensions to PCEP to enable active control of MPLS-TE and Generalized MPLS (GMPLS) tunnels. One of the extensions is the LSP object which contains a flag field; bits in the flag field are used to indicate delegation, synchronization, removal, etc. As defined in , the length of the flag field is 12 bits and the value from bit 5 to bit 11 is used for operational, administrative, remove, synchronize and delegate bits respectively. The bit value 4 is assigned in for create for PCE-Initiated LSPs. The bits from 1 to 3 is assigned in for Explicit Route Object (ERO)-compression, fragmentation and Point-to-Multipoint (P2MP) respectively. The bit 0 is assigned in to PCE-allocation. All bits of the Flag field has been assigned already. Thus, it is required to extend the flag field for the LSP Object for future use. This document proposes to define a new LSP-EXTENDED-FLAG TLV for an extended flag field in the LSP object.

Conventions used in this document

Terminology The terminology is defined as and .

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 when, and only when, they appear in all capitals, as shown here.

PCEP Extension The LSP Object is defined in Section 7.3 of . This document proposes to define a new LSP-EXTENDED-FLAG TLV for an extended flag field in the LSP object.

The LSP-EXTENDED-FLAG TLV The format of the LSP-EXTENDED-FLAG TLV follows the format of all PCEP TLVs as defined in and is shown in the .

Figure 1: LSP-EXTENDED-FLAG TLV Format

Type (16 bits): the value is TBD1 by IANA. Length (16 bits): multiple of 4 octets. LSP Extended Flags: this contains an array of units of 32-bit flags numbered from the most significant as bit zero, where each bit represents one LSP flag (for operation, feature, or state). Currently no bits are assigned. Unassigned bits MUST be set to zero on transmission and MUST be ignored on receipt. As an example of usage of the LSP-EXTENDED-FLAG TLV, the E-flag is requested for entropy label configuration as proposed in .

Processing The LSP Extended Flags field is an array of units of 32 flags and to be allocated starting from the most significant bit. The bits of the LSP Extended Flags field will be assigned by future documents. This document does not define any flags. Unassigned flags MUST be set to zero on transmission and MUST be ignored on receipt. Implementations that do not understand any particular flag MUST ignore the flag. This flags should follow the specification as per . Note that, PCEP peers MAY encounter different length of the LSP-EXTENDED-FLAG TLV. If a PCEP speaker receives the LSP-EXTENDED-FLAG TLV of a length more than it currently supports or understands, it will simply ignore the bits beyond that length. If a PCEP speaker receives the LSP-EXTENDED-FLAG TLV of a length less than the one supported by the implementation, it will consider the bits beyond the length to be unset.

Backward Compatibility The LSP-EXTENDED-FLAG TLV defined in this document does not introduce any interoperability issues. A router that does not understand or support the LSP-EXTENDED-FLAG TLV will silently ignore the TLV as per . It is expected that future document that define bits in the LSP-EXTENDED-FLAG TLV would also define the error case handling required for missing LSP-EXTENDED-FLAG TLV if it MUST be present.

IANA Considerations

LSP Object

PCEP TLV Type Indicators IANA is requested to allocate the following TLV Type Indicator value within the "PCEP TLV Type Indicators" subregistry of the "Path Computation Element Protocol (PCEP) Numbers" registry:

Value	Description	Reference
TBD1	LSP-EXTENDED-FLAG	[This document]

LSP Extended Flags Field IANA is requested to create a new subregistry called "LSP-EXTENDED-FLAG TLV Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry to manage the LSP Extended Flags field of the LSP-EXTENDED-FLAG TLV. New values are assigned by Standards Action . Each bit should be tracked with the following qualities:

• Bit number (counting from bit 0 as the most significant bit)
• Capability description
• Defining RFC

No values are currently defined.

Implementation Status [NOTE TO RFC EDITOR : This whole section and the reference to is to be removed before publication as an RFC] This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in . The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to , "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". At the time of posting this version of this document, there are no known implementations of this TLV. It is believed that this would be implemented along side the documents that allocate flags in the TLV.

Management Considerations Implementations receiving set LSP Extended Flags that they do not recognize MAY log this. That could be helpful for diagnosing backward compatibility issues with future features that utilize those flags.

Security Considerations sets out security considerations for PCEP when used for communication with a stateful PCE. This document does not change those considerations. For LSP Object processing, see . This document provides for future extension of PCEP. No additional security issues are raised in this document beyond those that exist in the referenced documents.

Acknowledgements The authors would like to thank Loa Andersson, Adrian Farrel, Aijun Wang, and Gyan Mishra for their review, suggestions and comments to this document.

