| Internet-Draft | PCEP extensions for Circuit Style Polici | May 2022 |
| Sidor, et al. | Expires 14 November 2022 | [Page] |
This document proposes a set of extensions for Path Computation Element Communication Protocol (PCEP) for Circuit Style Policies - Segment-Routing Policy designed to satisfy requirements for connection-oriented transport services. New TLV is introduced to control path recomputation triggers and new flag to add ability to request path with strict hops only.¶
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.¶
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Usage of Segment-routing and PCEP in connection-oriented transport services require path persistancy and hop-by-hop behavior for PCE computed paths.¶
Circuit-Style Policy introduced in [I-D.schmutzer-pce-cs-sr-policy] requires PCEP extensions, which are covered in this document.¶
This document:¶
PCEP extensions described in this document are applicable to RSVP-TE and SR-TE.¶
The following terminologies are used in this document:¶
O-flag is proposed in the LSP-EXTENDED-FLAG TLV, which was introduced in 5.1.2 of [I-D.ietf-pce-lsp-extended-flags] and extended with E-flag in [I-D.peng-pce-entropy-label-position]¶
The format of the LSP-EXTENDED-FLAG is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=TBD1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |O|E|
// LSP Extended Flags //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (16 bits): the value is TBD1 by IANA.¶
Length (16 bits): multiple of 4 octets.¶
O (Strict-Path): If set to 1, this indicates to the PCE that a path exclusively made of strict hops is required. Strict hop definition can be found in Section 4.1¶
This document defines new TLV for the LSP Object for encoding information about blocked path recomputation triggers.¶
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 = TBD2 | Length = 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |T|P| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Type (16 bits): the value is TBD2 by IANA.¶
Length (16 bits): 4 octets¶
PCC MAY set the O flag in LSP-EXTENDED-FLAG TLV in PCRpt message to the PCE to indicate that a path exclusively made of strict hops is required.¶
O flag cleared or LSP-EXTENDED-FLAG TLV not included indicates that a loose path is acceptable.¶
In PCUpdate or PCInitiate messages, when the O bit is set, this indicates that strict path is provided.¶
The flag is applicable only for stateful messages. Existing O flag in RP object MAY be used to indicate similar behavior in PCReq and PCRep messages as described in as described in Section 7.4.1 of [RFC5440].¶
If O flag is set to 1 for both stateful and stateless messages for SR paths introduced in [RFC8664], the PCE MUST use Adjacency SIDs only.¶
PCC MAY set flags in RECOMPUTATION-TRIGGERS-TLV to block specific triggers. If TLV is not included or all flags are set to 0, then the PCE MAY use any event to start path computation.¶
Disabled recomputation triggered by topology event is not blocking path computation started based PCRpt or based on updated state of associated LSP.¶
If trigger blocked by specific flag is not supported or allowed on the PCE, then PCE MAY ignore received flag value. The PCE SHOULD reflect blocked triggers in PCUpdate message.¶
TLV MAY be included in PCInitiate and PCUpdate messages to indicate, which triggers will be disabled on the PCE. PCC should reflect flag values in PCRpt messages to forward requirement to other PCEs in the network.¶
No additional security measure is required.¶
[I-D.ietf-pce-lsp-extended-flags] defines the LSP-EXTENDED-FLAG TLV. IANA is requested to make the following assignment from the "LSP-EXTENDED-FLAG TLV Flag Field" registry:¶
| Bit | Description | Reference |
|---|---|---|
| TBD1 | Strict-Path Flag (O) | This document |
IANA is requested to make the assignment of a new value for the existing "PCEP TLV Type Indicators" registry as follows:¶
| TLV Type | TLV Name | Reference |
|---|---|---|
| TBD2 | RECOMPUTATION-TRIGGERS TLV | This document |