Conveying Path Setup Type in PCE Communication Protocol (PCEP) Messages
updated by
- rfc-8664 — Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing
Extracted elements (24)
Each new PST definition document must include a Manageability Considerations section addressing criteria for use, migration path, coexistence with other PSTs, operational verification, and any required YANG model extensions. This ensures operational readiness for each new setup type.
RSVP-TE (PST=0) is the assumed default path setup type when no PATH-SETUP-TYPE TLV is present, preserving backward compatibility with existing PCEP deployments that only use RSVP-TE. New PSTs must be explicitly signaled.
A PCEP speaker that does not recognize the PATH-SETUP-TYPE-CAPABILITY TLV will ignore it per RFC 5440 rules, effectively treating the peer as supporting only RSVP-TE. Similarly, an unrecognized PATH-SETUP-TYPE TLV causes the receiver to default to RSVP-TE for path setup.
A PCEP speaker SHOULD include the PATH-SETUP-TYPE-CAPABILITY TLV in its OPEN object if it supports PSTs other than RSVP-TE. Absence of this TLV is equivalent to advertising only PST=0 (RSVP-TE).
Duplicate PST entries in the PATH-SETUP-TYPE-CAPABILITY TLV list MUST be ignored, and the PCEP speaker MUST pad the PST list with zeros so that it is a multiple of four bytes.
During PCEP initialization, if no PSTs are in common between peers, the PCEP speaker MUST send PCErr with Error-Type=21, Error-value=2 (Mismatched path setup type) and close the session.
If a PCEP speaker receives an OPEN object with more than one PATH-SETUP-TYPE-CAPABILITY TLV, it MUST ignore all but the first instance.
If a PCEP speaker receives only one PATH-SETUP-TYPE TLV in the RP or SRP object, only the first MUST be processed; the rest MUST be ignored.
If a PCRpt message is triggered by a PCUpd or PCInitiate message, the PST in the PCRpt MUST match the PST intended in the triggering message. If it does not match, the PCE MUST send PCErr Error-Type=21, Error-value=2 and close the session.
If the PCE does not support the PST requested in a PCReq, it MUST send PCErr with Error-Type=21, Error-value=1 (Unsupported path setup type) and close the PCEP session. If PSTs in PCReq and PCRep do not match, the PCC MUST send the same error and close the session.
If the peer has sent no PATH-SETUP-TYPE-CAPABILITY TLV, the PCEP speaker MUST infer that the peer supports at least RSVP-TE. Inference of other PST support is outside the scope of this document.
The Num of PSTs field in the PATH-SETUP-TYPE-CAPABILITY TLV MUST be greater than zero. If the TLV violates formatting rules, the receiver MUST send a PCErr with Error-Type=10, Error-value=11 (Malformed object) and MUST close the PCEP session.
The Reserved field in both the PATH-SETUP-TYPE-CAPABILITY TLV and the PATH-SETUP-TYPE TLV MUST be set to zero by the sender and MUST be ignored by the receiver.
When a PCC sends a PCReq message, it MUST include the PATH-SETUP-TYPE TLV in the RP object unless the intended PST is RSVP-TE. The PCE MUST respond using the appropriate ERO format for the intended PST.
When a PCC sends a PCRpt message for a non-RSVP-TE PST, it MUST include the PATH-SETUP-TYPE TLV in the SRP object and MUST include the SRP object even when the SRP-ID-number is the reserved value 0x00000000.
When a stateful PCE sends a PCUpd or PCInitiate message, it MUST include the PATH-SETUP-TYPE TLV in the SRP object unless the PST is RSVP-TE. If the PCC does not support the PST, it MUST send PCErr Error-Type=21, Error-value=1 and close the session.
The PATH-SETUP-TYPE-CAPABILITY TLV (Type 34) is carried in the OPEN object during PCEP session initialization to advertise which Path Setup Types (PSTs) a PCEP speaker supports. It contains a list of one-byte PST values, optional sub-TLVs, and a Num of PSTs field.
The PATH-SETUP-TYPE TLV (Type 28) is an optional TLV associated with the RP object (RFC 5440) and the SRP object (RFC 8231) used to specify which path setup method should be used for a given LSP. Absence of this TLV implies RSVP-TE (PST=0).
IANA allocated new error codes in the 'PCEP-ERROR Object Error Types and Values' registry: Error-Type 21 'Invalid traffic engineering path setup type' with Error-value 1 (Unsupported path setup type) and Error-value 2 (Mismatched path setup type); and Error-value 11 (Malformed object) under existing Error-Type 10.
IANA allocated two new entries in the 'PCEP TLV Type Indicators' registry: value 28 for PATH-SETUP-TYPE and value 34 for PATH-SETUP-TYPE-CAPABILITY, both referencing RFC 8408.
IANA created a new 'PCEP Path Setup Types' sub-registry within 'Path Computation Element Protocol (PCEP) Numbers', with allocation policy IETF Review. Initial value: 0 = Path is set up using the RSVP-TE signaling protocol.
If the security mechanisms of RFC 5440 and RFC 8281 are not used, a TCP man-in-the-middle attacker could inject error messages into the PCEP session to force the use of a specific PST, potentially enabling subsequent exploitation of weaknesses in that PST.
The PATH-SETUP-TYPE-CAPABILITY TLV has Type=34, a variable Length field, a Reserved field (24 bits), a Num of PSTs field (8 bits), a padded list of PST values (each 1 byte), and optional sub-TLVs. The PST list MUST be padded to a multiple of four bytes.
The PATH-SETUP-TYPE TLV has Type=28 and a fixed Length of 4 bytes. It contains a Reserved field (24 bits) and a one-byte PST field encoding the path setup type, and is associated with the RP or SRP objects.