Label Switched Path (LSP) Object Flag Extension for Stateful PCE
updated by
- rfc-9756 — Update to the IANA Path Communication Element Protocol (PCEP) Numbers Registration Procedures and the Allowance of Experimental Error Codes
Extracted elements (14)
A variable-length TLV (in multiples of 32 bits) was chosen over a fixed 32-bit length to allow future extensibility so that flags would never be exhausted and another new TLV would not need to be defined. This follows the same approach used for the PCE-CAP-FLAGS sub-TLV in RFC 5088 and RFC 5089.
The LSP-EXTENDED-FLAG TLV was introduced because all 12 bits of the original LSP object Flag field defined in RFC 8231 have already been assigned, necessitating an extensible mechanism for additional LSP flags.
An implementation that does not understand or support the LSP-EXTENDED-FLAG TLV MUST ignore the TLV, as per RFC 5440. Future documents defining bits in the TLV are expected to define error handling for cases where the TLV is missing when it MUST be present.
Flags that an implementation does not support MUST be set to zero on transmission; implementations that do not understand a particular flag MUST ignore it.
If a PCEP speaker receives an LSP-EXTENDED-FLAG TLV of a length less than the one supported by the implementation, it MUST act as if the bits beyond the length were not set.
PCEP peers MUST handle varying lengths of the LSP-EXTENDED-FLAG TLV.
The Length field of the LSP-EXTENDED-FLAG TLV MUST be in multiples of 4 and greater than 0.
The LSP Extended Flags field SHOULD use the minimal amount of space needed to encode the flag bits.
Unassigned bits in the LSP Extended Flags field MUST be set to zero on transmission and MUST be ignored on receipt.
The LSP-EXTENDED-FLAG TLV (Type=64) is a new TLV for the LSP object that provides an extended Flag field as an array of 32-bit flag units. It follows the standard PCEP TLV format with a 16-bit Type, 16-bit Length, and variable-length LSP Extended Flags field.
IANA allocated TLV Type Indicator value 64 for LSP-EXTENDED-FLAG within the 'PCEP TLV Type Indicators' registry of the 'Path Computation Element Protocol (PCEP) Numbers' registry.
IANA created the 'LSP-EXTENDED-FLAG TLV Flag Field' registry within the PCEP Numbers registry to manage the LSP Extended Flags field. New values are assigned by Standards Action. No values are currently defined; Bits 0-31 are initially marked Unassigned.
This document does not change the security considerations set out in RFC 8231 for PCEP with a stateful PCE. RFC 8231 recommends stateful PCEP extensions be authenticated and encrypted using TLS (RFC 8253), per RFC 9325 best practices, which would protect the extended flags.
The LSP-EXTENDED-FLAG TLV has Type=64 (16 bits), a Length field (16 bits) indicating the value portion in bytes, and an LSP Extended Flags field containing an array of 32-bit flag units numbered from the most significant bit as bit zero.