Contributors The following people have substantially contributed to this document:

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies the Path Computation Element (PCE) Communication Protocol (PCEP) for communications between a Path Computation Client (PCC) and a PCE, or between two PCEs. Such interactions include path computation requests and path computation replies as well as notifications of specific states related to the use of a PCE in the context of Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering. PCEP is designed to be flexible and extensible so as to easily allow for the addition of further messages and objects, should further requirements be expressed in the future. [STANDARDS-TRACK] RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Client (PCC) requests. Although PCEP explicitly makes no assumptions regarding the information available to the PCE, it also makes no provisions for PCE control of timing and sequence of path computations within and across PCEP sessions. This document describes a set of extensions to PCEP to enable stateful control of MPLS-TE and GMPLS Label Switched Paths (LSPs) via PCEP. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. Extensions to the Path Computation Element Communication Protocol (PCEP) to support stateful Path Computation Elements (PCEs) are defined in RFC 8231. One of the extensions is the Stateful PCE Request Parameters (SRP) object. That object includes a Flags field that is a set of 32 bit flags, and RFC 8281 defines an IANA registry for tracking assigned flags. However, RFC 8231 does not explain how an implementation should set unassigned flags in transmitted messages, nor how an implementation should process unassigned, unknown, or unsupported flags in received messages. This document updates RFC 8231 by defining the correct behaviors. Informative References There are various circumstances where it is highly desirable for a Path Computation Client (PCC) to be able to dynamically and automatically discover a set of Path Computation Elements (PCEs), along with information that can be used by the PCC for PCE selection. When the PCE is a Label Switching Router (LSR) participating in the Interior Gateway Protocol (IGP), or even a server participating passively in the IGP, a simple and efficient way to announce PCEs consists of using IGP flooding. For that purpose, this document defines extensions to the Open Shortest Path First (OSPF) routing protocol for the advertisement of PCE Discovery information within an OSPF area or within the entire OSPF routing domain. [STANDARDS-TRACK] There are various circumstances where it is highly desirable for a Path Computation Client (PCC) to be able to dynamically and automatically discover a set of Path Computation Elements (PCEs), along with information that can be used by the PCC for PCE selection. When the PCE is a Label Switching Router (LSR) participating in the Interior Gateway Protocol (IGP), or even a server participating passively in the IGP, a simple and efficient way to announce PCEs consists of using IGP flooding. For that purpose, this document defines extensions to the Intermediate System to Intermediate System (IS-IS) routing protocol for the advertisement of PCE Discovery information within an IS-IS area or within the entire IS-IS routing domain. [STANDARDS-TRACK] This document describes a simple process that allows authors of Internet-Drafts to record the status of known implementations by including an Implementation Status section. This will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. This process is not mandatory. Authors of Internet-Drafts are encouraged to consider using the process for their documents, and working groups are invited to think about applying the process to all of their protocol specifications. This document obsoletes RFC 6982, advancing it to a Best Current Practice. The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Client (PCC) requests. The extensions for stateful PCE provide active control of Multiprotocol Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE LSPs) via PCEP, for a model where the PCC delegates control over one or more locally configured LSPs to the PCE. This document describes the creation and deletion of PCE-initiated LSPs under the stateful PCE model. The Path Computation Element (PCE) has been identified as an appropriate technology for the determination of the paths of point- to-multipoint (P2MP) TE Label Switched Paths (LSPs). This document provides extensions required for the Path Computation Element Communication Protocol (PCEP) so as to enable the usage of a stateful PCE capability in supporting P2MP TE LSPs. Ciena Corporation Cisco Systems, Inc. Microsoft Corporation Huawei Technologies Huawei Technologies In order to provide greater scalability, network confidentiality, and service independence, Segment Routing (SR) utilizes a Binding Segment Identifier (SID) (called BSID) as described in RFC 8402. It is possible to associate a BSID to an RSVP-TE-signaled Traffic Engineering Label Switched Path or an SR Traffic Engineering path. The BSID can be used by an upstream node for steering traffic into the appropriate TE path to enforce SR policies. This document specifies the concept of binding value, which can be either an MPLS label or Segment Identifier. It further specifies an extension to Path Computation Element (PCE) communication Protocol(PCEP) for reporting the binding value by a Path Computation Client (PCC) to the PCE to support PCE-based Traffic Engineering policies. ZTE Corporation ZTE Corporation China Mobile This document proposes a set of extensions for PCEP to configure the entropy label position for SR-MPLS networks.

WG Discussion The WG discussed the idea of a fixed length (with 32 bits) for LSP- EXTENDED-FLAG TLV. Though 32 bits would be sufficient for quite a while, the use of variable length with a multiple of 32-bits allows for future extensibility where we would never run out of flags and there would not be a need to define yet another TLV in the future. Further, note that and use the same approach for the PCE-CAP-FLAGS Sub-TLV and are found to be useful.