Generalized SCSI: A Generic Structure for Interface Switching Capability Descriptor (ISCD) Switching Capability Specific Information (SCSI)
Extracted elements (14)
RFC 7138 introduced a sub-TLV structure for technology-specific SCSI fields, which allows greater flexibility in structure, ordering, and support for extensions. This document generalizes that approach into a reusable Generalized SCSI format for future technologies and Switching Capability types, avoiding per-technology reinvention.
The Generalized SCSI carries SCSI-TLVs that may be defined within the scope of a specific technology or shared across multiple technologies, enabling both technology-specific and cross-technology reuse of SCSI sub-elements.
Processing related to multiple SCSI-TLVs of the same type may be further refined based on the definition of that type, allowing type-specific handling of duplicates.
The Generalized SCSI is only applicable to ISCDs of technologies whose Switching Capability definition explicitly references this document; existing technology-specific formats are not modified.
SCSI-TLVs MUST be processed in the order received and, if re-originated, ordering MUST be preserved.
Sub-TLV parsing (format) errors MUST be treated as a malformed ISCD.
The Generalized SCSI MAY contain a sequence of zero or more SCSI-TLVs, giving implementations flexibility in how many capability sub-elements they advertise.
The Generalized SCSI MUST NOT be used for ISCDs of technologies whose Switching Capability definition does not reference this document.
The Length field MUST be set to the size, in octets, of the Value field, and its value MUST be zero or divisible by 4, implying the Value field can be omitted or contain padding.
Unknown SCSI-TLVs MUST be ignored and transparently processed, i.e., re-originated when appropriate.
The Generalized SCSI is composed of zero or more variable-length TLV fields called SCSI-TLVs. There are no specific size restrictions on SCSI-TLVs; size and formatting restrictions may be imposed by the routing protocol ISCD field.
IANA created the 'Generalized SCSI (Switching Capability Specific Information) TLV Types' registry under the 'Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters' registry. Value 0 is Reserved; values 1-65535 are Unassigned. New allocations require 'Specification Required' policy and must indicate applicable Switching Type values.
This document does not introduce security issues beyond those in RFC 4203 and RFC 5307. ISCD information is not used for SPF computation or normal routing, so extensions have no direct effect on IP routing. However, tampering with GMPLS TE Link State Advertisements may affect the underlying transport network, and mechanisms such as RFC 2154 and RFC 5304 are suggested to protect this information.
The SCSI-TLV format consists of a Type field (2 octets) indicating the type and structure of information, a Length field (2 octets) giving the size in octets of the Value field, and a variable-length Value field formatted according to the Type.