PCEP Extensions to support BFD parameters

PCEP Extensions to support BFD parameters Ribbon Communication

Hasivim 30, Petah-Tikva Israel

Ribbon Communication

Hasivim 30, Petah-Tikva

PCE Working Group This document proposes extension to PCEP to configure LSP parameters. Some of LSP parameters are needed to configure S-BFD for candidate paths. Each candidate path is identified in PCEP by its uniquely assigned PLSP-ID. The mechanism proposed in this document is applicable to to all path setup types. The need for these definitions first appeared for Segment Routing path setup type, both MPLS and IPv6 data planes of SR. 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.

Introduction Path Computation Element (PCE) Communication Protocol (PCEP) enables the communication between a Path Computation Client (PCC) and a Path Computation Element (PCE), or between two PCEs based on the PCE architecture . PCEP Extensions for the Stateful PCE Model describes a set of extensions to PCEP to enable active control of Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS) tunnels. 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. PCEP Extensions for Segment Routing specifies extensions to the Path Computation Element Protocol (PCEP) that allow a stateful PCE to compute and initiate Traffic Engineering (TE) paths, as well as a PCC to request a path subject to certain constraint(s) and optimization criteria in SR networks. PCEP Extensions for Establishing Relationships Between Sets of LSPs introduces a generic mechanism to create a grouping of LSPs which can then be used to define associations between a set of LSPs and a set of attributes (such as configuration parameters or behaviors) and is equally applicable to stateful PCE (active and passive modes) and stateless PCE. Segment Routing Policy for Traffic Engineering details the concepts of SR Policy and approaches to steering traffic into an SR Policy. This document specifies PCEP extensions to signal additional information to configure LSP attributes. This is accomplished via the use of the existing LSPA object, by defining a new capability and new TLVs.

Terminology The following terminologies are used in this document:

PCC: Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints.
PCEP: Path Computation Element Protocol. PCEP Tunnel: The entity identified by the PLSP-ID, as per [I-D.koldychev-pce- operational].

Motivation S-BFD protocol is used for detecting failures in different tunnels path setup types. There are several protocol parameters that need to be configured and exchanged between PCEP speakers. As the parameters are associated to LSPs or tunnels, they are exchanged via PCEP. The LSPS-BFD-Capability TLV, the LSP-SBFD TLV and its sub-TLVs, defined in this document, allow PCEP speakers to exchange additional information about S-BFD.

Overview of Protocol Extensions

Overview A new option to define S-BFD parameters is defined in this document. The S-BFD parameters are only meant to be used for SR LSPs and with PCEP peers which advertise SR capability. A PCEP speaker indicates its ability to support S-BFD parameters during the PCEP initialization phase, as follows. When the PCEP session is created, it sends an Open message with an OPEN object that contains the LSP-SBFD-Capability TLV (see ). If a PCEP speaker receives the PCEP LSP-SBFD-Capability TLV with B flag = 1 in the Open object, then it means its peer is capable to receive and to send S-BFD TLVs towards that peer. If a PCEP speaker has not received this TLV in the Open object, or if it receives it with B flag set to 0, then it MUST NOT send any S-BFD TLVs in LSPA object towards that peer.

Processing If a PCEP speaker is capable of S-BFD and its peer is capable of S-BFD, then the PCEP speaker MAY send LSP-SBFD TLV towards that peer, to report the S-BFD state (Enabled/Disabled) for the configured LSP. The LSP-SBFD TLV shall be sent as an optional TLV in the LSPA object. A PCC shall send it in the PCRpt message. A PCE shall send it in the PCInit or in the PCUpd message. If the LSP-SBFD TLV is received from a PCEP peer with the B flag set to 1, then S-BFD shall be applied for specified LSP. If PCC received this TLV via PCUpd with B=0 and there is no S-BFD applied for the LSP, then the PCC shall IGNORE the TLV. If PCE received this TLV with B=0 and there is no S-BFD applied for the LSP (editing a PCC-initiated LSP) then it may IGNORE it. If B=0 and LSP-BFD-Parameters sub-TLV is received, then the PCEP speaker shall IGNORE the sub-TLV. Ignoring or saving the S-BFD configuration is implementation decision. In some implementations there is limitation that LSPs in the same association group must have same S-BFD parameter values. Editor note: Alternatively, it can be defined implicitly as follows: If the LSP-SBFD TLV is not received from PCEP peer but there is S-BFD for that LSP then S-BFD shall be removed for specified LSP.

Objects and TLVs

LSP S-BFD Capability The LSP-SBFD-Capability TLV is an optional TLV. It MAY be carried within an OPEN object sent by PCEP speaker in an Open message to a PCEP peer to indicate it supports SBFD capability. The LSP-SBFD-Capability TLV has the following format:

S-BFD parameters

LSP S-BFD TLV The PCEP LSP-SBFD TLV is an optional TLV. It MAY be carried within the LSPA object. The PCEP LSP-SBFD TLV has the following format: Type: TBD2 Length: The total length in bytes of the remainder of the TLV, that is, excluding the Type and Length fields. B flag: Enable/Disable S-BFD for this LSP. If B=1 then S-BFD will be enabled. If B=0 then S-BFD will be disabled for that LSP. If the PCEP speaker received LSP-SBFD TLV from PCEP peer with B flag is set to 0, then S-BFD shall be removed (in case of PCE update) or shall not be applied (in case of PCE initiated message) for specified LSP

LSP-SBFD Parameters sub-TLV The PCEP LSP-SBFD-Parameters sub-TLV is optional. It MAY be carried within the LSP-SBFD TLV. The PCEP LSP-SBFD-Parameters sub-TLV has the following format: Procedure If B=0 and LSP-SBFD-Parameters sub-TLV is received, then the PCEP speaker shall IGNORE the sub-TLV.

LSP-SBFD-Discriminator sub-TLV The PCEP LSP-SBFD-Discriminator sub-TLV and is optional TLV. It MAY be carried within the LSP-SBFD TLV. The PCEP LSP-SBFD-Discriminator sub-TLV has the following format: Procedure If B=0 and LSP-SBFD-Discriminator sub-TLV is received, then the PCEP speaker shall IGNORE the LSP-SBFD-Discriminator sub-TLV.

Error Handling If a PCEP speaker has not received S-BFD-Capability TLV from a peer in the Open object, and it received an LSP S-BFD TLV (see ) from that peer, then it MUST ignore the content of the LSP S-BFD TLV, and it MUST return a PCErr message with Error-Type=19 "Invalid Operation" with Error-value = TBD5 "SBFD capability is not negotiated". If Multiplier value in the LSP-SBFD-Parameters sub-TLV is not in the legal range (1..255), then the PCEP Speaker MUST return a PCErr message with Error-Type=23 "Bad parameter value" and Error-value = TBD6 "Multiplier is out of range". If Remote Discriminator value in the PCEP LSP-SBFD-Discriminator sub-TLV is not in the legal range (i.e., it is zero), then the PCEP Speaker MUST return a PCErr message with Error-Type=23 "Bad parameter value" and Error-value = TBD8 "Remote Discriminator is out of range".

Implementation Note In some implementations there is limitation that LSPs in the same association group must have same S-BFD parameter values. If either the Min Tx Interval, the Multiplier or the Remote Discriminator values received in the LSP-BFD Parameters sub-TLVs for LSPs that are members in the same Association Group are not identical, then the PCEP Speaker SHOULD return a PCErr message with Error-Type=26 "Association Error" with Error-value TBD7 "Invalid S-BFD parameter value"

IANA Considerations

PCEP TLV Type Indicators This document defines new TLVs and sub-TLVs for carrying additional information about S-BFD. IANA is requested to make the assignment of new values for the existing "PCEP TLV Type Indicators" registry as follows:

PCEP Errors

Security Considerations This document defines one new type for association, which does not add any new security concerns beyond those discussed in , , , and in itself.

Acknowledgement Would like to thank Avantika Sushil, Alexander Ferdman, Itay Katz and Galina Mintz for review and suggestions.

References Normative References Informative References

Contributors

Dhruv Dhody: Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India Email: dhruv.ietf@gmail.com